Removal of Arsenic from Water using Manganese Oxides Adsorbents

Arsenic is a well known carcinogen which in natural waters poses a problem worldwide. In addition to natural sources of arsenic in groundwater, leaching of arsenic from ash in coal fly ash disposal facilities and from chemical landfills is a cause for concern due to possible contamination of groundwater. Therefore, applying effective methods and appropriate materials to selectively remove arsenic from natural waters is required. In this study, first several manganese oxides with different oxidation states [MnO, Mn2O3, Mn3O4 and MnO2] were tested for the removal of arsenic from water. Manganese oxides containing Mn3+ was able to adsorb more arsenic from water than other manganese oxides containing Mn2+ or Mn4+. The Mn2O3 was tested for As(III) and As(V) removal from natural groundwaters. The 10 g/L of the sorbent was able to remove greater than 95 percent of arsenic from both groundwaters. Two manganese oxide coated sand (MCS) sorbents, 5-hr MCS and 24-hr MCS, were developed as alternative, effective and potentially sustainable sorbents to remove As(V) and As(III) from water. The formation of arsenic inner-sphere complexes was evidenced by zeta potential measurements. The maximum adsorption of arsenic was obtained in the pH range from 3 to 10 suggesting that the MCS can be successfully utilized in water treatment without pre- and post- pH adjustment. The kinetics experiments were indicative of a rapid arsenic adsorption onto MCS during the first 60 min. A column study was performed to evaluate the removal of arsenic from water in a continuous flow system using both MCS sorbents. The breakthrough of arsenic occurred after 1,050 min for 24-hr MCS column and 1,440 min for 5-hr MCS column. The Adams-Bohart model was used to predict the initial breakthrough of arsenic from the column, while the Thomas model was in good agreement with experimental data and could be used to predict the overall performance of the column and the column exhaustion. For an initial arsenic concentration of 1,070 µg/L and a flow rate of 10 mL/min, the capacity of the MCS sorbents was 166 mg/kg for the 5-hr MCS and 127 mg/kg for the 24-hr MCS. .