Zinc is one of the strategic non-ferrous metal next only to Aluminium and Copper. It plays a very important role in country’s economy and development. It finds use in applications like galvanizing of iron and steel; die-casting alloys, brasses, dry cells, agriculture, chemicals, pharmaceuticals etc., with industrial development in India use of zinc has increased considerably, however, specific consumption is much lower as compared to other developing countries. The most important raw material for the production of zinc is the sulphide ore from which zinc is extracted either through pyro-metallurgical route or through hydro metallurgical – Roast – Leach – Electrowin (RLE) route. At present nearly 80 - 85% of the world’s production of primary zinc is through hydrometallurgical route, the balance is through pyro – metallurgical route. Zinc’s largest use is in corrosion protection. Galvanising is the main method of protection against corrosion of steel, i.e. the steel is coated with a layer of zinc in order to protect it from decay. Brasses are alloys of copper and zinc, and they have good mechanical properties and good corrosion resistance. Diecastings are precision castings that can be mass-produced. Rolled zinc is used for architectural and building applications, and for dry cell batteries. Zinc oxide has its main use in tyres and rubber products. Many other zinc chemicals are used in a wide range of applications.

1. 1.0 INTRODUCTION
Zinc is one of the strategic non-ferrous metal next only to Aluminium and
Copper. It plays a very important role in country’s economy and development.
It finds use in applications like galvanizing of iron and steel; die-casting alloys,
brasses, dry cells, agriculture, chemicals, pharmaceuticals etc., with industrial
development in India use of zinc has increased considerably, however,
specific consumption is much lower as compared to other developing
countries.
The most important raw material for the production of zinc is the sulphide ore
from which zinc is extracted either through pyro-metallurgical route or through
hydro metallurgical – Roast – Leach – Electrowin (RLE) route. At present
nearly 80 - 85% of the worlds production of primary zinc is through
hydrometallurgical route, the balance is through pyro – metallurgical route.
2.0 USES OF ZINC
Zinc’s largest use is in corrosion protection. Galvanising is the main method
of protection against corrosion of steel, i.e. the steel is coated with a layer of
zinc in order to protect it from decay.
Brasses are alloys of copper and zinc, and they have good mechanical
properties and good corrosion resistance.
Diecastings are precision castings that can be mass-produced.
Rolled zinc is used for architectural and building applications, and for dry cell
batteries.
Zinc oxide has its main use in tyres and rubber products. Many other zinc
chemicals are used in a wide range of applications
Zinc Smelter plant Concept Note 1 P R Chandna

2. The sectoral consumption of Zinc in the country is as follows:
SECTORAL ZINC CONSUMPTION IN INDIA
Chemicals &
Die Casting
Alloys
5%
10%
Dry Cell
10%
Galvanizing
75%
3.0 PROJECTED DEMAND – SUPPLY OF ZINC IN INDIA
The per capita consumption of Zinc in the world is about 1.5 kgs;
comparatively indigenous consumption is only 0.30 kgs. The demand supply
gaps of Zinc in India are presented below:
Year Demand Supply Gaps % Satisfaction
2002-03 306,300 236,000 70,300 77.0%
2007-08 419,600 350,000 69,600 83.4%
2011-12 539,900 360,000 179,900 66.7%
Zinc Smelter plant Concept Note 2 P R Chandna

3. The demand satisfaction, as can be seen from the above table, is presently
around 70%, which is likely to increase to around 83.4% in 2007-2008, once
the recently installed 170,000 tpa Zinc Smelter plant at Chanderiya is
commissioned in mid 2005. The demand satisfaction level will go down from
present 70% to 66.7% in the year 2011-2012, if the zinc production capacity in
the country is not supplemented in near future.
4.0 RECOVERABLE RESERVES OF LEAD – ZINC ORES AND METALS
The Zinc resource inventory of India is estimated at 416 million tonnes with
4.91% zinc. The state of Rajasthan contributes to 87% of the Lead Zinc ores
in the country.
The largest zinc mining regions in the world are:
• Latin America
• China
• Australia
• North America (mainly Canada)
Each of these mines has production capacities of more than 1.5 million tonnes
per year of zinc in concentrates.
The predominant regions for zinc metal production, however, are China,
Western Europe and Asia. It therefore follows that a major world export trade
exists in zinc concentrates, mainly out of Australia, Latin America and Canada
and into Asia (including China, which produces more zinc than it can mine)
and Western Europe, as can be seen from the following table:
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4. WORLD ZINC MINES PRODUCTION:
Thousand tonnes (Zinc content)
2000 2001 2002 2003
Europe 1063 1053 906 1017
Africa 256 236 242 259
America 3517 3769 3759 3795
Asia 2623 2549 2549 3058
Oceania 1379 1476 1444 1447
World Total 8838 8934 8900 9576
WORLD ZINC METAL PRODUCTION:
Thousand tonnes
2000 2001 2002 2003
Europe 2770 2884 2905 2742
Africa 129 135 147 193
America 1814 1717 1904 1932
Asia 3774 3936 4189 4438
Oceania 494 556 567 553
World Total 8981 9228 9712 9858
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5. 5.0 MAJOR PRIMARY ZINC PRODUCERS IN THE COUNTRY
Presently in India, primary Zinc metal is being produced mainly by M/s
Hindustan Zinc Ltd. and M/s Binani Zinc Ltd. The installed capacity for the
production of primary Zinc in India is 199,000 tonnes per annum. The major
primary producers in the country are as below:
Sl. No. Plants Company Installed Remarks
Capacity TPA
1. Binani Zinc Smelter, M/s Binani Zinc 30,000 RLE Process
Alwaye, Kerala Limited
2. Debari Zinc Smelter, M/s Hindustan 59,000 RLE Process
Udaipur, Rajasthan Zinc Limited
3. Vizag Zinc Smelter, M/s Hindustan 40,000 RLE Process
Visakhapatnam, Zinc Limited
Andhra Pradesh
4. Chanderiya Lead M/s Hindustan 70,000 Imperial
Zinc Smelter, Zinc limited Smelting
Chittaurgarh, Process (ISP)
Rajasthan
5. Chanderiya Lead M/s Hindustan 170,000 RLE Process
Zinc Smelter, Zinc limited
Chittaurgarh,
Rajasthan
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6. 6.0 PRIMARY ZINC PRODUCTION IN INDIA
Year HZL BZL TOTAL
1998-99 141,806 31,152 172,958
1999-00 145,790 29,162 174,958
2000-01 148,092 29,923 178,055
2001-02 176,395 28,814 205,209
2002-03 207,066 28,459 235,525
7.0 EXISTING LEAD ZINC MINES AND ORE DRESSING PLANTS AT
HINDUSTAN ZINC LIMITED (HZL)
I. RAMPURA AGUCHA MINE:
Commissioned 1991
Location 225 km north of Udaipur, Rajasthan, India
Capacity 2.4 Mtpa ore
Details An open cast mine with low strip ratio of 5:1 and good mineralogy
leading to higher recovery and overall low cost of production.
Onsite concentrator to produce zinc concentrate.
Concentrates Zinc 54 – 54.5%, Lead 63.7 – 67%
Zinc Smelter plant Concept Note 6 P R Chandna

7. II. RAJPURA DARIBA MINE:
Commissioned 1983
Location 75 km north-east of Udaipur, Rajasthan, India
Capacity 1 Mtpa ore
Details An underground mine with onsite concentrator and two vertical
access shafts. Mining is done through vertical crater retreat and
blast hole stoping. Ore is crushed underground before hoisting and
stockpiling for secondary and tertiary crushing.
Concentrate Zinc 51.5%, Lead 51.2 – 52.9%
III. ZAWAR MINES:
Commissioned 1942
Location 50 km South of Udaipur, Rajasthan, India
Capacity 1.2 Mtpa ore
Details An underground mining complex consisting of four underground
mines and one concentrator for all mines. Mining is done with
sublevel stoping with matching infrastructure.
Concentrate Zinc 54.3-55.2%, Lead 64.5 – 64.8%
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8. 8.0 PROCESS TECHNOLOGIES
GENERAL
The most important raw material (ZnS) ore commonly known as Zinc blende
for production of Zinc is Zinc Sulphide sphalerite. The principal processes by
which zinc is extracted from its ores can be categorized under pyro-
metallurgical processes and hydro-metallurgical processes.
A. Pyrometallurgical Processes:
1. Horizontal Retorts Process
2. Vertical Retorts Process
3. Electro-thermic Process
4. Imperial Smelting Process
B. Hydrometallurgical Processes;
1. Roast Leach Electrowin Process
2. Pressure Leaching Process
8.1 PYROMETALLURGICAL PROCESS
8.1.1 General
Presently about 15 – 20% of the world’s zinc production comes from pyromet-
allurgical route. The horizontal and vertical retort processes and electro-
thermal process were used in the past for zinc production but have become
obsolete due to high power consumption and low recovery. The only py-
rometallurgical process of importance presently is Imperial Smelting Process
(ISP).
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9. 8.1.2 Imperial Smelting Process (ISP):
Currently about 9 -10% of the world’s primary – zinc production are through
the Imperial Smelting Process. The process co-produces lead bullion in
addition to zinc metal using a mix of lead and zinc concentrates or complex
lead-zinc concentrates as raw material.
The Imperial Smelting Process is similar to blast furnace processes except
that it is operated with hot top whereby preventing reoxidation of zinc vapours.
The process consists of basic two operations namely; sintering and blast
furnace smelting of sintered lumps to extract lead and zinc simultaneously.
The Imperial Smelting Process has the following demerits:
i) Process requires mix of zinc and lead concentrates.
ii) It is a labour intensive process.
iii) Present demand scenario does not call for addition of lead smelting
capacity in the country.
iv) Because of high temperature involved in maintainability of the plant.
v) Low plant availability.
8.2 HYDROMETALLURGICAL PROCESS
8.2.1 General
About 80% of world’s total zinc output is produced through conventional
hydrometallurgical route i.e. roast-leach-electrowin (RLE) route. The three out
of the four plants installed in the country are operating on hydrometallurgical
process route, whereas the fourth one at Chittaurgarh, Rajasthan, which was
commissioned in the year 1991 is based on imperial smelting process route
for simultaneous extraction of lead and zinc.
Zinc Smelter plant Concept Note 9 P R Chandna

10. The pre-requisite condition for zinc metal extraction from sulphide concentrate
through a hydro-metallurgical route is the elimination of its sulphur content in
order to make it amenable to further treatment by leaching, i.e., the zinc
mineral into dissolved state in solution. Since zinc sulphide mineral is not
easily leached, it is first converted into zinc oxide, which is easily leached.
This is predominantly accomplished by roasting of zinc concentrate in fluid
bed roasters and fixation of SQ2 bearing off gases thus generated as sulphuric
acid by contact process. In the recent past, an alternative technology to
conventional roasting followed by leaching, has been developed by Sherritt-
Gordon of Canada, commonly known as “Pressure Leach Process” which
eliminates the need of roasting step prior to leaching. The process fixes the
sulphide content of concentrate as elemental sulphur, thus eliminates the
need for a separate sulphuric acid production facility, whereas the zinc metal
content of the concentrate is converted into a zinc sulphate solution, thus
combining both roast-leach steps of conventional process into a single unit
operation.
Thus there are two-process route for extraction of zinc hydrometallurgically:
1. Roast Leach Electrowin (RLE) Process
2. Pressure Leach Electrowin Process
8.2.2 Roast – Leach – Electrowin (RLE) Process:
ZINC ROASTER FURNACE
Zinc Smelter plant Concept Note 10 P R Chandna

11. The main purpose of roasting of zinc sulphide concentrate is to convert it into
a product, which is amenable to further treatment through hydrometallurgical
process for extraction of zinc. Secondly, to fix the sulphide contents into
sulphur dioxide gases for subsequent economical recovery as sulphuric acid.
The principal reaction during fluid bed roasting is:
2 ZnS + 3 02 = 2 ZnO + 2 S02
These rich gases are cleaned and cooled to recover dust content as zinc
calcine and to remove the various harmful impurities such as Hg, Se, F, Cl,
As, etc., before being led to conventional (DCDA) contact process for
manufacture of sulphuric acid.
The dead roasted product, zinc calcine, is subjected to leaching with recycled
electrolyte to extract zinc content. The enriched zinc sulphate solution is
further subjected to purification with zinc dust to eliminate impurities like
copper, cadmium, cobalt, nickel etc. before being subjected to electrolysis.
The zinc sulphate solution is fortified with return electrolyte solution,
undergoes electrolysis in lined concrete cells for deposition of zinc on alu-
minium cathodes. The lead- silver plates are used as anodes. The deposited
zinc on the cathodes are periodically stripped by automatic stripping
machines, melted in induction furnace and cast into saleable zinc ingots man
automatic casting and stacking machine.
Strapped Saleable Zinc Ingots
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12. In order to maximise zinc extractions the leach residues mainly zinc- ferrites,
a bye product of leaching process, are subjected to treatment to hydrolyse its
iron content into disposable Jarosite / goethite / hematite. The zinc plants are
also integrated with bye-product cadmium recovery unit in order to maximise
sales realization.
The standard zinc product is Special High Grade zinc (normally obtained from
RLE process route), with an assay of 99.995% zinc, i.e. it can contain a
maximum of 50 parts per million of impurities. There is also a grade of 98.5%
zinc, the main impurity being lead, and this used to be the standard grade,
called GOB (Good Ordinary Brand) or PW (Prime Western), normally a
product from the Imperial smelting process (ISP). A SHG product from the ISP
can also be produced by distillation process of refining.
The zinc extraction through roast leach electrowin (RLE) process block
diagram is given below:
Zinc Smelter plant Concept Note 12 P R Chandna

13. Zinc Smelter plant Concept Note 13 P R Chandna

14. 8.2.3 Pressure Leach Process
The pressure leach technique was first successfully commercially applied for
zinc extraction with the commissioning of first plant in 1981 at Cominco, Trail,
Canada.
There are presently three electrolytic zinc plants in the world where this
technique has been integrated into the existing facilities. A fourth green field
plant with two-stage counter-current pressure leach-electrowin is under
consideration.
In this process zinc sulphide or bulk zinc concentrates are oxidized under
oxygen overpressures of 1200 kpa abs. at a temperature of 1500 C in sul-
phuric acid medium to produce zinc sulphate solution directly and the sulphide
content is precipitated as elemental sulphur according to the following overall
reaction:
ZnS + H2S04 + 0.5 02 = ZnSO4 + H20 + Sº
The various factors influencing the kinetics of above reaction are the particle
size, mineralogy, surface active additives, acidities, reaction time, temperature
and oxygen over-pressures where by maximising metal extraction and fixation
of lead and iron constituents into disposable Jarosite and other types of
residues. The zinc sulphate solution thus produced is amenable to further
processing for final zinc extraction through conventional leach-electrowin
units.
Considering the technical merits/demerits and reliability of both the processes
the roast-leach-electrowin (RLE) stands apart from pressure leach process.
The size of zinc smelters varies from a few thousand tonnes per year zinc
capacity to more than 400,000 tonnes per year, the most common size,
except in China, being in the range 100,000 to 170,000 tonnes per year.
Zinc Smelter plant Concept Note 14 P R Chandna

15. 9.0 Environmental Aspects
Waste Characteristics
The principal pollutants emitted/ generated from the zinc extraction processes
are:
• Particulate matter
• Sulphur dioxide (SO2) from the roaster furnace
• Iron residues from leaching process, known as Jarosite
Fugitive emissions occur from materials handling and transport of ores and
concentrates. Some vapours are produced in hydrometallurgy and in various
refining processes. The principal constituents of the particulate matter are
lead/zinc and iron oxides, but oxides of metals such as arsenic, antimony,
cadmium, copper, and mercury are also present, along with metallic sulphate.
Wastewaters are generated by wet air scrubbers and cooling water. Scrubber
effluents may contain lead/zinc, arsenic, and other metals. Sources of
wastewater include spent electrolytic baths, slimes recovery, spent acid from
hydrometallurgy processes, cooling water, air scrubbers, wash downs, and
storm water. Pollutants include dissolved and suspended solids, metals, and
oil and grease.
The larger proportion of the solid waste is an iron residue from the leaching
processes produce residues, while effluent treatment results in sludges that
require appropriate disposal.
Pollution Prevention and Control
Process gas streams from roaster furnace containing over 9 –12 % sulphur
dioxide are usually used to manufacture sulphuric acid by DCDA process, as
described above. The other measures adopted are as below:
Zinc Smelter plant Concept Note 15 P R Chandna

16. • Use of suspension or fluidized bed roasters, to achieve high SO2
concentrations when roasting zinc sulphide.
• Use doghouse/ bag filters enclosures where appropriate; use hoods to
collect fugitive emissions from the raw material handling plants.
• Use of energy-efficient measures such as waste heat recovery from
process gases to reduce fuel usage and associated emissions.
• Recycle condensates, rainwater, and excess process water for washing,
for dust control, for gas scrubbing, and for other process applications
where water quality is not of particular concern.
• Recover of iron-bearing residues from zinc production and dispose of in a
secure lined landfill.
• Give preference to fabric filters over wet scrubbers or wet electrostatic
precipitators (ESPs) for dust control.
• Good housekeeping practices are key to minimizing losses and preventing
fugitive emissions. Losses and emissions are minimised by enclosed
buildings, covered conveyors and transfer points, and dust collection
equipment. Yards should be paved and runoff water routed to settling
ponds.
Treatment Technologies
ESPs and bag houses are used for product recovery and for the control of
particulate emissions. Dust that is captured but not recycled will need to be
disposed of in a secure landfill or in another acceptable manner.
Effluent treatment of process bleed streams, filter backwash waters, boiler
blowdown, and other streams is required to reduce suspended and dissolved
solids and heavy metals and to adjust pH. Residues that result from treatment
Zinc Smelter plant Concept Note 16 P R Chandna

17. are recycled back to the process wherever possible or plastic lined settling
ponds or disposed of in a secure landfill.
In the recent past zinc industries have developed, due to stringent
environmental pressures, the latest process of fixing the leach residue
(Jarosite) generated during zinc production, with cement into a product known
as “Jarofix” to be disposed to a secure land fill, as described in the block
diagram above.
Zinc Smelter plant Concept Note 17 P R Chandna

18. 10.0 Salient Features of Zinc Smelter Plant
Typical for a Roast Leach Electrowin (RLE) process Plant
Sl. No. Description UOM Quantities
1. Zinc Ingot Production TPA 100,000
2. Sulphuric Acid Production TPA 180,000
3. Cadmium Production TPA 380
4. Zinc Recovery Efficiencies % 96 - 97
5. Zinc Concentrate Requirement TPA 200,000
6. Water Requirement mgd 1.25
7. Power Requirement KWh / tonne 4000 - 4200
8. Iron Residue (Jarosite) for TPA 50,000 – 70,000
disposal as Jarofix
Zinc Smelter plant Concept Note 18 P R Chandna

19. ANNEXURE – I
ZINC CONCENTRATE - TYPICAL ANALYSIS
ELEMENT UNITS SPECIFICATIONS
Zn % 49 – 50
Pb % 4 – 4.5
Fe % 8 –10
Ag ppm 300
S (total) % 31
SiO2 % 1.5
Cu % 0.25
As ppm 1,000 – 3,000
Sb ppm 150
Cd ppm 2,500
Bi ppm < 50
Hg ppm 50
Co ppm 50
Ni ppm 20
F ppm 200
CaO % 0.25
MgO % 0.20
MnO % 0.35
Ba ppm < 20
Organic carbon % < 0.02
Ge ppm <1
Size, P80 micron 15
Zinc Smelter plant Concept Note 19 P R Chandna