Phosphorus Recovery by Chemical Extraction from Different Types of Air Pollution Control Ashes of Sludge Incinerators

Abstract BACKGROUND: Limited amounts of phosphorous in the lithosphere draw researchers' attention to finding alternative phosphorous sources. This study aimed to investigate the feasibility of sewage sludge incineration ashes of Bursa city in Turkey as a phosphorous source. The flue gases generated from the incineration plant are trapped by baghouse dust filter (BF-Ash) and multi-cyclone units (MC-Ash). The P2O5 contents of BF-Ash and MC-Ash were found as 17.36% and 11.49%, respectively. Chemical extraction methods by using oxalic acid, citric acid, sulfuric acid, and nitric acid were applied to investigate phosphorus recovery possibilities om BF-Ash and MC-Ash. Crystalline and amorphous phases, chemical compositions, particle sizes, and morphological structures of BF-Ash and MC-Ash were examined. Heavy metal leaching and morphological structures of the extraction residues were investigated. RESULTS: The phosphorus recovery potential of BF-Ash was found to be higher than that of MC-Ash, with extracted levels ranging between 0.01 and 91.42 mg/g for BF-Ash and 0.01 and 59.82 mg/g for MC-Ash. The highest phosphorus level was obtained when BF-Ash was treated with 1 mol/L of oxalic acid. Several heavy metals such as Zn, Ni, As, and Cr resulted in higher leaching levels than the regulation limits when chemical extraction was applied. CONCLUSION: Considering the high phosphate levels in the ashes and their solutions after acid leaching, that both ashes were found to be promising as phosphorus resources.