Microwave roasting and leaching of an oxide-sulphide zinc ore

In this paper, a novel combination of phase transformation and leaching is proposed to recover zinc from an oxide–sulphide zinc ore. Accordingly, various analytical technologies, such as X-ray diffraction, chemical analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, are employed. The phase transformation of a raw ore and the effects of microwave heating and Na2O2 addition on zinc leaching are investigated. The results show that the addition of a strong oxide Na2O2 can directly transform the refractory phases, particularly zinc sulphide, into zinc sulphate. As a result, SO2 emissions are avoided and an environmentally friendly zinc recovery process is realised. Both microwave heating and the Na2O2 level have significant effects on phase transformation and zinc leaching. The zinc leaching rate can reach 82.06% under the following conditions of microwave heating: adding Na2O2 at a mass ratio of 25%, leaching in an ammonium chloride solution with a total ammonium concentration of 7.5 mol/L and an ammonia/ammonium chloride molar ratio of 1:1, adding NaClO as an aid-leaching reagent and leaching for 1 h. By contrast, the zinc leaching degree for the ore samples roasted in a traditional electric resistant furnace is only 30.62%. Moreover, at the same oxidation degree, the total energy consumption by the proposed process is 0.78 kWh/(kg·ore), which is lower than that by traditional heating (same power). Thus, the combination technology of microwave-heated phase transformation and leaching is effective in treating oxide–sulphide zinc ore.