Adsorption and desorption of phosphate on biochars

Abstract

Biochar (BC) is regarded as a potential carbon sequesterer, a soil fertility enhancer, and a preventer of nutrient leaching. Phosphorus amended biochar could enhance soil fertility. This work investigated the adsorption and desorption of phosphate from aqueous solution on two different carbonized materials. Sugar cane bagasse (SC) and Miscanthus×giganteus(M) samples were carbonized at various temperatures (between 300°C and 700°C) for residence times of 20 or 60min. The largest surface area and the highest P adsorption at 20°C and pH 7 was obtained for M BC prepared at 700°C and at the longer residence time, compared to the SC BC made under the same conditions (approximately 15.5mgg−1 and 12.8mgg−1 for 400 mgdm−3 phosphate in solution, respectively). Adsorption of P on BCs was endothermic and increased with process temperature. The amount of desorbed P was proportional to its adsorption capacity. Two isotherm models (Freundlich and Langmuir) fitted the experimental results of phosphate adsorption onto the BC, and the Langmuir adsorption model described it better. Thermodynamic parameters are compared in the text with phosphate adsorption on other BCs reported in the literature. Our data suggest that adding phosphate to BC could provide a better way to apply P to soil in order to obetain better agronomic performances.