Capturing phosphorus (P) from effluent streams using biochar is potentially a transformative way to recycle P into agricultural soils. However, biochar ordinarily has low P sorption capacity. Here, we report the efficacy of a Fe-modified (FeSO4 pre-treated) corn stover biochar, produced by the autothermal (air-blown) fast pyrolysis at 500 C, for enhanced P sorption capacity. The Fe pre-treatment increased the dominance of the biochars’ acid functional groups, as indicated by the point of zero charge shift from pH 8.48 to 4.31. Sorption of P was about 11-12 times greater and the desorption of P was 3 times lower for the Fe-modified biochar than the unmodified biochar at environmentally relevant P concentrations. A sand matrix column leaching study showed that the Fe-modified biochar is effective for removing P from simulated agricultural wastewater for the studied pH range (~7-7.5) and in the presence of competing anions. XRD and SEM-EDS analyses showed P sorption occurred predominately through inner-sphere surface complexation followed by surface precipitation and that P is preferentially sorbed by hematite (α-Fe2O3) relative to magnetite (FeIII2O3 + FeIIO) or maghemite (γ-Fe2O3). This study demonstrates the efficacy of pyrolyzing corn stover with FeSO4 to produce Fe-modified biochar, which have potential to be used for recycling P as a slow-release P fertilizer.

Recycling phosphate using Fe-modified biochar for environmental applications

ACS Fall 2021

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