Effects of Inorganic and Organic Ligands On Retention-Release of Arsenate On Low-Cost Sorbents.

We studied  the sorption of arsenate As(V) on low-cost sorbents [ferrihydrite, Al-Mg and Fe-Mg layered double hydroxides (LDHs), Fe- and Al-based drinking-water treatment residuals (WTRs)]  as affected by pH and varying concentrations of selected  inorganic and organic ligands, and ii) the effect of residence time on the desorption of As(V) by ligands. The capacity of ligands to inhibit the fixation of As(V) at pH 6.0 followed the sequence: sulfate < oxalate < tartrate  < citrate < selenite << phosphate on ferrihydrite,  sulfate < selenite < tartrate < oxalate << phosphate on Al-Mg-LDH and sulfate < tartrate < oxalate < selenite << phosphate on Fe-Mg-LDH.  The effect of phosphate, citrate and oxalate on As(V) sorption/desorption on/from WTR samples was also studied. Arsenate sorption decreased with increasing pH and ligand concentration. The longer the As(V) residence time on selected sorbents  the less effective the competing ligands was in desorbing As(V).