A comparative study on phosphate removal from water using <italic toggle="yes">Phragmites australis</italic> biochars loaded with different metal oxides

Metal oxide-loaded biochars are a promising material to remove phosphate from polluted water to ultra-low concentrations. To facilitate preparing the metal oxide-loaded biochar with the best phosphate adsorption performance, five biochars loaded with Al, Ca, Fe, La and Mg oxides, respectively (Al-BC, Ca-BC, Fe-BC, La-BC and Mg-BC) were produced using Phragmites australis pretreated with 0.1 mol AlCl3, CaCl2, FeCl3, LaCl3 and MgCl2, respectively, characterized, and phosphate adsorption kinetics and isotherms of the biochars were determined. The maximum phosphate adsorption capacities (Qm) of the biochars ranked as Al-BC (219.87 mg g−1) > Mg-BC (112.45 mg g−1) > Ca-BC (81.46 mg g−1) > Fe-BC (46.61 mg g−1) > La-BC (38.93 mg g−1). The time to reach the adsorption equilibrium ranked as La-BC (1 h) < Ca-BC (12 h) < Mg-BC (24 h) = Fe-BC (24 h)