Atomic insights into the interaction mechanism underpinning carbonate ion adsorption in smithsonite flotation

Abstract

In industrial practice, smithsonite flotation separation and purification are nearly invariably conducted in highly alkaline environments. According to latest studies, sodium carbonate is a cheap, sustainable, stable, and safe substitute pH modifier that additionally assists with deep extraction recovery of smithsonite. In this work, the influence of carbonate as a pH modifier on smithsonite flotation behavior was comprehensively explored through flotation experiments, contact angle tests, X-ray photoelectron spectroscopy (XPS) investigations, and density functional theory (DFT) calculations. In comparison to sodium hydroxide, smithsonite exhibits far better floatability and hydrophobicity in the carbonate system, as demonstrated by the results of micro-flotation and contact angle experiments. XPS demonstrates that the underlying reason of the distinct pH modifications of smithsonite floatability in the carbonate system is the creation of different zinc-containing compounds, with the highly reactive CO32- forming a Zn5(CO3)2(OH)6 complex with Zn atoms at pH 10.5. Comprehensive DFT calculations further demonstrated that the hybridization reactions between Zn 2 s, O 2 s, and O 2p orbitals and the formation of stable Zn-O covalent bonds between OH- and Zn atoms shielded the preferential adsorption of oleate (OL-) on the smithsonite surface. Uniquely, the ionic bonding generated by carbonate is distinguished by the formation of a low-bonding-capacity Zn-O chemical bond, causing it susceptible to breaking during adsorption competition and allowing OL- to adsorb preferentially on Zn sites.