Zinc Smelter Project Report

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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.

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Zinc Smelter Project Report

  1. 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 applicationsZinc Smelter plant Concept Note 1 P R Chandna
  2. 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. 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:Zinc Smelter plant Concept Note 3 P R Chandna
  4. 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 9858Zinc Smelter plant Concept Note 4 P R Chandna
  5. 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, RajasthanZinc Smelter plant Concept Note 5 P R Chandna
  6. 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 28,459 235,5257.0 EXISTING LEAD ZINC MINES AND ORE DRESSING PLANTS AT HINDUSTAN ZINC LIMITED (HZL)I. RAMPURA AGUCHA MINE:Commissioned 1991Location 225 km north of Udaipur, Rajasthan, IndiaCapacity 2.4 Mtpa oreDetails 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. 7. II. RAJPURA DARIBA MINE:Commissioned 1983Location 75 km north-east of Udaipur, Rajasthan, IndiaCapacity 1 Mtpa oreDetails 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 1942Location 50 km South of Udaipur, Rajasthan, IndiaCapacity 1.2 Mtpa oreDetails 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%Zinc Smelter plant Concept Note 7 P R Chandna
  8. 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 Process8.1 PYROMETALLURGICAL PROCESS8.1.1 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).Zinc Smelter plant Concept Note 8 P R Chandna
  9. 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 PROCESS8.2.1 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. 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 Process8.2.2 Roast – Leach – Electrowin (RLE) Process: ZINC ROASTER FURNACEZinc Smelter plant Concept Note 10 P R Chandna
  11. 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 IngotsZinc Smelter plant Concept Note 11 P R Chandna
  12. 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. 13. Zinc Smelter plant Concept Note 13 P R Chandna
  14. 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. 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. 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 treatmentZinc Smelter plant Concept Note 16 P R Chandna
  17. 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. 18. 10.0 Salient Features of Zinc Smelter Plant Typical for a Roast Leach Electrowin (RLE) process PlantSl. 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 JarofixZinc Smelter plant Concept Note 18 P R Chandna
  19. 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 15Zinc Smelter plant Concept Note 19 P R Chandna

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