Utilization of coal fly ash in the adsorptive removal of fluoride from contaminated groundwater

Abstract 75% of the global production of fly ash (FA) totalling 562 million metric tonnes becomes solid waste causing major environmental and economic havoc. In this research, a comparative study was conducted on the utilization of raw and chemically modified FA adsorbents in the removal of fluoride (F − ) from contaminated water. The modification was done by using hydrochloric acid (HCl) and magnesium chloride (MgCl 2 ). Characterization of the adsorbents was done by using SEM-EDX analysis, specific surface area (S S ) and pH of zero point charge (pH zpc ). The characterisation confirmed that the modification process removed the impurities in FA and improved the S S . However, the shift of pH zpc from 10.71 to 4.94 was unfavourable for the F − removal due to the reduction in the pH range in which the adsorbents surface charge is positive. Adsorption studies indicated that raw adsorbent is more effective than the modified adsorbent. The maximum adsorption capacity obtained at the optimum conditions (pH = 2; contact time = 120 minutes; dosage =2.0 g/L) was 3.64 mg/g and at neutral pH it was 1.0 mg/g. In conclusion, raw FA adsorbent can be used as a low-cost adsorbent material to remove F − from contaminated water.