Chapter 8. 2 - Metal Processing and Metal Working Industry. GENERAL PROFILEThe metal smelting and refining industry processes metal ores and scrap metal to obtain pure metals. The metal working industries process metals in order to manufacture machine components, machinery, instruments and tools which are needed by other industries as well as by the other different sectors of the economy. Various types of metals and alloys are used as starting materials, including rolled stock (bars, strips, light sections, sheets or tubes) and drawn stock (bars, light sections, tubes or wire). Basic metal processing techniques include: . A wide variety of techniques are used to finish metals, including grinding and polishing, abrasive blasting and many surface finishing and coating techniques (electroplating, galvanizing, heat treatment, anodizing, powder coating and so forth). SMELTING AND REFININGPekka Roto**Adapted from the 3rd edition, Encyclopaedia of Occupational Health and Safety.

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In the production and refining of metals, valuable components are separated from worthless material in a series of different physical and chemical reactions. The end- product is metal containing controlled amounts of impurities. Primary smelting and refining produces metals directly from ore concentrates, while secondary smelting and refining produces metals from scrap and process waste. Scrap includes bits and pieces of metal parts, bars, turnings, sheets and wire that are off- specification or worn- out but are capable of being recycled (see the article . Pyrometallurgical processes use heat to separate desired metals from other materials. These processes use differences between oxidation potentials, melting points, vapour pressures, densities and/or miscibility of the ore components when melted. Hydrometallurgical technologies differ from pyrometallurgical processes in that the desired metals are separated from other materials using techniques that capitalize on differences between constituent solubilities and/or electrochemical properties while in aqueous solutions.

Pyrometallurgy. During pyrometallic processing, an ore, after being beneficiated (concentrated by crushing, grinding, floating and drying), is sintered or roasted (calcined) with other materials such as baghouse dust and flux. The concentrate is then smelted, or melted, in a blast furnace in order to fuse the desired metals into an impure molten bullion. This bullion then undergoes a third pyrometallic process to refine the metal to the desired level of purity. Each time the ore or bullion is heated, waste materials are created. Dust from ventilation and process gases may be captured in a baghouse and are either disposed of or returned to the process, depending upon the residual metal content.

Sulphur in the gas is also captured, and when concentrations are above 4% it can be turned into sulphuric acid. Depending upon the origin of the ore and its residual metals content, various metals such as gold and silver may also be produced as by- products. Roasting is an important pyrometallurgical process. Sulphating roasting is used in the production of cobalt and zinc. Its purpose is to separate the metals so that they can be transformed into a water- soluble form for further hydrometallurgical processing. The smelting of sulphidic ores produces a partially oxidized metal concentrate (matte).

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In smelting, the worthless material, usually iron, forms a slag with fluxing material and is converted into the oxide. The valuable metals acquire the metallic form at the converting stage, which takes place in converting furnaces. This method is used in copper and nickel production. Iron, ferrochromium, lead, magnesium and ferrous compounds are produced by reduction of the ore with charcoal and a flux (limestone), the smelting process usually taking place in an electric furnace. The high temperature required for the pyrometallurgical treatment of metals is obtained by burning fossil fuels or by using the exothermic reaction of the ore itself (e.

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The flash smelting process is an example of an energy- saving pyrometallurgical process in which iron and sulphur of the ore concentrate are oxidized. The exothermic reaction coupled with a heat recovery system saves a lot of energy for smelting. The high sulphur recovery of the process is also beneficial for environmental protection. Most of the recently built copper and nickel smelters use this process. Hydrometallurgy. Examples of hydrometallurgical processes are leaching, precipitation, electrolytic reduction, ion exchange, membrane separation and solvent extraction. The first stage of hydrometallurgical processes is the leaching of valuable metals from less valuable material, for example, with sulphuric acid. Leaching is often preceded by pre- treatment (e.

The leaching process often requires high pressure, the addition of oxygen or high temperatures. Leaching may also be carried out with electricity. From the leaching solution the desired metal or its compound is recovered by precipitation or reduction using different methods. Reduction is carried out, for example, in cobalt and nickel production with gas. Electrolysis of metals in aqueous solutions is also considered to be a hydrometallurgical process.

In the process of electrolysis the metallic ion is reduced to the metal. The metal is in a weak acid solution from which it precipitates on cathodes under the influence of an electrical current. Most non- ferrous metals can also be refined by electrolysis. Often metallurgical processes are a combination of pyro- and hydrometallurgical processes, depending on the ore concentrate to be treated and the type of metal to be refined. An example is nickel production.

Hazards and Their Prevention. Prevention of health risks and accidents in the metallurgical industry is primarily an educational and technical question.

Medical examinations are secondary and have only a complementary role in the prevention of health risks. A harmonious exchange of information and collaboration between the planning, line, safety and occupational health departments within the company give the most efficient result in the prevention of health risks. The best and least costly preventive measures are those taken at the planning stage of a new plant or process. In planning of new production facilities, the following aspects should be taken into account as a minimum: . Adequate warning notices should be included.

For example, areas in which arsine or hydrogen cyanide exposure might be possible should be under continuous monitoring. Excel Vba Update Links On Open Wounds. Regular fixed monitoring of gases, dusts and noise gives an overview of exposure but has only a complementary role in the evaluation of exposure dose. New workers in particular should be thoroughly informed about potential health risks and how to prevent them in their own working environments. In addition, training should be done whenever a new process is introduced. For example, poor personal hygiene by eating and smoking in the worksite may considerably increase personal exposure. The following are some of the specific hazards and precautions that are found in smelting and refining.

Injuries. The smelting and refining industry has a higher rate of injuries than most other industries. Sources of these injuries include: splattering and spills of molten metal and slag resulting in burns; gas explosions and explosions from contact of molten metal with water; collisions with moving locomotives, wagons, travelling cranes and other mobile equipment; falls of heavy objects; falls from a height (e. Precautions include: adequate training, appropriate personal protective equipment (PPE) (e. Heat. Heat stress illnesses such as heat stroke are a common hazard, primarily due to infrared radiation from furnaces and molten metal. This is especially a problem when strenuous work must be done in hot environments.