Selective recovery of phosphate from hydroxyapatite and magnesium ammonium phosphate by carbo-chlorination method

This research studied selective separation and recovery of phosphorus from hydroxyapatite (HAP) and magnesium ammonium phosphate (MAP), which are found following the recovery of phosphorus during sewage treatment, by chlorination and carbo-chlorination. When chlorination of HAP and MAP in Cl2 was performed at up to 1000 °C, no volatilization of Ca, Mg, or P was observed. However, when C was added to samples, volatilization of P occurred suddenly at 600–800 °C, and virtually 100 % was volatilized. At this time, no volatilization of the Ca or Mg was found. This showed that carbon reduction reactions play an important role in the volatilization of P. When H2O treatment was performed on the residue after chlorination of HAP/C and MAP/C, the residue could be separated into C, CaCl2, and MgCl2. This showed that Ca, Mg, and P can each be selectively separated from HAP and MAP using a combination of carbon reduction and chlorination reactions. [Display omitted] •Volatilization of Ca, Mg, and P does not occur by chlorination of HAP and MAP at up to 1000 °C.•Carbonaceous material addition promotes P volatilization during chlorination.•P in HAP or MAP almost completely can separate up to 800 °C by carbo-chlorination.