Impacts of pH and ammonia on the leaching of Cu(II) and Cd(II) from coal fly ash

• Published in: Chemosphere (Oxford) Vol. 64; no. 11; pp. 1892 - 1898
• Main Authors: Wang, Jianmin, Ban, Heng, Teng, Xinjun, Wang, Hao, Ladwig, Ken
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.09.2006; Elsevier
• Subjects: Adsorption; Ammonia; Ammonia - chemistry; Applied sciences; Cadmium - chemistry; Carbon - chemistry; Coal - analysis; Coal Ash; Copper - chemistry; Exact sciences and technology; Fly ash; Heavy metal; Hydrogen-Ion Concentration; Leaching; Models, Theoretical; Other wastes and particular components of wastes; Particulate Matter - chemistry; Pollution; Wastes; Fly ash; Ammonia; Adsorption; Leaching; Heavy metal; Copper II; Combustion residue; Environmental factor; Cadmium II; Risk assessment; Environment impact; Coal power plant; Solid waste; pH; Lixiviation; Bituminous coal; Speciation
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2006.01.041

Many coal-fired power plants are implementing ammonia-based technologies to reduce NO x emissions. Excess ammonia in the flue gas often deposits on the coal fly ash. Ammonia can form complexes with many heavy metals and change the leaching characteristics of these metals. This research tends to develop a fundamental understanding of the ammonia impact on the leaching of some heavy metals, exemplified by Cu(II) and Cd(II), under different pH conditions. Batch results indicated that the adsorption is the main mechanism controlling Cu(II) and Cd(II) leaching, and high concentrations of ammonia (>5000 mg/l) can increase the release of Cu(II) and Cd(II) in the alkaline pH range. Based on the chemical reactions among fly ash, ammonia, and heavy metal ion, a mathematical model was developed to quantify effects of pH and ammonia on metal adsorption. The adsorption constants (log K) of Cu 2+, Cu(OH) +, Cu(OH) 2, and Cu ( NH 3 ) m 2 + for the fly ash under investigation were respectively 6.0, 7.7, 9.6, and 2.9. For Cd(II), these constants were respectively 4.3, 6.9, 8.8, and 2.6. Metal speciation calculations indicated that the formation of less adsorbable metal–ammonia complexes decreased metal adsorption, therefore enhanced metal leaching.