Efficient simultaneous phosphate and ammonia adsorption using magnesium-modified biochar beads and their recovery performance

Phosphate and ammonia as important sources of eutrophication in water bodies, their removal and recovery are crucial for environmental management. In this study, magnesium-modified biochar beads (Ca/MgBC) capable of adsorbing PO_3–4 and NH⁺₄ simultaneously were prepared, the size of the biochar materials was successfully enlarged to realize recycling. Ca/MgBC has excellent simultaneous adsorption properties, compared to single PO_3–4 or NH⁺₄ solution, the adsorption capacity of PO_3–4 was increased almost twice and that of NH⁺₄ was increased almost 1.5 times in simultaneous adsorption solution. The Q_{max, PO3–4} was 253.95 mg/g and Q_{max, NH}⁺₄ was 177.25 mg/g. Characterization results indicated that struvite crystallization was the main adsorption mechanism of PO_3–4 and NH⁺₄ in the simultaneous solution, which was also the reason for the promotion effect of simultaneous adsorption. Besides, ion exchange, surface precipitation and electrostatic attraction were also the other mechanisms for the adsorption. NP-loaded Ca/MgBC has a better slow-release potential of N and P under neutral condition. The adsorbed saturated Ca/MgBC still had good removal effects on seven common soil heavy metals (Cd, Hg, Cu, Pb, Cr, Zn and Ni). These results suggest that Ca/MgBC is a kind of promising adsorbent for phosphate and ammonia with safe, green, and sustainable properties, and offers the possibility of soil fertilization and remediation for carbon neutrality.