Silicate ores dissolution

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... 

Leaching of ores, i.e. the separation of Fe oxides from silicate minerals has prompted investigations into the acid dissolution behaviour of natural goethites and hematites (Surana Warren, 1969 Warren Roach, 1971). Dissolution curves... 

Basically, the literature provides two dissolution methods sample preparation with sample weights of 0.2—1 g and large dilutions, or smaller sample weights with less dilution (III.B). The relatively large dilution, in general after a fusion [51], for the determination of main and lesser components, as for example in silicate analysis [2], the determination of Al, Ca, Mg, Mn and Si in slags [4], Si [55], Pb and Mn [143], and also Cd, Ca, Cu, Pb, Mg and Si in ores or iron sinter [97, 147] and Cr, Mg in refractories [93] is presently used in routine analysis. 

Tiemann (T8) studied the dissolution of silica from a siliceous iron ore by sintering the ore with sodium carbonate followed by leaching the sodium silicate with water. The reaction rates were found to be low after sintering for 4 hr at 1450°F. The residual concentrate was analyzed to be 56% iron, corresponding to 88% dissolution of the silica. Partial to complete fusion resulted when the temperature was increased. 

The removal of silica from a siliceous iron ore, such as the taconites found in Minnesota and Wisconsin, has been studied by Tiemann (T7, T9). Caustic concentrations from 25-500 gm/liter were used to digest the ore in a bomb at temperatures from 312 to 408°F. The leaching pressures in the bomb correspond closely to the equilibrium vapor pressures of the sodium hydroxide solutions used. A residual concentrate containing around 65% iron was obtained with —200 mesh material in 60 min of contact time. The high rate of dissolution of the silica was attributed to its occurrence in the form of microcrystalline (chalcedonic) varieties with high specific surface. The dissolution rate of pure quartz is directly proportional to the surface area and an average rate of 17 X 10 gm moles/cm sec was obtained for a 100 gm/liter NaOH solution at 312°F for the —400 mesh fraction. 

The sorption of uranium from acid sulfate leach liquors by strong base anion exchange resins is unusual since complexes of the type [U02(S04) ] " may be sorbed by both ion exchange and addition mechanisms. High concentrations of other species are present in the leach solution due to dissolution of pyritic and siliceous components of the ore, but, apart from iron, they do not interfere with the sorption of uranium as a complex anion. Iron(III) also forms an anionic sulfate complex, but is only weakly held by the resin and is displaced ahead of the uranium. The sorption of uranium may be represented by equations of the type ... 

During electrolysis, per mole of potassium permanganate one mole of potassium hydroxide is produced, which has to be recovered. This can be achieved, for example, by evaporating the mother liquor to 750 g KOH per L, whereupon the dissolved potassium manganate(Vl) and calcium hydroxide crystallize out and are removed. The potassium hydroxide can be returned to the dissolution step. Other dissolved impurities from the ores, such as silicates or aluminates, have to be removed from the alkali cycle. 

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