Electrokinetic Potential of Basic Zinc Sulfate and of Products of Its Ion Exchange

Basic zinc sulfate with an empirical formula of ZnSO₄∙3 Zn(OH)₂∙3.5 H₂O (or Zn₄SO₄(OH)₆∙3.5 H₂O) was precipitated using stoichiometric amounts of ZnSO₄ and NaOH, followed by drying and storage in air. The XRD pattern suggests that the product contains tri- and tetrahydrate of basic zinc sulfate. Penta-, mono-, and hemihydrates of basic zinc sulfate can be produced by storing the original material in air at various temperatures and humidity levels, and especially by immersion in aqueous solutions. The precipitate was characterized by its specific surface area and zeta potential, and it has an isoelectric point (IEP) at pH 8.9. Ion exchange with an excess of CuSO₄ results in conversion to brochantite Cu₄(OH)₆SO₄ (as detected by XRD) and in an increase in the specific surface area. The conversion was complete at room temperature with a sufficient excess of CuSO₄, but it was not complete at 50 or 60 °C. Apparently, the conversion into brochantite is exothermic. The IEP of brochantites obtained from ZnSO₄∙3 Zn(OH)₂∙3.5 H₂O by ion exchange was at a pH of about 10, which is higher than the previously reported IEP.