Adsorption of Hg(Ⅱ) from aqueous solution using thiourea functionalized chelating fiber

A fast and selective adsorbent for Hg(II) from aqueous solutions using thiourea(TU) functionalized polypropylene fiber grafted acrylic acid(PP-g-AA),PP-g-AA-TU fibers,was characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.The adsorption behavior of the functionalized chelating fibers for Hg(II) was investigated by static adsorption experiments,and the effects of some essential factors on adsorption of Hg(II) were examined,such as pH,initial concentration,adsorption time,coexisting cations,and temperature.The results showed that the adsorptive equilibrium could be achieved in 10 min,and the equilibrium adsorption quantity of PP-g-AA-TU fibers was 20 times that of PP-g-AA fibers.The PP-g-AA-TU fibers showed a very high adsorption rate and a good selectivity for Hg(II) over a wide range of p H.The adsorption isotherm can be well described with Langmuir model,with the maximum adsorption capacity for Hg(II) up to52.04 mg·g~(-1)and the removal of Hg(II) more than 97%.The kinetic data indicate that the adsorption process is best-fitted into the pseudo-second-order model.     

活性炭对苯酚的吸附研究

进行了活性炭处理含苯酚废水的应用研究,考察了影响苯酚吸附效果的因素。确定了处理水中苯酚的最佳条件:吸附平衡时间为30 min;最佳pH值为6左右;苯酚初始浓度为10 mg/L;投炭量为20～25 mg/L;苯酚的吸附率高达97.4%;温度对苯酚吸附率的影响不明显。研究了活性炭对苯酚的吸附动力学特性,分别用伪一级动力学方程、伪二级动力学方程、修正伪一级动力学方程和颗粒内扩散模型进行拟合,对于不同浓度的苯酚废水都只有伪二级动力学方程拟合程度比较高,伪二级动力学方程更为真实地反映苯酚在活性炭上的吸附机理。     

Adsorption of alcohols from aqueous solution by ZSM-5

Isotherms have been measured for the adsorption from aqueous solution of water soluble alcohols onto the zeolite ZSM-5. For methanol and ethanol the amount of alcohol adsorbed increases with increasing percentage of Al₂O₃, whereas for n-butanol the amount adsorbed decreases as the amount of Al₂O₃ increases. Adsorption of alcohols is also dependent on the cation form. For the alkali metal ion forms, the amount of alcohol adsorbed decreases as the ionic size increases, the effect being particularly pronounced for Cs⁺. Subsequent alcohol desorption was studied by thermogravimetry and mass spectrometry which showed that the zeolite retained a portion of the alcohol to temperatures (ca 250°C) sufficiently high that catalytic breakdown occurred. This reduces its likely potential for commercial alcohol concentration.     

An assessment of acid wash and bioleaching pre-treating options to remove mercury from coal

The United States Environmental Protection Agency is expected to begin regulating the release of vapor-phase mercury from coal-fired power plants in the year 2007. Chemical pre-treatment methods were investigated for mercury removal effectiveness from pulverized low-sulfur North Dakota lignite coal. More limited results were obtained for a pulverized high-sulfur Blacksville bituminous coal. A two-step acid wash treatment showed removal rates of 60-90%, compared to one-step treatments with concentrated HCl, which yielded removals of 30-38%. Removal effectiveness is similar for first step solvents of water, pH 5.0 acid, or pH 2.0 acid followed by concentrated HCl as the second step solvent, and is independent of first step incubation time. Neither of two bacterial strains, Thiobacillus ferrooxidans and T. thiooxidans, was found effective for mercury removal.     

A model for alkaline removal of sulfur from a low-rank coal

A low-rank coal cleaned by heavy-liquids separation was treated by 1 M KOH solution at room conditions for a maximum of 2 h. The desulfurization mechanism in terms of total sulfur was well described by the model of unreacted-shrinking core in a homogeneous coal particle of unchanging size during process development. The external diffusion stage might be omitted when modeling this process. A chemical reaction component was considered during diffusive flow of KOH through particle pores, too. It was possible to remove 50% of total sulfur after 2 h of treatment, although three-quarters of achieved conversion happened at first 30 min.     

An investigation of mercury distribution and speciation during coal combustion

A multi-field electrostatic precipitator (ESP) and a two-stage condensing heat exchanger (CHX^®) have been added to the pilot scale Vertical Combustion Research Facility (VCRF) in CETC-O to further research into integrated emissions control for coal fired power plants. A series of combustion trials were conducted on the VCRF with three different coals (bituminous, sub-bituminous and lignite) to study mercury distribution and speciation at various VCRF locations. Results showed that, with the bituminous coal, as the flue gas cools down from 700 to 200 °C, 80% of total mercury in the gas phase existed in oxidized form and 20% in elemental form. For sub-bituminous and lignite coals, elemental mercury was the dominant form throughout the system. Analysis of deposited ash samples showed that oxidized mercury can be absorbed on carbon-rich ash deposits, although overall only a very small percentage of total mercury was absorbed on the ash. The potential of the CHX^® at removing mercury from the flue gas was also explored. Results indicated that, using wet scrubbing, the CHX^® was able to remove 98% of oxidized mercury. Though elemental mercury went through the system unabated, it is suggested that, with appropriate agent to oxidize elemental mercury in the CHX^®, it is conceivable to use CHX^® to remove both oxidized and elemental mercury. Finally, mercury balance was performed and good mercury balance was obtained across the VCRF, validating our sampling procedures and analysis methods.     

新型复合吸附剂对NOx吸附性能的研究

为去除化工生产过程中产生的NOx废气,采用吸附能力强的天然沸石和能够与NOx发生反应的消石灰经特定工艺制成复合吸附剂.在常温常压下测定了不同空速和湿度下的吸附性能,结果显示在实验取值范围内空速越低,气体相对湿度越高,复合吸附剂对NOx的吸附效果越好.通过测定穿透曲线,得出该吸附剂对NOx的饱和吸附容量为0.18 g/g.     

Environmental chamber measurements of mercury flux from coal utilization by-products

An environmental chamber was constructed to measure the mercury flux from coal utilization by-product (CUB) samples. Samples of fly ash, FGD gypsum, and wallboard made from FGD gypsum were tested under both dark and illuminated conditions with or without the addition of water to the sample. Mercury releases varied widely, with 7-day experiment averages ranging from −6.8 to 73 ng/m² h for the fly ash samples and −5.2 to 335 ng/m² h for the FGD/wallboard samples. Initial mercury content, fly ash type, and light exposure had no observable consistent effects on the mercury flux. For the fly ash samples, the effect of a mercury control technology was to decrease the emission. For three of the four pairs of FGD gypsum and wallboard samples, the wallboard sample released less (or absorbed more) mercury than the gypsum.     

Adsorption of endocrine disrupting ethylparaben from aqueous solution by chemically activated biochar developed from oil palm fibre

The activated biochar (ABC) was prepared, characterized and examined the feasibility of removing ethylparaben (EP) from aqueous solution. The characterization results showed that ABC possessed multi-porous structure and high surface area. The adsorption isotherm was well fitted the Langmuir isotherm and the adsorption kinetic followed the pseudo-second-order model. The maximum adsorption capacity of EP onto ABC was 349.65 mg/g at 298 K. The adsorption capacity maintained 90.82% after five successive adsorption/desorption cycles. ABC possessed high adsorption capacity, usability and stability, which indicating that ABC has great potential to be a promising adsorbent for removal of EP from aqueous solution.     

Adsorption of chromium (III) ion from aqueous solution using rice hull ash

Rice hull was calcined to rice hull ash (RHA) at 500 °C under 20 mL air/s for 50 min. The RHA thus prepared has been found to be able to remove chromium (III) ion from aqueous solution, though not very efficient. The experiments indicated that the rate of removal of Cr³⁺ and the removal of Cr³⁺ at equilibrium was increased upon decreasing the RHA dosage. The removal could also be enhanced upon increasing the initial chromium concentration, or adsorption temperature. However, pH in the range of 2.5-5.4 or stroke speed higher than 120 stroke/min could not change the removal. The dependence of the RHA dosage and the initial chromium concentration on the removal have been found to be strong, while that of adsorption temperature is mild. An empirical equation correlating the relationship between the removal of Cr³⁺ and the adsorption time was determined.     

Adsorption of Cu from water using raw and modified coal fly ashes

In this study, we found that both raw and modified coal fly ashes effectively adsorb Cu²⁺ from wastewater. The adsorption capacities followed the order CFA> CFA-600> CFA-NaOH. The adsorption isotherms for Cu²⁺ on the raw and modified coal fly ashes fit the Langmuir, Freundlich, and DKR isotherms quite well. These adsorptions were endothermic in nature; the values of E (between 1.3 and 9.6 kJ mol⁻¹) were consistent with an ion-exchange adsorption mechanism. The adsorptions of Cu²⁺ onto CFA, CFA-600, and CFA-NaOH followed pseudo-second-order kinetics.     

Analysis of mercury species present during coal combustion by thermal desorption

Mercury in coal and its emissions from coal-fired boilers is a topic of primary environmental concern in the United States and Europe. The predominant forms of mercury in coal-fired flue gas are elemental (Hg⁰) and oxidized (Hg²⁺, primarily as HgCl₂). Because Hg²⁺ is more condensable and far more water soluble than Hg⁰, the wide variability in mercury speciation in coal-fired flue gases undermines the total mercury removal efficiency of most mercury emission control technologies. It is important therefore to have an understanding of the behaviour of mercury during coal combustion and the mechanisms of mercury oxidation along the flue gas path. In this study, a temperature programmed decomposition technique was applied in order to acquire an understanding of the mode of decomposition of mercury species during coal combustion. A series of mercury model compounds were used for qualitative calibration. The temperature appearance range of the main mercury species can be arranged in increasing order as HgCl₂ < HgS < HgO < HgSO₄. Different fly ashes with certified and reference values for mercury concentration were used to evaluate the method. This study has shown that the thermal decomposition test is a newly developed efficient method for identifying and quantifying mercury species from coal combustion products.     

Characteristics of coal combustion products (CCP's) from Kentucky power plants, with emphasis on mercury content

The Center for Applied Energy Research conducts a survey of Kentucky's coal-fired power plants every five years. The last survey was conducted in 2002 and covered most units at all of the plants in Kentucky. Special emphasis was placed on the spatial distribution of ash products, with each row of ESP's or baghouses samples wherever possible. In this manner, we can track the change in concentration of trace elements with relative temperature of the flue gas. Certain elements, such as Zn, Pb, and As, are known to be temperature dependent. The behavior of Hg, while also temperature dependent, is more complex owing to the adsorption of Hg on fly ash carbon. The survey provides a wide array of coal sources, ESP/baghouse collection temperatures, and fly ash carbon composition, all important in determining the behavior of Hg in the flue gas. In addition, many plants have FGD systems, allowing an assessment of the efficiency of FGD in capturing Hg from the post-ESP flue gas.     

Removal of Hg2+ from aqueous solution using a novel composite carbon adsorbent

A novel composite carbon adsorbent (GCA) has been prepared by immobilizing activated carbon and genipin‐crosslinked chitosan into calcium alginate gel beads via entrapment and applied to the removal of mercury (Hg²⁺) ions from aqueous solution (e.g., drinking water). Two bead sizes and two mixing ratios of components were obtained and characterized. Batch experiments were performed to study the uptake equilibrium and kinetics of Hg²⁺ ions by the GCA. The Hg²⁺ adsorption capacity of GCA was found to be dependent of pH and independent of size of the adsorbent. The Hg²⁺ adsorption rate of GCA increases with decreasing its bead size. However, both adsorption capacity and rate of GCA for Hg²⁺ increase with increasing its chitosan content. Otherwise, it was shown that the GCA has higher Hg²⁺ adsorption capacity and rate than activated carbon, which might be caused by the incorporation of chitosan into the GCA. The maximum Hg²⁺ adsorption capacity of GCA was found to be 576 mg/g, which is over seven times higher than that of activated carbon. Our results reveal the uniform distribution of activated carbon and chitosan within the alginate gel bead and that Hg²⁺ ions can diffuse inside the bead. It also demonstrated the feasibility of using this GCA for Hg²⁺ removal at low pH values. The Hg²⁺ absorbed beads of the GCA can be effectively regenerated and reused using H₂SO₄. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

活性碳纤维吸附水溶液中的二价铅离子

对活性碳纤维(ACF)吸附水溶液中的二价铅离子进行研究。分别运用静态和动态方法来考察ACF吸附Pb^2 的性能，测定了吸附等温线，探讨了吸附时间、DH值等因素对吸附的影响，并进行了ACF的再生实验。结果表明，ACF对水中二价铅离子的吸附特性良好，且吸附剂易于再生，可作为去除水中离子态重金属的优良吸附剂。     

Adsorption of elemental mercury vapor by impregnated activated carbon from a commercial respirator cartridge

In order to protect workers from the harmful effects of mercury vapor, adsorption technology using impregnated activated carbon is currently in use in respirator cartridges to capture mercury vapor in breathing air. Adsorption onto the activated carbon can be improved through the modification of the carbon surface by impregnation with certain reagents that enhance the bonding of mercury either physically or chemically. The first objective of this study was to characterize the chemisorption behavior of a commercial adsorbent (3M-6009) by measuring the mercury breakthrough using a bench-top apparatus. The second objective was to develop a kinetic model describing the breakthrough behavior. Dynamic breakthrough concentrations were measured using a fixed bed to study the effects of the following adsorption parameters at room temperature: air flow-rate, adsorbent amount, inlet mercury concentration, and bed diameter. A model was developed in which, the rate of irreversible chemisorption was proportional to the concentration of mercury in the airflow, and the concentration of active sites of the surface of the carbon. A model incorporating two different types of the active sites was applied in an effort to differentiate the high initial adsorption rate mediated by readily accessible open sites from the lower adsorption rate mediated by the availability of hindered sites within micro-pores. The model developed herein was superior to a traditional isotherm model for describing the chemisorption behavior of impregnated activated carbon.     

Impact of calcium chloride addition on mercury transformations and control in coal flue gas

Pilot-scale experiments were conducted to investigate mercury transformations in coal flue gas when firing subbituminous coal with a CaCl₂ additive. Cofiring the CaCl₂ additive with the subbituminous coal resulted in approximately 50% oxidized mercury, as a result of reactive chlorine species formed in coal flue gas, compared to the dominance of elemental mercury in the baseline flue gas. The mercury data indicate that mercury-flue gas chemistry reactions may occur at fairly high temperatures (>400 °C) in chlorine-enriched flue gas. Field tests were conducted to further demonstrate the impact of cofiring CaCl₂ on the eventual fate of mercury. These tests were completed on a 650-MW subbituminous coal-fired power plant equipped with selective catalytic reduction (SCR), a fabric filter (FF), and a wet scrubber. Overall mercury removals across the SCR-FF-wet scrubber system ranged from 75% to 96% with 200-800 ppm (coal basis) chlorine addition compared to 18-32% during baseline operations. Field data indicate that the SCR enhanced mercury oxidation, possibly as a result of the supplemental formation of reactive chlorine species and the aid of the SCR catalyst. As a result, most of the mercury in the flue gas was in an oxidized state and was removed in the downstream wet scrubber, indicating that cofiring CaCl₂ is an effective mercury control approach for a subbituminous coal-fired plant equipped with an SCR and wet scrubber.     

Metal sorbents for high temperature mercury capture from fuel gas

We have determined the Hg removal capacities of Pt and Pd supported on alumina at a range of different metal loadings from 2 to 9 wt% using Hg vapour in a simulated fuel gas feed. In the temperature range studied (204-388 °C) Pd proved far superior to Pt for Hg removal. The Hg removal capacity for both Pt and Pd increased with metal loading, though decreased with sorbent temperature. A shift in the 2θ position of the Pd XRD diffraction peak from 82.1 to 79.5 after Hg adsorption at 204 °C was consistent with the formation of a solid solution of Hg in Pd.     

Adsorption of glucose into zeolite beta from aqueous solution

Hydrophobic zeolites, including Ti‐ and Sn‐beta, have been found to adsorb and isomerize glucose into fructose. An experimental question has been the significance of the entropic contribution to the free energy of transfer of glucose from solution to zeolite. We here perform Gibbs ensemble Monte Carlo calculations to quantify the enthalpy, entropy, and free energy of transfer of glucose from the aqueous phase to the zeolite phase. We find that the entropic contribution is large and positive, nearly compensating for an unfavorable enthalpy of transfer in all‐silica zeolite beta. A significant component of the positive entropy of transfer from the aqueous phase to zeolite is the unstructuring of first coordination shell waters around glucose as it leaves the solution. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3523–3529, 2013     

An interpretation of flue-gas mercury speciation data from a kinetic point of view

Mercury emission from coal-fired power plants is causing great concern. Thermodynamic equilibrium calculations are commonly used for prediction of Hg speciation in the flue-gas. According to representative calculations, at temperatures below 725 K all Hg should exist in oxidized forms. However, Hg speciation measurements for flue-gas at much lower temperature showed a wide range of oxidized Hg fraction from 30 to 95%. A hypothesis that Hg equilibrium is frozen as the flue-gas cools could describe the data. However, a different interpretation of the measured results can be given based on kinetic considerations. Here, the oxidized Hg fraction is limited by the reaction rate of chlorine with elemental Hg in the flue-gas, while the differences in the degree of oxidation can largely be attributed to different time-temperature histories for the flue-gases. The residence time of flue-gas is likely to be a governing factor for the Hg speciation.