Leaching of hemimorphite in NH3–(NH4)2SO4–H2O system and its mechanism

The leaching process and evolution of the leaching residue of pure hemimorphite in an NH3–(NH4)2SO4–H2O system were investigated. The results show that in the leaching process, zinc rapidly dissolved in an NH3–(NH4)2SO4–H2O system when it existed as a hemimorphite. Zinc and silica in hemimorphite simultaneously dissolved in the solution, and amorphous silica was then precipitated from the leaching solution. The leaching efficiency of zinc reached 95%, whereas most of the silicon remained in the residue. The leaching residue exists in the form of amorphous silica based on the results of the thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Thus, the hemimorphite leaching process and mechanism in an NH3–(NH4)2SO4–H2O systems were determined.

► Zinc and silica in hemimorphite were simultaneously dissolved in the leaching process.
► The solubility of silica in the ammonia solution was very low.
► Amorphous silica was precipitated from the solution.
► Determined leaching residue exists as amorphous hydrate silicon dioxide.