Phosphorus recovery and high purity vivianite synthesis from residual sludge—Based on acid leaching-purification-electrocoagulation three-stage process
LIU Chang, WEI Tao-yuan, QIU Ao-xue, LIAO Wu-bin, HONG Hui, DENG Dan-ni, XIE Shi-wei
School of Urban Construction, Wuhan University of Science and Technology, Wuhan 430065, China
Abstract：An innovative technique for extracting phosphorus and synthesizing high-purity vivianite from incinerated sewage sludge ash was explored in this investigation, which experienced three principal stages, including leaching with sulfuric acid, purification via resin adsorption, and crystallization through iron electrocoagulation. The optimal conditions for acid leaching of phosphate (PO43-) from incinerated sewage sludge ash were examined by the response surface methodology, and the optimal operational parameters for the iron electrocoagulation process were determined by the Box-Behnken Design. The results indicate that phosphorus extraction efficiency of 92.80% was achieved at a liquid-to-solid ratio of 37.60mL/g, a sulfuric acid concentration of 0.125mol/L, and an acid leaching duration of 90.0min, the metal cations interfering with phosphate precipitation, such as Ca2+, Mg2+, Al3+, and Fe2+/3+ were efficiently removed by 732cation exchange resin, all phosphorus was removed from the solution successfully during the iron electrocoagulation process at an initial solution pH value of 2.00, a current of 2.00A, and a reaction time of 30.0min, meanwhile, vivianite with a purity of 97.37% were synthesized. The outcomes show that the three-step method facilitates phosphorus recovery from incinerated sewage sludge ash. 61.44% of the phosphorus was retrieved as high-purity vivianite through the three steps; the recovery process costs 14.66yuan per kilogram product of vivianite and yields a profit of 30.68yuan.
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