Qingbo Wen

Feasibility study on the application of coal gangue as landfill liner material

Coal gangue is one of the largest industrial solid waste all over the world, and many methods have been proposed for the recycling of coal gangue. In the present study, the feasibility of using coal gangue as landfill liner material is studied through a series of laboratory tests in terms of hydraulic conductivity, sorption characteristics and leaching behavior. The results indicated that the hydraulic conductivity of coal gangue could be smaller than the regulatory requirement 1×10-7cm/s with a void ratio less than 0.60. The batch sorption experiments performed on Pb2+ and Zn2+ illustrated that the coal gangue showed remarkable sorption capacity for the two heavy metals, and the sorption capacity for Pb2+ was larger than that for Zn2+. Both the pseudo first-order and pseudo second-order models fitted well with the sorption kinetics data of the Pb2+ and Zn2+ on the coal gangue, and the Langmuir model was found to best-fit the sorption isotherms. The sorption capacity decreased in presence of multiple heavy metals, both for Pb2+ and Zn2+. Concentrations of heavy metals leached from the coal gangue were all below the regulatory limits from China MEP and U.S. EPA. These desirable characteristics indicated that the coal gangue has potential to be used as landfill liner materials.

TRANSPORT AND EXCHANGE BEHAVIOR OF IONS IN BENTONITE DURING ELECTRO-OSMOTIC CONSOLIDATION

Electro-osmotic consolidation is considered to be an efficient technique for dewatering and consolidation of soft soil. In the present study, four experiments were conducted on a Na-rich bentonite using two reactive electrodes (copper and iron) and two inert electrodes (graphite and stainless steel) to study the transport and exchange behavior of ions during electro-osmotic consolidation. The results showed that the changes in pH and ion contents were limited to the zone close to the electrode due to the buffering capacity of bentonite and the significant reduction in electric current density. The ion concentration profiles indicated that Na+ ions were largely responsible for carrying the pore water to the cathode. The reactive electrodes are better at transporting Na+ ions and therefore induce better drainage than inert electrodes. Ion-exchange reactions occurred between the Cu2+ and Fe2+/Fe3+ ions released and pre-existing Na+ ions in the electrical double layer, causing decreased water adsorption capacity and plasticity index. The swelling and shrinkage characteristics of the bentonite were thus reduced, and electroosmotic consolidation may therefore provide a new way to improve the stability of expansive soils and slopes.

Effect of Adsorbate Concentration to Adsorbent Dosage Ratio on the Sorption of Heavy Metals on Soils

AbstractAdsorbent dosage and initial adsorbate concentration are usually used as two factors for a batch sorption experiment to investigate the sorption characteristics of heavy metals on soils. In...

Geotechnical Properties of Mine Tailings

AbstractThe engineering properties of tailings are important for the safety evaluation and engineering design of tailing dams. In the present study, laboratory experiments were performed to investigate the geotechnical properties of four different tailings, including two iron tailings (coarse and fine) and two copper tailings (coarse and fine). Compared to the copper tailings, the iron tailings showed higher compressibility, lower permeability, lower strength, and lower cyclic resistance. With the decrease in void ratio, the coefficient of consolidation almost kept constant for the fine iron tailings, whereas for the fine copper tailings, the coefficient of consolidation gradually increased. Under cyclic loading, the accumulation of pore water pressure was faster in the fine tailings than that in the coarse tailings. The cyclic resistance ratios (CRR) of the four tailings were found to be comparable with previous report data on other metal tailings, and the consolidation stress showed little impact on CRR...

Analytical Solution for Electroosmotic Consolidation Considering Nonlinear Variation of Soil Parameters

AbstractElectroosmotic consolidation can be used as an efficient technique for soft soil improvement. Considering the limitation in previous theories that soil parameters keep constant during electroosmotic consolidation, the nonlinear relationships between soil compressibility, hydraulic and electroosmosis conductivities, and void ratio are incorporated in a one-dimensional model in the present study. The analytical solutions for the ultimate excess pore-water pressure and surface settlement are derived. A comparison between the proposed analytical solutions and traditional theory indicates that the nonlinear variation of hydraulic conductivity results in a larger ultimate excess pore-water pressure, whereas the nonlinear variation of electroosmosis conductivity leads to a smaller one. The effects are more significant for soils with higher compressibility. The nonlinear variation of soil compressibility exhibits remarkable impact on the development of excess pore-water pressure when the nonlinear variati...

Effect of Adsorbent Dosage to Adsorbate Concentration Ratio on the Adsorption of Cd(II) on Coal Gangue

For the adsorption between the solid and liquid phases, the solid liquid ratio s/l and initial adsorbate concentration \( C_{0} \) are usually considered as the significant influence factors. The solid solute ratio s/a, i.e., the adsorbent dosage to adsorbate concentration ratio or the ratio of s/l to \( C_{0} \), has been proposed to be a new influence factor, and an empirical equation between the adsorption capacity and s/a has been developed to describe the adsorption characteristics of heavy metals on soil in previous studies. In the present study, the effect of s/a on the adsorption amount at equilibrium of coal gangue has examined by conducting a series of batch tests. For comparison, the influence of s/l and \( C_{0} \) were also investigated by the model fitting. The results indicate s/a could illustrate the effects of s/l and \( C_{0} \), and make it more succinctly to describe adsorption. Furthermore, the empirical equation was further verified by literature analysis, and it turned out to be generally applicable for various kinds of adsorbent and adsorbate not only heavy metal ions, but also organic matters. It’s possible to predict adsorption directly by using the empirical equation of s/a.

Numerical simulation of electro-osmotic consolidation coupling non-linear variation of soil parameters

Electro-osmotic consolidation is an effective method for soft ground improvement. A main limitation of previous numerical models on this technique is the ignorance of the non-linear variation of soil parameters. In the present study, a multi-field numerical model is developed with the consideration of the non-linear variation of soil parameters during electro-osmotic consolidation process. The numerical simulations on an axisymmetric model indicated that the non-linear variation of soil parameters showed remarkable impact on the development of the excess pore water pressure and degree of consolidation. A field experiment with complex geometry, boundary conditions, electrode configuration and voltage application was further simulated with the developed numerical model. The comparison between field and numerical data indicated that the numerical model coupling of the non-linear variation of soil parameters gave more reasonable results. The developed numerical model is capable to analyze engineering cases with complex operating conditions. A multi-field coupling model was developed for electro-osmotic consolidation.Non-linear variation of soil parameters showed remarkable impact.A case study was performed to examine the effectiveness of the numerical model.The numerical model is capable to analyze cases with complex operating conditions.