Efficient Beneficiation of Lepidolite Using an Amidoxime Collector in a Weak Acid Environment

The rapid development of the new energy industry has led to an increase in the demand for lithium metal. Lepidolite is the main source of lithium metal, but the common collector dodecylamine (DDA) can only separate lepidolite from its gangue (i.e., orthoclase) in a strong acid environment (pH ∼ 2) in the presence of depressants due to its weak selectivity. The heavy consumption of inorganic acid will corrode flotation equipment and bring challenges for wastewater treatment. In this study, the amidoxime collector 3-dodecylamine propyl amidoxime (DPA) was synthesized in our lab and introduced as the collector to efficiently recover lepidolite from orthoclase. In single mineral flotation, 80 mg/L DPA could float out 91.00% lepidolite and 85.50% orthoclase at pH 6.0, and DDA recovered 77.71% lepidolite and 90.02% orthoclase under the same conditions. For mixed mineral, 80 mg/L DPA combined with 100 mg/L sodium hexametaphosphate (SHMP) at pH 6.0 could obtain a Li₂O concentrate with a grade of 3.87% and a recovery of 76.86%. The surface contact angle of lepidolite could be selectively enhanced to 78°, but that of orthoclase only exhibited to 40°. Zeta potential and FTIR spectra exhibited that DPA would physically adsorb onto lepidolite. Quantum chemical calculations proved that compared with DDA⁺ (0.178 and 0.1942 a.u.), DPA⁺ had a larger electrostatic group (0.274) and a smaller ΔE_LUMO-HOMO (0.1431 a.u.) to adsorb on the lepidolite surface. Thus, the DPA-SHMP agent system had the ability to separate lepidolite from orthoclase in a weak acid environment.