Processing and Smelting

Primary tin metal is produced from tin concentrates, while some secondary tin metal is also recovered as the byproduct of other nonferrous metal extractive metallurgy or recycling from industries using tin or its alloys. 

Roasting. Usually, the tin concentrate undergoes a preroasting in a rotary kiln in order to remove deleterious impurities, especially arsenic and sulfur. The toxic fumes of arsenic trioxide (ASjOj) and corrosive sulfur dioxide are scrubbed with slacked lime. 

Smelting. Tin metal is obtained by the carbothermic reduction of cassiterite ore with coal 

Refining. After liquation the purified tin metal still requires further refining to remove metal impurities and to attain a metal purity suitable for commercial trade. Three methods are used to refine tin metal  

During fire-refining, molten sulfur is added to liquid tin to remove copper as a sulfide then arsenic, antimony, and nickel are removed by alloying with aluminum or sodium, while 

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Liquid-liquid distributions form the basis of solvent extraction and related processes, and smelting processes. 

Energy demand, the implementation of sulfur oxide pollution controls, and the future commercialization of coal gasification and liquefaction have increased the potential for the development of considerable supplies of sulfur and sulfuric acid as a result of abatement, desulfurization and conversion processes. Lesser potential sources include shale oil, domestic tar sands and heavy oil, and unconventional sources of natural gas. Current supply sources of saleable sulfur values include refineries, sour natural gas processing and smelting operations. To this, Frasch sulfur production must be added. 

The history of lead is as old as the recorded history of mankind. Its use as a valuable material in society has been equally long and varied. In more recent times awareness of lead s toxicity has restricted its widespread use and many older applications have been replaced by newer materials or have been phased out. Today the use of lead is dominated by the automotive lead-acid battery, and a key feature of this application is the ability to achieve a high level of recovery and recycle of scrap batteries. This attribute now makes lead the most recycled metal in use and approaching 60 per cent of the world s supply of lead is provided by recycled metal. Secondary processing and smelting is consequently as important a part of the extractive metallurgical industry as primary extraction from ores and concentrates. 

Pyrometallurgy. Metallurgy involved in winning and refining metals where heat is used, as in roasting and smelting. PyrometaHurgy is the oldest extractive process and is probably the most important. 

There are no fumes or effluents generated in the processing of powders and the requirements of state and federal environmental protection agencies are met without difficulty. However, the production of powders has been subjected to the same concerns as most other metal refining and smelting operations. 

The obvious destination for nickel waste is in the manufacture of stainless steel, which consumes 65% of new refined nickel production. Stainless steel is produced in a series of roasting and smelting operations. These can be hospitable to the various forms of nickel chemical waste. In 1993, 3 x 10 t of nickel from nickel-containing wastes were processed into 30 x 10 t of stainless steel remelt alloy (205,206) (see Recycling, nonferrous metals). This quantity is expected to increase dramatically as development of the technology of waste recycle coUection improves. 

Sulfur Dioxide Emissions and Control. A substantial part of the sulfur dioxide in the atmosphere is the result of burning sulfur-containing fuel, notably coal, and smelting sulfide ores. Methods for controlling sulfur dioxide emissions have been reviewed (312—314) (see also Air POLLUTION CONTROL PffiTHODS COAL CONVERSION PROCESSES, CLEANING AND DESULFURIZATION EXHAUST CONTROL, INDUSTRIAL SULFURREMOVAL AND RECOVERY). 

Fig. 5. Flash smelting process and equipment, (a) The Mitsubishi process. Courtesy of the Society of Mining Engineers (23). (b) Cutaway view of an...

For operations producing 30,000 tons or less of copper annuaHy, hydrometaHurgy offers an alternative to smelting that avoids problems associated with sulfur dioxide recovery and environmental controls. Techniques include the Anaconda oxygen—ammonia leaching process, the Lake Shore roast-leach-electrowin process, and ferric chloride leaching processes for the treatment of copper sulfides. AH the facHities that use these techniques encountered serious technical problems and were shut down within a few years of start-up. 

Some fugitive particulate emissions occur around copper mines, concentrating, and smelting facilities, but the greatest concern is with emissions from the ore preparation, smelting, and refining processes. Table 30-9 gives the emissions of SO2 from the smelters. 

Pollution prevention is always preferred to the use of end-of-pipe pollution control facilities. Therefore, every attempt should be made to incorporate cleaner production processes and facilities to limit, at source, the quantity of pollutants generated. The choice of flash smelting over older technologies is the most significant means of reducing pollution at source. Sulfur dioxide emissions can be controlled by ... 

In addition to the above processes, there are a number of newer processes such as Noranda, Mitsubishi, and Contop, which replace roasting, smelting, and converting, or processes such as ISA-SMELT and KTVCET, which replace roasting and smelting. For converting, the Pierce-Smith and Hoboken converters are the most common processes. 

Recovery of copper metal and alloys from copper-bearing scrap metal and smelting residues requires preparation of the scrap (e.g., removal of insulation) prior to feeding into the primary process. Electric arc furnaces using scrap as feed are also common. 

The largest releases of polycyclic aromatic hydrocarbons (PAHs) are due to the incomplete combustion of organic compounds during the course of industrial processes and other human activities. Important sources include the combustion of coal, crude oil, and natural gas for both industrial and domestic purposes, the use of such materials in industrial processes (e.g., the smelting of iron ore), the operation of the internal combustion engine, and the combustion of refuse (see Environmental Health Criteria 202, 1998). The release of crude oil into the sea by the offshore oil industry and the wreckage of oil tankers are important sources of PAH in certain areas. Forest hres, which may or may not be the consequence of human activity, are a signihcant... 

Later developments which have had more impact on copper smelting relate to an approach which combines roasting, smelting and converting steps in one reactor, thereby making the copper production process continuous. The three unique continuous processes tried in operation are (i) the Worcra process, (ii) the Noranda process and (iii) the Mitsubishi process. The principles of the processes are respectively shown in Figures 4.5 to 4.7. 

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