Oxygen smelting

Advantages of the Bottom Blown Oxygen Smelting Process... 

The process of extraction requires first smelting (to obtain the crude metal) and then refining. In smelting, iron ore (usually an oxide) is mixed with coke and limestone and heated, and hot air (often enriched with oxygen) is blown in from beneath (in a blast furnace). At the lower, hotter part of the furnace, carbon monoxide is produced and this is the essential reducing agent. The reduction reactions occurring may be represented for simplicity as ... 

Dried lead concentrate, flux, and return dust are added to the converter through a lance during the smelting cycle. Oxygen enriched air is injected at the same time to carry out the smelting reactions and maintain the temperature. Once smelting is completed, the air is shut off and the reduction carried... 

The dried charge is pneumatically fed to a burner mounted on the roof of the reaction shaft. Normally oxygen is used to get an autogenous smelt. The offgases analy2e around 70% SO2 and can be used for the manufacture of sulfuric acid after conventional gas cleaning. 

The equihbrium constants for these reactions are such that copper is not appreciably oxidi2ed by oxygen until most sulfur has been removed. This makes possible the production of bHster copper, 98.6—99.5% Cu that is low in both sulfur (0.02—0.1%) and oxygen (0.5—0.8%). The converter slag, however, contains a significant amount of copper and must be recycled to the smelting stage. 

Two processes, developed for the direct processing of lead sulfide concentrates to metallic lead (qv), have reached commercial scale. The Kivcet process combines flash smelting features and carbon reduction. The QSL process is a bath-smelting reactor having an oxidation 2one and a reduction 2one. Both processes use industrial oxygen. The chemistry can be shown as follows ... 

The ziac concentrate is first roasted ia a fluid-bed roaster to convert the ziac sulfide to the oxide and a small amount of sulfate. Normally, roasting is carried out with an excess of oxygen below 1000°C so that comparatively Htfle cadmium is eliminated from the calciaed material ia this operation (3). Siace the advent of the Imperial Smelting Ziac Furnace, the preliminary roasting processes for ziac and ziac-lead concentrates result ia cadmium recovery as precipitates from solution or as cadmium—lead fume, respectively, as shown ia Figure 1. 

Smelting. The term copper smelting designates the operations of melting the concentrate and extracting the copper by heat, flux, and the addition of oxygen. Copper concentrate is a mixture of the sulfides of copper, copper—iron, and iron with smaller amounts of gangue minerals. It normally contains 25—35% copper. 

Fire refining, the final smelting operation, removes further impurities and adjusts the oxygen level ia the copper by air oxidation followed by reduction with hydrocarbons, ammonia, or reformed gas (CO + H2). 

The Inco flash smelting process produces a very high strength sulfur dioxide gas by using pure oxygen for smelting. Liquid sulfur dioxide is obtained upon compression. 

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. 

In Western Mining s flash smelting proeess, reaetion air is preheated to 480°C (920°F) and enriehed until the oxygen eontent is 24%. The reaetion eharge and eombustion air are mixed, and heat for smelting eomes from the eombustion of fuel oil (some of it present in the flux) and sulfur in the eoneentrate. The proeess yields matte, a refined ore with 44% niekel eontent. 

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