The reactions between mercury ions and silver: dissolution and displacements

The results of polarization measurements for the reduction of mercury (I) and mercury (II) on a rotating platinum electrode, and the oxidation of silver and amalgamated silver at a rotating silver electrode are presented. For mercury (I) and mercury (II) diffusion coefficients were estimated from limiting current measurements as a function of rotation speed and temperature. The Values obtained for the diffusion coefficients at 25°C, and activation energies were:

The kinetics of the reactions between a rotating silver disc and solutions of mercury (I) and mercury (II) are also reported. The mercury (I) reaction is a displacement in which mercury is deposited and silver goes into solution. The kinetics are first order-first order reversible, and can be quantitatively accounted for by assuming that the diffusion of mercury (I) to the surface and silver (I) away from the surface are jointly rate controlling. At temperatures below 35°C, the mercury (II) reaction is a dissolution, controlled by the speed at which mercury (II) ions diffuse to the reacting surface. Above 35°C, the mercury (II)-silver reaction is a displacement, with somewhat irreproducible kinetics. The changeover between the two reactions at 35°C apparently occurs because the displacement reaction is thermodynamically favoured above 35°C.     

A new type of organic electrosynthesis reactor with a two-phase gas-electrolyte stream flowing through a mercury cathode,II. Limiting currents and mass-transfer studies in organotin electrosynthesis

A new electrochemical reactor involving a mercury cathode and a two-phase (gas-liquid) flow has been studied with a view to continuously manufacturing hexaphenyl and hexabutyldistannane b'y reduction of triorganotin chloride R₃SnCl. In each case the interpretation of the determining step of the process is discussed after a study of the electrochemical kinetics. In the reactor an efficient renewal of the cathodic surface is obtained by passing the electrolysis solution together with nitrogen gas through the mercury pool. Results of mass transfer rate studies with the cell working either as a plug-flow reactor or as a continuously stirred reactor are compared for different gas and electrolyte flows. The experiments show that gas and electrolyte flows through a mercury pool offer attractive possibilities of application for large-scale preparative electrolysis, by solving simultaneously the problems of mass transport and electrode surface renewal.     

Mercury(II) removal from aqueous solutions by adsorption on multi-walled carbon nanotubes

Our aim was to test how MWCNTs can be used as a new adsorbent for mercury(II). Multi-walled carbon nanotubes (MWCNTs) have been used for removal of mercury from aqueous solutions. Mercury removal from aqueous solutions by batch adsorption was investigated. Equilibrium isotherms, such as Freundlich, Langmuir, Temkin, Harkins-Jura, were tested. Kinetic studies based on Lagergren first-order, pseudo-second-order and Elovich rate expressions were done. The batch experiments were conducted at three different temperatures (17, 27 and 37 °C) and different pHs of the initial solution. Error function analysis shows that mercury(II) removal obeys pseudo-second order kinetics and Freundlich isotherm equation. Finally, the effects of solution pH and temperature on the adsorption were studied.     

Mercury removal from coal combustion by Fenton reactions. Paper B: Pilot-scale tests

This second paper in a series describes results of pilot-scale testing for mercury (Hg) removal from coal combustion flue gas using a scrubbing solution based on the Fenton reactions. The selected reagents contain hydrogen peroxide and iron salts. The mercury scrubbing was performed in a condensing heat exchanger (CHX) with flue gas generated by coal combustion in CANMET’s vertical combustor research facility (VCRF). Both the Ontario Hydro method and a Hg CEM were used for Hg sampling and speciation. The results, obtained with the combustion of three different pulverized coals – bituminous, sub-bituminous and lignite – showed that the CHX was very effective in removing oxidized mercury (Hg(II)). Concerning the performance of the scrubbing solutions, 30–40% of elemental mercury (Hg(0)) oxidation was achieved for the lignite coal, with the solution being preferably composed of FeCl₃ and H₂O₂ and with pH value between 1 and 3. Results also showed that better Hg removal results were achieved by combining sulphur removal and Hg removal in the same stage of the CHX. An additional test done on the pilot-scale research boiler with a conventional wet scrubber showed that the Hg removal capability using the Fenton reactions was not dependent on the configuration of the wet scrubber. Although the Hg(0) oxidation ratio was not particularly high compared to the achievements from bench-scale tests, considering the economic and non-toxic nature of the scrubbing solution and the readily available equipment, the current results are encouraging and deserve further work to develop a better understanding of the chemistry in order to determine if the method can be further optimized.     

The PCO process for photochemical removal of mercury from flue gas

A promising technology has been developed to capture and remove elemental mercury species from coal-fired power plants. Powerspan Corp. has licensed the technology and initiated a bench and pilot test program to develop the Photochemical Oxidation, or PCO™, process for commercial application with subbituminous and lignite fuels.The process has the potential to serve as a low cost mercury oxidation technology that will facilitate elemental mercury removal in a downstream SO₂ scrubber, wet electrostatic precipitator (WESP), or baghouse. It uses 254-nm (nanometer) ultraviolet light from a mercury lamp to produce an excited state mercury species in the flue gas, leading to oxidation of elemental mercury. This paper presents results of Powerspan's initial bench-scale testing on a simulated flue gas stream. Preliminary testing conducted in Powerspan's bench-scale facility showed greater than 90% oxidation and removal of elemental mercury. The process also has potential to serve as a low cost method for the removal of mercury from waste incinerator flue gases.     

The PCO process for photochemical removal of mercury from flue gas

A promising technology has been developed to capture and remove elemental mercury species from coal-fired power plants. Powerspan Corp. has licensed the technology and initiated a bench and pilot test program to develop the Photochemical Oxidation, or PCO™, process for commercial application with subbituminous and lignite fuels.The process has the potential to serve as a low cost mercury oxidation technology that will facilitate elemental mercury removal in a downstream SO₂ scrubber, wet electrostatic precipitator (WESP), or baghouse. It uses 254-nm (nanometer) ultraviolet light from a mercury lamp to produce an excited state mercury species in the flue gas, leading to oxidation of elemental mercury. This paper presents results of Powerspan's initial bench-scale testing on a simulated flue gas stream. Preliminary testing conducted in Powerspan's bench-scale facility showed greater than 90% oxidation and removal of elemental mercury. The process also has potential to serve as a low cost method for the removal of mercury from waste incinerator flue gases.     

Adsorption of Copper Ion with Metal Hydroxide from Ammonia Solution

Abstract

The removal of copper(II) from ammonia solution by adsorption on iron (III), aluminum(III), and tin(IV) hydroxide is studied. The effects of experimental parameters such as solution pH and concentration of total ammonia on adsorption are examined both from the change of solution composition and electrical properties of the solid surface. In a moderately high electrolyte concentration, an optimum solution pH is found for the solution composition when the sum of the species fractions of Cu(NH₃)²⁺, Cu(NH₃)₂ ²⁺, and Cu(NH₃)₃ ²⁺ reaches its maximum. The ligand number of aminecopper(II) of the solution is near 2.0 under this optimum condition. The decrease in adsorption in the more basic tetraamminecopper(II) solution is attributed to the competing reaction for copper(II) by the free ammonia in the solution. Adsorption isotherms at various concentrations of total ammonia show decreasing adsorption with high electrolyte concentration as a result of a highly positively charged surface and a reduction of available surface sites. The relative extent of adsorption is discussed for various experimental conditions based on the data and the surface complexation concept.     

Evaluation of mercury sorbents in a lab-scale multiphase flow reactor, a pilot-scale slipstream reactor and full-scale power plant

Due to its adverse effects on human health and ecosystem, mercury emission from the coal-fired utility boiler has been generating more and more concern. Sorbent injection upstream of the electrostatic precipitator (ESP) or bag-house has been deemed one of the recommended mature technologies to reduce mercury emission. Before a sorbent is used in practice, its mercury capture ability needs to be evaluated, but has until recently only been demonstrated in bench-, pilot- or full-scale experiments separately. In this paper, a lab-scale multiphase flow reactor and a pilot-scale slipstream reactor were set up and conducted such evaluation on the two scales. After that, some kinds of sorbents were injected at a full-scale power station. The experimental results show that the lab- and pilot-scale reactor systems in this paper can provide accurate information of sorbent evaluation under flue gas atmosphere. There was significant difference between the mercury removal efficiency of tested sorbents, varying from 98.3% down to 23%. SO₂ in the flue gas was shown to inhibit mercury oxidization and capture. The sorbents have higher mercury capturing efficiency with higher injection rate and longer residence time when other conditions were held constant. In the pilot-scale, four injection ports vertical to the flue gas flow direction could help improve mixture of sorbent and flue gas so that the mercury removal efficiency became higher. The pilot-scale data can be used to predict the full-scale results. Some of the chemical and physical mechanisms responsible for the mercury removal of the sorbents were identified.     

CO2在四丁基高氯酸铵-碳酸丙烯酯溶液中的电催化还原

设计了一种新型双室电解池,以四丁基高氯酸铵(TBAP)-碳酸丙烯酯(PC)溶液为阴极电解液,高效稳定地将CO2转化为CO. 结果表明,TBAP-PC溶液的电化学窗口达-2.48 V (vs. I-/I3-), CO2可在其中发生电还原反应;阴极电流密度稳定在7.4 mA/cm2,阴极气相产物主要为CO,生成CO的电流效率最高约为93%;由于阴极电解液中含残留水,阴极表面有氢气析出,电流效率约为5%;金电极表面无吸附物,电极未失活.     

UV/H_2O_2高级氧化工艺脱汞试验研究

烟气中的汞污染是燃煤电厂污染源之一,将烟气中的Hg~0氧化脱除是脱汞的重要思路。采用光化学鼓泡反应器研究UV/H_2O_2高级氧化工艺脱汞过程,结果表明,增加UV的功率可以提高Hg~0去除率;随着H_2O_2浓度提高,Hg~0去除率先上升后趋于下降;随着Hg~0初始浓度提高,Hg~0去除率呈下降趋势;而Hg~0去除率与溶液体积成正比。该UV/H_2O_2高级氧化工艺可为燃煤电厂烟气脱汞提供新思路。     

金属硫化物吸附剂脱除烟气汞研究进展

工业烟气排放的汞严重危害人体健康及生态环境,金属硫化物是一种新型的高效汞吸附剂,受到广泛关注。本文总结了近年来金属硫化物应用于脱除烟气汞的研究进展。归纳了不同金属硫化物的吸附性能,并对影响吸附性能的常见因素进行了梳理,已有研究表明金属硫化物在复杂的反应条件下仍具有优异的脱汞性能;进一步归纳了金属硫化物的汞吸附机理;总结出活性位和比表面积的调控是当前强化金属硫化物汞吸附性能的常见方法;最后对金属硫化物的再生方法进行了介绍。基于当前研究进展,未来的研究应关注如何强化金属硫化物在高温下的脱汞性能,以及如何在低温条件下实现汞的脱附从而避免当前高温热脱附方法对金属硫化物结构的破坏。     

溴元素改性椰壳活性炭对实际燃煤烟气的脱汞性能

以椰壳活性炭（YAC）为原料,通过NH₄Br溶液浸渍改性,制备了溴素改性椰壳活性炭脱汞吸附剂（YAC-Br）。在固定床实验台上开展了YAC和YAC-Br的汞脱除实验,主要研究了入口汞（Hg⁰）浓度对YAC-Br脱汞性能的影响,并结合BET、SEM、XRF等表征手段分析了YAC-Br的脱汞原理。在0.3MW燃煤循环流化床锅炉上对YAC-Br进行了烟气管道喷射吸附剂脱汞（ACI）实验,验证了其在实际燃煤烟气中对汞的脱除效果。结果表明：改性过程不会破坏椰壳活性炭原有的孔隙结构和微孔容积,而会使活性炭表面更加平整;化学改性后活性炭表面Br负载量提高,成为Hg⁰的主要活性吸附位。固定床实验结果说明：改性后椰壳活性炭的初始汞吸附效率和单位累积汞吸附量分别提高了6.02倍和21.8倍,吸附效率随汞浓度增大而降低。0.3MW燃煤循环流化床实验结果表明：改性后椰壳活性炭对元素汞和氧化汞均有很好的脱除作用,脱汞效率随着吸附剂喷射量的增加而增加,当喷射量为0.7kg/h时,脱汞效率可达到76.38%。     

The electrochemical behaviour of 2,2'-(bishydroxylamino)diphensulphide

2,2'-Dinitrodiphenylsulphide(I) is reduced at mercury and non-mercury electrodes to 2,2'- (bishydroxylamino)diphenylsulphide(II) which can undergo further electrochemical and chemical reactions depending on potential and on the pH value of the solution. The electrochemical behaviour of II is described in detail. The chemical follow-up reactions of II in strongly acidic and in alkaline solutions may be applied in simple ellectrochemical preparations of the cyclic azoxy derative IV and of the cyclic azo derative III in good yield. Dibenzo(b,f)-(1,4,5)-thiadiazepine(III) and its N-oxide(IV) result in an electrolytically intact solution if the solution is made alkaline. A preparative electrolytic cell with mercury, solid metal and graphite working electrodes is described in detail.     

污水处理厂污泥制备吸附剂对燃煤烟气中汞的吸附性能研究

以城市污染处理厂的活性污泥作为原料,采用不同的活化方式处理制备出环境友好的吸附剂,可供燃煤电厂烟气中除汞.污泥活化后收率在40%～55%之间,物理活化后收率随活化温度的升高而降低,比表面积、孔隙量和吸汞量随活化温度的升高而逐渐增大,但吸汞量随温度升高而急剧下降,说明物理活化的吸附剂主要以物理吸附的方式除汞;经化学活化处理的吸附剂性能好、收率高,比表面积、空隙率和吸汞量显著增加,且除汞效率受温度影响较小,除汞效率高.淋滤实验结果验证了活化处理后的吸附剂对汞具有较高的吸附稳定性,没有二次污染.     

The recovery and recycling of mercury from fluorescent lamps using photocatalytic techniques

BACKGROUND: Release of mercury from fluorescent lamps must be minimized to avoid its hazardous effects on human beings and other living organisms. Because of this, increasing attention is given to the improvement of existing techniques for its recovery as well as the development of new ones. This paper describes the application of heterogeneous photocatalysis for the selective reduction of mercury from fluorescent lamps. The whole process involves mercury chemical extraction using aqueous solutions of sodium hypochlorite. After pH adjustment of the resulting aqueous solution, the photocatalytic reduction of mercury is performed in the presence of titanium dioxide and citric acid as an auxiliary organic agent. RESULTS: Mercury removal from the aqueous solution is higher than 99% and the final residual concentration is 4 ppb. A mixture of different mercury compounds is obtained in solid form deposited on the titanium oxide photocatalyst which can easily be redissolved into a small volume of sodium hypochlorite. Metallic mercury could be obtained from the residual Hg(II) solution by conventional cementation techniques with iron as reducing agent. CONCLUSION: Results show high efficiencies of the photocatalytic technique for recovery and recycling of mercury from fluorescent lamps. Copyright © 2009 Society of Chemical Industry     

褐煤活性焦烟气脱汞的实验研究

燃煤电厂汞污染越来越受到关注,目前具有应用前景的脱汞方法为吸附脱汞,因此研发高效低成本的脱汞吸附剂被广泛研究。在搭建的固定床吸附反应系统上对自制的褐煤活性焦脱汞性能进行了实验研究,研究了汞污染物的入口浓度,吸附剂的量、烟气成分及吸附剂的种类对吸附汞的影响。结果表明:活性焦吸附剂对烟气中的气态汞均有一定的吸附能力,其吸附效果随着入口汞浓度和吸附剂量的增加而增加;烟气中的SO2、NO气体对活性焦吸附汞有一定的促进作用。活性焦脱汞效率与载硫活性炭、脱汞专用活性炭相比还存在一定差距,但可通过改进活性焦的活化方式提高脱汞性能。     

Role of mass transfer on hydrogen evolution in aqueous media

The process of hydrogen evolution during alkaline electrolysis of aqueous solutions is governed by mass transfer, growth of hydrogen bubbles and removal of hydrogen from the cathode. Two mechanisms are decisive for hydrogen removal: (i) hydrogen dissolved in the solution is carried off from the cathode surface by diffusion and convection, and (ii) gas bubbles are transported by a two- phase flow. The paper describes experiments to determine the local concentration of dissolved hydrogen and the void fraction of hydrogen bubbles in aqueous solutions. Measurements were performed in a flow channel by varying the height of the cathode (40–400mm), the current density (up to 6250Am–2) and the mean velocity of the electrolyte (up to 0.95 m s–1). Two operating regimes of the electrolyser are found. At high current densities a back flow is observed leading to an increase in the electrolyte resistance. Traces of dissolved oxygen are detected at high current densities. At low current densities the two-phase flow is confined to a thin layer along the cathode surface, the concentration of dissolved hydrogen being small.     

Electrochemical Separation of Hydrogen Sulfide from Natural Gas

Abstract

An electrochemical process has been developed for the removal of H₂S from contaminated natural gas. Removals as high as 80.7% have been achieved from a simulated process gas (2000 ppm H₂S). H₂S is removed by reduction to the sulfide ion and hydrogen gas at the cathode. The sulfide ion migrates to the anode through a molten electrolyte suspended in an inert ceramic matrix. Once at the anode it is oxidized to elemental sulfur and swept away for condensation in an inert gas stream. No materials are required beyond initial electrolyte membrane installation; the H₂S is converted in one step to elemental sulfur making it an economically attractive process both from the lack of raw materials and the lack of any solvent regeneration.     

Role of mass transfer on hydrogen evolution in aqueous media

The process of hydrogen evolution during alkaline electrolysis of aqueous solutions is governed by mass transfer, growth of hydrogen bubbles and removal of hydrogen from the cathode. Two mechanisms are decisive for hydrogen removal: (i) hydrogen dissolved in the solution is carried off from the cathode surface by diffusion and convection, and (ii) gas bubbles are transported by a two- phase flow. The paper describes experiments to determine the local concentration of dissolved hydrogen and the void fraction of hydrogen bubbles in aqueous solutions. Measurements were performed in a flow channel by varying the height of the cathode (40–400mm), the current density (up to 6250Am?2) and the mean velocity of the electrolyte (up to 0.95 m s?1). Two operating regimes of the electrolyser are found. At high current densities a back flow is observed leading to an increase in the electrolyte resistance. Traces of dissolved oxygen are detected at high current densities. At low current densities the two-phase flow is confined to a thin layer along the cathode surface, the concentration of dissolved hydrogen being small.     

Effect of the oxidation of activated carbon by hydrogen peroxide on its catalytic activity in the regeneration of Co(II)TETA

Cobalt(II) triethylenetetramine (Co(II)TETA) formed by soluble cobalt(II) salt combining with triethylenetetramine will be used as a wet denitration technique since it can interact with nitric oxide to accomplish quick absorption of NO from gas phase. However, the oxygen in the flue gas will oxidize Co(II)TETA to Co(III) TETA, resulting in the reduction of denitrification efficiency. Activated carbon has been used to promote the regeneration of Co(II)TETA due to its unique surface characteristics. Hydrogen peroxide solution is utilized as a modifier in the carbon modification to improve the catalytic performance of activated carbon. The experiments demonstrate that the best regeneration efficiency of Co(II)TETA is gained by the modified carbon impregnated in 0.05 mol L⁻¹ H₂O₂ solution at 70°C for 12 h with a solid/liquid ratio of 1/50 (g/mL) followed being activated at 400°C for 2 h in N₂. After being treated with hydrogen oxide solution, the surface area and acidity of the carbon is increased. Continuous experiments reveal that the NO removal efficiency gained by modified activated carbon is about 8.36% higher than that gained by the original carbon.