Transformation of phosphorus by MgCl and CaCl during sewage sludge incineration.

Phosphorus (P) recovery from sewage sludge (SS) have been regarded as an effective method of P recycling. The effects of incineration temperature, incineration time, and chlorine additives on the distribution of P speciation during sludge incineration were studied. Moreover, the reactions between model compounds AlPO and additives (MgCl and CaCl) were investigated by thermogravimetric differential thermal analysis and X-ray diffraction measurements. The results demonstrated that the increase in temperature and time stimulated the volatilization of non-apatite inorganic phosphorus (NAIP) instead of apatite phosphorus (AP). MgCl and CaCl can greatly promote the conversion of NAIP to AP. Additionally, AlPO reacted with MgCl are incinerated at 500-600 °C to form Mg(PO), which is mainly due to the reaction of the intermediate product MgO and AlPO. Reactions between AlPO and CaCl occurred at 700-750 °C and produced CaPOCl, which can be directly used with high bioavailability. These findings suggested that chlorine additives in the SS incineration process can obtain phosphorus-containing minerals with higher bioavailability to realize the resource utilization of P in sludge.