Enhanced Adsorption of Aqueous Cephalexin, Phosphorous, and Arsenic onto Lanthanum-Modified Magnetic Biochar: Synergetic Effect, Operational Variables, and Recyclability

A lanthanum-modified magnetic biochar (LaFeBC) was designed and prepared from wheat straw to remove three common aqueous pollutants, cephalexin (CEP), phosphorus [P(V)], and arsenic [As(III)]. The pristine wheat straw biochar was first ball-milled biochar (BBC), then iron and lanthanum were introduced to BBC via alkali precipitation, and then slow pyrolysis, which yielded LaFeBC. LaFeBC exhibited Langmuir maximum adsorption capacities of 78.2 mg g−1 for CEP, 112 mg g−1 for P(V), and 45.8 mg g−1 for As(III). CEP adsorption involved multiple surface interactions. Precipitation or complexation on the lanthanum oxide surface was dominant in P(V) adsorption. For As(III) adsorption, lanthanum oxide and iron oxide contributed similar magnitudes, with precipitation/complexation likely occurring. The estimated contribution of lanthanum to adsorption followed the order P(V)>CEP>As(III), whereas that of biochar followed the order As(III)>CEP>P(V). There were synergetic effects of biochar and the loaded lanthanum. Given the lower lanthanum release at higher pH levels, near pH values of 6.0–7.0 were found to be optimal for sorption operation. Temperatures between 10°C and 40°C had only a minimal impact on adsorption efficiency. Ca2+, K+, Cl−, SO42−, and NO3− at 10 mM had no significant impact on the adsorption of the three pollutants onto LaFeBC, while Mg2+ and HCO3− significantly decreased their adsorption (p<0.05). Fixed-bed adsorption for the CEP-P(V) or As(III)-P(V) system further demonstrated the practical potential of LaFeBC. Additionally, LaFeBC had good potential at actual water conditions and demonstrated good recyclability. This finding is beneficial for the innovative design of multifunctional and economically engineered biochar.