Yunmin Chen

Adsorption behavior and mechanism of Cd(II) on loess soil from China

Cadmium is a toxic heavy metal that has caused serious public health problems. It is necessary to find a cost effective method to deal with wastewater containing Cd(II). Loess soils in China have proven to be a potential adsorbent for Cd(II) removal from wastewater. The adsorption capacity of loess towards Cd(II) has been determined to be about 9.37 mg g(-1). Slurry concentration, initial solution pH, reaction time and temperature have also been found to significantly influence the efficiency of Cd(II) removal. The adsorption isotherms and kinetics of loess soil from China can be best-fit with the Langmuir model and pseudo-second order kinetics model, respectively. The thermodynamic analysis revealed that the adsorption process was spontaneous, endothermic and the system disorder increased with duration. The natural organic matter in loess soil is mainly responsible for Cd(II) removal at pH < 4.2, while clay minerals contribute to a further gradual adsorption process. Chemical precipitation dominates the adsorption stage at pH > 8.97. Further studies using X-ray diffraction, Fourier transform infrared spectra of Cd(II) laden loess soil and Cd(II) species distribution have confirmed the adsorption mechanism.

Adsorption behavior of Zn(II) on calcinated Chinese loess

Chinese loess has proven to be effective in removing Zn(II) from aqueous solutions, but the resultant adsorbent-water slurry is difficult to separate. In this paper, the crude loess was calcinated to improve the separation efficiency of slurries in terms of sedimentary rate by increasing the particle sizes of the adsorbent. The sorption capacities of different sorbents, including crude loess, calcinated loess, de-organic crude loess and acid-treated calcinated loess, were obtained and sequenced. The adsorption capacity of the calcinated loess towards Zn(II) was found to be as high as 113.6 mg g(-1). The adsorption isotherms and kinetics of calcinated loess were best-fit with the Freundlich isotherm and the pseudo-second order kinetics, respectively. The thermodynamic analysis revealed that the adsorption was exothermic and spontaneous with a high preference for Zn(II) removal. The adsorption of Zn(II) on calcinated loess implies an ion exchange of the solute with calcite and goethite due to the observed FT-IR and XRD patterns as well as the predicted mean free energies (-11.58 to -9.28 kJ mol(-1) by D-R model). The byproduct of adsorption can be purified and refreshed by using a 0.01 M HCl solution.

Aging and compressibility of municipal solid wastes

The expansion of a municipal solid waste (MSW) landfill requires the ability to predict settlement behavior of the existing landfill. The practice of using a single compressibility value when performing a settlement analysis may lead to inaccurate predictions. This paper gives consideration to changes in the mechanical compressibility of MSW as a function of the fill age of MSW as well as the embedding depth of MSW. Borehole samples representative of various fill ages were obtained from five boreholes drilled to the bottom of the Qizhishan landfill in Suzhou, China. Thirty-one borehole samples were used to perform confined compression tests. Waste composition and volume-mass properties (i.e., unit weight, void ratio, and water content) were measured on all the samples. The test results showed that the compressible components of the MSW (i.e., organics, plastics, paper, wood and textiles) decreased with an increase in the fill age. The in situ void ratio of the MSW was shown to decrease with depth into the landfill. The compression index, Cc, was observed to decrease from 1.0 to 0.3 with depth into the landfill. Settlement analyses were performed on the existing landfill, demonstrating that the variation of MSW compressibility with fill age or depth should be taken into account in the settlement prediction.

A theoretical solution for pile-supported embankments on soft soils under one-dimensional compression

Pile-supported embankments are increasingly being used for highways, railways, storage tanks, etc. over soft soil because of their effectiveness in accelerating construction and minimizing deformation. The stress transfer mechanisms among all of the components in a piled embankment, including the embankment fill, the piles and (or) caps, and the foundation soils, are complicated. In this study, a closed-form solution for one-dimensional loading was obtained taking into consideration the soil arching in the embankment fill, the negative skin friction along the pile shaft, and the settlement of the foundation soil. In the derivations, the piles, the embankment fill, and the foundation soil were assumed to deform one-dimensionally. This study investigated the stress concentration on top of the pile, the axial load and skin friction distributions along the pile, and the settlement of the embankment. Comparisons demonstrate that the results from this solution are in good agreement with those obtained using a f...

Activation of Firmiana Simplex leaf and the enhanced Pb(II) adsorption performance: Equilibrium and kinetic studies

Although various biosorbents have been reported effective to purify wastewaters containing heavy metals, the high tendency to decomposition in the environment makes them unsuitable for long-term persistent utilization. In this paper, a simple and new activation method was proposed to mineralize the Firmiana Simplex leaf (FSL) into an enhanced adsorbent for Pb(II) removal from aqueous solution. The leaves activated at various temperatures were characterized with BET N(2) adsorption test, FT-IR test and XRD test. After activation, the mass percent of inorganic components (including whewellite, quartz, phosphate and calcite) increased and the specific surface area increased from 0.08283 to 9.32 m(2)g(-1) with the increasing activation temperature (AT) from 100 to 400 degrees C. Proper activation temperature (200 degrees C) helps to preserve the beneficial groups (amine and carboxyl). The affinities of the adsorbents towards Pb(II) were increased with increasing AT from 300, 100, 200 to 400 degrees C according to the adsorption isotherms. The adsorbent activated at 200 degrees C (AL2) was found most suitable for Pb(II) adsorption regarding the high yield efficiency (36.52%), high Pb(II) adsorption capacity (136.7 mg g(-1) by Langmuir model), high adsorption affinity (H type isotherm) and rapid adsorption rate (within 20 min by kinetic study). The Pb(II) removal efficiency of AL2 was obviously affected by the solution pH rather than by the adsorbent dosage. The adsorption was viewed as a chemical process based on IR spectra along with a physical process based on the correlation between the average pore size of the adsorbent and the adsorption capacity. The activation method proposed in this paper was proved effective and potentially applicable in the treatment of Pb(II) polluted wastewaters.

Removal of Cd(II) from aqueous solution with activated Firmiana Simplex Leaf: behaviors and affecting factors.

Cadmium pollution is known to cause severe public health problems. This study is intended to examine the effect of an activated Firmiana Simplex Leaf (FSL) on the removal of Cd(II) from aqueous solution. Results showed that the active Firmiana Simplex Leaf could efficiently remove Cd(II) from wastewater due to the preservation of beneficial groups (amine, carboxyl, and phosphate) at a temperature of 250 degrees C. The adsorbent component, dosage, concentration of the initial solute, and the pH of the solution were all found to have significant effects on Cd(II) adsorption. The kinetic constants were predicted by pseudo-first-order kinetics, and the thermodynamic analysis revealed the endothermic and spontaneous nature of the adsorption. FT-IR and XRD analyses confirmed the strong adsorption between beneficial groups and cadmium ions, and the adsorption capacity was calculated to be 117.786 mg g(-1) according to the Langmuir isotherm.

Secondary Compression of Municipal Solid Wastes and a Compression Model for Predicting Settlement of Municipal Solid Waste Landfills

The estimation of the capacity and settlement of landfills is critical to successful site operation and future development of a landfill. This paper reports the results of a study on biodegradation behavior and the compression of municipal solid wastes. An experimental apparatus was developed which had a temperature-control system, a leachate recycling system, a loading system, and a gas and liquid collection system. Experiments were performed both with and without optimal biodegradation for comparative purposes. Test results indicated that settlement resulting from creep was relatively insignificant when the biodegradation process was inhibited. Compression due to decomposition under optimal biodegradation conditions was found to be much larger than compression associated with creep. The biodegradation process was significantly influenced by the operational temperature. A one-dimensional model is proposed for calculating settlement and estimating the capacity of the landfill under relatively optimal biodegradation conditions. The model was developed to accommodate the calculation of settlement in landfills when a multistep filling procedure was used. The calculation method is relatively simple and convenient for design purposes. Simulations of the physical processes showed that enhancing solid waste biodegradation during the filling stage can considerably increase the capacity of the landfill and reduce postclosure settlements.

Zn(II) Removal with Activated Firmiana Simplex Leaf: Kinetics and Equilibrium Studies

As is known, zinc pollution has been a public environmental issue for a long time. Accordingly, the major objective of this study is to examine the effect of activated Firmiana simplex leaf on Zn(II) removal from aqueous solution. The result shows that activated Firmiana simplex leaf can remove Zn(II) effectively at 250°C due to the preservation of amine, carboxyl, and phosphate groups. Several factors were determined to have significant effects on the adsorption of Zn(II), including the adsorbent component, dosage, initial concentration, solution pH, temperature, and duration. Pseudo first order and pseudo second order kinetics equations were used to predict the kinetic and thermodynamic constants that reveal the endothermic and spontaneous nature of the adsorption. Using the Langmuir model, the maximum zinc adsorption capacity was calculated to be 55.096  mg/ g, which was subsequently confirmed by Fourier transformed infrared radiation (FT-IR) analyses and X-ray diffraction (XRD) spectra.

Verification of the Soil-Type Specific Correlation between Liquefaction Resistance and Shear-Wave Velocity of Sand by Dynamic Centrifuge Test

Liquefaction of granular soil deposits is one of the major causes of loss resulting from earthquakes. The accuracy of the liquefaction potential assessment at a site affects the safety and economy of an engineering project. Although shear-wave velocity ( Vs ) -based methods have become prevailing, very few works have addressed the problem of the reliability of various relationships between liquefaction resistance (CRR) and Vs used in practices. In this paper, both cyclic triaxial and dynamic centrifuge model tests were performed on saturated Silica sand No. 8 with Vs measurements using bender elements to investigate the reliability of the CRR- Vs1 correlation previously proposed by the authors. The test results show that the semiempirical CRR- Vs1 curve derived from laboratory liquefaction test of Silica sand No. 8 can accurately classify the ( CRR, Vs1 ) database produced by dynamic centrifuge test of the same sand, while other existing correlations based on various sandy soils will significantly under o...

Large-Scale Modeling and Theoretical Investigation of Lateral Collisions on Elevated Piles

AbstractLarge deflection is mobilized in elevated piles of nonnavigable piers and some flexible protective systems subjected to lateral ship collisions. Because the current bridge design specifications are only suitable for the design of rigid foundations, new analysis and design methods are required for these flexible elevated piles. A large-scale lateral static load test and an additional three impact tests on piles in low liquid limit silt (ML) soil were carried out in a large soil tank. Both static and dynamic soil pressures on the pile shaft were measured, and then the soil-pile interaction was studied in detail. Based on the results, static hyperbolic p-y curves of the piles were derived for dynamic p-y curve models. Through investigations of three linear and nonlinear soil-pile dynamic interaction models, the dynamic p-y curve models with nonlinear static stiffness coefficients and constant damping coefficients are recommended for the analysis of piles subjected to lateral impact loading. Verified ...