Jiangshan Li

Investigation of the leaching behavior of lead in stabilized/solidified waste using a two-year semi-dynamic leaching test.

Long-term leaching behavior of contaminant from stabilization/solidification (S/S) treated waste stays unclear. For the purpose of studying long-term leaching behavior and leaching mechanism of lead from cement stabilized soil under different pH environment, semi-dynamic leaching test was extended to two years to investigate leaching behaviors of S/S treated lead contaminated soil. Effectiveness of S/S treatment in different scenarios was evaluated by leachability index (LX) and effective diffusion coefficient (De). In addition, the long-term leaching mechanism was investigated at different leaching periods. Results showed that no significant difference was observed among the values of the cumulative release of Pb, De and LX in weakly alkaline and weakly acidic environment (pH value varied from 5.00 to 10.00), and all the controlling leaching mechanisms of the samples immersed in weakly alkaline and weakly acidic environments turned out to be diffusion. Strong acid environment would significantly affect the leaching behavior and leaching mechanism of lead from S/S monolith. The two-year variation of De appeared to be time dependent, and De values increased after the 210th day in weakly alkaline and weakly acidic environment.

Effect of drying-wetting cycles on leaching behavior of cement solidified lead-contaminated soil.

Lead contaminated soil was treated by different concentration of ordinary Portland cement (OPC). Solidified cylindrical samples were dried at 40°C in oven for 48 h subsequent to 24h of immersing in different solution for one drying-wetting. 10 cycles were conducted on specimens. The changes in mass loss of specimens, as well as leaching concentration and pH of filtered leachates were studied after each cycle. Results indicated that drying-wetting cycles could accelerate the leaching and deterioration of solidified specimens. The cumulative leached lead with acetic acid (pH=2.88) in this study was 109, 83 and 71 mg respectively for solidified specimens of cement-to-dry soil (C/Sd) ratios 0.2, 0.3 and 0.4, compared to 37, 30, and 25mg for a semi-dynamic leaching test. With the increase of cycle times, the cumulative mass loss of specimens increased linearly, but pH of filtered leachates decreased. The leachability and deterioration of solidified specimens increased with acidity of solution. Increases of C/Sd clearly reduced the leachability and deterioration behavior.

Experimental study on the microstructure and mechanical behaviors of leachate-polluted compacted clay

The intent of this article is to investigate the microstructure characteristics and macroscopic mechanical behaviors of leachate-polluted compacted clays. X-ray diffraction, scanning electron microscope, and mercury intrusion porosimetry were used to observe the mineral component, microstructure of the compacted clays polluted by different concentrations of landfill leachate. One-dimensional swelling test, direct shear test, and permeability test were conducted to measure and analyze the swelling properties, shear strength, and permeability of leachate-polluted compacted clays. Results indicated that the leachate pollution caused a decrease in smectite content of compacted clays. Aggregate structure was destroyed by leachate pollution, causing an increase in the relative porosity of the smaller pores and a decrease in that of the larger pores. However, the total porosity increased with the leachate concentration because of the decrease in swelling deformation of compacted clay. Leachate pollution caused a significant increase in cohesion and a slight increase in internal friction angle of the compacted clays. Moreover, the permeability of the leachate-polluted compacted clays decreased with the increase in time and leachate concentration.

Precipitates in landfill leachate mediated by dissolved organic matters

Clogging of landfill leachate collection system is so ubiquitous that it causes problems to landfills. Although precipitations of calcite and other minerals have been widely observed, the mechanism of precipitation remains obscure. We examined the clog composition, dissolved organic matters, leachate chemical compositions and the correlation of these variables in view of the precipitation process. It is shown that Dissolved Organic Carbon (DOC) inhibits precipitation of landfill leachate. Using the advanced NICA-Donnan model, the analysis of aqueous chemical reactions between Mg-Ca-DOC-CO2 suggests a good agreement with experimental observations. Calcite and dolomite are both found to be oversaturated in most of the landfill leachate samples. DOC is found to preferentially bind with Mg than Ca, leading to more likely precipitation of Calcite than dolomite from landfill leachate. The NICA-Donnan model gives a reasonable estimation of dolomite saturation index in a wide range of DOC. Modeling confirms the major precipitation mechanism in terms of alkaline earth metal carbonate. Uncertainties in model parameters are discussed with particular focus on DOC composition, functional group types and density concentration and the influential factors.