Municipal solid waste incinerator (MSWI) bottom ash should be pretreated before reusing, which can reduce the risk of polluting the environment by leaching the heavy metals from bottom ash. It is significant scientific and engineering benefit of carbonization for stabilization of solid waste. Nevertheless, taking too much time is the defect of the carbonization. In this study, the retrieved water of washing bottom ash aerated carbon dioxide about 10% to become carbonated water. Let calcium from bottom ash and carbonate ion from carbonated water reacted to form calcium carbonate by dipping process to raise the stability rate of heavy metals.
The experiment of this study has divided into two parts of batch and circulation. In the batch experiment, the bottom ash through two steps of five minutes stirred and then dipped in carbonated water for 3, 6 and 18h. The aim of this experiment is to observe the concentrations of TCLP for heavy metals and the remove rate of chlorine ion. In the circulation experiment, the dripped solution would be recycled to substitute the tap-water of the first step wash water. The bottom ash through two steps of five minutes stirred and then dipped in carbonated water for 0.5, 1 and 3h. In a circle, the process needs to repeat three times.
The result of the batch experiment shows that the dripping process really can reduce the TCLP concentration of heavy metals. The concentrations of lead and cadmium do not decrease with the dripping time. Zinc and copper would increase the leaching rate with the dripping time increased. The leaching rates of the water-soluble chloride ion were 44.2%, 45.2% and 46.3% at dipping time of 3, 6 and 18 h respectively. The consummation of alkalinity in the water increases with the dripping time.
The results of the circulation experiment indicate that the leaching concentration of Pb, Zn, Cu and Cd were 0.02, 8.23, 1.49 and 0.09 mg/L and would be restrained after dripping time of o.5h. Specially, the Cr concentration was not detectable. The leaching amount of the water-soluble chloride increased with the dripping time increased. The leaching rates were 74.3%, 76.2% and 85.7% after dripping time of o.5, 1 and 3h respectively. The dripping time of 0.5h and dry in 105 oC of oven could reach the aim of stabilization of heavy metals and increase the leaching rate of chloride.