Transforming heavy metal sludge into spinel materials by high-temperature process
Date Issued
2012
Date
2012
Author(s)
Li, Nien-Hsun
Abstract
Heavy metal sludge from metal surface treatment, anodizing, plating, and printed circuit board manufacture are hazardous solid waste. Stabilizing metal sludge via thermal treatment has the potential to convert hazardous metal sludge into mineral phase and reusable product, such as spinel ceramics. Owing to the composition of the heavy metal sludge is similar to the precursors of spinel mineral, including divalent metal oxides and trivalent metal oxides, the sintering processes for stabilizing or transforming the metal oxides into spinel structure will be expected.
The goal of this study is to evaluate the technical feasibility of incorporating heavy metal sludge into high-value spinel ceramics by thermal process, and thus to reduce the environmental hazard and promote the economic value of solid waste. The study tried to apply thermal processes, including conventional way and microwave energy, on the transforamtion of heavy metal sludge. The effects of temperature, sintering time, microwave power and different oxides were investigated in the study. The reactive mechanisms of reactants and the feasibility of following applications were also discussed.
Results indicated that CuFe2O4 and CuAl2O4 were also effectively formed at around 800 °C by the ferric oxide and gamma alumina precursors with 3 h of short sintering, respectively. Transformation of CuFe2O4 was found on two crystallographic spinel structures: the low-temperature (800~900 °C) tetragonal phase (t-CuFe2O4) and the high-temperature (~1000 °C) cubic phase (c-CuFe2O4), and CuAl2O4 was only found one crystallographic structures during the thermal process. At higher temperatures (~1100 °C), the formation of cuprous ferrite delafossite (CuFeO2) and cuprous aluminate delafossite (CuAlO2) phase from the dissociation of spinel was also noted. Both CuFe2O4 and CuAl2O4 spinel had a better intrinsic resistance to the acidic environment when compared to the CuO phase according to results of the modified TCLP test. But the CuFe2O4 structure is more stable under acidic environment than the CuAl2O4 structure. The observation of tetrahedral and octahedral absorption bands from FTIR results proved the formation of spinel structure, and the shift phenomenon was also confirmed by the occupancy of cations in different sites. Tetragonal phase CuFe2O4 provided hard magnetic characteristic at low temperatures, and the cubic phase CuFe2O4 provided soft magnetic characteristics at high temperatures. Different characteristics of CuFe2O4 produced at different temperatures will affect further applications on the environmental engineering. In the sample with hematite and gamma alumina, copper oxide would prefer to incorporate with Fe2O3 for forming spinel structure. CuFe2O4 and CuAl2O4 spinel were also successfully synthesized by hybrid microwave process which could significantly reduce the processing time and energy. The raw heavy metal sludge without adjustment could be transformed into CuAl2O4 spinel at the temperature of 800 °C. However, the dissociation of CuAl2O4 was not observed at high temperature, which was due to the impurities existed in samples. The raw heavy metal sludge could also be transformed into CuAl2O4 and significantly decreased the Cu leaching concentration after adjustment by thermal process. The results confirmed that the spinel synthesized technique could be successfully applied to the filed heavy metal sludge to get the objective of stabilization.
The adsorption/reusability experiments demonstrated that CuFe2O4 particles could be used as a magnetic adsorbent by electrostatic attraction to remove various metal ions (Cu2+, Pb2+, Cd2+, Ni2+, and Zn2+). The removal efficiencies of Cu2+, Pb2+, Cd2+, Ni2+, and Zn2+ with 12 h of contacting time were about 92%, 90%, 81%, 80%, and 55%, respectively. The removal efficiency of Cu2+ and Pb2+ gradually increased with the increase of pH. The regeneration tests also showed that the removal efficiency of Cu2+ during six cycles was > 80%, and the magnetic CuFe2O4 particles could repeatedly be used for metal ions removal in aqueous environments. Therefore, transforming heavy metal sludge into spinel materials could not obtain only the objective of stabilization but also the reutilization of solid waste.
Subjects
Spinel
Copper
Heavy metal sludge
CuFe2O4
CuAl2O4
Stabilization
Adsorption
SDGs
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-101-D96541008-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):22acffb7d6ffc92449e1d08075825050