Recovery of phosphate from incineration ash of sewage sludge by chlorination and carbo-chlorination

In this study, the volatilization behavior of the constituent elements of sewage sludge incineration ash (SSA) with and without carbon during the chlorination was investigated for recovering P. For chlorination of SSA, Fe and K volatilized from 700 to 800 °C, no volatilization of P was observed. For chlorination of SSA with carbon, Fe, P, and Si volatilized from low temperatures, reaching volatility rates of 80, 55, and 35 %, respectively, at 1000 °C. When chlorinated SSA/C (sample with carbon added to chlorination residue prepared at 1000 °C for 30 min holding), P volatilized from 800 °C (10 %), reaching a volatilization rate of 75 % at 1000 °C. P volatilization increased from 10 to 55 % until 60 min holding at 800 °C without volatilization of Si, Mg, and K. Although P volatilization progressed at 900–1000 °C holding, Al, Mg, and Si also volatilized. These results indicate that combination of chlorination/carbo-chlorination is suitable for selective volatilization of P.