Dissolution mechanism and solubility of hemimorphite in NH₃-(NH₄)₂SO₄-H₂O system at 298.15 K

Abstract

The dissolution mechanism of hemimorphite in NH₃-(NH₄)₂SO₄-H₂O system at 298.15 K was investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The results show that hemimorphite is soluble in NH₃-(NH₄)₂SO₄-H₂O system and its residue exists in the form of an amorphous SiO₂ layer on the hemimorphite surface. The XPS data also indicate that the Si 2p3/2 and O 1s spectra of the hemimorphite are broadened and shift to higher binding energies and their binding energies are closer to silica with an increase of total ammonia and time. Solubility of hemimorphite in NH₃-(NH₄)₂SO₄-H₂O system was measured by means of isothermal solution method at 298.15 K based on the study of the dissolution mechanism of hemimorphite. The results show that the solubility of zinc in solution increases firstly and then decreases with the increase of c_T(NH₃) (total ammonia concentration) at different NH₃/NH₄⁺ ratios. The solubility of silicon in solution decreases from 0.0334 mol/kg in c_T(NH₃)=4.1245 mol/kg NH₃-(NH₄)₂SO₄-H₂O solution to 0.0046 mol/kg in c_T(NH₃)=7.6035 mol/kg NH₃-(NH₄)₂SO₄-H₂O solution.

Keywords

hemimorphite / ammoniacal solution / dissolution mechanism / solubility

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