Abstract
The extraction of rare earth metals from fluoroapatite rich phosphate concentrates often involves a weak acid leach of fluoroapatite and a sulphuric acid bake of leach residue followed by water leach and precipitation to obtain an intermediate product. The main aim of this study was to determine and rationalize the solubility of rare earth metal ions in synthetic solutions representing various process liquors at three temperatures 40, 60 and 80oC containing different acid and metal ion concentrations with respect to sulphuric acid, phosphoric acid and sulphate salts of sodium, magnesium, aluminium, potassium, calcium and iron(III). Solid mixture of rare earth metal carbonates was used as the source of rare earth metal ions. The solubility tests and characterization of solids using XRD were conducted at Murdoch University laboratories. The composition of initial carbonate solids and the solids and solutions formed after saturation were analysed for rare earth and other elements at TSW Analytical Laboratories in Perth using ICP-MS and ICP-OES. The precipitated solid in sodium rich acidic sulphate solutions is the double salt NaRE(SO4)2 based on the solid assays. However, in acidic solutions free of sodium or of low concentrations of sodium the precipitated solid appears to be RE2(SO4)3.