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In this research, the effect of different citric acid concentrations, ammonia concentration, temperature, leaching time, stirring speed and liquid-to-solid ratio on the zinc leaching from low-grade zinc oxide ore in a NH3-H3C6H5O7-H2O system were studied. The results showed that the zinc leaching rate is only 4.7% when the citric acid concentration is 0 M, and the leaching efficiency of Zn increased with increasing citric acid concentration. Under the conditions: citric acid concentration of 1.0 M, ammonia concentration of 6 M, temperature of 25 °C, leaching time of 60 min, stirring speed of 300 rpm and the starting solid-to-liquid ratio of 1:5, 81.2% of Zn is leached. The mineralogical changes of the low-grade zinc oxide ores during the processes were characterized by X-ray fluorescence (XRF), X-ray powder diffraction (XRD), Scanning Electron Microscopy associated with Energy Dispersive Spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FT-IR). From the evidence we deduced that citric ions complexed with zinc ions, forming a Zn-citrate complex. As a result, the zinc leaching rate was improved without the risk of pollution or pretreatment. This makes it as a good choice for a more ecological treatment of hemimorphite.
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Ma et al. (2016) studied this question.
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