Thermally activated laterite soil as an adsorbent for phosphate and fluoride removal from contaminated water

The present study examines the efficiency of thermal-activated laterite soil in different grain sizes as an adsorbent for removing phosphate and fluoride ions from contaminated water under laboratory conditions. The fresh laterite was collected from the inner layers of the weathering profile by auger drilling method. Collected soil samples were air-dried to remove the excess moisture content. Air-dried soil was crushed to prepare powdered material (2 and 0.5 mm). Thermally activated soil samples were prepared by heating the laterite at 100 degrees C, 200 degrees C, 300 degrees C, and 400 degrees C for 3 h in a muffle furnace. Adsorption conditions of phosphate and fluoride ions for the soil samples were determined by batch experiments conducted at room temperature and natural pH. Based on the results of studies, 300 degrees C and 400 degrees C (2 and 0.5 mm gran sizes) thermal-activated laterite soil proved to be an effective adsorbent and had higher removal capacities. The phosphate and fluoride removal efficiencies of 300 degrees C activated 0.5 mm laterite soil were 96.46% +/- 0.63% and 99.33% +/- 0.40%, respectively. Phosphate and fluoride removal efficiencies from 300 degrees C activated 2 mm laterite soil were 92.72% +/- 0.60% and 96.80% +/- 0.60%, respectively. In contrast, 20 min for 2 mm grain size and 10 min for 0.5 mm were the optimal contact times for maximum phosphate and fluoride ion removal. Phosphate removal efficiency was 91.93% +/- 0.24% and fluoride removal efficiency was 92.67% +/- 0.24% after 10 min at 300 degrees C, 0.5 mm laterite soil. At 20 min, the phosphate removal efficiency in 2 mm of 300 degrees C soil was 77.88% +/- 1.30%, and the fluoride removal efficiency was 81.60% +/- 0.31%. 0.75 g of laterite soil was identified as the optimum soil dosage for both grain sizes of phosphate and fluoride removal. The removal efficiency of phosphate and fluoride from 0.75 g, 300 degrees C 0.5 mm laterite soil were 90.08% +/- 0.30% and 93.53% +/- 0.30%, respectively. Phosphate and fluoride removal efficiency from 0.75 g, 300 degrees C 2 mm laterite soil were 84.88% +/- 0.10% and 79.33% +/- 0.10%, respectively. The results concluded that the percentage of removal rises with the increase in temperature. In contrast, results revealed that thermal-activated laterite soil has a strong ability to remove phosphate and fluoride from water.