Role of sodium citrate in leaching of low-grade and multiphase zinc oxide ore in ammonia-ammonium sulfate solution

In this paper, a novel system for leaching of low-grade and multiphase zinc oxide ore is presented, in which ammonia-ammonium sulfate is chosen as leaching agent, meanwhile adds a small amount of sodium citrate to strengthen the complexation behavior. The thermodynamics is studied by using chemical equilibrium modeling to predict the zinc species distribution diagrams for the Zn (II)-NH3-Cit3 − system. Through employing various analytical technologies, such as X-ray diffraction (XRD), chemical analysis, and Fourier transform infrared spectroscopy (FT-IR), compositions, bond structures and chemical states are obtained. Moreover, effect of sodium citrate is studied by X-rays photoelectron spectroscopy (XPS) analysis, and it can be established that addition of sodium citrate is favorable for zinc leaching by inhabiting the formation of low complexation compound Zn(NH3)i2 + (i = 1, 2) and lowering the fraction of Zn(NH3)32 +. The leaching rate can reach 96.91% with a cit3 − concentration of 0.2 M/L. Once above it, diffusion rate of zinc would decrease, which causes the dropping of zinc leaching.