Studies of Microwave Stabilization Processes for The Copper-contaminated Sludge after Acid Extraction
Date Issued
2008
Date
2008
Author(s)
Chen, Ching-Lung
Abstract
Copper-contaminated sludge is hazardous industrial waste yielded in huge quantities in Taiwan. After the copper-contaminated sludge passed through an acid-extraction process to reclaim most of the copper ions in it, the residue, called the low copper-contaminated sludge, may still need to be treated by stabilization technologies. The common method for stabilization of the hazardous waste in Taiwan is by cement solidification. However, this method has the disadvantage of an increase in waste volume, which will shorten the service life of a landfill. In this study, the characteristics of microwave energy were used to offer a new method that can avoid this disadvantage of the cement solidification. Microwave stabilization processes used in this study include the direct microwave process, the microwave process with stabilizers, the stabilizer-inertia gas-hybrid microwave process, the microwave process with iron powder, and the microwave sintering process. The stabilization effects of these processes were promoted by changing the microwave power and reaction time, adding some agents, leading inert gas, and altering operating procedures. Furthermore, the microwave sintering process was used to transform copper-contaminated sludge into a sinter, thus stabilizing it and producing a material for public construction at the same time. From the results, it was found that the moisture in sludge was removed quickly and that organic matter was burned by a microwave heating. At the point of stabilization of the low copper-contaminated sludge, the direct microwave process could stabilize only some batches of sludge. When the microwave process with stabilizers was performed for sludge stabilization, it was effective and a short reaction time was required. In addition, the stabilizer amount used in this method was less than that without any assisting process. However, when the reaction time was longer, the leaching concentration of copper ions from the treated sludge increased suddenly. The stabilizer-inertia gas-hybrid microwave process could overcome the disadvantage of the microwave process with stabilizers at the long reaction time. Moreover, the dosage of sodium sulfide as a stabilizer required in the former was smaller than that in the latter. The microwave process with iron powder was also effective in the stabilization of the low copper-contaminated sludge and the reaction time required in this method was little more than those in the later methods. However, re-leaching of copper ions from the sludge treated by the microwave process with iron powder did not occur, even when the reaction time was long and inertia gas was not used. The results of the microwave sintering process show that a hard sinter could be acquired after synthetic sludge of high copper concentration passed through the improved microwave sintering process. No matter whether ferric oxide or iron powder was used in this method, the XRD results showed that cuprospinel (CuFe2O4) was formed in sinters. Besides, the leaching concentration of copper ions from the sinter transformed from synthetic sludge with iron powder by the improved microwave sintering process was lower than the limit value specified in the Toxicity Characteristic Leaching Procedure.
Subjects
copper-contaminated sludge
sludge stabilization
microwave process
microwave sintering
iron powder
ferric oxide
sodium sulfide
Type
thesis
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