2019 Volume 52 Issue 9 Pages 778-782
To obtain calcium phosphates—a phosphate rock equivalent—from the incineration ash of chicken manure, which is obtained from power generation systems that use the manure as fuel, the incineration ash was treated with an aqueous solution of nitric acid to elute phosphorus. By using 0.3 M HNO3, most of the phosphorus could be eluted from 1.0 g of ash within 0.1 h. Unlike in the case of composted chicken manure which was previously examined in our laboratory, the concentration of HNO3 was increased for elution from the incineration ash. The use of incineration ash of chicken manure enabled the removal of inorganic species at a lower boiling or sublimation temperature, and organic species by calcination in the power generation system. The phosphorus contents of the incineration ash and nitric acid extract were higher than that of composted chicken manure. XRD analysis showed that the treatment of the obtained nitric acid extract with aqueous NH3 yielded a precipitate of poorly-crystallized calcium hydroxyapatite (Ca10(PO4)6(OH)2), which is one of the main components of phosphate rock. To confirm the formation and purity of calcium phosphate species, precipitation calcination was conducted at 1,078 K for 5 h. XRD analysis revealed that the calcined solid was tricalcium phosphate, and no contamination was evident. These results reveal that a phosphate rock equivalent could be easily obtained from the incineration ash of chicken manure, which implies that approximately 14% of the phosphate rock that is currently being imported into Japan could be replaced by this product.