Abstract:

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.

Key words: sewage sludge, hydrochar, phosphorous, morphology, metal, extraction

摘要：

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。

关键词: 污泥, 水热炭, 磷, 形态, 金属, 浸取