Smelted ores, impurities

Ore Dressing. The principal lead mineral, galena, in most cmde ores, is separated from the valueless components, or gangue. Other valuable minerals that are present in the ore may be recovered either together with the lead, or in a separate step (2,3). Occasionally, the ores are sufftciendy rich in lead and low in impurities to be smelted direcdy. 

Pyrometa.llurgica.1 Methods. To prepare blast furnace bulhon for commercial sale, certain standards must be met either by the purity of the ores and concentrates smelted or by a series of refining procedures (r6—r8,r20,r21). These separated impurities have market value and the refining operations serve not only to purify the lead, but also to recover valuable by-products. 

Smelt/Smelting. Any metallurgical operation in which metal is separated by fusion from those impurities with which it may be chemically combined or physically mixed, such as in ores. 

Zinc Zinc is processed very similarly to copper and lead. The zinc is bound in the ore as ZnS, sphalerite. Zinc is also obtained as an impurity from lead smelting, in which it is recovered from the blast furnace slag. 

Smelting iron ores produces large amounts of sulfur dioxide, which is catalytically oxidized to sulfur trioxide for sulfuric acid production. This process is declining due to pollution control measures and the presence of some impurities in the product acid. 

Acid rain is caused primarily by sulfur dioxide emissions from burning fossil fuels such as coal, oil, and natural gas. Sulfur is an impurity in these fuels for example, coal typically contains 2-3% by weight sulfur.1M Other sources of sulfur include the industrial smelting of metal sulfide ores to produce the elemental metal and, in some parts of the world, volcanic eruptions. When fossils fuels are burned, sulfur is oxidized to sulfur dioxide (SO2) and trace amounts of sulfur trioxide (SC>3)J21 The release of sulfur dioxide and sulfur trioxide emissions to the atmosphere is the major source of acid rain. These gases combine with oxygen and water vapor to form a fine mist of sulfuric acid that settles on land, on vegetation, and in the ocean. 

Steel is an impure form of iron, the most common contaminants being carbon (from the coke that fuels the smelting process) and sulphur from the iron oxide ore. 

In about 3600 bce, ores containing both arsenic and copper were known and mined by the early Greeks and Romans, as well as by Chinese alchemists. This is about the time when copper was smelted and alloyed to make bronze. Some ores of copper produced harder metals than others because of impurities. One of these impurities was arsenic. Because the workers were becoming ill when smelting these types of ore, the process was abandoned, and tin was added to copper to form bronze. Bronze may have been the Persian (Iranian) word for copper. ... 

The lead concentrate must he roasted for effective removal of sulfur and then smelted in a blast furnace. Sulfur is mostly removed hy a sinter process. The galena concentrate or the ore itself, if its impurity content is low, is mixed with silica and other slag-forming reagents and roasted in sinter machines to produce lead oxide, lead silicate, and some metallic lead. The principal reactions are ... 

About 90% of manganese ore is used in steel smelting. Although there are more than 300 manganiferous minerals, the common ore minerals are largely mixtures of manganese oxides and hydrated oxides. The usual field terms are psilomelane for a hard massive mixture of oxide minerals, pyrolusite for a soft black earthy mixture, and wad for impure, brown earthy oxides and hydrated oxides. LIBS sorting may be effective in this case (Fig. 8.11). 

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