Development of characteristics of laterite soil-based mixtures for the removal of nitrate from drinking water

The main objective of this study is to investigate surface adsorption characteristics and physical conditions of laterite for the removal of nitrate in aqueous solutions with the appropriate amendment for the effective removal of nitrate from drinking water. The physico-chemical properties of laterite soil were analyzed. The effects of various operational parameters such as solution pH, adsorbent dosage, contact time, and the initial concentration of nitrate were examined on nitrate adsorption by laterite and laterite-limestone soil mixtures using the batch experiments. The obtained results showed that the maximum percentage of nitrate adsorption attained by raw laterite was at initial pH 3, after 60 min of contact time, and with an adsorbent dose of 2 g. Pseudo-first-order kinetic model and Langmuir isotherm model showed the best fit for the experimental adsorption data, and a maximum adsorption capacity of 0.628 mg/g was observed. Laterite-limestone mixture containing 60% laterite showed the highest removal efficiency. The results obtained by the limestone-laterite mixture showed that the maximum removal efficiency attained was at pH 3, after 180 min of contact time, and with an adsorbent dose of 2 g. Although the optimum pH was similar in both soil samples, the final pH of the solution had increased to 6.75 +/- 0.17. Pseudo-second-order kinetic model and Freundlich isotherm model showed the best fit for the experimental adsorption data. This soil mixture was used to determine the effect of competing anions on the nitrate removal efficiency. It was found that phosphate ions have shown maximum influence.