title: Cadmium Stabilization Efficiency and Leachability by CdAl4O7 Monoclinic Structure.
abstract: This study investigated the stabilization efficiencies of using an aluminum-rich precursor to incorporate simulated cadmium-bearing waste sludge and evaluated the leaching performance of the product phase. Cadmium oxide and γ-alumina mixtures with various Cd/Al molar ratios were fired at 800-1000 °C for 3 h. Cadmium could be crystallochemically incorporated by γ-alumina into CdAl4O7 monoclinic phase and the reaction was strongly controlled by the treatment temperature. The crystal structure details of CdAl4O7 were solved and refined with the Rietveld refinement method. According to the structural refinement results, the stabilization efficiencies were quantified and expressed as a transformation ratio (TR) with optimized processing parameters. The preferred treatment temperature was found to be 950 °C for mixtures with a Cd/Al molar ratio of 1/4, as its TR value indicated the cadmium incorporation was nearly completed after a 3 h treatment scheme. Constant-pH leaching tests (CPLT) were conducted by comparing the leachability of the CdO and CdAl4O7 phases in a pH 4.0 environment. A remarkable reduction in cadmium leachability could be achieved via monoclinic CdAl4O7 structure formation to effectively stabilize hazardous cadmium in the waste stream. The CPLT and X-ray photoelectron spectroscopy (XPS) results suggested incongruent dissolution behavior during the leaching of the CdAl4O7 phase.
authors.affiliation: Department of Civil Engineering, The University of Hong Kong , Pokfulam Road, Hong Kong, China.
authors.forename: Minhua
authors.initials: M
authors.lastname: Su
authors.affiliation: Department of Civil Engineering, The University of Hong Kong , Pokfulam Road, Hong Kong, China.
authors.forename: Changzhong
authors.initials: C
authors.lastname: Liao
authors.affiliation: Department of Safety, Health, and Environmental Engineering, Central Taiwan University of Science and Technology , Taichung, Taiwan.
authors.forename: Kui-Hao
authors.initials: KH
authors.lastname: Chuang
authors.affiliation: Department of Environmental Engineering, National Chung Hsing University , Taichung, Taiwan.
authors.forename: Ming-Yen
authors.initials: MY
authors.lastname: Wey
authors.affiliation: Department of Civil Engineering, The University of Hong Kong , Pokfulam Road, Hong Kong, China.
authors.forename: Kaimin
authors.initials: K
authors.lastname: Shih
mesh_terms: D000535:Aluminum / Q000737:chemistry; D000537:Aluminum Oxide / Q000737:chemistry*; D002104:Cadmium / Q000737:chemistry*; D019187:Cadmium Compounds / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D010087:Oxides / Q000737:chemistry; D012722:Sewage / Q000737:chemistry*; D013696:Temperature; D018505:Waste Management / Q000379:methods*
chemical_list: D019187:Cadmium Compounds; D010087:Oxides; D012722:Sewage; D002104:Cadmium; C029663:cadmium oxide; D000535:Aluminum; D000537:Aluminum Oxide