Zhenze Li

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.

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.

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.

Cd(II) adsorption on various adsorbents obtained from charred biomaterials.

Cadmium could cause severe toxicant impact to living beings and is especially mobile in the environment. Biomass is abundant and effective to adsorb heavy metals, but is easy to be decomposed biologically which affects the reliability of long-run application. Several biomasses were charred with and without additives at temperatures less than 200°C in this study. The prepared adsorbents were further testified to remove Cd(II) from aqueous solution. Equilibrium and kinetic studies were performed in batch conditions. The effect of several experimental parameters on the cadmium adsorption kinetics namely: contact time, initial cadmium concentration, sorbent dose, initial pH of solution and ionic strength was evaluated. Kinetic study confirmed (1) the rapid adsorption of Cd(II) on GC within 10 min and (2) the following gradual intraparticle diffusion inwards the sorbent at neutral pH and outwards at strong acidic solution. The grass char (GC) was selected for further test according to its high adsorption capacity (115.8 mg g(-1)) and affinity (Langmuir type isotherm). The Cd(II) removal efficiency was increased with increasing solution pH while the highest achieved at sorbent dosage 10.0 g L(-1). The ionic strength affects the sorption of Cd(II) on GC to a limited extent whereas calcium resulted in larger competition to the sorption sites than potassium. Spectroscopic investigation revealed the adsorption mechanisms between Cd(II) and surface functional groups involving amine, carboxyl and iron oxide. The long-term stability of the pyrolyzed grass char and the potential application in engineering practices were discussed.

Woods Charred at Low Temperatures and Their Modification for the Adsorption of Cr(VI) Ions from Aqueous Solution

Despite being prepared at higher temperatures and involving greater energy consumption, activated carbons always show a smaller capacity and affinity towards the adsorption of Cr(VI) ions. After a brief review regarding Cr(VI) ion contamination and treatment, the preparation of a novel biosorbent from pyrolyzed wood char for Cr(VI) ion adsorption is described. Pyrolysis was conducted at temperatures within the range 200–350 °C, thereby helping to protect beneficial functional groups, saving energy and hence reducing costs. The influence of pH, concentration, adsorbent dosage, ionic strength and equilibration time on Cr(VI) ion adsorption by this biosorbent was investigated. It was shown that the char obtained at 200 °C possessed the highest Cr(VI) ion retention capacity (31.96 mg/g) but required the longest equilibration time (> 47 d). Coating the char with nano-scale iron oxide greatly improved its adsorption affinity towards Cr(VI) ions, with a higher adsorption affinity (Henrys law Kd = 2.988 ℓ/mg) and an enhanced Cr(VI) ion adsorption capacity (53.45 mg/g) being accomplished within a much shorter equilibration time (24 h). Spectroscopic studies confirmed that complexation of Cr(VI) ions occurred via surface hydroxy groups. The methods proposed for preparing and modifying wood char are likely to be applicable in industrial wastewater treatment.

Application of grass char for Cd(II) treatment in column leaching test

Various adsorbents as well as toxicants have been investigated regarding the adsorption behaviors and mechanisms. However, most of these reports were based on batch test. The discrepancy in adsorption behaviors between batch test and column test has been recognized recently. This study was to investigate the sorption behavior of Cd(II) in a novel adsorbent made from Reed char. Batch adsorption test and column leaching test were both conducted. Various influence factors including confining pressure, pH, velocity, concentration and ionic strength were studied. The velocity was found to have negligible effect on the breakthrough of Cd(II). The adsorption affinity was observed for the first time to decrease from a high value (R(d) = 130.00) to a negligible one (R(d) = 1.20) with increasing confining pressure from 0 to 100.00 kPa. The breakthrough of acid Cd(II) solution was earlier for solutions with less pH and higher ionic strength. The Cd(II) laden adsorbent was reclaimed by flushing chelants through the column. The recycled adsorbent appeared to be applicable in the following adsorption treatment. Suggestions were provided regarding the potential engineering applications.

Removal of Heavy Metal from Aqueous Solutions Using Chinese Loess Soil

Loess soil, a relatively abundant and inexpensive material in China, is being investigated as an adsorbent to remove heavy metals from aqueous solutions. Pb(II), Cu(II) and Zn(II) can be removed very efficiently with loess soil, and the adsorption capacity of loess soil towards those three heavy metal ions follows the order: Pb(II) (270.3 mg g-1)> Zn(II) (215.9 mg g-1)> Cu(II) (108.9 mg g-1). Factors relevant to adsorption process such as reaction time, pH and loess dosage were discussed in this paper. The clay minerals and organic matter were found to play important roles in adsorption process and the adsorption mechanism included ion exchange, surface complex and surface precipitation.

Influence of Compaction Degree on Membrane Behavior of Compacted Clay Amended with Bentonite

Bentonite has been proved to be effective to enhance the membrane behavior of pure clay for barrier performance improvement against the migration of contaminants. In this study, the membrane behavior of locally available natural Fukakusa clay, amended with 5% sodium bentonite, was evaluated. The chemico-osmotic efficiency coefficient, ω, which quantifies how much a certain soil acts as a semipermeable membrane, was obtained under different concentrations of KCl solution (0.5, 1, 5, 10 and 50 mM) and at different compaction degrees that ranged from 80% to 100%. According to the results, membrane behavior, ω continually decreased as the KCl concentration increased, which is consistent with Gouy-Chapman theory. Compaction degree was found to have a significant effect on membrane behavior, especially at 100% compaction degree conditions, by which the membrane behavior was 30% higher than that at 80% compaction degree conditions.