Recovery of rubidium and potassium alums from lithium-bearing minerals

Abstract Rubidium was recovered from lithium-containing solution from processing zinnwaldite, (KAl(Fe,Li)(Si 3 Al)O 10 F 2 ), concentrate after Li 2 CO 3 crystallization as a mixture of rubidium and potassium alums (RbAl(SO 4 ) 2 .12H 2 O and KAl(SO 4 ) 2 .12H 2 O). 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 (Al 2 (SO 4 ) 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.