Understanding the impact of ammonium salt on the sulfidization of smithsonite from coordination chemistry

Here, a systematic investigation from coordination chemistry was performed to investigate the principles met by the ammonium salt to enable it to impact the sulfidization of smithsonite. We found that during the smithsonite sulfidization with ammonium salt modification, the HS, NH3, and OH (H2O) can only be bonded to Zn on smithsonite surface by & sigma;-bonding instead of & pi; back-bonding, thus they were in a competitive coordination relationship on smithsonite surface. Furthermore, we found that due to the different electron-donating abilities, the stability of Zn-S, Zn-N, and Zn-O bonds was in the order of Zn-S > Zn-N > Zn-O, and the coordination ability of HS, NH3, and OH (H2O) to surface Zn was in the order of HS > NH3 > OH (H2O). Moreover, we found that with ammonium salt modification, the hydration film on smithsonite surface was easily broken through, repelled, and dissolved by ammonium salt, and thus the sulfidization pathway made a change, which greatly reduced the adsorption energy. However, the final sulfidization product remained unchanged. Therefore, ammonium salt only accelerated the sulfidization rate of smithsonite as a catalyst role to strengthen sulfidization. XPS and ICP tests further supplemented experimental support. This work is instructive for the modifier strengthening sulfidization of oxide ore.