Mineral processing : foundations of theory and practice of minerallurgy

1. From the Big Bang to mineral processing 1.From the Big Bang to mineral processing 23 VI.Salts of oxy-acids (nitrates, iodates, carbonates, selenates, tellurates, borates, sulfates, chromates, molybdates, tungstates, phosphates, arsenates, antimonates, vanadates, uranates, geramanates, silicates and aluminosilicates) VII.Ammonium minerals VIII.Organic compounds and their derivatives.The alteration of minerals takes continuously place on the Earth since it is a highly dynamic body in terms of geology and mineralogy.Cycle of processes taking place in the Earth crust, after Serkies (1970), is shown in Fig. 1.4.The cycle distinguishes the following processes: magmatic, post-magmatic, weathering, transportation, sedimentation, diagenesis, metamorphosis, anatexis, and palingenesis.In the magmatic process sulfides and silicates are formed.Mineral composition of silicates depends on the composition of the initial magma and the conditions of a particular silicate precipitation.Subsequently formed minerals from magma are described by the so-called Bowen series.The anorthite arm of the Bowen series consists of bytownite, labrador, andesine, oligoclase and alkaline feldspars, while the olivine part consists of pyroxene, hornblende, biotite and alkaline feldspars.Crystallization of minerals described by the Bowen series can be stopped at each stage in the series or it can reach final stage and result in quartz or muscovite crystallization.After the magmatic period, complicated post-magmatic processes including pegmatite, pnematolitic and hydrothermal take place.In pegmatite processes, potassium-sodium feldspars, quartz, monazite, beryl and minerals of light elements such as Li, Ta, Nb, Br, Mn as well as minerals of rare earths chemical elements are formed.In the pnematolitic processes, the following minerals are typically formed: quartz, muscovite, molybdenite, cassiterite, wolframite, bismuthinite, and minerals of F, B, Mo, W, and Sn.In the process of forming hydrothermal minerals a characteristic feature is the presence of quartz, sericite, albite, chlorite, calcite, dolomite and the compounds of Cu, S, As, Sb, Zn, Pb, Ag, Au, Hg, F, and Ba.The chemicals which are active on the Earth surface, i.e. atmospheric oxygen, carbon dioxide, water and organic compounds cause diverse alterations in the mineral matter.These changes are called weathering and can lead to leaching and transforming some rocks, decreasing their cohesion and, in consequence, disintegration.The main weathering processes are: dissolution, hydration, hydrolysis, carbonatization, and oxidation.Dissolving is a long lasting process of a high importance since it leads to the destruction of rocks and shifting mineral mass.Hydration is the process of alteration of anhydrous minerals into hydrated ones.This process can cause transformation of mineral mass but it does not lead to its destruction.The best example of hydration is alteration of anhydrite into gypsum.Hydration usually occurs together with other processes, and it will be discussed later. From the Big Bang to mineral processing Part I. Introduction to mineral processingMagmatic deposits are connected with magmatic rocks.The deposits of copper and nickel sulfides, native platinum, chromite, titanomagnetite, apatite and corundum are usually of this type.Magmatic rocks are used as building materials.Scarn (metamorphic) deposits formed at the contact of magma and surrounding rock are a result of magma penetration.The scarn deposits may contain iron, copper, wolfram, zinc, lead, graphite, apatite, asbestos, and boron.Pneumatolitic and hydrothermal deposits are also connected with magmatic processes of rock formation.This processes are the source of tin ores, wolfram, molybdenum, copper, gold, silver, zinc, lead, nickel, cobalt, bismuth, arsenic, antimony, mercury, iron, manganese, magnesium ores and barite, fluorite, topaz, and quartz deposits.Sedimentary deposits are formed due to sedimentation processes.Deposits of coal, sandstones, silts, gravels, crude oil, natural gas, limestone, dolomites, marls, iron ores, manganese, bauxite, phosphates belong to this category.Sedimentary deposits are a source of copper, zinc, lead, uranium ores and pyrite, sulfur, clay, and rock salt deposits.Weathering deposits constitute a separate group.They are formed as a result of deposit disintegration by atmospheric factors.Typical weathering deposits are platinum, gold, zirconium, scheelite, silicate, nickel, iron, manganese ores, and nickel hydroxides, and kaolinite deposits.A deposit, after the approval by geologists as to its size and content, becomes a documented deposit, and after initiation of exploitation it becomes mined material.Mined materials can be classified into industrial rocks and minerals, ores, and energy raw materials.Industrial minerals include for instance: fluorite, barite, rock salt, kaolin while industrial rocks include granite, basalt, and limestone.Typical ores are copper, lead, tin, iron, and nickel ores, while energy raw materials are crude oil, natural gas, brown coal, hard coal and peat.Useful minerals are the subject of interest of mining and mineral processing.The are open pit and underground mines.In the latter ones mines useful minerals are mined down to about 1000 meters.If the temperature at that depth is not too high, i.e. the so-called geothermal degree is near the typical value of 3 o C per 100 meters of depth, exploitation is possible at a considerable depth.There are known examples of exploitation down to 3000 meters under the ground surface, like Oragun gold mine in India operating at the depth of 2835 m.The run-of-mine material requires processing in order to make it a marketable product and therefore it is directed for mineral processing.Mineral processing treatments are based on separation processes.Sometimes it is simple separation process which depends on, for example, removing moisture or classification according to grain size.Usually transformation of a mined material into a marketable product requires many separation processes.For example, copper ore has to be ground, screened, subjected to hydraulic classification, flotation, filtration and drying before a final product 1.From the Big Bang to mineral processing 29 in the form of copper concentrates is achieved.The concentrates are next directed to metallurgy plants to produce metallic copper.

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