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

•ZnCO3 rather than CaCO3 could be efficiently floated by C16Gly at pH 10.•The DFT method successfully predicted the flotation selectivity of C16Gly.•C16Gly reacted with the ZnCO3/CaCO3 surface forming bidentate binding models.•C16Gly preferred to binding with the ZnCO3 surface rather than the CaCO3 surface. Flotation separation of smithsonite (ZnCO3) from calcite (CaCO3) 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 ZnCO3 from CaCO3 in this work. The flotation selectivity of C16Gly was predicted by DFT calculations. The calculation results showed that the C16Gly anion adsorbed on the ZnCO3/CaCO3 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 ZnCO3 surface was more stable. Therefore, this collector may be used as a specific collector for ZnCO3 rather than for CaCO3. The DFT results were confirmed by experimental results. Single-mineral flotation and contact angle results both suggested that C16Gly efficiently floated ZnCO3 rather than CaCO3 at pH ≥ 10. As for the 1:1 ZnCO3 and CaCO3 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 ZnCO3/CaCO3 surface were involved in the reaction of C16Gly with the mineral surface. In addition, a good coverage of C16Gly on the ZnCO3 surface was observed by the time-of-flight secondary ion mass spectrometry system. In contrast, this collector was not found on the CaCO3 surface due to its poor adsorption capacity. These experimental results confirmed that C16Gly is a promising collector for the selective flotation of ZnCO3 from CaCO3 and DFT calculations are a powerful tool to predict the flotation behavior of C16Gly for the ZnCO3–CaCO3 system.