Scandium extraction from multicomponent systems by crystallization of complex sulfates

Abstract Red mud generated from alumina production is one of the most promising scandium resources. Leaching for concentrating scandium and other valuable metals is often performed with the use of acid solutions in specially selected conditions. Different precipitants can be employed for selective precipitation of scandium in the form of poorly soluble compounds. A new method for the crystallization of ammonium scandium sulfates from sulfuric solutions was carried out in this study. Depending on the ammonium cation concentration, precipitation is possible in the form of NH4Sc(SO4)2 or (NH4)3Sc(SO4)3. The solubility values for NH4Sc(SO4)2 and (NH4)3Sc(SO4)3 in water established by the isothermal saturation method were 9.02 and 12.89 g/l Sc2O3, respectively. Complete precipitation of the most promising gravimetric form of scandium represented by NH4Sc(SO4)2 was achieved at 5-6 M H2SO4 and 0.5 M NH4 +. The product of crystallization from sulfuric solution used for treating poor scandium concentrate produced from red mud is a mixture of polymorphs of the composition NH4Sc(SO4)2. Co-precipitated impurities of Al, Fe, Ti, Zr etc. are separated after repeated dissolution and precipitation of ammonium scandium sulfate under analogous conditions. The recrystallization product after calcination at 1000°C contains 99% Sc2O3.