Flotation separation of smithsonite from calcite using an amino-acid collector

Abstract

• ZnCO 3 rather than CaCO 3 could be efficiently floated by C16Gly at pH 10. • The DFT method successfully predicted the flotation selectivity of C16Gly. • C16Gly reacted with the ZnCO 3 /CaCO 3 surface forming bidentate binding models. • C16Gly preferred to binding with the ZnCO 3 surface rather than the CaCO 3 surface. Flotation separation of smithsonite (ZnCO 3 ) from calcite (CaCO 3 ) is not commonly satisfied using traditional fatty acids, and thus, more selective collectors are required. In this regard, a new collector, N-hexadecanoylglycine (C16Gly) was used to selectively collect ZnCO 3 from CaCO 3 in this work. The flotation selectivity of C16Gly was predicted by DFT calculations. The calculation results showed that the C16Gly anion adsorbed on the ZnCO 3 /CaCO 3 surface via two Zn–O/Ca–O bonds. Moreover, as the new Zn–O bonds were more covalent than Ca–O bonds, the adsorption of C16Gly on the ZnCO 3 surface was more stable. Therefore, this collector may be used as a specific collector for ZnCO 3 rather than for CaCO 3 . The DFT results were confirmed by experimental results. Single-mineral flotation and contact angle results both suggested that C16Gly efficiently floated ZnCO 3 rather than CaCO 3 at pH ≥ 10. As for the 1:1 ZnCO 3 and CaCO 3 mixture, the Zn recovery was much higher than that of CaO with 3 × 10 -4 mol/L of collector at pH 10, and the separation efficiency reached 64.53% under the same conditions. XPS analysis revealed that Zn/Ca atoms on ZnCO 3 /CaCO 3 surface were involved in the reaction of C16Gly with the mineral surface. In addition, a good coverage of C16Gly on the ZnCO 3 surface was observed by the time-of-flight secondary ion mass spectrometry system. In contrast, this collector was not found on the CaCO 3 surface due to its poor adsorption capacity. These experimental results confirmed that C16Gly is a promising collector for the selective flotation of ZnCO 3 from CaCO 3 and DFT calculations are a powerful tool to predict the flotation behavior of C16Gly for the ZnCO 3 –CaCO 3 system.