The efficient separation of apatite and dolomite using sodium dextran sulphate as an eco-friendly depressant: Flotation performances and atom-scale interaction mechanism

Abstract

The upgrading of Apa (Apatite) from Dol (Dolomite) by flotation is an extremely challenging job because of their resembling surface characteristics and the inferior selectivity of conventional fatty acid. In this work, an eco-friendly polymer surfactant dextran sulfate sodium (DSS) was evaluated as a novel Dol inhibitor to separate Dol and Apa and the selective depression mechanism was unveiled from atom-scale prospective. The results proved that DSS selectively depressed Dol while scarcely influenced the flotation of Apa. The wettability and zeta potential results suggested that DSS preferred to adsorb on Dol than Apa, which impeded NaOL (sodium oleate) to interact with Dol and made its surface hydrophilic. X-ray photoelectron spectroscopy (XPS) results confirmed that the intense chelation of −OSO₃^2- groups with both Ca²⁺ and Mg²⁺ sites on Dol surface. While DSS species physiosorbed on Apa and they were easy to be replaced by NaOL. DFT calculation suggested that the 2p orbital of O₁, O₂ and O₃ atoms within −OSO₃^2- groups bonded with Mg 3s and Ca 4s orbital orbitals to form ionic −O-Ca, −O-Mg bonds, respectively. While only small portion of −OSO₃^2- groups within DSS adsorbed on Ca sites weakly through electrical interaction because of the steric hindrance effect and the difference in atoms distribution density. As an eco-friendly surfactant, DSS shows good selectivity and compatibility in conjunction with NaOL via direct flotation, which has good prospects to substitute conventional reverse flotation to simplify the flotation processes and lower the flotation cost.