Effect of washing on accelerated carbonation of incineration bottom ash
Heng, Kim Soon.
Date of Issue2013
School of Civil and Environmental Engineering
Residues and Resource Reclamation Centre
This project serves to investigate the effect of washing on accelerated carbonation of incineration bottom ash (IBA), before utilizing or recycling them for environmental purposes. The focus was divided into 3 sections. The first part was to evaluate the optimal parameters for washing. Washing was conducted using deionized water as the main solvent. Preliminary investigations showed that performing 1-hour of washing with a liquid to solid (L/S) ratio of 10 was effective in removing soluble salts (i.e. chlorides and sulfates) from IBA. The second part of the project was focused on evaluating the effectiveness of washing on accelerated carbonation on IBA. After carbonation, the total inorganic carbon (TIC) content in washed IBA was observed to be higher as compared to unwashed IBA, thus indicating that washing was able to improve the carbonation efficiency in IBA. In terms of moisture content, IBA containing 15%MC proved to be the most effective for 35°C carbonation. The last part was to monitor the leaching behavior of heavy metals and soluble salts after washing and carbonation. 24-hour leaching tests were conducted using deionized water as the leachant. Carbonation was able to reduce the leaching of zinc and lead effectively. Washing coupled with carbonation was capable of reducing significant amounts of barium, copper, chlorides, dissolved organic carbon (DOC) and total nitrogen (TN) being leached out from the IBA leachates. However, carbonation was not effective in reducing the leaching of chromium, molybdenum and antimony. Washing coupled together with carbonation did not seem to solve this problem either. One interesting result was that the leaching of sulfates increased after carbonation. Carbonation may have caused the decomposition of ettringite in IBA to form soluble gypsum, causing sulfates to be leached out from the IBA leachates (Alba et al., 2001). This means that the formation of sulfates after carbonation is directly proportional to the carbonation efficiency. Implementing washing together with carbonation causes the leaching of sulfates to increase further, implying that washing indeed has the potential to improve the efficiency of the carbonation process. All in all, the implementation of washing together with accelerated carbonation yields positive results. Washing seems to benefit the carbonation process and reduce the leaching behavior of most heavy metals and chlorides. Further studies will be required to solve the increased leaching of chromium, molybdenum, antimony and sulfates from IBA after washing and carbonation.
Final Year Project (FYP)
Nanyang Technological University