Design and optimization of a reactive crystallization process for high purity phosphorus recovery from sewage sludge ash

In this work, a reactive crystallization process was designed and optimized for separating high purity phosphorus (P) in the form of CaClH2PO4·H2O crystals from sewage sludge ash (SSA). The conceptual design procedure applied in the present work ensured to eliminate the co-precipitation of the undesired impurities as well as the optimal P recovery yield. Furthermore, the optimization of the key operating parameters for the crystallization process improved the particulate properties, which facilitated the separation of the crystals from the mother liquor in the down-stream filtration process. The experimental results showed that high purity crystals (Al and Fe impurities ∼0.021 wt%) can be produced from the SSA with a high P-yield (≥61.2%, based on the P in SSA). The production cost of US$ 3.0/(kg P) has been estimated for the proposed process.