Evaluation of treatment of gas cleaning residues from MSWI with chemical agents

In order to evaluate the treatment of MSWI (municipal solid waste incineration) residues with chemical agents, the performance of three kinds of treated materials are compared with the behaviour of the untreated MSWI fly ash. The treatment processes involved are: treatment with a chelating agent, phosphate treatment, ferrite treatment. In the characterization of the leaching behaviour, the Japanese leaching test (JLT-13), the availability test, a pH dependent leaching test, a redox property test, and the serial batch test under open condition and closed condition are performed. The tortuosity of the compacted materials was tested separately in diffusion tubes using Na-22-tracer. Each treated material shows good results for JLT-13 test, however, the other test results vary from each other. The chelating treated material showed a high reducing capacity and strong retention for metals over a wide pH range. The phosphate treated material showed a significant decrease in availability, especially for lead. The ferrite treated material showed an increased physical retention. The changes in leaching behaviour of elements as a function of pH were compared with the buffering properties of the treated materials. From the serial batch tests, differences between open test and closed test in view of pH and ORP due to CO2 and O-2 in the air are recognized. (C) 2000 Elsevier Science Ltd. All rights reserved.