Study On Cement-Based Solidification/Stabilization Of Sludge Using Calcium-bentonite As Additive

In order to solve the problem of treatment and disposal of sludge in China, at the short time realizing the safe landfill of huge and widely distributed sludge and at the long term adjusting kinds of measures to local conditions to reuse the sludge were put forward. Based on the skeleton construction method for solidification treatment of sludge, the practical skeleton construction method was brought forward with cement solidifying/stabilizing sludge using calcium-bentonite as additive. The basic geotechnical properties and pollutants stabilization control were assessed to solidified sludge, and the mechanical development of strength of sludge was discussed too. The main contents of the article are shown as follows:(1) The compositions of dredged sludge as skeleton constructing material and its effects on solidification/stabilization (S/S) of sludge were analyzed. Based on these, effects of different clay minerals as additive on development of compressive strength and stabilization of pollutants of solidified sludge were compared. The results show that bentonite which contains high montmorillonite has a better effect on solidification/stabilization (S/S) of sludge than other clays. Furthermore, taking the cost of treatment of sludge into account, the practical skeleton construction method was put forward using calcium-bentonite as additive during cement based S/S of sludge.(2) Geotechnical properties of sludge after S/S treatment were evaluated from the aspects of compressive strength, volume change, permeability and wet and dry duration. The results show that adding calcium-bentonite can keep the solidified sludge with high compressive strength at low cement content, with low permeability, low volume change and good wet and dry duration.(3) Leaching toxicity extraction test was performed to assess the stability of heavy metal and organics in solidified sludge. The results show that calcium-bentonite reduces the leaching ratio of Zn, Pb from the solidified sludge and the bad influence of strong alkalinity on stability of Cu and organics in the solidified sludge. Macroscopical physical encapsulation ability of pollutants in the solidified sludge was studied by flexible-wall permeability test. The results show that bentonite can greatly reduce the permeability of solidified sludge, and improves its monolith, therefore reduces the release of pollutants from sludge.(4) Mechanical development of strength of the solidified sludge was understood by pore fluid analysis, X-ray diffraction analysis and Scanning Electron Microscope/Energy Dispersive X-ray Spectrometry (SEM/EDS) analysis. The results show that calcium-bentonite has two effects on development of stregth of solidified sludge, one hand to construct skeleton...