Stabilizing cadmium into aluminate and ferrite structures: Effectiveness and leaching behavior.
The inappropriate disposal of sludge, particularly for those enriched in heavy metals, is highly hazardous to the environment. Thermally converting sludge into useful products is a highly promising technique as heavy metals are immobilized and organic substances are mineralized. This work investigated the feasibility of stabilizing simulated cadmium-laden sludge by sintering with Al-and Fe-rich precursors. To simulate the process, cadmium oxide was alternatively mixed and sintered with γ-Al2O3and α-Fe2O3. Cadmium was crystallographically incorporated into aluminate (CdAl4O7) monoclinic structure and ferrite (CdFe2O4) spinel, dependent on the type of precursor used. The CdFe2O4formation was initialed at about 150-300 °C lower than that of CdAl4O7. With Rietveld refinement analysis of the collated XRD data, the weight percentages of crystalline phases in the fired samples were quantified. To evaluate the cadmium incorporation efficiency, a transformation ratio (TR) index was devised. The TR values revealed that, to effectively incorporate cadmium, 950 °C was favored by γ-Al2O3and 850 °C was for α-Fe2O3within a 3-h sintering treatment. Constant pH leaching test (CPLT) was used to assess the metal stabilization effects, revealing a remarkable reduction of cadmium by transformation into CdAl4O7and CdFe2O4. Both CdAl4O7and CdFe2O4were incongruently dissolved in an acid solution. The overall finding indicated a potentially feasible technology in cadmium-laden sludge stabilization.
School of Environmental Science and Engineering, Guangzhou University, Guangzhou, 510275, PR China; Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China. Electronic address: minhua_su@connect.hku.hk.
Minhua
M
Su
Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
Kaimin
K
Shih
School of Environmental Science and Engineering, Guangzhou University, Guangzhou, 510275, PR China; Guangdong Provincial Key Laboratory of Radioactive Contamination Control and Resources, Guangzhou University, Guangzhou, 510275, PR China. Electronic address: kongl_jun@163.com.
Lingjun
L
Kong
D000537:Aluminum Oxide / Q000737:chemistry*; D002104:Cadmium / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D006801:Humans; D007220:Industrial Waste; D019216:Metals, Heavy / Q000737:chemistry*; D012722:Sewage / Q000737:chemistry*; D018505:Waste Management
D005290:Ferric Compounds; D007220:Industrial Waste; D019216:Metals, Heavy; D012722:Sewage; D002104:Cadmium; C001215:ferrite; D000537:Aluminum Oxide
Aluminate; Cadmium; Constant-pH leaching test (CPLT); Ferrite; Sludge; Stabilization