| Xiawan Stream flows through Zhuzhou City and finally flows into Xiangjiang River. Various wastewater containing heavy metals from metallurgical industry, chemical engineering industry was discharged into the Xiawan creek and accumulated in the sediments over about 50 years.It brought enormous pollution to the Xiangjiang River and thus be one of the largest potential sources of risk to Xiang River water quality. So the dredged sediments is required to be treatmented before final disposal.Stabilization/solidification (S/S) is one of the best demonstrated available technologies to treat certain industrial wastes and contaminated dredged sediments. The aim of the study was to prove S/S process used by Ordinary Portland cement and coal fly ash(anthracite by huayin power plant in zhuzhou) is an effective and environmental for disposal and management of contaminated dredged materials. In order to determine the efficiency attained by the S/S process,the compressive strength of the solidified waste, USEPA TCLP and GANC leaching tests have been determined. And in order to study the influence of the environmental conditions in which setting occurs, experiments were carried out with samples of the same composition, under different setting conditions: laboratory environment, stove at a temperature of 60℃and setting in a hermetically sealed plastic bag at room temperature. we can find that when the percent of cement is lower (10%), the addition of coal fly ash increasing from 5% to 10%, the strength increased from 0.28Mpa to 0.49Mpa. When the replacement of cement by coal fly ash increasing from 0% to 30%, the strength decreased from 2.3Mpa to 0.94Mpa. when the sediment/binder ratio is 1, the leachate pH of samples decreased drastically from 12.50 to 11.49 with the percentage of coal fly ash increasing from 0% to 30% and the concentration of znic, lead and cadmium also generally decreased. But when the sediment/binder ratio is 2.5, the leachate metal concentration increased for the lower content of cement in the binder. And the concentration of zinc, lead and cadmium decreased greatly from the specimens cured for 1 day to that cured for 3 days, while the concentration of heavy metals was nearly same between the specimens cured for 3 days and that cured for 7 days. This showed that humidity and temperature during curing period played an important role.The effect of partial replacement of cement by coal fly ash on stabilization/ solidification(S/S) of the sediments at different curing times (7days and 28days) was investigated. The leaching test results showed that all the heavy metal concentrations in TCLP leachates were lower than the limits of the Identification Standards for Hazardous Wastes-Identification for Extraction Toxicity (GB5085.3-2007); under a constant leachate pH of 4, coal fly ash/total solid ratio (CFA/TS) should be lower than 30%, to keep the Cd, Pb and Zn concentration in leachates lower than the limits of GB 5085.3-2007. The appropriate coal fly ash addition and longer curing time improved heavy metal immobilization. Compared with S/S specimens without coal fly ash addition, the unconfined compressive strength of the S/S specimen with a CFA/TS of 5% was improved, but the further coal fly ash addition led to its continuous decrease. The unconfined compressive strength of S/S specimens cured for 28 days nearly doubled that cured for 7days. The environmental resistance tests showed that wetting and drying cycle deteriorated insignificantly, while freeze and thawing cycle deteriorated significantly the S/S specimens. When the CFA/TS was higher than 30%, the mass loss of S/S specimens cured for 28days was higher than 30%. With a binder/sediment ratio of 1.5, the appropriate CFA/TS of 5%-20% make the S/S specimens be suitable for landfill or other applications.
|
PDF Full Text Request