Conceptual reactive crystallization process design for separation and purification of phosphorus from complex sludge ash

A conceptual reactive crystallization process design method was introduced in the present work, in order to be served as the background for identifying the target phosphate product (CaClH2PO4 center dot H2O) and the optimum operating pH range of the reactive crystallization. Operating the process within the selected optimum pH range guaranteed the elimination of undesired co-precipitating species. Meanwhile, the yield of the crystallization process was maximized as the operating pH assured the minimum solubility of the target P-product. Secondly, the filterability of the P-crystal was optimized by operating the process with the selected parameters that favored the crystal growth. By applying this conceptual design, 89% P was recovered through crystallization whereas the concentration of Al, Fe and other heavy metals in the obtained crystals were all below the upper limit for the purpose of environmental protection.