Title of Invention

"AN IMPROVED PROCESS FOR EXTRACTION OF ZINC FROM SULPHIDE CONCENTRATE"

Abstract The present invention provides an improved process for extraction of zinc from its sphalerite concentrate by oxidative leaching with persulphate salt thereby dissolving zinc in sulphuric acid medium and producing elemental sulphur, which enters the residue phase. The leach liquor is purified by known manner and electrolysed to produce the zinc metal.
Full Text The present invention relates to an improved process for extraction of zinc from sulphide concentrate.
This invention particularly relates to the extraction of zinc from its sphalerite concentrate by oxidative leaching with persulphate salts thereby dissolving zinc in sulphuric acid medium and producing elemental sulphur, which enters the residue phase. The invention is important in view of developing innovative process know-how because of increasing demand of zinc globally including India.
The current production and consumption of zinc world over is nearly 8 million tons. The production capacity in India is of the order of 1,82,000 MTPY (metric tonnes per year) in the primary sector and 50,000 MTPY in the secondary sector. About 70% of zinc produced in India is used for galvanising applications and the consumption of zinc is going to increase further. Therefore, to meet the ever-growing demand and environmental norms, the effort has been made to provide a cost effective process for recovery of zinc.
Conventional methods for recovery of zinc from zinc concentrate usually follow roasting - leaching - electrowinning or pressure leaching - electrowinning processes. The problem associated with former one is emission of SO2 gas in the roasting step and setting up of sulphuric acid plant as a prerequisite for zinc smelters, whereas latter has several problems associated with the operation and maintenance of the autoclaves. Therefore, direct oxidative leaching is one of the options that needs to be explored.
Several attempts have been made to recover zinc from zinc sulphide by direct leaching process. Leaching of sphalerite under oxygen atmosphere in concentrated ammonium chloride solution in presence of cupric ion has been studied by Limp (Limp J. L., Revista de metallurgia, 1997, Vol. 33, p. 258). The process introduces copper as one of the ingredients, which needs to be recovered by cementation/solvent extraction prior to zinc recovery, thus requiring additional steps upsetting the economic return. Simultaneous dissolution of Sphalerite and pyrolusite in acidic media is reported by several researchers for production of zinc metal and electrolytic manganese dioxide (Pandey A. M., Gupta K. N. and Altekar V. A., Hydrometallurgy, 1982, Vol. 9, P. 57; Altekar V. A., Pandey, A. M. and Gupta K. N., Indian Patent No. 147948; Srinivasa Rao K. and Paramaguru R. K., Mineral and Metallurgical
processing , 1998, Vol. 15(1), p.-29; Lo W. W. Surges, L. J. and Hancock, H.A., Nov. 10-13, 985,
Cong. : Complex sulphides - Processing of ores, Concentrates and by-products, San Diego,
California, p-907). The process suffers from the drawbacks of high energy requirement in leaching,
solution purification and electrowinnng have to be carried out at 85 - 95°C, besides the possible
problem of cell operation involving both the active electrodes for the purpose of deposition. Behavior
of ferric ionin acid media on dissolution kinetics of sphalerite concentrate is also investigated by
several workers (Zim Z. M., Warren G.W. and Henein H., 1993, Int . J. Min. Processing, Vol. 37, P.-
223; Lachmann J. and Pedlick M., Hydromet 1995, Vol. 37, p.-89). The poor zinc recovery was
observed in these investigations even in presence of surfactants, because of firm adherence of freshly
generated sulphur and other reaction products on the unreacted sphelerite particles.
Though several attempts have been made for oxidative leaching of sphalerite concentrate in presence
of oxidizing substances such as Cu(ic), Fe(ic) salts and oxygen for recovery of zinc, till date no report
appears for using ammonium/sodium persulphates as oxidant for direct leaching from its sulphide
concentrate/ore.
The main objective of the present invention is to provide an improved process for extraction of zinc
from sulphide concentrate which obviates the drawbacks as detailed above.
Another objective of the present invention is to an improved process for extraction of zinc from its
sphalerite concentrate by oxidative leaching with persulphate salt thereby dissolving zinc in sulphuric
acid medium and producing elemental sulphur, which enters the residue phase.
Accordingly, the present invention provides an improved process for extraction of zinc from sulphide
concentrate characterized in that:
i) preparing a solution comprising sulphuric acid and an oxidizing agent selected from
ammonium and sodium persulphate salt in an amount such as herein described , ii) adding zinc concentrate to the above solution and stirring by a magnetic needle and
maintaining the solid liquid ratio in the range of 1/5 - 1/15 (wt. /vol,.), iii) keeping the temperature of the slurry obtained in step (ii) in the range of 30 to 100°C for a
period of 0.5 to 5 h to effect oxidative leaching of zinc with persulphate salt,
iv) filtering the slurry by conventional manner to obtain leach liquor containing zinc,
v) purifying and electrolyzing the leach liquor by conventional manner to obtain zinc metal.
In an embodiment of the present invention, the zinc concentrate used may be selected from sphalerite
concentrate having particle size in the range of -150 µm to +53 µm and may have composition in
the range:
Zn 40-60% Pb 0.5-2.0%
Fe 5-12% Si02 : 0.5-2%
S 25-35% Al203 : 2-5%
In another embodiment of the present invention, the oxidants may be selected from ammonium and
sodium persulphate salts of laboratory reagent grade and may have concentration in the range of 10 -
40.%
In still another embodiment of the present invention, the used sulphuric acid may be of commercial
grade and may have concentration upto 10 vol%. This acid concentration is obtained after mixing
with the wash solution generated from the leaching step earlier and is used for further leaching.
In the process of present invention, the leach slurry is filtered and the residue is washed with diute
sulphuric acid solution . The wash liquor containing 2-20 g/L Zn is recycled for the leaching of the
fresh concentrate by adding the desired amount of acid.
In the process of the present invention sphalerite concentrate is leached in sulphuric acid medium
using ammonium and sodium persulphates as the oxidants. Dissolution of zinc from sulphide
concentrate in presence of persulphate is accompanied by the formation of elemental sulphur as
shown below:
(Formula Removed)
The slurry is filtered to get leach liquor containing zinc while sulphur in elemental form reports in the
residue. The leach liquor is purified for different impurities by the known process and electrolysed to
produce the zinc metal. The sulphur from the washed residue can be recovered by the established
process based on flotation.
Novelty of the present invention is the use of a strong oxidising reagent like persulphate salts which has not been used earlier for direct leaching of zinc from its sulphide concentrate. Another feature of the invention is the zinc dissolution from its concentrate without any prior treatment such as roasting.
The following examples are given by way of illustration and should not be construed to limit the scope of invention.
EXAMPLE - 1
40 g (40 wt%) of ammonium persulphate (APS) is dissolved in 100 ml of water containing 10 vol.% of concentrated sulphuric acid in a conical flask. The volume of the content is made up to 200 ml and the flask is kept over a thermostatically controlled hot plate fitted with stirring arrangement by a magnetic needle. Temperature of the solution is maintained at 45 °C and 20 g of zinc concentrate of composition A, containing 49.1% Zn, 8.9% Fe, 31.5% S, 0.8% Pb, 1% SiC>2 and 3.75% AI2O3 is added to the preheated solution. Temperature of the slurry is immediately raised to 60 °C which is maintained through out the leaching experiment which is started with agitation. Samples collected at different time intervals are filtered and analysed for zinc content. The results given in Table 1 show that recovery increases with increasing the time of leaching. Maximum of 95.5% zinc recovery is achieved in 5 hours of leaching under this condition.
Table 1 : Percentage zinc recovery at different time intervals
(Table Removed)
EXAMPLE - 2
In 100 ml of water containing 10 vol.% of concentrated sulphuric acid, 50 g of ammonium persulphate is dissolved in a conical flask. The volume of the solution is adjusted to 200 ml. The flask is then kept over a thermostatically controlled hot plate fitted with a magnetic stirrer. Temperature of the solution is raised to 45 °C and 20 g of zinc concentrate with the composition A is added to the solution at this stage to get
a S/L ratio of 1/10 (wt./vol.). The temperature of the slurry is quickly raised to 60 °C which is maintained through out the leaching experiment. Once the leaching proceeded with stirring, the samples are collected at different time intervals, filtered and analysed for zinc. Recovery of zinc increases with leaching time of 2 h after which it decreases. Data of zinc extraction at different time intervals are incorporated in Table 2. Maximum of 86.2% zinc recovery is achieved in 2 h and further decrease in the recovery value is due to the possible crystallisation of double salt (NH4)2Zn(S04)2.
Table 2 : Zinc recovery at different time intervals

(Table Removed)
EXAMPLE - 3
In a conical flask containing 100 ml of water with 4vol.% concentrated sulphuric acid, 40 g of ammonium persulphate is added. After making up the volume to 200 ml, the flask is kept over a thermostatically controlled hot plate fitted with a magnetic stirring system. The solution temperature is raised to 45 °C and 20 g of zinc concentrate of the composition A is added to the solution. Temperature of the slurry is immediately raised to 60 °C and leaching started while stirring and maintaining the same temperature through out the leaching experiment. Samples collected at different time intervals are filtered and the leach liquor analysed for zinc. Recovery data at different time intervals are incorporated in Table 3. Maximum of 76.9% zinc recovery is achieved in 5 hours of leaching.
Table 3 : Effect of various parameters on the percentage zinc recovery at different
time intervals
(Table Removed)
EXAMPLES - 4
In 100 ml of water containing 10 vol.% of concentrated sulphuric acid in a conical flask, 40 g of ammonium persulphate is dissolved. After making up the volume of the content to 200 ml, the flask is kept over a thermostatically controlled hot plate fitted with a magnetic stirrer. Temperature of the solution is raised to 60 °C and 20 g of zinc concentrate having composition A is added to the solution to start the leaching. Temperature of the slurry is immediately raised to 80 °C which is maintained through out the leaching experiment. Leaching is carried out by agitating the slurry. Samples collected at different time intervals are filtered and leach liquor is analysed for zinc. Zinc recovery data at different time intervals are incorporated in Table 4. Only 71.6% of zinc recovery is achieved in 1 h of leaching time and further increase in time is of no significance for the metal dissolution. Table 4 : Effect of various parameters on the percentage zinc recovery at different
time intervals
(Table Removed)
EXAMPLE - 5
In a conical flask containing 100 ml of water with 10 vol.% of concentrated sulphuric acid, 40 g of sodium persulphate (SPS) is dissolved. The volume of the solution is made up to 200 ml and the flask is kept over a thermostatically controlled hot plate fitted with a magnetic stirring arrangement. Temperature of the reaction is
raised to 45 °C and 20 g of zinc concentrate of composition A is added to the preheated solution. The temperature of the slurry is raised to 60 °C which is maintained through out the leaching experiment. Samples collected at different time intervals are filtered and leach solution is analysed for zinc content. Zinc recovery at different time intervals is summarised in Table 5. Maximum of 86.2% of zinc recovery is achieved in 3 h of leaching ; the recovery remains unaltered by prolonging the leaching time. Table 5 : Effect of various parameters on the percentage zinc recovery at different
time intervals
(Table Removed)
The major advantages of the present invention are given here ;
1. Elimination of roasting step which is carried out at higher temperature, prior to acid leaching as required in the conventional process, results in energy saving.
2. With no sulphur dioxide gas emission, the process is much ecofriendly.
3. In the present invention the requirement of sulphuric acid plant which is considered a prerequisite for conventional process can be altogether eliminated.
4. Conversion of sulphur to elemental form as a part of residue makes it usable for different applications as per need.
5. The process operates at normal pressure and therefore special material of construction is not required as in case of pressure leaching.
6. The process is much less corrosives compared to ferric chloride leaching system.
7. The process is much easier with lesser number of steps.






We Claim:
1. An improved process for extraction of zinc from sulphide concentrate characterized in that
i) preparing a solution comprising sulphuric acid and an oxidizing agent selected from
ammonium and sodium persulphate salt in an amount such as herein described' , ii) adding zinc concentrate to the above solution and stirring by a magnetic needle and
maintaining the solid liquid ratio in the range of 1/5 - 1/15 (wt. /vol,.), iii) keeping the temperature of the slurry obtained in step (ii) in the range of 30 to 100°C
for a period of 0.5 to 5 h to effect oxidative leaching of zinc with persulphate salt, iv) filtering the slurry by conventional manner to obtain leach liquor containing zinc, v) purifying and electrolyzing the leach liquor by conventional manner to obtain zinc
metal.
2. An improved process as claimed in claim 1 wherein the zinc concentrate used are
selected from sphalerite concentrate having particle size in the range of -150 urn to
+53 urn and have composition range
Zn 40-60% Pb 0.5-2.0%
Fe 5-12% SiO2 0.5 -2%
S 25-35% Al2O3 : 2-5%
3. An improved process as claimed in claims 1 - 2 wherein the used sulphuric acid is of commercial grade and have concentration upto 10 vol.%.
4. An improved process for extraction of zinc from sulphide concentrate substantially as herein described with reference to the examples.

Documents:

360-del-2001-abstract.pdf

360-del-2001-claims.pdf

360-del-2001-complete specification (granted).pdf

360-del-2001-correspondence-others.pdf

360-del-2001-correspondence-po.pdf

360-del-2001-description (complete).pdf

360-del-2001-form-1.pdf

360-del-2001-form-18.pdf

360-del-2001-form-2.pdf

360-del-2001-form-3.pdf


Patent Number 244467
Indian Patent Application Number 360/DEL/2001
PG Journal Number 50/2010
Publication Date 10-Dec-2010
Grant Date 07-Dec-2010
Date of Filing 27-Mar-2001
Name of Patentee COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 KAMALA KANT SAHU NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, JHARKHAND, INDIA.
2 BANSHI DHAR PANDEY NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, JHARKHAND, INDIA.
3 MATCHA NANI BABU NATIONAL METALLURGICAL LABORATORY, JAMSHEDPUR, JHARKHAND, INDIA.
PCT International Classification Number C22B 19/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA