Microwave Enhanced Reclamation of Heavy Metal Sludge
Date Issued
2008
Date
2008
Author(s)
Hsieh, Ching-Hong
Abstract
The leaching concentration of heavy metal sludge is above the TCLPriteria for land disposal (< 15 mg/L) and regarded as a hazardous solid waste.ithout proper treatments, the hazardous sludge would contaminate the soil andround water and even human health. Therefore, a stabilizing process for theremendous amount of heavy metal sludge is required before land disposal andeuse. In this study, microwave processes were conducted for the stabilization ofeavy metal sludge. The effects different processes, stabilizing agents, processime, microwave power, reaction atmosphere, microwave adsorbents, microwaveybrid process and temperature variation were investigated. The solid stateeaction and adsorption study of stabilized sludge were also discussed.esults indicated that better stabilization ratio was reached when microwaveadiation was applied coincided with the addition of reductive metal powder. Thedding dose of metal powder at same stabilization ration was in reverse order ofetal reactivity. As copper was stabilized, Fe and Al also leached out duringCLP process. Al3+, Fe2+ and Cu0 (or CuO) was formed as redox reaction wasccurred. The stabilization efficiency improved at higher microwave power, buthe thermal pressure caused by higher microwave power could decline theIeproducibility of experimental data. For raw heavy metal sludge (TD10), theludge would smolder under oxygen atmosphere leading to the leaching of metalons when only microwave radiation was applied. Moreover, as microwaveadiation was served coupled with stabilizing agent to TD10, an inert reactiontmosphere (N2) during heating and oxidizing atmosphere (air) for cooling gaveetter performance. Oxidation heat released from the oxidation of aluminumowder may be attributed to the formation of CuO. When metal powder wasdded into inorganic sludge (De10) with microwave radiation at N2/N2, theicroarcing process may be responsible for the dehydration reaction of sludge.ppropriate amounts of microwave adsorbents in the sludge would increasehe homogeneity of microwave energy to increase the reactions betweentabilizing agents and copper. In Hybrid Microwave process, when processingime was longer than 18 min and AC dosage was more than 3 g, a minor portionf the De10 was vitrified and leading to low copper leachability. Addingarbonaceous materials in the samples would enhance the transformation ofopper into CuAl2O4 due to the additional burning heat. Also, in this process, theeduction reaction may be attributed to the formation of Cu2S. In the solid stateeaction, the transformation of CuAl2O4 was higher at 900 ℃. Calcination ofixture of CuO and γ-Al2O3 gave better transformation ratio of CuAl2O4 whenIIompared with mixture of CuO and α- Al2O3. The diffusion rate of solid particles,ormation of surface layer, lattice structure, and amorphous intermediate productay be attributed to the differences of transformation ratio.n the adsorption study, the surface charge of stabilized-sludge was negativet the pH range of 2-11. The removal of copper ions increased as the initial pHose, and the final pH maintained at a constant of pH 7.2 while the initial pH isrom 6 to 8. In the kinetic study, the adsorption of copper ions onto adsorbentas fitted to the pseudo-second order model with great correlation coefficient (R2 0.994). This result shows the adsorption of copper ions onto stabilized-sludgeo be an activated adsorption mechanism. The experimental data was alsonalyzed by the isotherm equations and correlation coefficient of the Langmuirquation was better than that for the Freundlich equation. In isotherm experiment,oth the Q0 and b increased as the temperature ure rose from 15℃ to 55℃. Thismplies that this adsorption reaction was an endothermic reaction which can alsoe demonstrated by the thermodynamic study with the parameters, ΔG0, ΔH0 andS0. The adsorption capacity of copper ions onto stabilized-sludge was around5-23 mg/g, which was greater than that on many other solid wastes.
Subjects
Heavy metal sludge
Copper
Microwave
Stabilization
Adsorption
Type
thesis
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