Laterite concentrates

The treatments used to recover nickel from its sulfide and lateritic ores differ considerably because of the differing physical characteristics of the two ore types. The sulfide ores, in which the nickel, iron, and copper occur in a physical mixture as distinct minerals, are amenable to initial concentration by mechanical methods, eg, flotation (qv) and magnetic separation (see SEPARATION,MAGNETIC). The lateritic ores are not susceptible to these physical processes of beneficiation, and chemical means must be used to extract the nickel. The nickel concentration processes that have been developed are not as effective for the lateritic ores as for the sulfide ores (see also Metallurgy, extractive Minerals recovery and processing). 

The benefits of high selectivity He in the abiUty to produce high purity cobalt in a limited number of stages. This minimises capital and operating costs. It is particularly important when the solution in question contains low concentrations of cobalt. Eor example, solutions derived from laterite deposits may only contain 0.5—2 g/L Co but 90—100 g/L Ni. 

A similar process has been devised by the U.S. Bureau of Mines (8) for extraction of nickel and cobalt from United States laterites. The reduction temperature is lowered to 525°C and the hoi ding time for the reaction is 15 minutes. An ammoniacal leach is also employed, but oxidation is controlled, resulting in high extraction of nickel and cobalt into solution. Mixers and settlers are added to separate and concentrate the metals in solution. Organic strippers are used to selectively remove the metals from the solution. The metals are then removed from the strippers. In the case of cobalt, spent cobalt electrolyte is used to separate the metal-containing solution and the stripper. MetaUic cobalt is then recovered by electrolysis from the solution. Using this method, 92.7 wt % nickel and 91.4 wt % cobalt have been economically extracted from domestic laterites containing 0.73 wt % nickel and 0.2 wt % cobalt (8). 

Valuable mineral deposits which form by residual concentration pertain to iron, manganese, aluminum, nickel, clays, tin and gold. Aluminum comes almost exclusively from residual concentrations of bauxite, which result from the laterihsation of alumina rich igneous rocks like syenites under tropical and subtropical climatic conditions. Laterites also contribute nearly 80% of the world s reserves of nickel at grades better than 1% Ni. They form by residual concentrations as a result of weathering of mafic and ultramafic igneous rocks, which are relatively enriched in nickel. 

It has been mentioned in an earlier chapter that nickel deposits are basically of two types sulfidic and lateritic (oxide). The scenario of nickel extraction from nickel sulfide concentrates and nickeliferrous pyrrho tite (these two are the two products of physical beneficiation of nickel sulfide ores), and from limonitics and gamieritics (these are the common lateritic ores) has been presented in Figure 5.6. It can be seen that nickel is extracted from its various sources by pyro, pyro-hydro and hydroprocessing. The account given here pertains to the latter two processes applied to the various nickel sources. 

Societe Le Nickel (SLN) employ similar chemistry at their operations to treat mattes obtained from the pyrometallurgical treatment of Ni-bearing oxidic laterite ores.104 It has demonstrated at laboratory scale that Ni-containing lateritic ores may be directly leached into HC1 acid solution without pyrometallurgical pre-concentration at atmospheric pressure and relatively low temperature (ca. 70 °C).105... 

More than 90% of the nickel and cobalt in laterite ores (1.0-1.6% nickel) can readily be leached by sulfuric acid at >240 °C, typically producing large volumes of relatively dilute leach solution containing 3-6 gL-1 of nickel and around 40 gL-1 H2S04.98 In addition to nickel and cobalt these leach solutions contain Al, Cr, Ca, Cu, Fe, Mg, Mn, Na, Si, and Zn.89 The design of reagents and protocols for the separation and concentration of metal values in these streams has depended heavily on differences in the coordination chemistry of the components. 

Resmi et al. [59] used laterite stones for the immobilization of Pseudomonas putida (MTCC 1194). The amount of bacterial biomass attached to the support was 8.64 g/100 g of stones on dry weight basis. Packed bed reactor was used for treating mixture of seven azo dyes. With the help of immobilized bacterial strain, dye mixture was degraded to nontoxic smaller molecules. It was reported that even after 2 months, bacteria-coated pebbles were stable and suitable for the aerobic degradation of azo dyes. With the help of TLC and HPLC, 61.7% degradation was reported at the concentration of 50 pg/mL of dye. 

Element Laterites from basalts (n SI) Accumulation factor with respect to parent rock Lateritic soils of Western Australia (n 39) Range of Correlation coefficient with concentration Fe concentration ... 

The lateritic hydrous nickel silicate ores are formed by the weathering of rocks rich in iron and magnesium in humid tropical areas. The repeated processes of dissolution and precipitation lead to a uniform dispersal of the nickel that is not amenable to concentration by physical means therefore, these ores are concentrated by chemical means such as leaching. Fateritic ores are less well defined than sulfide ores. The nickel content of lateritic ores is similar to that of sulfide ore and typically ranges from 1% to 3% nickel. Important lateritic deposits of nickel are located in Cuba, New Caledonia, Indonesia, Guatemala, the Dominican Republic, the Philippines, and Brazil. Fossil nickeliferous laterite... 

LATERITE. The suh-aerial decay of rocks in tropica) regions, ha mg a distinctly moist or rainy climate, results in the development of a residual, reddish, and usually sticky soil frequently containing concretions. The principal products of laicri/alion are the hydrated oxides of aluminum and iron cither in the crystalline ur amorphous form. If the concentration of iron oxide is sufficiently high the laicrite may be valuable as an iron ore. If. on the other hand, the concentration of alumina is high the laleritc may he valuable as an ore ol that metal. 

The role of chemical weathering has long been recognized in economic geology. Tropical bauxites, which account for most of world s aluminum ores, are typical examples of residual concentration of silicate rocks by chemical weathering over long time periods (Samma, 1986). Weathering of ultramafic silicates such as peridotites forms residual lateritic deposits that contain... 

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