Study On The Retention Characteristics Of Bentonite On Heavy Metal Ions

Bentonite, with montmorillonite as the main ingredient, has chemical and mechanicalbarrier function when using as the engineering barrier material. In many landfill constructionsand in nuclear waste repository, bentonite is also used as the most appropriate cushioningmaterial to construct the engineering barriers. The engineering barrier performance ofbentonite depends to a large extent on the performance of its physical characteristics andchemical adsorption characteristics. So it is necessary to study on retention characteristics ofbentonite on heavy metal ions. This study aims to investigate the adsorption/desorptionbehavior and mechanism of Cr(Ⅲ) on the GMZ bentonite on the basis of laboratoryexperiments．Several factors (i.e. solid-liquid ratio, pH, ionic strength, temperature etc.) havebeen studied with regarding their effects on adsorption/desorption characteristics and therelevant mechanisms. At the same time, the permeability, diffusion and retentioncharacteristics were employed to analyze the retention mechanism of compacted bentoniteused as engineering barriers. With practical engineering in the background,by establishing 3Dflow and transport model which can take convection and dispersion of contaminant intoconsideration, the contaminant transport characteristics of the heavy metal Cr(Ⅲ) in thegroundwater environment was numerically analyzed, and the retention effects of theengineering barriers of compacted bentonite to the Cr(Ⅲ) was also researched. Acquire somemeaningful conclusions.1) The pH value, ionic strength and some other factors have big impact on the adsorption ofCr (Ⅲ) on the bentonite, the maximum adsorption capacity was 4.68 mg/g under the givenexperimental conditions. The Freundlich adsorption isotherm models were conducted forthe description of the adsorption process. And the absorption reaction is endothermicprocess.2) The bentonite could be used to deal with Cr(Ⅲ) wastewater, which indicates that thebentonite has a good regeneration ability and reusability. The pH value is an importantfactor in the Cr(Ⅲ) desorption from the GMZ bentonite. Within the appropriate pH range,desorption rate is decreasing as pH value of the solution increasing, and desorptionefficiency can be reach to 89.4% in strong acidic environment (pH=1). Within certaintemperature range, the higher the temperature is more disadvantageous to the desorptionof Cr(Ⅲ) from the GMZ bentonite，which is exothermic reaction. 3) Through the model of numerical analysis, the heavy metal contaminant of Cr (Ⅲ) transportis obvious in the research region, and the heavy metal contaminant spreads around overtime in the situation without engineering barriers. After the engineering barriers ofcompacted bentonite constructed, the contaminant transport will be restricted in the frontregion of the engineering barriers. The retention efficiency of the engineering barriers tocontaminant migration is about 99% in the studied condition.