Removal of Aluminum from Leaching Solution of Lepidolite by Adding Ammonium

Lepidolite is a kind of low-grade lithium ore (3.5–4.0% Li2O) which contains more than 22% Al2O3 and 8% K2O. Removal and utilization of the Al and K will be very important for the economic extraction of lithium from this ore. In this paper, a novel method is proposed to remove Al from the leaching solution of lepidolite by adding ammonium from (NH4)2SO4. The results indicate that adding NH4 + could remove more aluminum and have a smaller loss of lithium in comparison to adding K+ for removing aluminum in the leaching solution. The Al removal reached up to 80.44% at (K+ + NH4 +)/Al3+ molar ratio of 0.95, while the amount of Li+ (99.84%) still remained in the leaching solution. In addition, the phase equilibrium in the quaternary K2SO4-Al2(SO4)3-(NH4)2SO4-H2O system at 278.2 K was investigated to support the above conclusion. The results verify that the addition of ammonium could remove more Al3+ by easily forming potassium alum (KAl(SO4)2·12H2O) and ammonium alum (NH4Al(SO4)2·12H2O).