Minor amounts of cobalt and nickel are structurally incorporated in jarosite precipitates and the extent of incorporation increases as the concentration of dissolved cobalt or nickel increases. Potassium jarosite incorporates more cobalt or nickel (～1% Co or Ni) than does sodium jarosite or ammonium jarosite (～0.4% Co or Ni). Elevated temperatures increase the incorporation of Co or Ni in the jarosite precipitates, but the increase is modest. Increasing concentrations of Na_2SO_4, (NH_4)_2SO_4 or K_2SO_4 result in an increase in the Co and Ni contents of the jarosite precipitates. The extent of Co or Ni incorporation also increases as the pH of the synthesis solution increases. In contrast, elevated concentrations of ferric sulphate reduce the extent of Co or Ni incorporation in jarosite precipitates. The parametric dependencies suggest that Co(Ⅱ) and Ni(Ⅱ) substitute to a limited extent for Fe(Ⅲ) in the jarosite structure, and the X-ray determined cell parameters of the precipitates support this hypothesis. The oxidation of Co(Ⅱ) to Co(Ⅲ) results in a modest increase in the Co content of the jarosite precipitates, but the common presence of poorly crystalline Co(Ⅲ) oxyhydroxide (heterogenite) accounts for at least part of the increase.
展开▼
