Release of Arsenic from Model Wastewater Treatment Solids: A Mechanism Based on Surface Ligand Exchange

The loss of arsenic from model wastewater treatment solids has been studied by neutron activation analysis. The data show that the loss of arsenic from unstirred solids is controlled by a surface exchange reaction and also clearly demonstrate that arsenic is not retained in a solid solution. This is in contrast to metal ions which are retained in crystalline solids as solid solutions. The activation energy Eafor the exchange reaction is calculated to be 40 kJ/mol. Data were retrieved for the half-time of arsenic exchanging from these solids. The presence of arsenic, either in the solid or in the aqueous phase contacting the solid, altered the kinetics of transformation to and the crystalline nature of the final products. These data have implications for the disposal of wastes to landfill.