High capacity aqueous phosphate reclamation using Fe/Mg - layered double hydroxide (LDH) dispersed on biochar

Phosphate is a primary plant nutrient, serving integral role in environmental stability. Excessive phosphate in water causes eutrophication; hence, phosphate ions need to be harvested from soil nutrient levels and water and used efficiently. Fe-Mg (1:2) layered double hydroxides (LDH) were chemically co-precipitated and widely dispersed on a cheap, commercial Douglas fir biochar (695 m2 /g surface area and 0.26 cm3 /g pore volume) byproduct from syn gas production. This hybrid multiphase LDH dispersed on biochar (LDHBC) robustly adsorbed (~5h equilibrium) phosphate from aqueous solutions in exceptional sorption capacities and no pH dependence between pH 1–11. High phosphate Langmuir sorption capacities were found for both LDH (154 to 241 mg/g) and LDH-modified biochar (117 to 1589 mg/g). LDHBC was able to provide excellent sorption performance in the presence of nine competitive anion contaminants (CO 2/3- , As 3/4- , SeO2/4- , NO-3,Cr2O2/7, CI-F and Mo2/4) and also upon remediating natural eutrophic water samples. Regeneration was demonstrated by stripping with aqueous 1 M NaOH. No dramatic performance drop was observed over 3 sorption-stripping cycles for low concentrations (5 ppm). The adsorbents and phosphate - laden adsorbents were characterized using Elemental analysis, BET, PZC, TGA, DSC, XRD, SEM, TEM, and XPS. The primary sorption mechanism is ion-exchange from low to moderate concentrations (10–500 ppm). Chemisorption and stoichiometric phosphate compound formation were also considered at higher phosphate concentrations (>500 ppm) and at 40 C. This work advances the state of the art for environmentally friendly phosphate reclamation. These phosphate - laden adsorbents also have potential to be used as a slow - release phosphate fertilizer.