Characterisation and performance of thermally treated rice husk as efficient adsorbent for phosphate removal

Phosphate is an important macronutrient for the growth of aquatic plants and algae but its excessive supply in water bodies causes eutrophication. The wide range of phosphate utilisation also affects the substantial measure of phosphate-bearing waste. This study aims to synthesise and characterise the bio-adsorbent form rice husk for phosphate removal. Rice husk ash was prepared by heating the rice husk at 105 °C for 24 h while the activated carbon from rice husk was further carbonised in a muffle furnace at three different temperatures from 450 to 750 °C. Efficiency of adsorbent was analysed using synthetic phosphate solution. Overall findings show that the thermally treated rice husk at 750 °C promoted the best phosphate removal of around 97% with 2 mg/L initial phosphate concentration and pH value of 9.0. The adsorption behaviour was fixed with Langmuir adsorption isotherm when R² for the fitting of the experimental data was 0.991 with low chi-square value and the results indicated a monolayer adsorption mechanism. The findings show that the rice husk can be an efficient and eco-friendly adsorbent for phosphate removal and promotes a good alternative use of abundant agriculture waste.