Research On Leaching Characteristics Of Heavy Metals In Stabilization/Solidification Of Grate Fly Ash With Ordinary Portland Cement

The property and heavy-metal leaching characteristics of the grate fly ash gathered under fabric filter in a MSW incineration plant are studied in this paper. On the basis of it, the leaching characteristics of heavy metals are researched on stabilization/solidification of fly ash with cement and addition of additives. It is significant to non-hazardous treatment of MSW fly ash.Firstly, the property and heavy-metal leaching characteristics of the grate fly ash are studied in this paper. The property of fly ash consists of chemical composition, particle size distribution, relation of particle size distribution and heavy-metal contents.. After the influencing factors of heavy-metal leaching are grasped, leaching characteristics are studied at different PH value, L/S ratio and leaching time.The results shows that the content of heavy metals in fly ash of small size particles is relatively high, but small size particles account for little among total amount of fly ash. Heavy m etals i n t he f ly a sh are v ery easy to 1 each i n acid condition, w hile h ardly leach in alkaline condition.Base on it, leaching characteristics of solidified products are studied and analysed in different mixed proportions of fly ash and cement and solidified time. The leaching characteristics of solidified products are researched in different PH value and L/S ratio. As a result, a conclusion is reached that heavy metals in solidified products never leach in appropriate PH value and L/S ratio. The results show that leaching characteristics of heavy metals in fly ash and the solidified products are similar and leaching values of heavy metals in the solidified products fulfill the leaching toxicity standard values for hazard waste in China at PH>6 and L/S<70.It is considered that additives are added in the mixtures of fly ash and cement because heavy metals such as chromium and cadmium and so on in solidified products leach much more than the other heavy metals. The research of leaching characteristics of heavy metals in solidified products is influenced by the addition of additives, especially heavy metals which leach more than others. The results show that the joining of several kinds of additives chosen can reduce the leaching of heavy metals. The adding amount of the addtive should be appropriate, generally about 5%.