Cd2+ and Pb2+ contamination in water systems causes a severe challenge to environmental sustainability and threatens human health, making efficient removal strategies urgent needed. Biochar is an attractive, green, and low-cost adsorbent for the removal of heavy metals from aqueous solutions, but its adsorption performance is often insufficient. Its modification significantly improves the adsorption performance of heavy metals. We synthesized a new tea branch biochar comodified with phosphoric acid and magnesium chloride (PMTB) for the efficient removal of Cd2+ and Pb2+ from aqueous environments. The physicochemical properties, adsorption performance, and contributions of different mechanisms of PMTB were investigated through batch adsorption tests and characterization analyses. PMTB was identified as a disordered mesoporous carbon matrix decorated with numerous oxygen-containing functional groups. PMTB possessed superior affinity for Cd2+ and Pb2+, with maximum adsorption values of 140.43 mg g–1 for Cd2+ and 237.70 mg g–1 for Pb2+ at pH 6.0 and an adsorbent dosage of 2 g L–1. PMTB also demonstrated exceptional selectivity, maintaining a high removal efficiency even in the presence of common competing cations (K+, Ca2+, Na+, and Mg2+). In a binary metal system, PMTB exhibited a stronger affinity for Pb. Additionally, PMTB remained quite reusable. Kinetic and isotherm studies confirmed that the predominance of adsorption occurred via a monolayer chemical process. Through quantitative contribution analysis, complexation and precipitation were identified as the dominant mechanisms for Cd2+ (68.81%) and Pb2+ (73.75%) adsorption. Cation exchange and coordination of π electrons were also enhanced after comodification. Therefore, PMTB emerged as an efficient adsorbent with significant potential for treating wastewater containing Cd2+ or Pb2+.
Lin et al. (Tue,) studied this question.