論文ID: TETSU-2021-046
Japan relies on imports for almost the entire amount of phosphorus, which is indispensable for human life and industrial materials. Therefore it is required to recover phosphorus from dephosphorization slag and sewage sludge which are promising unutilized phosphorus resources. Aiming wholesale recovery of phosphorus from the slag and sludge, a fundamental study on condensation of phosphorus in solid phase through high temperature phase separation was carried out. The experiments at 1573 K on principal [CaO-SiO2-P2O5] ternary model sample and Al2O3 and Fe2O3 added therein showed unsaturation with CaO and precipitation of solid 3CaO・P2O5 as the phosphorus-concentrated phase in all the sample. The contamination of the other components in 3
CaO・P2O5 was low, especially less than 1 mass% for Al2O3 added samples. The liquid phase was also formed with Al2O3 or Fe2O3 addition, and the liquidus composition in quaternary samples were consistent with those appeared in [CaO-SiO2-Fe2O3] and [CaO-SiO2-Al2O3] ternary diagram. P2O5 content in the quaternary liquid phases were lower in Al2O3 added samples than those in Fe2O3 added samples. Such difference was discussed in terms of optical basicity and CaO activity for liquid phase. Due to the coexistence of solid SiO2 phase at Fe2O3 addition, the SiO2 content in liquid phase became lower compared to Al2O3 addition, and led to higher optical basicity, which would allow higher P2O5 capacity in liquid phase. These considerations strongly suggest that an effective control of composition would be key technology for the phosphorus recovery through condensation and separation of phosphorus concentrated phase.
