Preparation of arsenical-natroalunite solid solutions with high crystallinity by hydrothermal method

Abstract

The substitution of AsO4-for-SO4 in natroalunite has been investigated as a potentially eco-friendly method for arsenic immobilization/stabilization. The maximum amount and the best filterability of the arsenic-free natroalunite can be gained at the condition of pH 3.00 and 200°C for 3 h. Then the arsenic was introduced into the structure of natroalunite to prepare the arsenical-natroalunite under the preferred conditions. For arsenic concentration ≤ 3500 mg/L, the pure phase of arsenical-natroalunite solid solution could be synthesized, and the maximum arsenate substitution observed in the natroalunite structure was ∼11% molar. For arsenic concentration = 4200 mg/L, the spheroidal amorphous aluminum arsenate phases were formed. Additionally, leaching tests demonstrated that the arsenic solubility of arsenical natroalunite remained stabilized at 0.1 to 0.8 mg/L in 20 weeks at pH 4–9. However, amorphous aluminum arsenate phases were not appropriate for long-term storage under the same conditions with arsenic concentration between 3 to 6.8 mg/L.