Galvanizing Manual - Kingfield Equipment

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TABLE OF CONTENTS 
TABLE OF CONTENTS................................................................................................................... 
 
BRIEF SUMMARY OF MANUAL CONTENTS.............................................................................. 3 
 Introduction.............................................................................................................. .... 3 
 
1 DEGREASER.............................................................................................................. .... 4 
 1.1 Introductory Comments............................................................................................... 4 
 1.2 Summary of Recommended Operating Conditions for the Degreaser....................... 5 
 1.3 Analysis Procedures for the Degreaser........................................................................ 5 
 1.3.1 Sodium Hydroxide Content and Ration Determination................................... 6 
 
2 ACID PICKLE......................................................................................................... ......... 8 
 2.1 Introductory Comments............................................................................................... 8 
 2.2 Summary of Recommended Operating Conditions for the Acid Pickle....................... 9 
 2.3 Analysis Procedures for the Acid Pickle........................................................................ 9 
 2.3.1 Hydrochloric Acid Content.............................................................................. 10 
 2.3.2 Iron Content in the Acid Pickle (Titration Method)........................................ 12 
 2.3.3 Iron Content in the Acid Pickle (Nomographic Method)................................ 14 
 2.4 Procedure for Initial “Make-Up” of the Acid Pickle................................................... 16 
 2.5 Procedure for Adjustment of the Acid Pickle during Operation................................ 16 
 2.5.1 PEARSON’S SQUARE........................................................................................ 16 
 2.5.2 BATH ADJUSTMENT........................................................................................ 17 
 
3 PREFLUX..................................................................................................................... 19 
3.1 Introductory Comments............................................................................................. 19 
 3.1.1 Effect of ZnCl2 to NHCl4 Ratio Imbalance.................................................... 20 
 3.2 Summary of Recommended Operating Conditions for the Preflux......................... 22 
 3.3 Analysis Procedures for the Preflux.......................................................................... 23 
 3.3.1 Iron Content in the Preflux............................................................................ 24 
 3.3.2 Zinc Chloride Content in the Preflux............................................................. 26 
 3.3.3 Ammonium Chloride Content in the Preflux................................................. 28 
 3.3.4 Chloride Content in the Preflux..................................................................... 31 
 3.3.5 Density Measurement of the Preflux............................................................ 34 
 3.3.6 ZAC Concentration vs S.G. at room temperature......................................... 35 
 3.3.7 Conversion of Density to Baumé................................................................... 36 
 3.3.8 MEASUREMENT OF SPECIFIC GRAVITY......................................................... 37 
 3.3.9 pH Measurement of the Preflux.................................................................... 38 
3.4 Procedure for Initial “Make-Up” of the Preflux Solution.......................................... 39 
3.5 Procedure for Adjustment of the Preflux During Operation..................................... 40 
3.6 Iron Control Procedures for the Preflux..................................................................... 41 
 
 
 
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4 QUENCH (Dichromate Solution)................................................................................ 43 
 4.1 Introductory Comments............................................................................................ 43 
 
 4.2 Summary of Recommended Operating Conditions for the Quench........................ 44 
 4.3 Analysis Procedures for the Quench......................................................................... 44 
 4.3.1 Chromium Content in the Quench................................................................ 45 
 4.3.2 Chloride Content in the Quench.................................................................... 47 
 4.3.3 pH Measurement of the Quench................................................................... 49 
 
5 ZINC BATH METAL SAMPLING................................................................................... 50 
 5.1 Procedure for Zinc Bath Sampling............................................................................. 50 
 5.1.1 Spectrographic Button Mould........................................................................ 51 
 5.1.2 STEEL LADLE FOR ZINC BATH METAL SAMPLING.......................................... 52 
 
6 APPENDIX 1 – Facilities and Equipment..................................................................... 53 
 6.1 Facilities Required...................................................................................................... 53 
 6.1.1 Laboratory Equipment Required.................................................................... 53 
 6.1.2 Safety Equipment............................................................................................ 53 
 6.2 Titration Equipment.................................................................................................... 54 
 6.2.1 TITRATION APPARATUS.................................................................................. 55 
 6.3 Distillation Equipment................................................................................................ 56 
 6.3.1 DISTILLATION APPARATUS (Analysis of Ammonia in Preflux Solution).......... 58 
 
7 APPENDIX 2 – Reagents and Indicators...................................................................... 59 
 7.1 Preparation of Reagents and Indicators..................................................................... 60 
 
8 APPENDIX 3 – Quality Check and Preparation of Standard Solutions......................... 61 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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BRIEF SUMMARY OF MANUAL CONTENTS 
Introduction 
The reaction between molten zinc and steel to form a continuous adherent coating can only 
occur if the steel surface is free from foreign materials such as oil, grease, paint, rust, 
millscale and dirt of various kinds. A correctly prepared surface is obtained by pretreating 
the steel surface with solutions which remove the foreign materials and replaces them with 
a thin layer of flux. Cool down of the galvanized article is generally conducted in a water 
tank to which additions of sodium dichromate passivator are made for the purpose of 
reducing the risk of white rusting. 
 
These process solutions will only work effectively and efficiently if they are of the correct 
composition and it is important that proper control procedures be used to maintain the 
compositions of the solutions during their working life. 
 
 
Galvanizing Process Solutions 
 
This manual covers the following process solutions (liquors);Degreaser 
 Acid Pickle 
 Preflux Quench 
 
And provides information on; 
 The function of each liquor. 
 The operating conditions and procedures to adjust each liquor. 
 The procedures used to analyse each liquor. 
 
Simple illustrations along with photographs of the various equipment necessary to carry out 
the analyses are also provided. 
 
Zinc Bath Metal 
 
In addition to the above analytical procedures, incorporated in this manual are 
recommendations for sampling zinc bath metal for analysis. 
 
 
 
 
 
 
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1 DEGREASER 
 
1.1 Introductory Comments 
This solution is used to remove oil and greases from the steel surface. The following information 
refers specifically to caustic soda based degreasing solutions which are the most commonly used in 
practice. 
The speed at which steel articles are cleaned is dependent on temperature and sodium hydroxide 
content. The solution is usually heated between 70-90°C and the sodium hydroxide content is 
usually maintained between 50-100g/L. Some commercially available degreasers may contain 
additional cleaning agents to improve the cleaning efficiency and extend the life of the bath. 
For optimum performance, two properties need to be monitored and adjusted as necessary. These 
are; 
i. Free alkali 
 
This is the alkali available for cleaning. This is the sodium hydroxide content. 
 
ii. Total alkali 
 
This is the sum of the free alkali and the combined alkali. The combined alkali is the 
alkali which is combined with the soil and is not available for cleaning. 
 
The ratio of free alkali to total alkali is used to give an indication of the cleaning capacity. It indicates 
how much free alkali is remaining to remove soil as a proportion of the total alkali. For example, a 
high ratio of 0.9 shows that there is a large amount of alkali available for cleaning whereas a ratio of 
0.5 shows that there is a low level of free alkali so the cleaning capacity is low. 
 
As the bath ages, the proportion of by-products increases and thus the ratio of free alkali to total 
alkali decreases. The ratio should always be maintained above 0.5 by additions of fresh degreaser. 
When the amount of by-products build up to a level where the ratio cannot be maintained above 0.5 
the solution may need to be partially of totally dumped. 
 
Although zinc may be present in the degreaser from carry-over from work jigs, it is not usually 
present at high levels so is not considered a problem. 
 
 
 
 
 
 
 
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1.2 Summary of Recommended Operating Conditions for the Degreaser 
 
Temperature 
 
Working Range: 70 – 90°C 
 
Sodium Hydroxide Content (NaOH) 
 
Working Range: 50-100g/L 
 
Ratio (“Free” to “Total Alkali”) 
 
 Minimum: 0.5 
 
Any proprietary additions to the degreaser must be maintained according to the suppliers’ 
instructions. 
 
 
 
1.3 Analysis Procedures for the Degreaser 
 
On a routine basis, e.g., once a month, analysis needs to be made of free alkali (sodium 
hydroxide) and total alkali, from which the ratio can be determined. Then adjustment to the 
solution can be made according to ensure operating conditions as above are maintained. 
The test procedures are outlined on the following pages which include; 
 
1. Sodium hydroxide content, i.e., the “free alkali” content (Section 1.3.1). 
2. Ration determination (Section 1.3.1). 
 
 
 
 
 
 
 
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1.3.1 Sodium Hydroxide Content and Ratio Determination 
Equipment Required 
- 100mL measuring cylinder 
- 50mL burette 
- 250mL conical flask 
- adjustable pipette (adjust to 1mL) 
- 100mL plastic bottle with a screw top lid 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
 
- 1L of 0.1N hydrochloric acid 
- 100mL phenolphthalein indicator 
- 100mL bromocresol green indicator 
 
Method 
 
1. Take a sample of about 100mL from the degreasing bath in a plastic bottle and allow 
it to stand to cool to room temperature and to settle any sediment. 
 
2. Using the clean pipette, take 1mL of solution from the sample and transfer it into the 
clean conical flask, add about 100mL of water, and add a few drops of 
phenolphthalein indicator. The solution will turn pink. 
 
3. Fill the clean burette to the zero mark with 0.1N hydrochloric acid and titrate slowly 
with this solution, while swirling the conical flask, until the pink colour vanishes. 
 
4. Record the burette reading. This is the first endpoint (Titration, A). 
 
5. To the above solution add a few drops of bromocresol green indicator. The solution 
will turn blue. 
 
6. Continue titrating slowly with the standard 0.1N hydrochloric acid until the solution 
turns permanent yellow. 
 
7. Record the burette reading. This is the second endpoint (Titration, B). 
 
 
 
 
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Calculation 
Sodium Hydroxide Content (NaOH) 
If the bath contains caustic soda only, then its concentration is calculated as follows; 
Where A is the first titration endpoint and B is the second titration endpoint the 
sodium hydroxide content is; 
 
 NaOH g/L – [A – (B – A)] x 4.0 
If the bath is a proprietary solution, this can only be used as a guide. For formulated 
baths the factor will not be 4.0 but one specific to the product, usually between 5.5 - 
7.0. 
 
Ratio Determination 
Gives an indication of the cleaning capacity of the bath and is calculated as follows; 
 Ratio = Titration A 
 Titration B 
 
Example 
 
If the titration to the first endpoint is 22mL and the titration to the second endpoint is 24mL, 
then 
 
 NaOH g/L = [22 – (24-22)] x 4.0 
 = [22-2] x 4.0 
 = 20 x 4.0 
 = 80.0 g/L 
 
 Ratio = 22 
 24 
 = 0.92 
 
Quality Check 
Using the above method, check the accuracy of the results with the standard sodium 
hydroxide solution. Preparation of this standard solution is outlined in Appendix 3 on page 
61. 
 
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2 ACID PICKLE 
 
2.1 Introductory Comments 
This acid pickle is used to remove rust, millscale and other iron oxides from the steel surface. The 
following information refers specifically to hydrochloric acid pickling as this is the most commonly 
used acid in galvanizing plants. 
Hydrochloric acid is normally used at ambient temperature. The efficiency of the pickle depends on 
the free acid concentration, iron content and acid circulation (agitation). Recommended normal 
practice is to start with approximately 15% (150 g/L) acid concentration. Commercially supplied 
hydrochloric acid is typically 28-30% concentration, which means diluting this 1: 1 water. 
For overseas customers who carry out pipe galvanizing, due to high required throughput 
(tonnes/hour), acid concentration is usually higher to maximise the pickling rate. The acid 
concentration may be up to 20-25%, however, this does result in the production of 
considerable acid fume. 
 
During use, two changes occur; 
i. The free acid content decreases 
Normally when the hydrochloric acid concentration level falls to about 10% or 
11% (110-110g/L) the pickle should be adjusted back to 15% (150g/L) using fresh 
acid. The method for adjusting this is outlined in Section 2.5 on page 16-17. 
 
ii. The iron content increases 
General practice is to discontinue the above acid make-up additions when the 
iron level in the bath reaches 120g/L. Above this level, the acid is saturated with 
iron and pickling efficiency is significantly reduced. Adding more acid will not 
improve the situation. Normal practice is that when 110-120g/L iron is reached, 
continue to use the acid until its strength drops to 50g/L. When this is reached 
the acid is no longer used for pickling steel but can be used for removing(stripping) zinc from rework items. 
 
Agitation of steelwork in the pickling tank, or forced circulation of acid (pumping), will 
considerably improve the pickling rate due to removal of iron build-up in the pickle adjacent 
to the steel surface which would otherwise have a partial inhibiting effect on the pickling 
reaction. 
 
Zinc contamination in operating pickling baths, for example from work jigs/rework, should 
be avoided if possible as it reduces significantly the rate of pickling of steel surfaces. For this 
reason, if possible, attempt to limit any zinc contamination to only one operating tank and 
one which has been in service for an extended period of time (i.e. iron content is high). 
 
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2.2 Summary of Recommended Operating Conditions for the Acid Pickle 
Temperature 
 Working Range: ambient temperature (approx. 20-30°C) 
 
Hydrochloric Acid Content (HCl) 
 New Solution: 150g/L (15%) 
 Optimum Operation: 100 – 150g/L (11-15%) 
 
Iron Content (Fe) 
 Maximum: 120g/L 
 
Pickle Agitation preferable 
 
 
2.3 Analysis Procedures for the Acid Pickle 
Acid strength and iron content should be checked frequently (frequency is dependent on throughput 
and tank capacity). The analysis methods are outlined on the following pages which include; 
 
1. Hydrochloric acid content (Section 2.3.1). 
2. Iron content by titration (Section 2.3.2). 
3. Iron content by the nomographic method (Section 2.3.3). 
 
 
 
 
 
 
 
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2.3.1 Hydrochloric Acid Content 
Equipment Required 
- 100mL measuring cylinder 
- 25mL burette 
- 250mL conical flask 
- adjustable pipette (adjust to 2mL) 
- 100mL plastic bottle with screw top lid 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
- 1L of 0.548N sodium bicarbonate 
- 100mL bromocresol green indicator 
 
 
Method 
 
1. Take a sample of about 100mL from the pickling bath in a plastic bottle and allow it 
to stand to cool to room temperature and settle any sediment. 
 
2. Using the clean pipette, take 2mL of solution from the sample and transfer to the 
clean conical flask, and add about 100mL of water. 
 
3. To this solution add a few drops of bromocresol green indicator. The solution will 
turn yellow. 
 
4. Fill the clean burette to the zero mark with 0.548N sodium bicarbonate and titrate 
slowly with the above solution, while swirling the flask, until the solution turns 
permanent blue/green. 
 
5. Record the burette reading. This is the endpoint (Titration, C). 
 
 
 
 
 
 
 
 
 
 
 
 
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Calculation 
Titration, C, gives a direct measure of the hydrochloric acid content in the bath as percent 
weight per volume, i.e. % w/v. 
HCl % w/v = C 
To convert this to grams/litre; 
 HCl g/L = C x 10 
 
Example 
If the endpoint of the HCl titration is 12mL, then 
 HCl = 12% w/v 
OR 
 HCl g/L = 12 x 10 
 = 120g/L 
 
Quality Check 
Using the above method, check the accuracy of the results with the standard acid solution. 
Preparation of this standard solution is outlined in Appendix 3 on page 61. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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2.3.2 Iron Content in the Acid Pickle (Titration Method) 
Equipment Required 
- 250mL measuring cylinder with a stopper 
- 100mL measuring cylinder 
- 25mL burette 
- 250mL conical flask 
- adjustable pipette (adjust to 10mL) 
- small plastic funnel 
- box of No.1 Whatmanfilter papers 
- 100mL plastic bottle with screw top lid 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
- 1L of 0.02M potassium permanganate 
- 1L Zimmermann-Reinhardt reagent 
 
 
Method 
 
1. Take a sample of about 100mL from the pickling bath in a plastic bottle and allow it 
to stand to cool to room temperature and settle any sediment. 
 
2. Filter some of this sample into clean 25mL measuring cylinder to the 25mL mark 
exactly. 
 
3. Pour this sample into clean 250mL measuring cylinder and make up to 250ml mark 
exactly with water. Stopper the measuring cylinder and invert several times. 
 
4. Using the clean pipette, dispense 10mL of this dilute solution into the clean conical 
flask and add 15mL of Zimmermann-Reinhardt reagent. 
 
5. Fill the clean burette to the zero mark with 0.02M potassium permanganate and 
titrate slowly with the above solution, while swirling the conical flask, until the colour 
turns permanent pale pink. 
 
6. Record the burette reading. This is the endpoint (Titration, D). 
 
 
 
 
 
 
 
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Calculation 
Where D is the titration endpoint, the iron content of the acid pickle is calculated as follows; 
Fe g/L = D x 5.6 
 
Example 
If the endpoint from the iron titration is 10mL, then 
 Fe g/L = 10 x 5.6 
 = 56 g/L 
 
Quality Check 
Using the above method, check the accuracy of the results with the standard acid solution. 
Preparation of this standard solution is outlined in Appendix 3 on page 61. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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2.3.3 Iron Content in the Acid Pickle (Nomographic Method) 
Alternatively, iron content can be determined by the nomographic method. The 
nomographic method is shown on the following page. 
 
 
Equipment Required 
- Hydrometer for Specific Gravity (density range 1000 to 1200, with 0005 subdivisions) 
- 100mL measuring cylinder 
- nomograph 
- 30cm ruler 
 
Method 
 
1. Take a 100mL sample from the pickling bath and allow it to stand to cool to room 
temperature and settle any sediment. 
 
2. Pour about 60-70mL of the clear sample into the clean measuring cylinder. 
 
3. Place the hydrometer in the measuring cylinder and spin it to eliminate surface 
tension effects. 
 
4. Read off the specific gravity (S.G.) at the fluid line. 
 
5. Read off the specific gravity of the flux sample. 
 
6. Determine the HCl concentration by the method described previously. 
 
7. Get a ruler and line up the “Specific Gravity (Density)” on the left-hand side of the 
graph with the “Hydrochloric Acid Content” on the right-hand side of the graph. 
 
8. The “Iron Content” can be read off the middle column where the line intersects the 
column. 
 
 
Example 
 
If the specific gravity was measured to be 1.165 and the HCl content was determined to be 
115g/L (11.5% w/v), then the line between the two outer columns intersects the middle 
column at; 
 
 Fe content = 55 g/L 
 
 
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NOMOGRAPHIC METHOD 
 
Determination of Iron in Hydrochloric Acid 
 
 
 
 
 
 
 
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2.4 Procedure for Initial “Make-Up of the Acid Pickle 
 
Using 30% w/v hydrochloric acid (the usual strength as-supplied) add to water in the 
approximate ration 1:1 to give approximately 15% w/v concentration. For safety reasons, 
always add acid to water, not vice versa, due to possible splashing from the resultant acid-
water reaction. 
 
 
2.5 Procedure for Adjustment of the Acid Pickle during Operation 
 
During use of the acid pickle the hydrochloric acid concentration will decrease. When the 
hydrochloric acid concentration is approaching the lower limit of 100g/L (10% w/v) consider 
bringing the hydrochloric acid concentration up again. However, first check the iron 
concentration and decide whether it is better to discard the bath or part of it before putting 
hydrochloric acid in. The iron concentration should not exceed 100g/L (10% w/v). If it is 
decided to increase the HCl strength, then proceed as follows; 
 
Set up Pearson’s Square following steps 1 to 6; 
 
1. Put current bath strength % in Box 1. 
2. Put required bath strength % in Box 2.3. Put new acid strength % in Box 4. 
4. Subtract Box 1 from Box 2 to get Box 3. 
5. Subtract Box 2 from Box 4 to get Box 5. 
6. Add Box 3 and Box 5 to get Box 6. 
 
2.5.1 PEARSON’S SQUARE 
 
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To calculate the adjustment to be made to the bath follow steps 7 to 11; 
7. Put current acid volume (litres) in Box 7. 
 
8. Put full bath capacity (litres), up to the freeboard level at the top of the bath, in Box 
8. 
 
9. Divide Box 8 by Box 6 and multiply this figure by Box 5 to determine the usable 
amount of the current bath, Box 9. 
 
10. Subtract Box 9 from Box 7 to determine the amount of old acid to discard from the 
bath. 
 
11. Subtract Box 9 from Box 8 to determine the amount of new acid to add to the bath. 
 
 
2.5.2 BATH ADJUSTMENT 
 
 
 
 
 
 
 
 
 box 6 
 box 8 
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Example 
 
There is currently 4500L (Box 7) of weak acid in the bath and its strength is 9% w/v (Box 1). 
We require a bath strength of 14% w/v (Box 2) by adding new acid at 37% w/v (Box 4). The 
full bath capacity is 5000L (Box 8), up to the freeboard level at top of the bath. 
 
Set up Pearson’s Square as follows; 
 
 
 
 
Then calculate bath adjustment as follows; 
 
 
 
Therefore, to adjust the current acid pickle at 9% w/v up to 14% w/v, we will need to discard 
393L from the current bath and then add 893L of new acid at 37% w/v. 
 
 9 
 28 
 5 37 
 14 
 23 
 4500 
 5000 
 28 
 5000 23 
 4107 
 4107 
 4107 
 4500 
 5000 
 393 
 893 
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3 PREFLUX 
 
3.1 Introductory Comments 
The purpose of the preflux is to provide a protective layer on the steel surface to prevent 
oxidation prior to galvanizing and to break down the zinc oxide layer on the molten zinc 
surface at the point of entry of the steel into the galvanizing bath. These conditions are 
critical to achieving a metallurgical reaction between the molten zinc and the steel surface. 
 
The following information refers specifically to preflux solutions consisting of zinc 
ammonium chloride (ZAC) “triple salt” dissolved in water. Zinc ammonium chloride “triple 
salt” is the most commonly used form of preflux and has the formula ZnCl2.3NH4Cl. The 
components are zinc chloride (ZnCl2) and ammonium chloride (NH4Cl) in the ration 46%:54% 
by weight, respectively. 
 
Important parameters influencing flux performance and which must be monitored are: 
 
i. Zinc ammonium chloride (ZAC) concentration 
A concentration of 20 – 30% by weight is normally used. Measurement of the 
preflux density will give an approximate indication of the ZAC concentration. 
Usually, density is measured as either Specific Gravity (S.G.) or °Baumé (Bé). 
Pages 35-37 show the relationship between these density measurements and 
ZAC concentration. It should again be stressed that density measurements 
provide only an approximation of ZAC concentration in that significant 
departures from the optimum ratio (refer below) can introduce some error. 
 
Procedures for preparation of a new preflux solution to a particular desired ZAC 
concentration are outlined in Section 3.4 on page 39. 
 
During use, the concentration of ZAC in the preflux will be reduced. Procedures 
for adjusting the preflux to the required concentration by addition of ZAC are 
outlined in Section 3.5 on page 40. 
 
ii. Zinc chloride to ammonium chloride ratio 
The ratio in the preflux solution should be maintained in the proportions similar 
to that in the solid crystal form, i.e. 46% ZnCl2 : 54% NH4Cl. During operation, the 
ration can change and accordingly, adjustments may be required from time to 
time to restore the ratio. Relatively small departures from the optimum ratio do 
not have any detrimental consequences, however, if the ratio imbalance 
becomes excessive some adverse effects can be experienced (refer to diagram on 
the following page). 
 
In order to determine the ratio, measurement must be made of the individual 
components of the ZAC solution, i.e. Zinc content, ammonia content and chloride 
content. Procedures for analysing these are given in Section 3.3 on pages 23-32. 
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3.1.1 Effect of ZnCl2 to NH4Cl Ratio Imbalance 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
iii. Iron content in the preflux 
During operation of the preflux, the solution becomes contaminated with iron. 
The major sources of iron are: 
 
 Reaction of the preflux with the surface of the steel articles. 
 
 Carry-over of iron salts on the surface of the steel articles from the acid 
pickle (water rinsing after the acid pickle removes most but not all of the 
iron salts). 
 
This iron contamination in the preflux will be transferred on the steelwork into 
the galvanizing zinc bath, resulting in increased dross production. It is therefore 
very important in that the preflux be routinely measured and that steps be taken 
to reduce this contamination to a minimum. It is generally accepted that the 
iron content should not exceed 10g/L and through good practice many 
galvanizers are able to achieve less than 5g/L. 
 
 
High ZnCl2 
Results in slow drying after 
fluxing causing excessive 
splashing during entry of steel 
items into galvanizing bath. 
High NH4Cl 
Causes excessive 
galvanizing fumes 
Low NH4Cl 
Can cause “black spotting” of 
galvanized coatings 
 
 
 ZnCl2:NH4Cl 
 Ratio 
Low ZnCl2 
Results in reoxidation of steel 
surface during drying after 
fluxing, reducing the fluxing 
efficiency and increases dross 
production during galvanizing. 
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It is important to note that iron in the preflux exists in two forms: 
 
1. Insoluble iron hydroxide. This form is responsible for the orange-brown 
colouration of the preflux solution after it has been in use for a period of 
time. Most of this settles as sludge in the bottom of the tank and 
therefore does not present a major problem in the galvanizing process. 
This sludge must be removed periodically otherwise it will be carried over 
into the galvanizing bath. 
 
2. Soluble iron chloride. Typically, in the preflux solution, the soluble iron 
content far exceeds the insoluble form and it is the soluble iron which is 
therefore of greatest concern. Besides causing increased dross 
production during galvanizing, it also reduces the effectiveness of the 
preflux to chemically clean the steel surface. 
 
Optimum operation of the preflux tank requires, firstly, that water rinsing after pickling is 
carried out as effectively as possible to minimise iron salt carry over and, secondly, that as 
much of the soluble iron in the preflux solution is converted to insoluble iron hydroxide. To 
achieve this conversion, the following procedures are commonly used; 
 
a) Control of the preflux pH between 4.0–5.5. If preflux pH falls below 4.0, 
insoluble iron hydroxide will tend to reconvert to soluble iron. Solutions 
with pH values less than 4.0 can be best adjusted to the optimum range 
(pH 4.0–5.5) by addition of ammonium hydroxide solution (NH4OH). 
 
b) Oxidation of the soluble iron content by either continuous air sparging of 
the preflux solution or by hydrogen peroxide treatment (refer Section 3.6 
on page 41). 
 
 
iv. pH of the preflux solution 
 
As indicated above pH should preferably be maintained in the range 4.0 - 5.5. 
The importance of the 4.0 minimum has been discussed above. Above the 5.5 
maximum, zinc chloride will precipitate from solution as zinc hydroxide and is 
therefore not available for prefluxing the steel. Usually, preflux solutions 
stabilize under normal operating conditions below pH 5.5; however if the pH 
should exceed 5.5 the prefluxsolution can be adjusted back to the optimum 
range by addition of hydrochloric acid. 
 
 
 
 
 
 
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3.2 Summary of Recommended Operating Conditions for the Preflux 
 
Temperature 
 
 Working Range: 60 - 80°C (to facilitate drying of the steel prior to galvanizing) 
 
 
Zinc Ammonium Chloride Concentration (ZAC) 
 
 Optimum Concentration: 200g/L – 300g/L 
 
 
Zinc Chloride to Ammonium Chloride Ratio 
 
 Optimum Ratio: 46% ZnCl2 : 54% NH4Cl 
 
Iron Content (Fe) 
 
 Maximum: 10 g/L 
 Preferable: < 5 g/L 
 
 
Density measured at room temperature 
 
 Working Range: 1,100 – 1,150 Specific Gravity (S.G.) 
 13.2 – 18.9 °Baumé (Bé) 
 
pH 
 
 Working Range: 4.0 – 5.5 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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3.3 Analysis Procedures for the Preflux 
 
A full analysis of the preflux is recommended on a monthly basis. Measurement of density, 
pH and iron content should be done more frequently (e.g. Weekly) and adjustments made 
as appropriate. The analysis procedures are outlined in the following pages and include: 
 
1. Iron content (Section 3.3.1) 
2. Zinc chloride content (Section 3.3.2) 
3. Ammonium chloride content (Section 3.3.3) 
4. Total chloride content (Section 3.3.4) 
5. Density/specific gravity or °Baumé measurement (Sections 3.3.5 – 3.3.8) 
6. pH measurement (Section 3.3.9) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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3.3.1 Iron Content in the Preflux 
 
Equipment Required 
 
- 250mL measuring cylinder with a stopper 
- 25mL measuring cylinder 
- 25mL burette 
- 250mL conical flask 
- adjustable pipette (adjust to 10mL) 
- small plastic funnel 
- Box of No.41 Whatman filter papers 
- 100mL plastic bottle with a screw top lid 
 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
 
- 1L 0.02M potassium permanganate 
- 1L Zimmermann-Reinhardt reagent 
 
 
Method 
 
1. Take a sample of about 100mL from the preflux bath in a plastic bottle and allow it to 
stand to cool to room temperature and settle any sediment. 
 
2. Filter some of this sample into clean 25mL measuring cylinder to the 25mL mark 
exactly. 
 
3. Pout this sample into clean 250mL measuring cylinder and make up to 250mL mark 
exactly with water. Stopper the measuring cylinder and invert several times. 
 
4. Using the clean pipette, dispense 10mL of this dilute solution into the clean conical 
flask and add 15mL Zimmermann-Reinhardt reagent. 
 
5. Fill the clean burette to the zero mark with 0.02M potassium permanganate and 
titrate slowly with the above solution, while swirling the conical flask, until the colour 
turns permanent pale pink. 
 
6. Record the burette reading. This is the endpoint (Titration, E). 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 25 of 62 
 
 
Calculation 
 
Where E is the titration endpoint, the iron content of the preflux is calculated as follows; 
 
 Fe g/L = E x 5.6 
 
 
Example 
 
If the endpoint from the iron titration is 1.7mL, then 
 
 Fe g/L = 1.7 x 5.6 
 = 9.5 g/L 
 
 
Quality Check 
 
Using the above method, check the accuracy of the results with the standard preflux 
solution. Preparation of this standard solution is outlined in Appendix 3 on page 61. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 26 of 62 
 
 
3.3.2 Zinc Chloride Content in the Preflux 
 
Equipment Required 
- 1L volumetric flask, Morbank 
- 150mL beaker 
- 25mL measuring cylinder 
- 50mL burette 
- 250mL conical flask 
- adjustable pipette (adjust to 10mL) 
- small plastic funnel 
- Box of No.41 Whatman filter papers 
- 100mL plastic bottle with a screw top lid 
 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
- 1L 0.01M EDTA solution 
- 500mL 30% hydrogen peroxide 
- 1L hydrochloric acid, technical (30% w/v) 
- 1L buffer solution (pH – 10) 
- 100mL Erichrome black T (Erio T) indicator 
 
 
Method 
CAUTION: Perform this determination in a well-ventilated room or fume cupboard 
because of ammonia fumes 
 
1. Take a sample of about 100mL from the preflux bath in a plastic bottle and allow it to 
stand to cool to room temperature and settle any sediment. 
 
2. Using the clean pipette, take 10mL of solution from the sample and add to the clean 
volumetric flask, and add water to the 1L mark exactly. 
 
3. To this solution add about 2mL of the hydrochloric acid, stopper the volumetric flask 
and invert several times. 
 
4. Using the clean pipette, measure a 10mL sample from this dilute solution into the 
clean beaker, add a few drops of hydrogen peroxide and about 10mL of the buffer 
solution. (NOTE: The solution will have an orange-brown iron precipitate floating in 
it. This is normal and there is no need for concern). 
 
5. The solution will need to be filtered through a No. 41 paper into the clean conical 
flask to remove the iron. After the solution has filtered through, rinse with water 
through the filter paper a few times into the flask. 
 
 ______ Galvanizing Manual_____________ 
Page 27 of 62 
 
6. To the filtered solution add a few drops of Erio T indicator and swirl the flask until 
the indicator mixes. The solution will turn dark red. 
 
 
7. Fill the clean burette to the zero mark with 0.01M EDTA solution and titrate slowly 
with the above solution, while swirling the conical flask, until the colour turns 
permanently dark blue/green. 
 
8. Record the burette reading. This is the endpoint (Titration, F). 
 
 
Calculation 
 
Where F is the titration endpoint, the zinc content of the preflux is calculated as follows; 
 
 Zn g/L = F x 6.538 
 
To convert this to zinc chloride ZnCl2, 
 
 ZnCl2 g/L = Zn g/L x 2.08 
 
 
Example 
 
If the endpoint from the zinc titration is 10mL, then 
 
 Zn g/L = 10 x 6.538 
 = 65.4 g/L 
 
To convert this to zinc chloride ZnCl2, 
 
 ZnCl2 g/L = 65.4 g/L x 2.08 
 = 136 g/L 
 
 
Quality Check 
 
Using the above method, check the accuracy of the results with the standard preflux 
solution. Preparation of this standard solution is outlined in Appendix 3 on Page 61. 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 28 of 62 
 
 
3.3.3 Ammonium Chloride Content in the Preflux 
 
Equipment Required 
- 250mL measuring cylinder 
- 100mL measuring cylinder 
- 150mL beaker 
- 50mL burette 
- 250mL conical flask 
- adjustable pipette (adjust to 1mL) 
- 100mL plastic bottle with a screw top lid 
- distillation apparatus (see Appendix 1, pages 56-58) 
 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
- 1L 0.1N Sulphuric acid 
- 1L 0.1N sodium hydroxide 
- 1L 40% sodium hydroxide 
- 100mL methyl red indicator 
 
 
Method 
CAUTION: Perform distillation behind a Perspex screen or fume cupboard because of 
possible explosion from an acid-base reaction. 
 
1. Set up the distillation apparatus as per diagram. 
 
2. To the clean 150mL beaker (collection vessel), add exactly 50.0mL of the 0.1N 
sulphuric acid, then add a few drops of the methyl red indicator. The solution will 
turn a dark pink. 
 
3. Place this collection vessel below the condenser tip of the distillation apparatus. 
Make sure the tip is immersed in the acid solution. 
 
4. Take a sample of about 100mL from the preflux bath in a plastic bottle and allow it to 
stand to cool to room temperature and settle any sediment. 
 
5. Using a clean pipette, add 1mL of solution from the sample to the clean distillation 
flask with about 150ml of water. 
 
6. To this solution add 50mL of the 40% sodium hydroxide. Seal the flask immediately 
with the glass stopper as the reaction of releasing ammonia takes place immediately. 
 
7. When the distillation is fully set up turn water on at a moderate rate so that it flows 
through the condenser tube continuously duringdistillation. 
 
 ______ Galvanizing Manual_____________ 
Page 29 of 62 
 
 
8. Heat the contents in the distillation flask with a Bunsen burner until boiling occurs. 
Then lessen the heat, continue to boil for 10 minutes and collect the distillate in the 
collection vessel. 
 
9. When distillation has finished (after about 10 minutes); 
 
i. Remove the collection vessel from under the condenser tip, 
ii. Then turn off the Bunsen burner and the water. 
CAUTION: It is important to do this step in this precise order to prevent the distillate 
being sucked back into the distillation flask and causing an EXPLOSION from 
the resultant acid-base reaction. 
10. Empty contents of collection vessel into the clean conical flask. 
11. Fill the clean burette to the zero mark with 0.1N sodium hydroxide and titrate slowly 
with the above solution, while swirling the conical flask, until the colour turns 
permanent yellow. 
12. Record the burette reading. This is the endpoint (Titration, G). 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 30 of 62 
 
 
Calculation 
Where G is the titration endpoint, the ammonia content of the preflux is calculated as 
follows; 
 NH4⁺ g/L = (50.0 – G) x 1.8 
To convert this to ammonium chloride, NH4Cl, 
 NH4Cl g/L = NH4⁺ g/L x 2.96 
 
Example 
If the endpoint from the ammonia titration is 20mL, then 
NH4⁺ g/L = (50.0 – 20) x 1.8 
 = (30) x 1.8 
 = 54 g/L 
To convert this to ammonium chloride, NH4Cl, 
 NH4Cl g/L = 54 x 2.96 
 = 160 g/L 
 
Quality Check 
Using the above method, check the accuracy of the results with the standard preflux 
solution. Preparation of this standard solution is outlined in Appendix 3 on page 61. 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 31 of 62 
 
3.3.4 Chloride Content in the Preflux 
Comment: Determination of chloride content is a useful cross-check procedure, i.e., it 
cross-checks the accuracy of the zinc chloride and ammonium chloride measurements. 
Total chloride content as-measured should not substantially differ from the combined 
chloride contents in the zinc chloride and ammonium chloride determination. Refer to the 
example below. 
 
Equipment Required 
- 100mL measuring cylinder with a stopper 
- 50mL burette 
- 250mL conical flask 
- adjustable pipette (adjust to 1mL for Step 2, then adjust to 10mL for Step 3) 
- 100mL plastic bottle with a screw top lid 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
- 1L of 0.1N silver nitrate 
- 100mL potassium chromate indicator 
- 20L distilled water (IMPORTANT: Water should have no chloride present to affect the 
result) 
 
 
Method 
 
1. Take a sample of about 100mL from the preflux bath in a plastic bottle and allow it to 
stand to cool to room temperature and settle any sediment. 
 
2. Using the clean pipette, take 1mL of solution from the sample and transfer it to the 
clean 100mL measuring cylinder and make up to the 100mL mark with distilled 
water. Stopper the measuring cylinder and invert several times. 
 
3. Using the clean pipette, measure 10mL of this dilute solution into a clean conical 
flask and add about 100mL of distilled water. 
 
4. To this solution, add a few drops of the potassium chromate indicator. The solution 
will turn bright yellow. 
 
5. Fill the clean burette to the zero mark with 0.1Nsilver nitrate and titrate slowly with 
the above solution, while swirling the conical flask, until the colour turns permanent 
orange/brown. 
 
6. Record the burette reading. This is the endpoint (Titration, H). 
 
 ______ Galvanizing Manual_____________ 
Page 32 of 62 
 
 
Calculation 
 
Where H is the titration endpoint, the chloride content of the preflux is calculated as 
follows; 
 
 Cl g/L = H x 35.46 
 
 
Example 
 
If the endpoint of the chloride titration is 5.0mL, then 
 Cl g/L = 5.0 x 35.46 
 = 177 g/L 
Cross-check with ZnCl2 and NH4Cl Determinations 
 
Chloride component of Zinc Chloride 
Where x is the chloride component in zinc chloride, the following formula is used to 
calculate the chloride contribution; 
 y = NH4⁺ g/L x 1.97 
 
Total Chloride 
The total chloride is the sum of the chloride components in zinc chloride and ammonium 
chloride. 
Total Cl g/L = x + y 
 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 33 of 62 
 
 
Cross- check Example 
Using the results from the previous examples of the determination of ZnCl2 and NH4Cl, 
Cl¯ in ZnCl2, 
 x = 65.4 x 1.09 
 = 71 g/L Cl¯ 
Cl¯ in 
 y = 54 x 1.97 
 = 106 g/l Cl¯ 
 
Therefore total Cl¯, 
x + y = 71 + 106.3 
 = 177 g/L Cl¯ 
 
 
Quality Check 
Using the above method, check the accuracy of the results with the standard preflux 
solution. Preparation of this standard solution is outlined in Appendix 3 on page 61. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 34 of 62 
 
 
3.3.5 Density Measurement of the Preflux 
Density of the flux solution at room temperature is a quick but only approximate indication 
of ZAC concentration. The following page shows a graph of ZAC concentration versus 
density, expressed as specific gravity (S.G.), at room temperature. A table converting 
density, in g/mL, to °Baumé (Bé) is also provided on page 36. 
 
 
Equipment Required 
- Hydrometer for Specific Gravity (density range 1000 to 1200, with 0005 subdivisions) 
- 100mL measuring cylinder with a stopper 
 
 
Method 
 
1. Take a 100mL sample from the preflux bath and allow it to stand to cool to room 
temperature and settle any sediment. 
 
2. Pour about 60-70mL of the clear sample into the clean measuring cylinder. 
 
3. Place the hydrometer in the measuring cylinder and spin it to eliminate surface 
tension effects. 
 
4. Read off the specific gravity (S.G.) at the fluid line. 
 
5. Record the specific gravity of the preflux sample. 
 
(See schematic diagram and photograph of specific gravity measurement on pages 37). 
 
NOTE: For example, the S.G. figure read from the hydrometer is 1170, the true 
representation of S.G. is 1.170. 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 35 of 62 
 
 
3.3.6 ZAC Concentration vs S.G. at room temperature 
 
ZAC Concentration vs Specific 
 
 
 
 
 
 
 
 
 
 
 
1.00
1.05
1.10
1.15
1.20
1.25
1.30
100 200 300 400 500 600
S.
G
. 
ro
o
m
 t
e
m
p
e
ra
tu
re
 
ZAC Concentration 
 ______ Galvanizing Manual_____________ 
Page 36 of 62 
 
 
3.3.7 Conversion of Density to °Baumé (Bé) 
There is a formula which can be used to convert density in g/mL to °Baumé (Bé) and vice 
versa. This is shown below: 
Where the density is known and the °Baumé scale is required the following formula can be 
used; 
Bé = °Baumé Bé = 145 – (145) 
d = density in g/mL d 
 
Example 
If the density of the solution is measured to be 1.100 g/mL, then 
 
Bé = 145 – (145) = 13.2 °Baumé 
 1.100 
 
 
 
Conversely, where the °Baumé scale is known and the density is required the following 
formula can be used; 
 
Bé = °Baumé d = 145 
d = density in g/mL (145 – Bé) 
 
Example 
If the of the solution is measured to be 13.2g/mL, then 
 
 d = 145 = 1.100 g/mL 
 (145 – 13.2) 
 
The following table lists the conversion of density in g/mL to °Baumé at room temperature. 
 
Conversion Table 
 
 Density (g/mL) °Baumé (Bé) 
1.000 0 
1.050 6.9 
1.100 13.2 
1.150 18.9 
1.200 24.2 
1.250 29 
1.300 33.5 
 
 
 ______ Galvanizing Manual_____________ 
Page 37 of 62 
 
 
3.3.8 MEASUREMENT OF SPECIFIC GRAVITY 
 
 
 
 
 
 
This photograph and diagram demonstrate how the specific gravity of a particular path 
sample is measured. NOTE; S.G. is read off at the fluid line. In this example the density of 
the sample is 1170 which is expressedas S.G. – 1.170. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 38 of 62 
 
 
3.3.9 pH measurement of the Preflux 
 
The pH level of the preflux should be checked on a regular basis using a portable pH meter 
of pH indicator paper test strips. 
 
 
Equipment Required 
 
a) A portable pH meter 
OR 
b) A box of pH indicator papers 
(The papers should cover the range pH 0 – pH 7 and be graduated in pH = 0.1 
intervals). 
 
 
Method 
 
A. The pH meter needs to be calibrated before use. Refer to manufacturers 
recommendations in the operating manual. Take a preflux sample of about 20mL 
and allow cooling to room temperature, placing the tip of the pH meter in the 
sample and reading off the pH on the digital display. 
(IMPORTANT: Rinse the tip of the pH meter in water and wipe the tip between 
samples). 
 
OR alternatively, 
 
B. Take a preflux sample of about 20mL and allow to cool to room temperature. Take a 
test strip, dip it in the quench sample for a few seconds and upon removal, and 
compare the colours on the test strip to the colour chart on the box. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 39 of 62 
 
 
3.4 Procedure for initial “Make-Up” of the Preflux Solution 
 
1. From Table 1, select the concentration of ZAC (%) required (column 1) to make up 
1000 litres of solution. 
 
2. Read off from the columns 3 and 4 how much ZAC and water are required for every 
1000 litres. 
 
3. Find how many thousands of litres are required to fill the bath. Multiply this with the 
amount of flux and water obtained from the table for the required concentration. 
 
4. Add about half the amount of water to the tank. Then add all the ZAC and mix. 
 
5. Add the remaining water and mix. Then heat up to the required temperature. 
 
 
Table 1. Preparation of ZAC Solution 
 
1 (NB1) 2 3 4 
% ZAC SG (density) at room 
temperature 
kg ZAC for 1000 
litres of solution 
Litres water for 
1000 litres of 
solution 
% w/w % w/v 
5 5.2 1.032 52 980 
10 10.5 1.054 105 949 
15 16.2 1.080 162 918 
20 22.1 1.107 221 885 
25 28.3 1.132 283 850 
30 34.8 1.160 348 812 
35 41.6 1.188 416 772 
40 48.0 1.201 480 721 
 
NB1: 
 
i. % w/w (weight/weight) means grams per 100 grams. If % w/w is multiplied by 
10, grams per kilogram are obtained (g/Kg). 
 
ii. % w/v (weight/volume) means grams per 100 millilitres. If % w/w is multiplied by 
10, grams per litre are derived (g/L). 
 
iii. % w/w and % w/v are related by the Specific Gravity/Density (S.G.), i.e., if % w/w 
is multiplied by S.G., % w/v is obtained. Similarly if % w/v is divided by S.G., % 
w/w is derived. 
 
i.e., % w/w = % w/v 
 S.G. 
 ______ Galvanizing Manual_____________ 
Page 40 of 62 
 
 
3.5 Procedure for Adjustment of the Preflux during Operation 
 
Adjustment of the ZAC Concentration 
During use, the quantity and concentration of the ZAC solution will be decreased. Adjust the 
solution as follows; 
 
Equipment Required 
- 1 hydrometer (density range 1000 to 1200, subdivision 0005) 
- 1 measuring cylinder (100mL) 
 
Method 
1. Take a 60-70mL preflux sample, allow it to cool to room temperature, then pour it 
into the measuring cylinder. 
2. Carefully place the hydrometer in the sample and read off the specific gravity (S.G.) 
of the solution. For example, the figure read from the hydrometer is 1056, this 
should be expressed as 1.056. 
3. Refer this value to the nearest “As measured S.G. (at room temperature)” value in 
Table 2. 
4. Find the “Required S.G.” or “% w/w” on the left hand column. 
5. Move into the middle of the table and read off the point where the two S.G. values 
meet. 
6. This value is the amount of preflux, in kilograms, to add to 1000 litres of flux to 
obtain the desired strength. 
 
Table 2. Adjustment of the ZAC solution 
 
Required 
SG 
%w/w As measured SG (room temperature) 
1.032 1.054 1.080 1.107 1.135 1.16 1.188 
5 10 15 20 25 30 35 
1.032 5 
1.054 10 54 
1.080 15 110 57 
1.107 20 170 116 59 
1.132 25 232 179 122 63 
1.160 30 296 243 186 127 64 
1.188 35 364 311 254 195 132 68 
1.201 40 434 381 324 265 202 138 70 
 
Example: 
The “As Measured S.G. at room temperature” is 1.056. Find the nearest value on the top 
line, i.e., 1.054. You require to increase the preflux concentration to 20% w/w or S.G. 1.107. 
Find this value in the left-hand column. Move to the right from 20% w/w until it reaches the 
column under 1.054. You find 116. Therefore, add 116 kg of ZAC to every 1000 L of preflux 
solution. 
 
If the volume is still too low, find out how many more litres have to be added and refer to 
Table 1 for the quantities, the same as would be done for making up a new small batch. 
 ______ Galvanizing Manual_____________ 
Page 41 of 62 
 
3.6 Iron Control Procedure for the Preflux 
 
Iron is present in the preflux in two forms: an insoluble iron hydroxide (which gives the 
solution its familiar orange-brown colour) and a soluble iron chloride. Typically, the soluble 
iron content far exceeds the insoluble from and it is the soluble iron which is therefore of 
greatest concern. 
 
Excessive (>10 g/L) iron in the preflux impedes fluxing action and results in increased dross 
production. Removal of soluble iron from the preflux may be done in several ways, as 
follows: 
 
i. Air Sparging 
This method is very slow as it requires the bubbling of air through the preflux for 
an extended period. The pH of the preflux must be maintained between 4.0-5.5 
to prevent iron converting back to the soluble form. 
 
Air sparging is carried out on a continuous basis in the operating tank. The 
operation is not efficient, as only a portion of the soluble iron is oxidised and it 
results in disruption to the process. 
 
ii. Hydrogen Peroxide Oxidation 
This is a far more effective method and involves the addition of hydrogen 
peroxide to the preflux in order to rapidly oxidise the soluble iron to the insoluble 
(hydroxide) form. 
 
Traditionally, the operation is done as a batch process, i.e., the preflux is pumped 
into a spare tank and treated. The insoluble iron is then allowed to settle which 
can take a considerable period of time. The clear solution is eventually pumped 
back to the operating preflux tank. 
 
As an alternative, peroxide can be added to the operating tank on a semi-
continuous basis. 
 
In both cases, as the addition of hydrogen peroxide lowers the pH, regular additions of 
ammonium hydroxide (not to be confused with ammonium chloride) are required to ensure 
that pH is maintained between 4.0-5.5. The pH of the preflux should be monitored 
throughout the process so that the appropriate additions of ammonium hydroxide can be 
made. If the pH of the preflux is allowed to drop below pH 4.0, the oxidised iron will begin 
to convert back to the soluble form. It is therefore strongly advised that the hydrogen 
peroxide is not all added at once but instead, progressive separate additions are made, 
with a pH check after each addition and pH adjustment with ammonium hydroxide if 
necessary. 
 
The amount of hydrogen peroxide (H2O2) required depends on H2O2 strength, iron content 
and the volume of the bath. As a guide, one litre of 30% H2O2 is required for every 1300 
grams of iron in the preflux. 
 
 ______ Galvanizing Manual_____________ 
Page 42 of 62 
 
 
Example: 
 
A 20,000 litre preflux with an iron content of 35 g/L. To reduce iron content to say 5 
g/L, H2O2 required; 
 
20,000 litres x 30 g/L = 600,000 grams of iron; 
 
600,000 / 1300 = 460 litres. 
 
Therefore approximately 460 litres of are required to reduce iron in the preflux from 35 g/L 
to 5 g/L. Normally double the amount (920 litres) of ammonium hydroxide is required for 
pH corrections. 
 
 
The level of iron in a preflux can normally be maintained below 10 g/L by paying careful 
attention to pH control and iron carry-over fromthe acid pickle. The pH of the preflux 
should be monitored regularly to prevent it falling below 4.5. Adjustments can be made by 
using ammonium hydroxide. Efficient rinsing after acid pickling will prevent an excessive 
iron carry-over to the preflux. 
 
After treatment has been completed, the preflux liquor strength needs to be checked and 
any appropriate adjustments made. 
 
WARNING – Hydrogen peroxide and ammonium hydroxide are dangerous chemicals and 
require careful handling with all appropriate safety equipment. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 43 of 62 
 
4 QUENCH 
 
4.1 Introductory Comments 
The quench has two functions. The primary function is to cool the freshly galvanized articles 
to a temperature suitable for subsequent handling. The other function of the quench is, 
where sodium dichromate (Na2Cr2O7.2H2O) is intentionally added to water, to apply a thin 
chromate conversion coating to the galvanized coating to prevent white rusting. This is 
termed chromate passivation. 
 
The three main factors controlling the effectiveness of passivation are; 
 
i. The sodium dichromate concentration 
 
Start-up fresh tank 
A recent survey of several galvanizers by ZTS has shown 0.3-0.5 g/L to be an indicative 
sodium dichromate (anhydrous) concentration for start-up (fresh tank). This equivalent to a 
chromium content of 120-200 mg/L (ppm). 
 
To ensure rapid and full dissolution of the chromate, dissolve it into a quantity of hot water 
(>70C) prior to addition to the tank. After one week of operation, increase the chromate 
progressively to the “working tank” levels below. 
 
Working Tank 
A recent survey of several galvanizers by ZTS has shown 0.8-1.2 g/L to be a indicative sodium 
dichromate (anhydrous) concentration for a working tank of quench water. At this 
concentration, the level of free chromium will be 320-480 mg/L (ppm). 
 
Higher concentration solutions may discolour the galvanized coating whilst lower 
concentration solutions may not provide sufficient passivation. The concentration may be 
adjusted by adding sodium dichromate or water to the bath. 
 
These are indicative levels only and individual galvanizers may need to alter sodium 
dichromate concentrations depending on the thickness of work or the atmospheric 
conditions. 
 
ii. The pH of the quench 
The pH of the solution is also important as the passivation process requires a slightly acidic 
solution. The quench pH should be maintained between 5.0-6.5 and sulphuric acid can be 
used to bring pH down to the desired level. 
 
iii. Chloride (Cl) content 
The chloride content is a function of ash/flux carry-over from the galvanizing bath. Chloride 
level should be maintained below 0.5% or 5 g/l. 
 
Although zinc is present in the quench from jigs and galvanized articles, it is not considered a 
problem. 
 ______ Galvanizing Manual_____________ 
Page 44 of 62 
 
 
4.2 Summary of Recommended Operating Conditions for the Quench 
 
Temperature 
 
Working Range: 60-80C 
 
Sodium Dichromate (anhydrous) Concentration (Na2Cr2O7.2H2O) 
 
 Start up (fresh tank) 0.3 – 0.5 g/L 
 
 Working Range: 0.8 – 1.2 g/L 
 
Very thick steel sections can develop a greenish colouration at these chromate levels. If 
plant throughput contains a very substantial proportion of thicker sections, reducing the 
chromate to 0.1% or marginally less should be considered. 
 
Chromium Content (Cr) 
 
 Start up (fresh tank) 120 - 200 mg/L 
 
 Working Range: 320 – 480 mg/L 
 (for the above concentration of sodium dichromate). 
 
Chloride Content (Cl) 
 
 Maximum: 5 g/L (0.5%) max 
 
pH 
 
 Working Range: 5.0 – 6.5 
 
 
4.3 Analysis Procedures for the Quench 
 
A full analysis of the quench should be done on a monthly basis. The methods of analysis 
are outlined over the page which include: 
 
1. Chromium content (Section 4.3.1) 
 
2. Chloride content (Section 4.3.2) 
 
3. pH measurement (Section 4.3.3) 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 45 of 62 
 
 
4.3.1 Chromium Content in the Quench 
 
Equipment Required 
 
- 25mL measuring cylinder 
- 25mL burette 
- adjustable pipette (adjust to 10mL) 
- 100mL plastic bottle with a screw top lid 
- a teaspoon 
 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
 
- 1L 0.1N sodium thiosulphate 
- 1L 10% sulphuric acid 
- 500 g solid potassium iodide 
- 100mL starch solution (VITEX) indicator 
 
 
Method 
 
1. Take a sample of about 100mL from the quench bath in a plastic bottle and allow it 
to stand to cool to room temperature and settle any sediment. 
 
2. Using a clean pipette, measure 10mL of the sample into the clean conical flask, and 
add 20mL of sulphuric acid. 
 
3. To this solution add 2g (about half a teaspoon) of potassium iodide. The solution will 
turn yellow through to red/brown depending on the chromate content. Stir 
vigorously for 5 minutes. 
 
4. Add a few drops of starch (VITEX) indicator. The solution will turn dark brown/black. 
 
5. Fill the clean burette to the zero mark with 0.1N sodium thiosulphate and titrate 
slowly with the above solution, while swirling the conical flask, until the black colour 
turns clear. 
 
6. Record the burette reading. This is the endpoint (Titration, J). 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 46 of 62 
 
 
Calculation 
 
Where J is the titration endpoint, the chromium content of the quench is calculated as 
follows; 
 
 Cr mg/L = J x 173.4 
 
 
Example 
 
If the endpoint of the chromium titration is 3mL, then 
 
 Cr mg/L = 3 x 173.4 
 
 = 520.2 mg/L 
 
 
Quality Check 
 
Using the above method, check the accuracy of the results with the standard quench 
solution. Preparation of this standard solution is outlined in Appendix 3 on page 61. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 47 of 62 
 
 
4.3.2 Chloride Content in the Quench 
 
Equipment Required 
 
- 100mL measuring cylinder 
- 25mL burette 
- 250mL conical flask 
- adjustable pipette (adjust to 5mL) 
- 100mL plastic bottle with a screw top lid 
 
 
Reagents Required (see preparation of these in Appendix 2, page 59) 
 
- 1L 0.1N silver nitrate 
- 100mL potassium chromate indicator 
- 20L distilled water 
(IMPORTANT: Water should have no chloride present to affect the result) 
 
 
Method 
 
1. Take a sample of about 100mL from the quench bath in a plastic bottle and allow it 
to stand to cool to room temperature and settle any sediment. 
 
2. Using a clean pipette, measure 5mL of the sample into the clean conical flask, and 
add about 100mL of distilled water. 
 
3. To this solution, add the potassium chromate indicator. The solution will turn bright 
yellow. 
 
4. Fill the clean burette to the zero mark with 0.1N silver nitrate and titrate slowly with 
the above solution, while swirling the conical flask, until the colour turns permanent 
orange/brown. 
 
5. Record the burette reading. This is the endpoint (Titration, K). 
 
 
 
 
 
 
 
 
 
 
 ______ Galvanizing Manual_____________ 
Page 48 of 62 
 
 
Calculation 
 
Where K is the titration endpoint, the chloride content of the quench is calculated as 
follows; 
 
 Cl g/L = k x 0.7092 
 
 
Example 
 
If the endpoint of the chloride titration is 3mL, then 
 
 Cr mg/L = 3 x 0.7092 
 
 = 2.1 g/L 
 
 
Quality Check 
 
Using the above method, check the accuracy of the results with the standard quench 
solution. Preparation of this standard solution is outlined in Appendix 3 on page 61. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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4.3.3 pH Measurement of the Quench 
 
The pH level of the quench should be checked on a regular basis using a portable pH meter 
of pH indicator paper test strips. The method for this is outlined below. 
 
 
Equipment Required 
 
c) A portable pH meter 
OR 
d) A boxof pH indicator papers 
(The papers should cover the range pH 0 – pH 7 and be graduated in pH = 0.1 
intervals). 
 
 
Method 
 
C. The pH meter needs to be calibrated before use. Refer to manufacturers 
recommendations in the operating manual. Take a quench sample of about 20mL 
and allow to cool to room temperature, place the tip of the pH meter in the sample 
and read off the pH on the digital display. 
(IMPORTANT: Rinse the tip of the pH meter in water and wipe the tip between 
samples). 
 
OR alternatively, 
 
D. Take a quench sample of about 20mL and allow to cool to room temperature. Take a 
test strip, dip it in the quench sample for a few seconds and upon removal, and 
compare the colours on the test strip to the colour chart on the box. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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5 ZINC BATH METAL SAMPLING 
Procedures for in-house analysis of zinc metal are relatively complex. For this reason, it is 
recommended that a zinc bath sample be forwarded to Nyrstar Technical Support for 
analysis on a regular basis. The instrumentation used by Nyrstar is an Optical Emission 
Spectrophotometer (OES). This requires that samples be submitted in the form of a disc 
that can be readily accommodated in the instrument. This zinc disc is often referred to as a 
spectrographic button. The following page provides a drawing of the mould required to 
produce the zinc disc. The recommended procedure for sampling the zinc bath metal is 
provided below. 
 
Results of analysis of samples submitted to Nyrstar in the above form can usually be 
despatched to the galvanizer within 48 hours from time of receipt. Non-standard sample 
shapes may require lengthy preparation for analysis and consequently, much longer 
turnaround times can be expected. In some circumstances, this may render the analysis 
result less representative of the current bath composition. 
 
 
5.1 Procedure for Zinc Bath Sampling 
 
Equipment Required 
- skimming table (skimmer) 
- small ladle (see photo on page 52) 
- spectrographic button mould (see drawing over page) 
 
Method 
1. Scrape the ash off the surface of the zinc bath with the skimming blade prior to 
sampling. 
2. Use the small steel ladle to scoop a sample from the surface of the galvanizing bath. 
Ensure ladle is heater prior to sampling to prevent splashing of the molten zinc. 
IMPORTANT: Do not take a zinc bath sample straight after additions of 
aluminium or nickel have been made as the results may not be representative. 
3. Cast the molten zinc sample from the small ladle into the dry spectrographic button 
mould and allow to solidify. 
IMPORTANT: Do not use hot spectrographic button moulds as they produce 
button samples that are not representative of the galvanizing bath due to 
segregation during solidification of the sample. 
 
CAUTION: Do not cast molten zinc into a wet spectrographic mould as an explosion 
can occur due to the resultant hot metal-water reaction. 
 
4. Discard the sample that has been cast then repeat the procedure from Step 2. 
Retain this second sample for analysis. 
IMPORTANT: This double sampling is recommended as the first sample can 
be affected by any residual moisture, e.g. from condensation, in the mould. 
5. Remove the spectrographic button from the mould when cool enough to do so and 
send to Nyrstar for analysis. 
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5.1.1 Spectrographic Button Mould 
 
 
 
 
 
 
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5.1.2 STEEL LADLE FOR ZINC BATH METAL SAMPLING 
 
 
This photograph shows an example of the type of small steel ladle that can be used to 
transfer a sample of molten zinc bath metal to the spectrographic button mould. 
 
 
 
 
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6 APPENDIX 1 – Facilities and Equipment 
6.1 Facilities Required 
Preferably analysis of process liquors should be done in a dedicated room around 3m x 3m 
in size. If this is not available, alternatively, the equipment can be stored in cupboards and 
used as required. The following facilities are required, in either situation; 
- running water with a sink. 
- electricity for lighting and power. 
- gas supply either on-line or bottle for the Bunsen burner. 
- air conditioning to maintain clean environment. 
 
6.1.1 Laboratory Equipment Required 
- 50mL (PMP or TPX) plastic beaker 
- 150mL (PMP or TPX) plastic beaker 
- 1L (PMP or TPX) plastic volumetric flask, Morbank 
- 250mL measuring cylinder with a stopper 
- 100mL measuring cylinder with a stopper 
- 25mL measuring cylinder 
- 0-10mL adjustable pipette 
- dropper 
- teaspoon 
- small plastic funnel 
- 250mL plastic wash bottle 
- 100mL plastic bottles 
- a box of No.41 Whatman filter papers 
- hydrometer (density range 1000-1200, 0005 graduations) 
- portable pH meter of pH indicator papers (pH – 0.1 intervals) 
- measuring balance (optional) – (necessary when preparing own reagents, indicators 
and standard solutions). Able to measure up to 150g and be accurate to 0.01g. 
- titration apparatus (see pages 54-55 for set up details) 
- distillation apparatus (see pages 56-58 for set up details) 
- Perspex screen or fume cupboard with a sink and running water for distillation 
 
Note: PMP and TPX are special high temperature, high clarity plastics. 
 
6.1.2 Safety Equipment 
- safety glasses 
- rubber gloves 
- leather shoes 
- laboratory coat (optional) 
- face shield (optional) 
- safety shower and eyewash station 
 
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6.2 Titration Equipment 
 
A schematic diagram, is shown below, along with a photograph of the set on the following 
page. 
 
 
Equipment Required 
 
- burette clamp 
- burette stand 
- 50mL (PMP or TPX) plastic burette 
- 25mL (PMP or TPX) plastic burette 
- 250mL (PMP or TPX) plastic conical flask 
 
 
 
 
 
 
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6.2.1 TITRATION APPARATUS 
 
 
 
This photograph shows the typical set up for the titration apparatus. 
 
 
 
 
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6.3 Distillation Equipment 
A schematic diagram along with a photograph of the set up is included on the following 
pages. 
 
Equipment Required 
- 1 x Bunsen burner (with gas supply) 
- 2 x Bossheads 
- 2 x clamps 
- 1 x stand 
- 1 x 150mL beaker 
- 1 x 250mL round bottom flask, two necks: (side neck at 20 angle, socket size 
19/24) 
 (centre neck socket size 24/29) 
 
- 1 x glass stopper: (cone size 19/24) 
 
- 1 x splash head condenser, straight: (cone size 24/29) 
 (jacket length 250mm) 
 
- 1 x condenser tube (Leibig): (socket size 24/29) 
 (jacket length 250mm) 
 
- 2 x adapters: cone to nozzle, without stopcock: 
 1 to fit splash head, angled nozzle 90 - (cone size 19/24) 
 (angled nozzle 8mm OD) 
 
 1 to fit condenser tube, straight nozzle - (cone size 24/29) 
 (straight nozzle 8mm OD) 
 
- 2 x 0.5 PVC plastic tubing: 
 1 for cold water from tap to condenser inlet (8mm ID) 
 1 for cold water from condenser outlet to sink (8mm ID) 
 
- 1 x 0.5m high temperature plastic tubing: 
 Join splash head adapter nozzle with condenser tube adapter nozzle (8mm ID). 
 
IMPORTANT: For safety reasons the distillation will need to be performed in a fume 
 cupboard or behind a Perspex screen. 
 
A sink and running water in the fume cupboard is preferred. 
 
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6.3.1 DISTILLATION APPARATUS (Analysis of Ammonia in Preflux Solution)This photograph shows the general set up of the distillation apparatus. 
 
 
 
 
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7 APPENDIX 2 - Reagents and Indicators 
Reagents Required 
Available as “off the shelf” Reagents 
- 1L 0.1 N hydrochloric acid 
- 2.5L hydrochloric acid, technical (30% w/v) 
- 500mL 30% hydrogen peroxide 
- 500g potassium iodide 
- 1L 0.02 M potassium permanganate 
- 1L 0.1 N silver nitrate 
- 1L 0.1 N sodium hydroxide 
- 1L 0.1 N sodium thiosulphate 
- 1L 0.1 N sulphuric acid 
- 1L 10% w/w sulphuric acid 
 
 
Reagents to be Prepared (see details of preparation on page 60) 
- 1L buffer solution (pH – 10) 
- 1L 0.01 M EDTA solution 
- 1L 0.548N sodium bicarbonate 
- 1L 40% sodium hydroxide 
- 1L Zimmermann-Reinhardt reagent 
 
 
Indicators Required (see details of preparation listed on page 60) 
- 100mL bromocresol green indicator 
- 100mL eriochrome black T (Erio T) indicator 
- 100mL methyl red indicator 
- 100mL phenolphthalein indicator 
- 100mL potassium chromate indicator 
- 100mL starch solution (VITEX) 
 
 
Other Chemicals Required (for preparation of reagents and indicators) 
- 500g ammonium chloride 
- 2.5L ammonium hydroxide 
- 20L distilled water 
- 2.5L ethanol 
- 500g magnesium sulphate, hydrated 
- 2.5L 85% phosphoric acid 
- 2.5L 98% sulphuric acid 
- 2.5L triethanolamine 
 
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7.1 Preparation of Reagents and Indicators 
Reagents 
Buffer solution (pH 10) – Weigh out 70g ammonium chloride, then dissolve in 568mL of 
ammonium hydroxide and make up to the 1L mark exactly in a volumetric flask with distilled 
water. 
0.01M EDTA solution – Dissolve 3.72g of A.R. disodium dihydrogen ethylenediaminetetra-
acetate dehydrate (EDTA) in distilled water and make up to the 1L mark exactly in a 
volumetric flask with distilled water. 
0.548N Sodium Bicarbonate – Dissolve 46g of sodium bicarbonate in distilled water and 
make up to the 1L mark exactly in a volumetric flask with distilled water. 
Zimmermann-Reinhardt Reagent – Dissolve 70g of manganese sulphate in 500mL of water, 
cautiously add 125mL (98%) sulphuric acid and 125mL (85%) phosphoric acid, and make up 
to 1L mark exactly with water. 
 
CAUTION: 40% sodium hydroxide solution and Zimmermann-Reinhardt reagent. 
(Preparation of these solutions must be performed in a fume cupboard or behind a Perspex 
screen for safety reasons as an explosion can result). 
 
Indicators 
Bromocresol Green – generally available as “off the shelf” solution. 
 Dissolve 0.1 g of bromocresol green in 100mL of distilled water. 
 
Eriochrome Black T (Erio T) 
 Dissolve 1g of eriochrome black T dyestuff in 75mL of triethanlamine and 25mL of ethanol. 
 
Methyl Red – generally available as “off the shelf” solution. 
 Dissolve 0.1 g of methyl red, water soluble sodium salt, in 100mL of distilled water. 
 
Phenolphthalein 
 Dissolve 0.5g of solid phenolphthalein in 50mL of absolute alcohol, then add 50mL of 
 distilled water. 
 
Potassium Chromate 
 Dissolve 5g of solid potassium chromate in 100mL of distilled water. 
 
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Starch Solution (VITEX) 
 Dissolve 1g of solid VITEX indicator in 100mL of distilled water. 
 
8 APPENDIX 3 Quality Check & Preparation of Standard 
Solutions 
 
Equipment Required 
 
- 500mL (PMP or TPX) plastic volumetric flasks 
- 500mL (PMP or TXT) plastic beaker 
- measuring balance 
- 250mL measuring cylinder 
 
 
Reagents Required 
 
- distilled water 
- 2.5mL hydrochloric acid, technical (30% w/v) 
- 500g iron (II) sulphate, heptahydrate (FeSO4.7H2O) 
- 500g sodium chloride 
- 500g sodium dichromate 
- 500g sodium hydroxide pellets 
- 500g sodium carbonate, anhydrous 
- 1L 10% w/w sulphuric acid 
- 500g zinc ammonium chloride (ZAC) 
 
 
Preparation of Standard Solutions 
 
Sodium hydroxide (Standard composition: NaOH – 80 g/L; Ratio – 0.9) 
Dissolve 40g of sodium hydroxide pellets along with 5g of sodium carbonate in about 
150mL of distilled water in a clean beaker. Transfer this solution to a clean 
volumetric flask and make up to the 500mL mark exactly with distilled water. 
Stopper the flask and invert several times. 
 
Acid (Standard composition: HCl – 120 g/L : Fe – 50 g/L) 
Add 174mL of hydrochloric acid to about 150mL of distilled water in a clean beaker, 
then dissolve 125g of iron sulphate. Transfer this solution to a clean volumetric flask 
and make up to the 500mL mark exactly with distilled water. Stopper the flask and 
invert several times. 
 
Preflux (Standard composition: Fe 10g/L, Zn 65g/L, NH4⁺ 55g/L, Cl 180g/L) 
Dissolve 150g of ZAC along with 25g of iron sulphate in about 150mL of distilled 
water in a clean beaker. In addition, 10mL of sulphuric acid will need to be added to 
the solution to stop the iron oxidising to form a precipitate. Transfer this solution to 
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a clean volumetric flask and make up to the 500mL mark exactly with distilled water. 
Stopper the flask and invert several times. 
 
 
Quench (Standard composition: Cr 500mg/L, Cl 2g/L) 
Dissolve 0.72g of sodium dichromate along with 1.64g of sodium chloride in 150mL 
of distilled water in a clean beaker. Transfer this solution to a clean volumetric flask 
and make up to the 500mL mark exactly with distilled water. Stopper the flask and 
invert several times. 
 
 
Perform the analysis on each standard solution as per the relevant method described in 
Section 8.3 through to Section 8.6. 
 
Check the accuracy of your bath samples with those of your prepared solutions. 
 
 
NOTE: The results from those standard solutions should be recorded as part of your Quality 
 assurance.