Leaching of pyrolusite using molasses alcohol wastewater as a reductant

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Minerals Engineering 22 (2009) 207–209
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Minerals Engineering
journal homepage: www.elsevier .com/locate /mineng
Technical Note
Leaching of pyrolusite using molasses alcohol wastewater as a reductant
Haifeng Su, Yanxuan Wen, Fan Wang, Xuanhai Li, Zhangfa Tong *
School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
a r t i c l e i n f o a b s t r a c t
Article history:
Received 21 December 2007
Accepted 22 May 2008
Available online 9 July 2008
Keywords:
Pyrolusite
Molasses alcohol wastewater
Sulfuric acid leaching
Reductive leaching
0892-6875/$ - see front matter � 2008 Elsevier Ltd. A
doi:10.1016/j.mineng.2008.05.006
* Corresponding author. Tel.: +86 771 3233728; fax
E-mail addresses: bioche@gxu.edu.cn, zhftong@sin
Extraction of manganese from a pyrolusite ore was investigated using molasses alcohol wastewater as a
reducing agent in dilute sulfuric acid medium. The effects of molasses alcohol wastewater dosage, con-
centration of sulfuric acid, leaching temperature and reaction time were studied. High manganese recov-
ery, coupled with relatively low Fe and Al extraction yields, was obtained with this leaching process. The
optimal leaching conditions were obtained using 1.9 mol/L H2SO4 and 2.0 mL/g ratio of molasses alcohol
wastewater to pyrolusite for 120 min at 90 �C. These conditions resulted in leaching yields of 93% for Mn,
with relatively low recoveries of 37% for Fe and 25% for Al.
These results demonstrate that molasses alcohol wastewater is a low cost resource, containing renew-
able and non-hazardous reducing agents (when compared to other available reagents) that can be used
for manganese leaching under mild acidic conditions. In short, the method provides a good extraction
yield while making an economically productive use of molasses alcohol wastewater.
� 2008 Elsevier Ltd. All rights reserved.
1. Introduction
Hydrometallurgical treatment of low-grade manganese oxide
ores has attracted great attention in recent years. Various routes
have been developed and reported for use in the aqueous leaching
of manganese oxide ores. Specifically, the ores can be treated by
reduction roasting, followed by acid leaching (Sahoo and Srinivasa,
1989) or directly by reductive acid leaching using different acidic
reducing agents and acids (Vegliò and Toro, 1994; Kanungo,
1999; Momade and Momade, 1999; Naik et al., 2000; Trifoni
et al., 2001; Furlani et al., 2006; Hariprasad et al., 2007).
The use of organic reductants to leach pyrolusite has been
shown to be both simple and efficient. However, there has been lit-
tle commercial application of this technique, due to the expense of
the reductant and its high consumption rate in the process.
At the same time, fermentation of cane sugar molasses to produce
ethyl alcohol is a very large and growing agro-based chemical indus-
try in China, India and South America. 12–17 m3 of wastewater are
generated for every 1 m3 of alcohol produced. This wastewater has
a high chemical oxygen demand (COD) (6 � 104�2 � 105 mg/L)
and biochemical oxygen demand (BOD) (2.5 � 104�7.5 � 104 mg/
L), reflecting the presence of high concentrations of carbohydrates,
reducing sugars, dissolved lignin, proteins, alcohols, waxes and
other organic compounds. This organic content gives the wastewa-
ter a high reducing capacity in an acid medium, which can be
exploited as an extraction medium to recover metals (including
Mn) in metallic ores. The chemical reactions which take place during
ll rights reserved.
: +86 771 3233718.
a.com (Z. Tong).
dissolution of the manganese dioxide in the presence of sucrose (Ve-
gliò and Toro, 1994) or glucose (Trifoni et al., 2001) can be described
by the following reactions:
24MnO2 þ C12H22O11 þ 24H2SO4 ¼ 24MnSO4 þ 12CO2 " þ35H2O
ð1Þ
12MnO2 þ C6H12O6 þ 12H2SO4 ¼ 12MnSO4 þ 6CO2 " þ18H2O
ð2Þ
2. Materials and methods
2.1. Materials
Manganese ore was obtained from Mugui Manganese Mine,
Guangxi, China. Both the bulk and sieved samples were character-
ized by powder X-ray diffraction (XRD, Rigaku model D/max-2500,
Rigaku Co., Japan) to define the mineralogical structure and phase
purity. From the XRD pattern, the main metallic minerals were
determined to include pyrolusite (MnO2), hematite (Fe2O3) and gan-
gue minerals consisting primarily of quartz (SiO2) and kaolinite (Al2-
Si2O5(OH)4). The ore sample used in the experiment contains 25.21%
Mn, 13.58% Fe, 8.47% Si, 5.36% Al, 0.516% Ca, 0.064% Mg, 0.003% S and
0.095% P. The ore was crushed, ground, and passed through a 0.147
mm (100 mesh) sieve prior to use in the experiment.
Molasses alcohol wastewater (Nanning Sugarcane Refinery,
Guangxi, China), containing 7.3% organic compounds, 2.9% reduc-
ing sugars, CODCr 1.3 � 105 mg/L, BOD5 7.0 � 104 mg/L, was used
in this work.
All other chemicals used in this study were of analytical grade
and were used without further purification.
208 H. Su et al. / Minerals Engineering 22 (2009) 207–209
2.2. Leaching procedure
The leaching experiments were carried out in a 250 mL three-
neck flask equipped with an impeller stirrer, thermometer, sampler
and condenser and immersed in a thermostatically controlled water
bath. In a typical experiment, the liquid-to-solid ratio was fixed as
5:1 (mL/g). A measured sample of 10.0 g sieved (100 mesh) manga-
nese ore was first added to an aqueous sulfuric acid solution (e.g.,
1.9 mol/L). An amount of molasses alcohol wastewater was added
to make to a specific wastewater-to-pyrolusite ratio mixture (e.g.,
2.0 mL/g). The mixture was stirred at�200 rpm at constant temper-
ature (e.g., 90 �C) for a certain period of time (e.g., 150 min), after
which the slurry was filtered and the residue washed with distilled
water. The filtrate plus washwater was diluted with a HNO3 solution
(maintaining pH = 2) prior to analysis of the Mn, Fe, and Al content by
an inductively coupled plasma spectrophotometer (ICP, Optima
5300 DV, Perkin–Elmer, USA). Chemical oxygen demand (COD) and
biochemical oxygen demand (BOD) were also determined, using
standard methods for the examination of water and wastewater
(APHA, AWWA, WPCF, 1998).
3. Results and discussion
3.1. Effect of molasses alcohol wastewater dosage on leaching efficiency
In order to evaluate the effect of molasses alcohol wastewater
dosage on the leaching efficiency, a series of leaching experiments
was carried out in which the ratio of molasses alcohol wastewater
to pyrolusite varied from 0.0 to 2.5 mL/g while keeping the initial
H2SO4 concentration fixed at 2.0 mol/L, the temperature at 90 �C
and the extraction time at 150 min (Table 1). Under these condi-
tions the leaching efficiencies of Mn increased with increasing
molasses alcohol wastewater dosage. The amount of Al extracted
increased at a lower rate and the amount of Fe extracted actually
decreased after a point, a phenomenon that has been reported else-
where (Momade and Momade, 1999). The leaching efficiency of
Mn reached a plateau of about 93% around 2.0 mL/g ratio of molas-
ses alcohol wastewater to pyrolusite.
Table 1
Effect of molasses alcohol wastewater, H2SO4, temperature and time upon the
leaching efficiencies of Mn, Fe and Al
Rwp
a (mL/g) H2SO4 (mol/L) T (�C) t (min) Leaching efficiency (%)
Mn Fe Al
0.0 2.0 90 150 0.6 1.9 18.2
0.4 2.0 90 150 55.4 46.1 23.7
1.0 2.0 90 150 80.4 43.3 25.7
1.5 2.0 90 150 87.6 39.7 25.6
2.0 2.0 90 150 93.7 37.8 25.9
2.5 2.0 90 150 96.7 37.5 27.3
2.0 0.0 90 150 0.0 0.0 0.0
2.0 0.4 90 150 58.4 9.4 7.2
2.0 0.8 90 150 67.0 12.4 13.5
2.0 1.5 90 150 85.1 26.1 20.8
2.0 1.9 90 150 93.5 37.4 25.4
2.0 2.3 90 150 97.3 44.3 30.0
2.0 1.9 30 150 27.6 21.3 16.3
2.0 1.9 50 150 57.4 24.6 18.6
2.0 1.9 70 150 80.8 27.7 20.9
2.0 1.9 80 150 88.6 31.8 22.7
2.0 1.9 90 150 93.4 37.6 25.5
2.0 1.9 95 150 94.9 39.8 27.1
2.0 1.9 90 10 51.4 11.4 7.8
2.0 1.9 90 30 78.2 23.4 12.7
2.0 1.9 90 60 85.3 29.5 18.0
2.0 1.9 90 90 88.5 32.6 22.3
2.0 1.9 90 120 93.2 37.3 25.3
2.0 1.9 90 180 96.1 38.9 27.6
a Rwp is the ratio of molasses alcoholwastewater to pyrolusite.
3.2. Effect of H2SO4 concentration on leaching efficiency
A series of leaching experiments was carried out using a 2.0 mL/
g ratio of molasses alcohol wastewater to pyrolusite at different
initial H2SO4 concentrations, ranging from 0.0 to 2.3 mol/L. The
data in Table 1 show that the leaching efficiencies of all three met-
als – Mn, Fe and Al – increased as the H2SO4 concentration in-
creased. The leaching efficiency of Mn was 93.5% at an acid
concentration of 1.9 mol/L. Increasing the H2SO4 concentration
from 1.9 to 2.3 mol/L slightly improved the leaching efficiency of
Mn from 93.5% to 97.3%. However, the Fe extraction increased from
37.4% to 44.3% and the Al extraction increased from 25.4% to 30.0%.
Therefore, 1.9 mol/L for the initial H2SO4 concentration is sufficient
to recover more than 90% of the manganese, with acceptably lower
levels of Fe and Al being co-recovered.
3.3. Effect of temperature on leaching efficiency
The data in Table 1 show that metal extraction from the manga-
nese ore also strongly depends on the reaction temperature. As the
temperature was increased from 30 to 95 �C, the leaching effi-
ciency for Mn increased from 27.6% to 94.9%. At the same time,
the extraction of Fe increased from 21.3% to 39.8% and extraction
of Al increased from 16.3% to 27.1%.
3.4. Effect of time on leaching efficiency
Controlled experiments on leaching time were conducted to
gain further insight into the most favorable reaction conditions.
The data in Table 1 show that the leaching efficiencies of Mn, Fe
and Al increased with increasing leaching time and plateaued
when the leaching time is over 120 min.
4. Conclusions
A reductive leaching process for a pyrolusite ore has been suc-
cessfully demonstrated for the first time using a mixture of sulfuric
acid and molasses alcohol wastewater as a reductant. The results
indicate that the leaching efficiencies of all the studied metal quan-
tities increase as the H2SO4 concentration, reaction time and tem-
perature increase. When the molasses alcohol wastewater dosage
increases, the leaching efficiency of Mn increases while there is
comparatively little change in Al recovery, and after a point the
Fe recovery actually decreases.
This leaching technology is optimized at 1.9 mol/L H2SO4 and
2.0 mL/g ratio of molasses alcohol wastewater to pyrolusite at
90 �C for 120 min. The leaching efficiency of Mn is more than
93% under these conditions while the Fe and Al recoveries are
about 37% and 25%, respectively.
In a subsequent step when the pH > 5, the Al3+ and Fe3+ in the
solution would be transformed into hydroxide precipitate which
can be removed easily, leaving only the manganese in solution.
Therefore, reductive atmospheric leaching of pyrolusite ore
using molasses alcohol wastewater and sulphuric acid medium is
a feasible technology for extracting manganese. Considering that
the process productively uses molasses alcohol wastewater from
the sugar industry, the technology should be beneficial from both
an economic and an environmental perspective.
Acknowledgements
This work was financially supported by Natural Science Foun-
dation of Guangxi (Grant No. 0832035) and Scientific Research Pro-
ject of Education Department of Guangxi, China (No. [2006]26).
The authors wish to express their gratitude to Dr. Donald Barnes,
H. Su et al. / Minerals Engineering 22 (2009) 207–209 209
guest professor of Guangxi University, for helpful discussion and
edition in grammar.
References
APHA, AWWA, WPCF, 1998. Standard Methods for Examination of Water and
Wastewater, 20thed., United Book Press, Ind. Maryland, USA.
Furlani, G., Pagnanelli, F., Toro, L., 2006. Reductive acid leaching of manganese
dioxide with glucose: identification of oxidation derivatives of glucose.
Hydrometallurgy 81, 234–240.
Hariprasad, D., Dash, B., Ghosh, M.K., Anand, S., 2007. Leaching of manganese ores
using sawdust as a reductant. Miner. Eng. 20, 1293–1295.
Momade, F.W.Y., Momade, Zs.G., 1999. Reductive leaching of manganese ore in
aqueous methanol–sulphuric acid medium. Hydrometallurgy 51, 103–113.
Naik, P.K., Sukla, L.B., Das, S.C., 2000. Aqueous SO2 leaching studies on Nishikhal
manganese ore through factorial experiment. Hydrometallurgy 54, 217–228.
Kanungo, S.B., 1999. Rate process of the reduction leaching of manganese nodules in
dilute HCl in presence of pyrite. Part 1: Dissolution behavior of iron and sulphur
species during leaching. Hydrometallurgy 52, 313–330.
Sahoo, P.K., Srinivasa, R.K., 1989. Sulphating-roasting of low grade manganese ore:
optimisation by factorial design. Int. J. Miner. Process 25 (1–2), 147–152.
Trifoni, M., Toro, L., Vegliò, F., 2001. Reductive leaching of manganiferous ores by
glucose and H2SO4: effect of alcohols. Hydrometallurgy 59, 1–14.
Vegliò, F., Toro, L., 1994. Fractional factorial experiments in the development of
manganese dioxide leaching by sucrose in sulphuric acid solutions.
Hydrometallurgy 36, 215–230.