No abstract

Modified calcium bentonite (Ca-bentonite) is extensively used in engineered barrier systems (EBSs) for municipal and industrial disposal sites due to its high swelling potential and low hydraulic conductivity. However, few studies have focused on the micromechanism of hydration and swelling under the effect of inorganic chemical solution. In this study, free swell index (FSI) and the type and content of modified Ca-bentonite bound water under the inorganic chemical solution were quantitatively studied by using the free swell test and nuclear magnetic resonance (NMR). According to the results, modification of sodium and polymer significantly increases the FSI of Ca-bentonite, bringing it close to that of natural sodium bentonite. In addition, the chemical stability of polymer-modified bentonite is significantly higher than that of sodium-modified bentonite but less than that of natural Na-bentonite. The FSI of modified Ca-bentonite decreases with the increase of cation valence and ionic strength. T2 distribution curves of the two types of modified bentonite are three-peak curves. With the increase of ionic strength, the content of total water and permeated hydrated water (accounting for 69%–95%) in bentonite decreases gradually, whereas the surface hydration water (accounting for 2%–31%) and free water content (accounting for 0–15%) increase. A uniform linear relationship exists between the FSI and corresponding total peak area of NMR (independent of ion valence, concentration, and bentonite type). Furthermore, a linear relationship exists between the FSI of the same type of bentonite and the T2 relaxation time. Research results can provide data and theoretical basis for quantitative analysis and mechanism of the hydration swelling of bentonite.

A quantitative description of aerobic waste degradation is important in evaluating landfill waste stability and economic management. This research aimed to develop a coupling model to predict the degree of aerobic waste degradation. On the basis of the first-order kinetic equation and the law of conservation of mass, we first developed the coupling model of aerobic waste degradation that considered temperature, initial moisture content and air injection volume to simulate and predict the chemical oxygen demand in the leachate. Three different laboratory experiments on aerobic waste degradation were simulated to test the model applicability. Parameter sensitivity analyses were conducted to evaluate the reliability of parameters. The coupling model can simulate aerobic waste degradation, and the obtained simulation agreed with the corresponding results of the experiment. Comparison of the experiment and simulation demonstrated that the coupling model is a new approach to predict aerobic waste degradation and can be considered as the basis for selecting the economic air injection volume and appropriate management in the future.