Neutralization of arsenic pollutants, contained in natural waters: The theoretical analysis of solubility of some arsenates and optimization of the processes

Abstract

Arsenic belongs to chemical elements, which are often found in natural waters and make it unsuitable for consumption without special treatment. Neutralization of arsenic pollutants of natural waters by converting them into insoluble form is one of the perspective methods of dearsenication. Precipitation (by iron or aluminium coagulants, lime) and adsorption (by oxides and hydroxides of iron, aluminium or manganese) are among the most popular dearsenication methods. The use of these chemicals entails the formation of poorly soluble arsenates. Since the possibility of the release of arsenic compounds into the water due to the dissolution of formed arsenates depends on its solubility under appropriate conditions, it is necessary to have information about the dependence of arsenates solubility on pH. According to the calculations the solubilities of arsenates of iron(III), aluminium, manganese(II) and calcium are highly dependent on pH. At pH<4, the solubilities of these arsenates increase in the sequence FeAsO4 – Mn3(AsO4)2 – AlAsO4 – Ca3(AsO4)2. Above рН 4 dependence changes and solubilities of these arsenates increase in the sequence FeAsO4 – AlAsO4 – Mn3(AsO4)2 – Ca3(AsO4)2.

Keywords

• solubility
• equilibrium concentration
• iron(iii) arsenate
• aluminium arsenate
• manganese(ii) arsenate
• calcium arsenate