THE REACTIVITY AND DURABILITY OF ZINC FERRITE HIGH TEMPERATURE DESULFURIZATION SORBENTS

Cylindrical pellets of zinc ferrite high temperature desulfurization sorbent have been prepared using a number of formulation recipes and induration conditions. Physical and structural properties of the resultant sorbents were measured, and reactivity and durability screening tests were carried out using a single pellet electrobalance reactor. The formulation variables studied were ZnO to Fe₂O₃ ratio, Fe₂O₃ source, and the addition of inorganic (bentonite) and organic (methocel) binders to the sorbents. Pellet induration conditions ranged from 0.25 hours at 815^°C to 4.0 hours at 1038°C. Stronger pellets having greater attrition resistance resulted when 5% bentonite was added to the formulation recipe and when the pellets were indurated at high temperature for extended times. In contrast, bentonite content was not a significant factor in determining sorbent reactivity and durability, both of which were improved by mild induration conditions. Sorbent regeneration temperature was found to be an important factor in improving reaction durability, as was the addition of 0.5% methocel to the formulation recipe. Pellets containing catalyst-grade Fe₂O₃ were more reactive than those containing pigment-grade Fe₂O₃. This effect, however, was less important than the effect of induration conditions.     

Hydrothermal synthesis and spark plasma sintering of NaY zeolite as solid-state matrices for cesium-137 immobilization

Hydrothermal synthesis of NaY-type zeolite was carried out and the effect of temperature on the phase composition, crystal structure, textural characteristics, particle size and morphology, as well as sorption properties to Cs⁺ ions was studied. Solid-state matrices based on NaY zeolite the Faujasite structure containing 26.1 wt% cesium were obtained by spark plasma sintering (SPS) with high values of compressive strength (to 132.9 MPa) and Vickers microhardness to HV~ 698, Fracture toughness (K_1c) ~ 1.26 MPa m^1/2. The kinetics of ceramic matrices consolidation, phase composition and morphology using dilatometric studies, XRD, and SEM were studied. The thermogravimetric analysis shown the high thermal stability of the obtained samples up to 1300 °C. The high hydrolytic stability of CsAlSiO₄ ceramic was proven (leaching rate of 2.33 ×10^?8 g·cm^?2·day^?1 and cesium diffusion coefficient De 1.41 ×10^?13), which exceeds the requirements of GOST R 50926–96 and ISO 6961:1982 for solid-state matrices.     

Sol–gel-derived mesoporous γ-alumina granules

Synthesis of stable boehmite sols and structural properties of the sol–gel-derived γ-alumina using alkoxides, commercial boehmite powders, and aluminum chloride were studied for cost-effective preparation of high quality γ-alumina granules. Stable boehmite sols could be prepared from aluminum butoxide, aluminum isopropoxide, and commercial boehmite powders but not from aluminum chloride. The stable sol-derived γ-alumina has large surface area and nanopore size with uniform pore size distributions. Mesoporous spherical γ-alumina granules were prepared by an oil-drop process from aluminum butoxide, aluminum isopropoxide and a commercial boehmite powder under specific conditions. The sol–gel-derived γ-alumina granules are better than the commercial γ-alumina granules in terms of the pore structure and mechanical strength. The successful synthesis of γ-alumina granules by the sol–gel method from the commercial boehmite powder provides a basis for large-scale, cost-effective production of the high quality γ-alumina granules for use as sorbents or catalysts in industrial processes.     

SURFACE AREA FORMATION IN DRY FGD SORBENTS

Dry flue gas desulfurization (DFGD) technologies are being developed which require sorbents with high specific surface areas capable of large sulfur dioxide uptake. Specifically, novel methods of controlling S0₂ in a fiuidized bed absorber are being studied which will have the capability of isothermal operation at optimum temperature for S0₂ uptake with alkaline sorbents. This paper reports on a study of surface area development with respect to time for three sorbent materials (pure calcium carbonate, dolomitic limestone and pressure hydrated dolomitic limestone) undergoing thermal decomposition in the temperature range of 600-850°C (1100-1550°F). Two of these sorbents (calcium carbonate and dolomitic limestone) confirm observations made by others of a lag time between recrystalization of the product from the reactant and the development of the maximum surface area. A model is presented which predicts the surface area development by accounting for the surface area generated by thermal decomposition and the surface area lost due to sintering. The parameters necessary for the model were obtained from the experimental data. The ability of the model to predict the surface area change with respect to time is shown to be good for the conditions tested.     

New Sorbents for Metal Salts based on Cation Exchange Extractants and Anion Exchange Resins: Their Preparation and Properties

Preparation and properties of binary sorbents containing a salt of cation exchange organic extractant in the matrix of a strongly basic anion exchanger were studied. Analysis of isotherms of exchange of chloride ions for dialkyldithiophosphate ions in the systems of various anion exchangers led to the conclusion that the stability of the binary sorbents depends on the amount of free water in the sorbent matrix. To improve the stability, it was proposed to use low cross-linked anion exchange resins or to use cation exchange extractants of moderate molecular volume. On the example of anion exchanger ММ-22x6.5 in the dibutyldithiophosphate form, it was shown that the binary sorbents efficiently recover chlorides of non-ferrous metals. The recovery increases in the series Ca²⁺<<Ni²⁺<Zn²⁺<<Cu²⁺. Because, in the systems studied, the anions are recovered together with cations, this leads to an increase in metal recovery in the presence of salting-out agents, and allows the desorbtion of the salts with water or with solutions of complexing agents. The binary sorbents offer good prospects for the recovery and separation of metal salts.     

Abatement of Gas-Phase Mercury—Recent Developments

Among various pollutants, mercury has a significant impact on the environment, human beings, and wildlife with its different forms, namely, elemental mercury (Hg⁰), oxidized mercury (Hg²⁺), and particle-bound mercury (Hg_p). Mercury dispersions mainly occur from coal burning, which is the world's major energy source. Among the three forms, Hg²⁺ and Hg_p are relatively easy to remove from the flue gas by employing typical air pollution control devices; on the other hand, Hg⁰ is difficult to remove. Various methods are available to detain elemental mercury. Recent developments in mercury removal options, especially during the last years, are reviewed. Main concentration has been focused on the removal methods of elemental mercury by novel sorbents and catalytic systems. A current challenge is to develop novel nanomaterials meeting rigorous requirements (easy separation, recyclability, and cost-effectiveness) for eventual exploitation.     

Mercury control testing in a pulverized lignite-fired system

The Energy & Environmental Research Center (EERC) is evaluating and developing advanced and innovative concepts for controlling Hg emissions from North Dakota lignite-fired power plants with the goal of achieving 50%–90% Hg removal at one-half to three-fourths the current estimated costs. Pilot-scale tests were performed to evaluate potential sorbents and fuel additives for removing Hg from North Dakota lignite (Freedom and Center Mines) combustion flue gases. The Hg sorbents and Hg⁰ oxidation and sorbent enhancement additives were evaluated separately, and most were also tested in combination. A 580 MJ/h (550,000 Btu/h) pulverized coal combustion system was used to conduct sorbent injections and/or lignite additive additions upstream of three particulate control devices (PCDs): 1) an electrostatic precipitator (ESP), 2) a spray dryer and fabric filter, and 3) a retrofit advanced hybrid particulate collector (AHPC) filter (an ESP followed by an AHPC filter). ASTM International Method D6784-02 (Ontario Hydro method) and continuous Hg monitors were used to measure Hg species concentrations across the control devices. The effects of sorbent injection and coal additive addition rates on Hg removal were evaluated for each PCD option. The effects of continuous injection and batch addition of sorbents on the Hg removal performance of the ESP/AHPC filter system were also investigated. Increasing injection and additive rates and improving contact between the sorbents and flue gases generally promoted Hg capture. Most of the coal additives tested significantly enhanced PCD Hg removal, especially in the presence of a sorbent.     

Hydrothermal synthesis of zeolites from coal fly ash

The fly ash, from the combustion of coal to produce energy and heat, is an industrial waste, in which large accumulations represent a serious environmental threat. To reduce the environmental burden and improve the economic benefits of energy production, the science and industry focus on the transformation of coal combustion byproducts into new functional materials. The fly ash was studied by modern analytical methods. As a result of the hydrothermal reaction, several types of zeolites were synthesised from the fly ash: analcime, faujasite (zeolite X) and gismondine (zeolite P). It was shown that the experimental conditions (temperature, reaction time and alkali concentration) have a significant influence on the type of zeolite and its content in the reaction products. The series of experiments resulted in building approximate crystallisation field of zeolites and other phases as the first stage of the formation of ceramic membrane and other materials.     

纳米磁吸附技术在工业废水处理中的应用研究

纳米磁吸附是 2 0世纪 90年代国外用于处理工业废水的一种新技术。我们利用白俄罗斯研制的新的纳米磁吸附剂 ,通过实验表明 ,在处理工业废水时 ,该纳米磁吸附剂对重金属离子的去除率可达 99 5 % ,具有固液分离速度快、能再生重复使用多次、操作简单等显著的特点。根据工业废水的具体情况 ,纳米磁吸附技术可以单独使用也可与其他方法相结合联合使用 ,发挥其联合法的综合作用。纳米磁吸附剂应用于工业废水处理中将有光明的前景     

Effectiveness and mechanisms of high-temperature lead capture by various Aluminum-Silicate minerals

The relative effectiveness of seven inorganic sorbents for the capture of gaseous lead chloride was investigated by using a high-temperature packed bed sorption reactor. The investigated sorbents were alumina, bauxite, andalusite, chamotte, kaolin, pyrophyllite and silica. Except for alumina, all other tested sorbents showed good potential for the capture of lead chloride, since they were good for limiting leachability of captured lead species. Combining the two sorbent criteria of increased metal uptake on sorption and reduced leachability by the toxicity characteristic leaching procedure (TCLP), kaolin and pyrophyllite appeared to be the most-promising sorbents for lead capture. From the analysis of post-sorption sorbent samples, three different capturing mechanisms for lead capture by high-temperature inorganic sorbents were suggested: 1) chemical reaction to form water-insoluble lead-mineral complexes such as PbO· Al₂O_3.2SiO₂, 2) physical adsorption of gaseous chloride to form water-soluble lead chloride (PbCl₂), and 3) formation of water-insoluble lead oxide (PbO) on sorbent surface. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.