Selective adsorption behavior and mechanism of phosphate in water by different lanthanum modified biochar

Lanthanum-based adsorbents are promising phosphate (P) adsorbents and their selectivity determines their potential for application in P recovery. However, there have been few systematic studies for quantifying the selectivity of lanthanum-based adsorbents for P. In this study, lanthanum carbonate/biochar (LCB300) and lanthanum hydroxide/biochar (LHB800) composites were synthesized to quantify their selectivity for P adsorption. Batch adsorption experiments were conducted to investigate the influence of environmental factors on their selectivity. The results showed that both LCB300 and LHB800 exhibit similar maximum adsorption capacities for P (64.3 and 65.0 mg g-1, respectively). However, the selectivity of LHB800 (90-100%) for P was higher than that of LCB300 (73-99%), and the former was less susceptible to environmental conditions than the latter. In addition, competing ions accelerated the intermediate process of P adsorption by LHB800, but slightly inhibited the adsorption rate of LCB300 for P. These results show that the form of lanthanum on the adsorbent affects its adsorption mechanism and corresponding selectivity for P. Moreover, LHB800 demonstrates significant potential for application in the recovery of phosphate from wastewater.