1 Recovery of phosphorus from incinerated sewage sludge ash by combined two-step extraction and selective precipitation Le Fang a , Jiang-shan Li a,# , Shane Donatello c , C. R. Cheeseman b , Qiming Wang a , Chi Sun Poon a,* , Daniel C. W. Tsang a . a Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong b Department of Civil and Environmental Engineering, Imperial College London, London, United Kingdom c Eduardo Torroja Institute of construction sciences, Department of cement and materials recycling, Madrid, Spain *corresponding author: cecspoon@polyu.edu.hk # corresponding author: jiangshan.li@polyu.edu.hk Abstract: The recovery of phosphorus (P) from acid extracts of incinerated sewage sludge ash (ISSA) is invariably complicated by the co-dissolution of metal(loid)s. An extra purification treatment step is thus needed, which reduces the efficiency of P recovery. This study developed a two-step extraction method which can produce highly purified P-extract where ISSA is treated first with ethylenediaminetetraacetatic acid (EDTA) and then with sulphuric acid. The recovery conditions of this two-step extraction method were optimized (pre-extraction by 0.02 mol/L of EDTA at a liquid to solid ratio (L/Kg) of 20:1 during 120 min, then extraction by 0.2 mol/L sulphuric and at a liquid to solid ratio of 20:1 during 120 min). Compared with direct extraction by sulphuric acid (namely, single-step leaching), the two-step extraction method dissolved 2.34 mmol/kg ISSA less of P, but with 5.16 mmol/kg ISSA less of *Revised Manuscript (clean for typesetting) Click here to view linked References