Arsenic removal from contaminated water by natural iron ores

Natural iron ores were tested as adsorbents for the removal of arsenic from contaminated water. Investigated parameters included pH, adsorbent dose, contact time, arsenic concentration and presence of interfering species. Iron ore containing mostly hematite was found to be very effective for arsenic adsorption. As(V) was lowered from 1 mg/L to below 0.01 mg/L (US standard limit for drinking water) in the optimum pH range 4.5–6.5 by using a 5 g/L adsorbent dose. The experimental data fitted the first-order rate expression and Langmuir isotherm model. The adsorption capacity was estimated to be 0.4 mg As(V)/g adsorbent. The presence of silicate and phosphate had significant negative effects on arsenic adsorption, while sulphate and chloride slightly enhanced. The negative effect of silicate could be minimised by operating at a pH around 5. The interference of phosphate would necessitate the use of a relatively high dose of the adsorbent to achieve arsenic levels conforming to drinking water standards. The mechanisms of interference of silicate and phosphate on As(V) adsorption are also discussed.