Effects of Chelating Agent Preparation Conditions on Settlement Formation in Fly Ash Stabilization

Abstract

Fly ash generated from waste incineration contains hazardous substances such as heavy metals and small amounts of dioxins. Incineration plants in Taiwan stabilized fly ash by mixing it with a heavy-metal chelating agent, cement, and mixing water. Settlement formed in the mixture may adhere to mixers and block transportation pipelines, thereby prolonging processing time and reducing efficiency. Through simulation experiments, it was found that the amount of settlement is low at a mixing speed of 30 rpm, a rotational speed of 50 rpm, a mixing time of 20 min, and a maximum settling time of 30 min. Also, the results of correlation analyses on control parameters showed that settlement formation mainly depended on water hardness level, whereas the other control parameters have trivial effects. Subsequent analysis on the relation between the rate of settlement formation and water hardness showed that an equation obtained from the power method gave the highest correlation; thus, this equation was used for calculating the rate of settlement formed in the mixture of heavy metal chelating agents and mixing water.