污泥水热碳化中磷的形态变化及金属浸出行为

在不同温度下进行污泥水热碳化实验,利用Hedley顺序提取法探究水热炭中磷的形态变化,并结合钙、铁、铝的浸出行为进一步解释含磷物质的形态分布。结果表明,磷主要富集在水热炭中,水热碳化促进有机磷(P_o)向无机磷(P_i)转化,NaOH溶解态磷(NaOH-P)转化为HCl溶解态磷(HCl-P)和残渣态(Res-P)。污泥和水热炭中Ca、Fe主要以HCl溶解态为主;Al则由NaOH溶解态转化为HCl溶解态。并且水热碳化过程促使污泥中磷形态从磷酸铝盐(Al-P)、磷酸铁盐(Fe-P)向磷酸钙盐(Ca-P)、磷酸镁盐(Mg-P)转化。通过理论分析,水热炭中Al-P可能以Al₂PO₄³⁺和AlHPO₄⁺络合物为主;羟基磷灰石是Ca-P的主要存在形态;部分磷酸盐可能被铁氧化物或氢氧化物固定。为后续水热炭的回收利用提供理论基础。

Morphology of phosphorus and metal extraction behavior in sewage sludge during hydrothermal carbonization treatment

Hydrothermal carbonization (HTC) treatment of sewage sludge was conducted at different temperatures. The conventional fractionation of phosphorus in hydrochar was investigated by Hedley fractional extraction method, and to achieve a comprehensive understanding of the morphology of phosphorus-containing substances with consideration of Ca, Fe, Al. The results showed that phosphorus was mainly concentrated in the hydrochar. organophosphorus (P_o) almost transformed into inorganic phosphorus (P_i), and NaOH-extractable P (NaOH-P) converted to HCl-extractable P (HCl-P) and residue state (Res-P) in the process of HTC. Ca and Fe in the sludge and hydrochar were dominantly extracted by HCl whereas Al was transformed from NaOH-soluble to HCl-soluble. Moreover, the HTC process promoted the transformation of phosphorus form aluminum phosphate (Al-P) and iron phosphate (Fe-P) to calcium phosphate (Ca-P) and magnesium phosphate (Mg-P). Finally, a theoretical simulation of P-containing minerals suggested the existence of Al₂PO₄³⁺ and AlHPO₄⁺ complex in the hydrochar. Hydroxyapatite was the main existing form of Ca-P. Part of the phosphate may be fixed by iron oxides or hydroxides. This work provides a theoretical basis for the subsequent recycling of hydrochar.