Effects on leaching characteristics of heavy metals in municipal solid waste incinerator residues by accelerated carbonation

• Main Authors: Zhao-yu Chen, 陳昭羽
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/72738852564174089829

碩士 === 逢甲大學 === 環境工程與科學所 === 99 === This research investigated that the accelerated carbonation reaction effects on leaching characteristics of heavy metals and stabilization of municipal solid waste incineration (MSWI) bottom ash and fly ash (referred to as ash). The experiments were conducted by controlling 25 weight percentage of moisture content of ash, carbon dioxide concentration (10% and 20%) and fly ash addition ratio (10%, 20% and 30%), respectively. This research was also established the kinetics parameters of accelerated carbonation reaction using Thermogravimetric analysis (TGA) method, and evaluated the carbon reduction and/or carbon dioxide capture efficiency by MSWI ash during accelerated carbonation reaction process. The experimental results showed that higher CO2 concentration will help to accelerate the carbonate reaction, and to reduce the required time for MSWI ash stabilization. Meanwhile, the higher MSWI fly ash addition ratio will enhance the carbonate reaction rate and ash stabilization degree, due to its good moisture holding capacity. Besides, the calcium carbonate (CaCO3) formed in ash was more that the ash stabilization will be better. According to results of leaching concentration of tested heavy metals of ashes by accelerated carbonation, the tested heavy metals, such as zinc (Zn), cadmium (Cd) and lead (Pb), their leaching concentration decreased with carbonate reaction time increased. However, the copper (Cu) leaching concentration increased from 0.42±0.02 mg/l to 1.12±0.06 mg/l with an increase the carbonation time. According to results of MINTEQA2 model for prediction of heavy metals speciation formed in ash, the Cu speciation will be Cu2OCl2 (Melanothallite) that it will reduce the saturation index (SI: -19.361) and increase the solubility of ash. Therefore, the Cu leaching concentration will increase after accelerated carbonation reaction. In summary, the toxicity characteristics leaching procedure (TCLP) concentration of tested metals in accelerated carbonation ash were all in compliance with the current Taiwan’s regulation thresholds. All tested hazardous MSWI ashes have converted to non-hazardous ashes by accelerated carbonation process that will promote the potential application in further resourcification and reutilization of ash. According to analysis results of carbonate reaction kinetic, the slow carbonation reaction occurred at controlling of high CO2 concentration and smaller particle size of ash. This is due to the smaller particle size of ash has a low relatively porosity. When higher CO2 concentration will be enhanced the carbonation reaction rate and then formed calcium carbonate crystals on the ash surface. It could clog the ash pores and inhibit the diffusion of CO2. According to the analysis results of activation energy, the smaller particle size of ashes (ranged between 0.074 mm and 0.149 mm) has a lower activation energy (ranged between 17 kJ/mole and 76 kJ/mole). However, when the particle size increased to 0.149-0.420 mm, its activation energy will be increased approximately between 62 kJ/mole and 159 kJ/mole. According to the relationships between pH and carbon dioxide variation, the stabilization index (ΣΔpH/ΣΔCO2/Ca) for evaluating accelerated carbonation reaction was established. The results of stabilization index of accelerated carbonation ash were approximately between 1.2 and 2.6. Based on the results of accumulated amounts of CO2 uptake by MSWI ash, in the case of 10% CO2 concentration, every 100 grams of MSWI ash could capture the amounts of CO2 were approximately ranged between 43 grams and 45 grams during the accelerated carbonation. The overall effectiveness of carbon dioxide capture and reduction was also estimated approximately between 310 thousands and 370 thousands every year in Taiwan if all MSWI ash treated by accelerated carbonation process. In summary, the results of this study can provide further information for selection of potential technology in resourcification and reutilization of accelerated carbonation ash, but will also evaluate the benefits of carbon dioxide capture and reduction by accelerated carbonation process.