The most common eutrophication causing nutrients are nitrates and phosphates that are found in fertilizers and detergents. Phosphate removal using Douglas fir biochar treated with NaOH and different ratios of Mg/Al sulfate (5 % w/w) has been studied. The composite with the highest phosphate adsorption at pH 7 and 25 °C was Mg/Al 2:1 at pH 13 (AMBC), and was subjected to several batch sorption experiments. Phosphate removal of the AMBC with different initial pH concentrations, contact time, equilibration temperature and initial concentration of phosphate was determined. The percentage of removal is found to gradually increase with the pH. The optimum pH was found to be 11 with 95 % phosphate saturation achieved in 15 minutes- following a pseudo-2<sup>nd</sup>-order kinetics model. Sorption data was best fitted into the Sips isotherm model giving a 41.8 mg/g capacity at 25 °C and pH 11. The adsorption affinity was correlated with temperatures by using van’t Hoff’s plots, and sorption was determined to be of an endothermic and spontaneous nature. Phosphate sorbed and virgin adsorbents were characterized by: BET, Elemental analysis, XRD, SEM, TEM, EDS, XPS and, TGA. The exhausted AMBC composite has a potential to recycle as a slow-release phosphate fertilizer which could be part of an environmentally friendly alternative agricultural management plan.

Adsorption of phosphates onto Mg/Al-sulfate/hydroxide impregnated Douglas fir biochar

ACS Spring 2022

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