Stabilizing cadmium into aluminate and ferrite structures: Effectiveness and leaching behavior.

Title Stabilizing cadmium into aluminate and ferrite structures: Effectiveness and leaching behavior.
Authors M. Su; K. Shih; L. Kong
Journal J Environ Manage
DOI 10.1016/j.jenvman.2016.10.037
Abstract

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 ?-Al2O3 and ?-Fe2O3. Cadmium was crystallographically incorporated into aluminate (CdAl4O7) monoclinic structure and ferrite (CdFe2O4) spinel, dependent on the type of precursor used. The CdFe2O4 formation 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 ?-Al2O3 and 850 °C was for ?-Fe2O3 within 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 CdAl4O7 and CdFe2O4. Both CdAl4O7 and CdFe2O4 were incongruently dissolved in an acid solution. The overall finding indicated a potentially feasible technology in cadmium-laden sludge stabilization.

Citation M. Su; K. Shih; L. Kong.Stabilizing cadmium into aluminate and ferrite structures: Effectiveness and leaching behavior.. J Environ Manage. 2017;187:340346. doi:10.1016/j.jenvman.2016.10.037

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