Amidoxime collectors: Lead-free flotation performance and adsorption mechanism in the separation of wolframite, quartz and calcite

The novel amidoxime-based collectors, 4-pyridylamidoxime (PA), 3-ethyl-4-pyridylamidoxime (EPA), and 3-methyl-5- tert -butyl-4-pyridylamidoxime (MBPA), were introduced in the lead-free flotation separation of wolframite from quartz and calcite. Compared with PA, EPA, and the traditional collector benzohydroxamic acid (BHA), MBPA exhibited a better separation and recovery capacity to wolframite ore. 4.0 × 10 -4 mol/L MBPA recovered more than 80 % wolframite, ∼24 % calcite, and ∼ 26 % quartz at pH 8.0 without Pb 2+ ions. Under the same conditions, BHA only floated out less than 35 % wolframite. The adsorption amount results exhibited a stronger adsorption ability of MBPA than BHA on wolframite surface. Further, the results of zeta-potential, FTIR, XPS and density functional theory (DFT) calculation revealed that MBPA could chemisorb on wolframite surface to form −N-Fe and −O-Fe bonds. MBPA had stronger electron-donating ability and weaker electron-accepting ability than BHA, which exhibited higher reaction activity. It was clear that MBPA was an excellent collector in the lead-free flotation separation of wolframite from calcite and quartz.