Selective separation of cassiterite from quartz using (2-ethylhexyl) phosphonic acid mono-2-ethylhexyl ester

This study evaluates the effectiveness of mono-2-ethylhexyl-2-ethylhexyl phosphonate (PC-88A) as a novel collector for the flotation separation of cassiterite from quartz. PC-88A exhibited stronger collecting power than benzohydroxamic acid (BHA) across a wide pH range. At pH 8.0±0.2 and a PC-88A concentration of 10.0×10 - 5 mol/L, high-quality concentrates were obtained, yielding 74.61% SnO 2 grade with 95.36% recovery. Contact angle measurements indicated that PC-88A adsorption significantly enhanced the hydrophobicity of cassiterite. AFM revealed a higher adsorption density of PC-88A on cassiterite than on quartz. Zeta potential results suggested chemisorption between negatively charged PC-88A anions and cassiterite surfaces. XPS and FTIR confirmed that P=O and P-OH groups of PC-88A chemically adsorbed onto Sn sites on cassiterite, forming P-O-Sn bonds. DFT simulations identified the two oxygen atoms in the PO(OH) group as the primary reactive centers, showing high chemical activity. The selective adsorption of PC-88A is therefore attributed to chemical bonding between its PO(OH) group and Sn active sites on the cassiterite surface.