|Title of Invention||
"AN IMPROVED PROCESS FOR THE EXTRACTION OF ZINC FROM SIKKIM ZINC CONCENTRATE"
|Abstract||The present invention recites a process for the extraction of zinc and other minor metals from zinc concentrates. The dissolution process takes place at room temperature, atmospheric pressure and lixivant containing 9K medium along with acidophilic microorganisms. The zinc dissolution kinetics was faster compared to copper. Due to dissolution of pyrite, the acid consumption was less.|
|Full Text||The present invention relates to an improved process for the recovery of zinc from
Sikkim zinc concentrate.
The invention particularly relates to a process for recovery of zinc and other
minor elements present in the zinc concentrate using acidophilic microorganism.
The total estimated reserve of complex sulphides in Sikkim is around 1 million
tonne. The complex sulphide reserve in Sikkim is under Sikkim Mining Corporation
(SMC). SMC produces the individual concentrates using flotation technology. SMC is
capable of producing 1.5 tonne of zinc concentrate. Due to difficult terrian the
transportation being high, therefore the profitability comes down drastically. In order to
utilise the concentrate profitably, SMC likes to process the same at the mine site to sale
process product. The zinc concentrate contains Zinc, Iron, Sulphur, miner amounts of
Copper, Cobalt and Nickel.
Reference may be made to Konishi, Yasuhiro; Nishimura, Hirotugu and Assai,
Satora, "Bioleaching of sulphide by the acidophilic thermophile Acidianus brierleyi",
Hydrometallurgy, 1998, 47(2-3), 339-352; Tipre, D.R; Vora, S.B and Dave, S.R,
"Comparative copper and zinc bioextraction at various stages of scale up using
Thiobacillus ferrooxidans consortium", Process Metall, 1999, 9A 219-227; Konishi,
Yasuhiro and Assai, Satoru , "Bioleaching of sulphide mineral in stirred tank reactors
operated in a varity of modes", Miner. Process. Extr. Metall. Rev., 1998, 19(1-4)129-
140; Gomez, C; Blazquez, M.L and Ballester, A, "Bioleaching of a Spanish complex
sulphide ore bulk concentrate", Miner. Eng., 1999(pub 1998) 12(1) 93-106.
Various processes developed for recovery of metal values from zinc concentrates,
that can be classified under two subheadings based on temperature such as roastingleaching
and leaching For zinc concentrate leaching generally two lixivants are used such
as Fe2(S04)3-H2SO4 and FeCl3-HCl.
The main drawbacks of the above processes for the processing of zinc sulphide
are outlined in the same seanence and mentioned below.
a. The roasting-leaching process requires high temperature, emission of
sulphur fumes and capital intensive.
b. The dissolution of zinc concentrate by Fe2(SO4)3-H2SO4 requires
reoxidation of Fe(II) to Fe(III) in order to continue the leaching operations.
c. The use of FeCb-HCl suffers from the same drawback and moreover
chloride atmosphere being corrosive requires adequate protection to the
equipment as well as the operators.
Dissolution of zinc concentrate requires an oxidant. By using
during concentrate dissolution Fe(III) is reduced to Fe(II). By using acidophilic
microorganisms the oxidation of Fe(II) to Fe(III) can be carried out . There are number of
reports regarding the dissolution of sulphide concentrate by using acidophilic
microorganisms. Tipre, D.R. et al have compared copper and zinc extraction from the
polymetallic concentrate in shake flasks, stirred tanks and large reactors. Konishi,
Yasuhiro et al have studied the kinetics of leaching of sphalerite in a batch stirred reactor.
Gomez, C. et al has extracted about 58% zinc from Spanish complex sulphide
concentrate at 10% pulp density. But the initial use of Fe[III] creates a problem in the
later period due to precipitation of iron.
The main objectives of the present invention are to provide a process for the recovery of
zinc from zinc concentrate using acidophilic microorganisms.
Another objective of the present invention is to carry out the leaching without initial iron
dose to increase the extraction efficiency.
The culture of Thiobacillus ferroxidans is available as laboratory stock culture at Biomineral Department of IMMT with a disingnation 'IMMTBM-2'.
Accordingly, the present invention provides an improved process for the extraction of zinc from Sikkim zinc concentrate using Thiobacillus ferroxidans 'IMMTBM-2', wherein the steps comprise:
[a] preparing a conventionally known 9K medium and charging the said medium in a reactor by adding 10% fully grown Thiobacillus ferroxidans culture;
[b] adding Sikkim zinc concentrate to the charged medium of step [a], wherein the ratio of the sikkim zinc concentrate to medium is in the range of 1:1 to 1:5 and adjusting the pH in the range of 1 to 2 by adding dropwise concentrated sulphuric acid followed by stirring and aeration, at a speed of 400 to 600 rpm, at a flow rate of l00cc per minute, at a temperature in the range of 20 to 30 degree C to obtain the desired product.
In an embodiment of the present invention the stirring speed is preferably 500 rpm. In another embodiment the pH of the culture medium is preferably 1.5. In yet another embodiment wherein the 9K medium comprises 3.0 g/1 (NH4)2SO4, 0.5 g/1 MgSO4, 0.5 g/1 K2HPO4, 0.1 g/1 KCl.
In yet another embodiment the Sikkim zinc concentrate is having a composition of 35% zinc, 23% sulphur and 16% iron.
In yet another embodiment the zinc concentrate used has particle size of 150 microns.
The major steps in the process are
a. Isolation and adaptation of acidophilic microorganisms.
b. Inoculation of the microorganisms in the lixivant
c. Leaching of zinc concentrate
The following examples are given by the way of illustration and therefore should not
construed to limit the scope of the invention.
1620 ml of 9K" medium was taken in a 2 litre glass reactor. 36gm of zinc
concentrate was added to it. Then 180 ml of fully- grown Thiobacillus ferrooxidans
culture was added. The pH was adjusted to 1.5 by the addition of cone. H2SO4 dropwise.
Leaching was carried out at room temperature and atmospheric pressure. The air flow
rate and stirring speed was lOOcc/min and 500 rpm respectively. Samples were taken at
regular intervals and were analysed for zinc, ferrous iron, total iron and bacterial
concentration. After 126 hours the zinc extraction was 86.42% with 2.23 gpl iron in the
1620 ml of 9K" medium was taken in the 2 litre glass reactor. 180 ml of fullygrown
Thiobacillus ferrooxidans culture was added to it. Then 180gm of zinc concentrate
was added. The pH of the slurry was adjusted to 1.5. Leaching was carried out at room
temperature and atmospheric pressure. The air flow rate and stirring speed were
lOOcc/min and 500 rpm respectively. Samples were drawn periodically and analysed for
zinc, ferrous iron, total iron and bacterial concentration. After 144 hours the zinc
extraction was 50.85% and total iron in the leach liquor was 5.24 gpl.
The main advantages of the present invention are:
a. The leaching operation is carried out at moderate temperature. Since the bacterial
dissolution of pyrite is an exothermic reaction, therefore during dissolution heat
would be generated which would be sufficient to maintain the activity of
b. The process does not use corrosive chemicals.
c. The effluent after recovery of metal values can be recycled, thereby overcoming the
waste disposal problem.
d. The process neither requires sophisticated instrumentation nor skilled manpower.
e. The process is economical even at moderate scale.
f. The end product, ZnSO4, can be used directly as a fertiliser. Apart from above there is
a global demand of zinc due to its wide use for galvanisation and alloy formation.
g. The non-use of initial dose of iron helps in achieving higher metal values recovery.
1. An improved process for the extraction of zinc from Sikkim zinc concentrate using
Thiobacillus ferroxidans, wherein the steps comprise:
[a] preparing a conventionally known 9K medium and charging the said medium in a reactor by adding 10% fully grown Thiobacillus ferroxidans 'IMMTBM-2' culture;
[b] adding Sikkim zinc concentrate to the charged medium of step [a], wherein the ratio of the sikkim zinc concentrate to medium is in the range of 1:1 to 1:5 and adjusting the pH in the range of 1 to 2 by adding drop wise concentrated sulphuric acid followed by stirring and aeration, at a speed of 400 to 600 rpm, at a flow rate of l00cc per minute, at a temperature in the range of 20 to 30 degree C to obtain the desired product.
2. A process as claimed in claim 1, wherein the stirring speed is preferably 500 rpm.
3. A process as claimed in claim 1, wherein the pH of the culture medium is preferably 1.5.
4. A process as claimed in claim 1, wherein the 9K medium comprises 3.0 g/1 (NH4)2SO4, 0.5 g/1 MgSO4, 0.5 g/1 K2HPO4, 0.1 g/1 KCl.
5. A process as claimed in claim 1, wherein the Sikkim zinc concentrate is having a composition of 35% zinc, 23% sulphur and 16% iron.
6. A process as claimed in claim 1, wherein the zinc concentrate is having a particle size of 150 microns.
7. An improved process for the extraction of zinc from Sikkim zinc concentrate substantially as herein described with reference to the foregoing examples.
|Indian Patent Application Number||369/DEL/2002|
|PG Journal Number||33/2008|
|Date of Filing||28-Mar-2002|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110 001, INDIA.|
|PCT International Classification Number||C12P 1/04|
|PCT International Application Number||N/A|
|PCT International Filing date|