Electrokinetic properties of smithsonite and its floatability with anionic collector

The effect of the smithsonite/water interface properties on the floatability of the mineral without and in the presence of sodium carbonate was examined through zeta potential measurements, microflotation tests, and the concentration of Zn2+ ions measurement, in the pH range from 7 to 11. The isoelectric point value of the mineral was achieved at pH 8.0, and the species Zn2+, OH−, HCO3−, CO32−, and H+, as well as the reabsorption of hydrolysis products would determine the smithsonite–solution interface properties. Smithsonite presents high floatability with sodium oleate (1.5 × 10−4 mol/L) between pH 7.0 and 8.0. Above pH 8.0, the smithsonite floatability decreases abruptly, and the polymeric zero-charged Zn(II) hydrolyzed species [ Zn ( OH ) 2 ( H 2 O ) 2 ] n 0 is proposed for depressing the floatability of smithsonite. With the sodium carbonate added into the solution, the isoelectric point value of the mineral was achieved at pH 8.2. The smithsonite interface, having more surface cation sites and zinc species in the Stern layer, gives rise to the floatability in the pH range from 7.0 to 8.7. Due to the formation of Zn(CO3)22−, the decrease of the concentration of the hydrolyzed species [ Zn ( OH ) 2 ( H 2 O ) 2 ] n 0 makes smithsonite more floatable than that without the Na2CO3 at 8.7 < pH < 10 (flotation recovery from 30% to 75% at pH 9.5). The results show that the anionic flotation of smithsonite is a promising route to recover Zn with the sodium carbonate.