Adsorption of As(V) from Water over a Hydroxyl-Alumina Modified Paddy Husk Ash Surface and Its Sludge Immobilization

Abstract

Arsenic (As) is considered as one of the most hazardous elements found in the groundwater. It is present in water in both arsenate (As(V)) and arsenite (As(III)) forms. On exposure for a considerable length of time to water having As concentration above the maximum permissible limit of 10 μg/L, there is a serious threat of developing various health problems including cancer. There is frequent reporting about the development of different newer methods for the removal of arsenic from water. In this present approach, a low-cost product namely modified paddy husk ash (PHA) was used as an adsorbent for the adsorption of arsenic from water. The adsorbent is important from the point of its easy availability in the tropical paddy producing countries. For improved removal efficiency and disposal of spent adsorbent, the surface of the PHA was activated with an aluminum oligomeric solution called as hydroxyl-alumina. To understand the process, various techniques such as XRD, SEM–EDS, particle size determination, and zeta potential measurements were used and the effects like variation of adsorbent dose, pH, initial arsenic concentration, and contact time were studied. The Freundlich adsorption isotherm and pseudo-second-order kinetic models were found to be the best fitted adsorption isotherm and kinetic data models respectively thereby confirming the adsorption as a multilayer chemisorption process. Finally, the issue of disposal of the spent sludge through the successful formation of cement clinkers was studied.