Recovery of rubidium and potassium alums from lithium-bearing minerals

Rubidium was recovered from lithium-containing solution from processing zinnwaldite, (KAl(Fe,Li)(Si3Al)O10F2), concentrate after Li2CO3 crystallization as a mixture of rubidium and potassium alums (RbAl(SO4)2.12H2O and KAl(SO4)2.12H2O). The course of individual reactions aiming at rubidium alum separation from carbonated solutions containing potassium as a main contaminant was studied on synthetic solutions. Before the alum precipitation, the original carbonated solution was converted to sulphate solution. Rubidium recovery efficiency at least 95% was achieved if the amount of the precipitation agent (Al2(SO4)3) ranged between 3.5 and 4.0 multiples of stoichiometric amount related to rubidium concentration in the processed solution. Under such conditions, precipitates obtained contain between 4.10 and 3.62% Rb and from 6.02 to 6.25% K and consist of on average 24% rubidium alum and 75% potassium alum.