Oxidation metallic mineral deposits

The elements from lanthanum (Z = 57) through lutetium (Z = 71) are variously called the lanthanide, lanthanoid, or rare earth elements. The rare earth elements are "rare" only relative to the alkaline earth metals (group 2). Otherwise, they are not particularly rare. Ce, Nd, and La, for example, are more abundant than lead, and Tm is about as abundant as iodine. The lanthanides occur primarily as oxides, and mineral deposits containing them are found in various locations. Large deposits near the California-Nevada border are being developed to provide oxides of the lanthanides for use as phosphors in color monitors and television sets. 

Minerals belonging to the category of insoluble oxide and silicate minerals are many in number. Insoluble oxide minerals include those superficially oxidized and those of oxide type. The former category comprises mainly superficially oxidized sulfide minerals, including metals such as aluminum, tin, manganese, and iron which are won from their oxidic sources. As far as silicate minerals are concerned, there can be a ready reference to several metals such as beryllium, lithium, titanium, zirconium, and niobium which are known for their occurrence as (or are associated with) complex silicates in relatively low-grade deposits. 

In the deposits where oxide cobalt is present, it is common to have oxide copper minerals. The cobalt is, therefore, recovered in a bulk copper-cobalt concentrate that is processed using a hydrometallurgical technique to produce separate copper and cobalt metals. Oxide... 

The raw minerals mined from natural deposits comprise mixtures of different specific minerals. An early step in mineral processing is to use crushing and grinding to free these various minerals from each other. In addition, these same processes may be used to reduce the mineral particle sizes to make them suitable for a subsequent separation process. Non-ferrous metals such as copper, lead, zinc, nickel, cobalt, molybdenum, mercury, and antimony are typically produced from mineral ores containing these metals as sulfides (and sometimes as oxides, carbonates, or sulfates) [91,619,620], The respective metal sulfides are usually separated from the raw ores by flotation. Flotation processes are also used to concentrate non-metallic minerals used in other industries, such as calcium fluoride, barium sulfate, sodium and potassium chlorides, sulfur, coal, phosphates, alumina, silicates, and clays [91,619,621], Other examples are listed in Table 10.2, including the recovery of ink in paper recycling (which is discussed in Section 12.5.2), the recovery of bitumen from oil sands (which is discussed further in Section 11.3.2), and the removal of particulates and bacteria in water and wastewater treatment (which is discussed further in Section 9.4). 

The key technological goals include replacement of environmentally toxic metal coatings, deposition of new alloys and semiconductors and new coating methods for reactive metals. The main driving force for non-aqueous electrolytes has been the desire to deposit refractory metals such as Ti, Al and W. These metals are abundant and excellent for corrosion resistance. It is, however, the stability of their oxides that makes these metals difficult to extract from minerals and apply as surface coatings. 

Use. All acids must be used in a fume hood. Let the acid soak in the glassware for a short (or long) period of time (as necessary). Swirling with a magno-stirrer and/or heating the acid or oxidizer by use of a steam bath (do not use a direct flame) can facilitate the action. Mineral deposits can often be removed by hydrochloric acid. Metal films can often be removed by nitric acid. 

Before we examine the structures and properties of metallic classes in further detail, it is useful to consider the natural sources of the metals, generally as oxide and/or silicate-based mineral formations. If the mineral deposit contains an economically recoverable amount of a metal, it is referred to as an ore. The waste material of the rock formation is known as gangue, which must be separated from the desired portion of the ore through a variety of processing steps. 

Primary minerals formed in the ore deposit prior to weathering and erosion, including a wide variety of metal sulfides and sulfosalts, metal oxides, metal- and alkaline-earth carbonates, sulfates, crystalline silica, clays, and other silicates. Many metal sulfides (especially iron sulfides such as pyrite), when exposed by erosion or mining to atmospheric oxygen and water, can form acid-rock drainage (ARD). 

Asbestos, the first inorganic fiber material used, is currently still exclusively produced from natural mineral deposits. It is formed by the hydrothermal conversion of basic and ultrabasic volcanic rock (olivine and pyroxene) to serpentine upon which the actual asbestos formation takes place leading to two asbestos sorts with different structures serpentine asbestos and amphibole asbestos. Asbestos can be produced synthetically by several hours heating of a polysilicic acid/metal oxide mixture (e.g. Mg, Fe, Co, Ni) in water at 300 to 350°C and 90 to 160 bar. The properties of four important asbestos types are summarized in Table 5.2-2. 

It is possible that Gottschalk and Buehler (1912) carried out the oxidation with an excess of oxygen which would not occur in nature at the oxidation interface of a mineral deposit. Granger and Warren (1969) conducted experiments to investigate the oxidation of iron sulphides by an aerobic aqueous phase in a sterile system. The objective was to study the formation of unstable intermediate ions during the oxidation process. The intermediate sulphur species detected were sulphite and thiosulphate. In general these products are more easily oxidised than the metallic sulphides and are stable only if removed from the oxidising environment. 

In addition to dilution of acid rock/mine drainage under oxidizing conditions, neutralization can occur under mildly or highly anaerobic conditions. This will create distinctive environments in which microorganisms thrive and nanoparticles form as a result of their activity. We describe two examples of such subsurface systems below. However, before turning to these topics, we note that Fe-based microbial ecosystems are not only found in association with metal sulfide deposits, but may be broadly relevant in the subsurface where Fe-rich minerals (biotite, olivine, pyroxenes, etc.) are present in reasonable abundance and dissolve, releasing aqueous ferrous iron. 

Metal items constitute an appreciable amount of solid waste, with their percentage varying between 5 and 15 percent in most cases. As the revenue from solid-waste processing plants is derived from the sale of the separated products, among which ferrous and nonferrous metal items, the recovery and recycling of metallic objects support considerably the construction and operation of solid-waste treatment plants. The recycling of metal items is very important, as it contributes in mineral deposits conservation and in the prevention of environmental pollution from the oxidation and dissolution of various metals, being in alloyed form. 

As the twelfth most abundant element in the earth s crust (0.106% in crustal rocks), manganese is found in over 250 different minerals of which some 10-15 are of commercial importance. In primary hydrothermal deposits the metal occurs as silicates, but as it is readily depleted from igneous and metamorphic rocks by weathering, particularly under acid conditions, it is normally found in commercially useful ores as oxides or carbonates, deposited, as are iron and aluminum, under alkaline conditions [9]. 

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