The structural analysis of orthophosphate crystal and the solubility of phosphorus when melting sewage sludge incineration ashes and its calcium salt mixture with a high temperature electric furnace were investigated.
Consequently, in that which the heat treatment sludge incineration ashes which have not added the condensation agent melted, crystallization with calcium progressed by calcium salt addition. The ratio of the phosphoric acid content which melts 2 % citric acid phosphoric acid contents increased from 5 % order over or below 80 %.
However, in that which melted the incineration ashes of the sludge which has added lime and chlorination iron, since original calcium content was as high as 25 %, addition of calcium salt had not affected a crystalline degree. Moreover, the rate of the phosphoric acid which melts into a citric acid suited the tendency which decreases rather from 85% order by calcium salt addition.
The generated orthophosphate crystal was considered to be a gehlenite or a silicocarnotite by melting as a result of the X ray diffraction. Moreover, by heat treatment sludge, existence of the phosphorus distributed uniformly consisted spot-like of K α X-rays image of phosphorus by EPMA by addition of calcium. Since phosphorus concentrated in part by existence of calcium and it existed, it was able to consider that phosphorus and calcium were a crystal.
After mixing calcium salt with sludge incineration ashes, making it melt can raise the validity of phosphorus, when the condensation agent of a lime system is not being used. However, when the condensation agent of a lime system is being used, the effect done not exist.
It may be an effective means to melt sewage-sludge incineration ashes when re-circulation of the phosphorus resources becomes an urgent subject although a large amount of needs to be invested in equipment.