Arsenate removal and residual water quality during treatment with iron modified zeolite

The environmental value of an adsorbent depends on the quality of the treated water and the amount of contaminated solid generated, as well as its percentage removal. This study examined these relationships for iron-modified zeolite using 27 batch tests with synthetic arsenate solutions. Initial arsenic concentration, adsorbent dose, pH and contact time ranged from 0.5 to 5 mg/L, 0.5 to 3 g/L, 5 to 7 and 30 to 180 min, respectively. Removal and apparent uptake were recalculated from the recorded aqueous concentrations, and matched operating conditions were compared without assuming experimental replication. Removal ranged from 9.48% to 53.60%. Increasing dose from 0.5 to 3 g/L increased removal by a mean of 30.07 percentage points across seven matched comparisons. Increasing initial concentration reduced percentage removal by 9.08 points on average, whereas increasing contact time added 4.58 points. The highest removal produced a residual concentration of 0.232 mg/L at an initial concentration of 0.5 mg/L, a dose of 3 g/L, pH 6 and 180 min. The largest apparent uptake, 1.138 mg/g, occurred at a different condition and corresponded to only 11.38% removal. All residual concentrations exceeded the World Health Organization provisional drinking-water guideline of 0.010 mg/L. The results establish a dose-dependent reduction in aqueous arsenic loading, but do not demonstrate drinking-water treatment or long-term immobilization. Evaluating removal, residual concentration and uptake together provides a more defensible basis for selecting subsequent treatment and spent-solid investigations.