Transformation of mineral matter during pyrolysis, gasification and combustion of biosolid chars

During thermochemical processing of biosolids in sewage sludge, different forms of phosphor-containing compounds are generated in biosolid chars (biochars). This paper describes how biochar-processing conditions affect the mineral compounds formed under pyrolysis, gasification and combustion of biosolids, and the key factors that influence the kinetics of phase formation. Our results show identified phase transformations through experiments in a laboratory tube furnace followed by X-ray diffraction analysis. Laboratory processing samples were verified and in situ phase transformations were observed through a synchrotron powder diffraction study. It was found that under a neutral atmosphere, crystalline oxide phases formed at lower temperatures and much faster than iron phosphide formed, while gasification and combustion conditions led to the formation of crystalline phases in phosphate forms. These forms of phosphor compounds in by-products of biosolids thermochemical treatment can be used as agricultural fertilizers.