Stabilization of Ni-Cr contained sludge by high temperature NiCr2O4 synthesis process
Date Issued
2009
Date
2009
Author(s)
Chen, Yen-Hsin
Abstract
In recent years, ferrite synthesis method has been investigated for heavy metal sludge stabilization. The ferrite formation processes could be divided into two categories. The first one is wet process, aqueous divalentetal ions co-precipitate with iron ions to form hydrous iron oxides and then divalent metals are fixed onto the ferrite by dehygration process. The second one is high temperature ferritization, which is more simpler than wet process. In this study, high temperature spinel synthesis process is performed on chromium and nickel contained sludge. To understand the spinel synthesis stabilized efficiency, various operating parameters included sintering temperature, reaction ambient gas, salt quantity and Cr/Ni molar ratio were discussed. Stability of sintered specimens was evaluated by toxicity characteristic leaching procedure (TCLP). The crystalline phases of sintered specimens were studied using X-ray powder diffraction (XRD). The microstructural characteristics of the powders were examined by scanning electron microscopy (SEM). Chromium and nickel containing sludge could be more stable by thermal process. According to TCLP results and XRD patterns, chromium and nickel would be stabilized by inserting the chromium and nickel ion into the stable NiCr2O4 spinel crystalline structures during thermalreatment. When suitable quantity of salts exists in sludge, both of chromium and nickel would be more stable and the spinel crystalline structure could be more complete. Relationship between chromium stability and Cr/Ni molar ratio is hard to distinguish, but raise Cr/Ni molar ratio could improve nickel stability. The high-temperature spinel synthesis technique for chromium and nickel sludge stabilization is applicable.
Subjects
sludge
spinel
nickel
chromium
leaching behavior
Type
thesis
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