0523196 Dempsey This project seeks to evaluate the mechanisms for very high removal capacities of arsenic (As) by granular activated carbon (GAC) that has been pretreated with iron-citrate. Previous studies by the PIs found this phenomenon of high capacity, which cannot be explained by conventional equilibrium models involving sorption onto ferric hydroxide or iron-arsenic precipitates. The study will test the hypothesis that removal of As(V) at a greater than 1:1 molar ratio of As:Fe is due to reduction and subsequent precipitation of arsenic sulfides within the pores of GAC. The PIs also will investigate the importance of various basic water quality/chemistry characteristics, such as pH, alkalinity, and concentrations of natural organic matter and dissolved oxygen, on rates and extent of As removal. The speciation of As after its removal by tailored GAC will be determined using extended x-ray absorption fine-structure spectroscopy (EXAFS) and Mossbauer spectroscopy.
