Adsorption of phosphorus by calcium-flour biochar: Isotherm, kinetic and transformation studies

Discharging phosphorus (P)-contaminated water directly into the aquatic environment leads to resource loss and eutrophication . Thus, removing P from waste streams is imperative. In this study, calcium-decorated biochar (Ca-BC) in different mass ratios of Ca to BC was designed to effectively adsorb P from solution. Ca-BC was characterized through X-ray diffraction (XRD) analysis, followed by isotherm and kinetic adsorption experiments. The decorated Ca on the BC surface was found to have preferred P adsorption ability. A design of calcium hydroxide (Ca(OH) 2 ) to flour in a mass ratio of 2:1 was found to have a maximum adsorption capacity of 314.22 mg g −1 for P. The Langmuir and pseudo-second-order models fit the sorption process adequately. XRD analysis indicated that the preferable adsorption ability to P was due to the reaction of Ca(OH) 2 and PO 4 3− , forming the hydroxylapatite (Ca 5 (PO 4 ) 3 (OH)) crystal. The P in solution was transformed to the crystal. Thus, Ca-BC is an environmental friendly and low-cost sorbent for P removal.