Adsorption of Phosphates onto Mg/Al-Oxide/Hydroxide/Sulfate-Impregnated Douglas Fir Biochar

Nitrates and phosphates, found in fertilizers, are the most common eutrophication-causing agents. Douglas fir biochar (BC), a syngas byproduct, was treated with different Al/Mg ratios of sulfate (5% w/w metal loading) followed by an NaOH treatment. The greatest phosphate uptake at 25 degrees C and pH 7 was attributed to the composite with a Mg/Al 2:1 ratio prepared at pH 13 (AMBC). Batch AMBC phosphate uptake was optimized for initial pH, equilibrium time, temperature, and initial phosphate concentration. Phosphate removal following pseudo-2nd-order kinetics and increases gradually before reaching a max at pH 11, with 95% phosphate uptake in 15 mins. The Sips isotherm model provided the best sorption data fit resulting in a 42.1 mg/g capacity at 25 degrees C and pH 11. Endothermic and spontaneous adsorption were determined using van 't Hoff's plots. BET, XRD, XPS, SEM, TEM, and EDS were used to characterize the biochar before and after phosphate sorption. Used AMBC has the potential to be exploited as a phosphate fertilizer as a key part of an environmentally friendly agricultural management plan.

Automated summary

By studying the treatment of Douglas fir biochar with different Al/Mg ratios of sulfate and NaOH, it was found that the composite with a Mg/Al ratio of 2:1 had the highest phosphate uptake capacity. The composite achieved a 95% phosphate removal rate in 15 minutes. The study suggests that the composite has the potential to be used as a phosphate fertilizer in environmentally friendly agricultural management plans.