Phosphorus recovery and leaching of trace elements from incinerated sewage sludge ash (ISSA)

• Published in: Chemosphere (Oxford) 2018-02, Vol.193, p.278-287
• Main Authors: Fang, Le, Li, Jiang-shan, Guo, Ming Zhi, Cheeseman, C.R., Tsang, Daniel C.W., Donatello, Shane, Poon, Chi Sun
• Format: Article
• Language: English
• Subjects: Chelating agents; Chemical extraction; Incineration ash; Metals/metalloids removal; Phosphorus recovery; Sewage sludge
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2017.11.023

Chemical extraction of phosphorus (P) from incinerated sewage sludge ash (ISSA) is adversely influenced by co-dissolution of metals and metalloids. This study investigated P recovery and leaching of Zn, Cu, Pb, As and Ni from ISSA using inorganic acids (sulphuric acid and nitric acid), organic acids (oxalic acid and citric acid), and chelating agents (ethylenediaminetetraacetic acid (EDTA) and ethylene diamine tetramethylene phosphonate (EDTMP)). The aim of this study was to optimize a leaching process to recover P-leachate with high purity for P fertilizer production. The results show that both organic and inorganic acids extract P-containing phases but organic acids leach more trace elements, particularly Cu, Zn, Pb and As. Sulphuric acid was the most efficient for P recovery and achieved 94% of total extraction under the optimal conditions, which were 2-h reaction with 0.2 mol/L H2SO4 at a liquid-to-solid ratio of 20:1. EDTA extracted only 20% of the available P, but the leachates were contaminated with high levels of trace elements under optimum conditions (3-h reaction with EDTA at 0.02 mol/L, pH 2, and liquid-to-solid ratio of 20:1). Therefore, EDTA was considered an appropriate pre-treatment agent for reducing the total metal/metalloid content in ISSA, which produced negligible changes in the structure of ISSA and reduced contamination during subsequent P extraction using sulphuric acid. •Co-dissolution of P and metal (loid)s from ISSA were investigated by three kinds of extractants.•Sulphuric acid was the most efficient for P recovery.•EDTA was the optimal pre-leaching agent for reducing the total metal (loid)s content.•Leaching conditions by EDTA and sulfuric acid were optimized.•Treatment with EDTA has little effect on morphology and mineralogy characteristics of ISSA.