Selective leaching of zinc from carbonate source using glycine as an ecofriendly lixiviant

•A successful selective Zn leaching process by glycine as a green lixiviant.•Glycine was the most significant factor on Zn leaching in studied range of factors.•At optimum conditions, leaching of iron (1%) and silicon (1.1%) were negligible.•Statistically interaction between pH and glycine was confirmed thermodynamically. In the present study, a selective leaching process of zinc from a low-grade carbonate source is proposed by the use of a green lixiviant, namely glycine. Response surface methodology (RSM) coupled with central composite design (CCD), was applied to optimize the levels of glycine concentration, pH and temperature and to quantify the significance of the factors and the interactions among them. Under optimum conditions, glycine concentration = 1.5 M, pH = 9.5 and temperature = 70 ℃, more than 90% of zinc was leached while the leaching percentages of main impurities were negligible. Finally, zinc was removed from the leaching solution through the precipitation process by Na2S solution in the form of ZnS. The thermodynamic aspect of the leaching process was elucidated and it was attempted to justify the results obtained from statistical modeling.