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Taylor, Orlando C. (Orlando Clearchus). "In-situ reduction of hexavalent chromium by electroremediation with ferrous iron." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10260.
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CORREIA, THIAGO OLIVEIRA FERREIRA. "SYNTHESIS OF NANOSTRUCTURED FE0-NI0/SIO2 PARTICLES FOR THE REDUCTION OF HEXAVALENT CHROMIUM TO TRIVALENT CHROMIUM." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36037@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
No presente trabalho, foram abordadas duas formas alternativas de materiais para a redução do cromo hexavalente. Para um dos materiais foram sintetizadas nanopartículas de ferro metálico, níquel metálico e sílica como suporte, e o outro material visando menor custo e maior acessibilidade foi uma lã de aço comercial. Ambos têm como objetivo a diminuição ou remediação de cromo hexavalente através de soluções de dicromato de potássio em concentrações que visam simular contaminações geradas por diversas operações industriais. A função destes materiais é de atuar como um forte agente redutor, doando elétrons para reduzir o cromo hexavalente em cromo trivalente. As nanopartículas de ferro zero valente, níquel zero valente suportadas em sílica foram sintetizadas empregando sulfatos em uma técnica de redução com borohidreto de potássio em solução aquosa. As nanopartículas foram caracterizadas com o auxílio da técnica de difração de raio-X para determinar as fases presentes, e de microscopia eletrônica de varredura com espectroscopia por dispersão de energia, definindo a composição química elementar e a morfologia das superfícies, e ICP para quantificar a composição dos elementos ferro e níquel. Finalmente, foram realizados os testes de redução do cromo hexavalente em cromo trivalente através do Espectrofotômetro UV-VIS, sendo quantificada a concentração de cromo hexavalente presente na solução através da técnica colorimétrica com o reagente altamente seletivo, o 1,5-difenilcarbazida (DFC). As nanopartículas e a lã de aço demonstraram eficiência na redução do cromo hexavalente em concentrações de 8,32 ppm (K2Cr2O7 80 Mmol/L), 6,241 (K2Cr2O7 60 Mmol/L) e 4,161 ppm (K2Cr2O7 40 Mmol/L) com tempos inferiores a 5 minutos. Contudo, as nanopartículas de Fe0-Ni0 suportadas em SiO2 reduziram o cromo hexavalente com uma quantidade em massa de Fe0 aproximadamente 110 vezes menor em relação a lã de aço, considerando que este é constituído unicamente por ferro metálico. Credita-se esta efetividade à maior área superficial por unidade de massa das partículas nanoestruturadas.
In the present work, two alternative forms were approached using different materials. For one of the materials, nanoparticles of metallic iron, metallic nickel and silica as support were synthesized, and the other material aiming at lower cost and greater accessibility will be steel wool. Both have the objective of reducing or remediation of hexavalent chromium through solutions of potassium dichromate in concentrations that aim to simulate contaminations generated by various industrial operations. The function of these materials is to act as a strong reducing agent by donating electrons to reduce the hexavalent chromium to trivalent chromium. The nanoparticles of zero-valent Iron, zero-valent nickel supported on silica was synthesized using sulfates in a reduction technique with potassium borohydride in aqueous solution. The nanoparticles were characterized with the help of the XRD technique, from the diffraction pattern generated and quantifying the present phases, and SEM / EDS, defining elemental chemical composition and surface morphology and ICP to quantify the elemental composition. Finally, the tests of reduction of the hexavalent chromium in trivalent chromium through the UV-VIS spectrophotometer were carried out, and the concentration of hexavalent Chromium present in the solution was quantified through the Colorimetric technique with the highly selective reagent, 1,5-diphenylcarbazide (DFC). Nanoparticles and steel wool showed efficiency in the reduction of hexavalent chromium at concentrations of 8,32 ppm (K2Cr2O7 80 Mmol/L), 6,241 (K2Cr2O7 60 Mmol/L) e 4,161 ppm (K2Cr2O7 40 Mmol/L) with times less than 5 minutes. However, as Fe0-Ni0 nanoparticles supported in SiO2, they reduced the hexavalent content of a quantity of steel mass in relation to steel wool, considering that it consists only of metallic iron. The effectiveness in the most superficial part by the mass unit of the nanostructured particles is credited.
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Ng, Nai Hong 1979. "Investigation of the role of electron mediators and siderophores on the concurrect biodegradation of naphthalene and reduction of hexavalent chromium." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82623.
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The concurrent biodegradation of polycyclic aromatic hydrocarbons (PAHs) and transformation of heavy metals by redox reactions has been demonstrated by several studies. The mechanisms and reactions that result in heavy metal transformation in such systems is, however, poorly understood. This study explored the role of metabolic intermediates, metabolic end-products, and microbial chelators generated by a PAH-degrading microorganism, Pseudomonas putida ATCC 17484, in reducing or transforming Cr(VI). This study investigates the role of 1,2-naphthoquinone to serve as potential redox mediators in the reduction of Cr(VI) to Cr(III). Laboratory experiments were conducted to evaluate the extent of Cr(VI) reduction in the presence of various concentrations of the naphthalene biodegradation by-product 1,2-naphthoquinone, and the metabolic intermediate 1,2-dihydroxynaphthalene. Rapid, but limited reduction of Cr(VI) was observed in the presence of 1,2-dihydroxynaphthalene. The effect of siderophore Desferrioxamine B (DFB), a common chelator produced by the soil microorganisms, on the biodegradation of naphthalene was also investigated. Synthesized DFB was added directly into the test systems, and resulted in instantaneous binding to chromium (VI). The chelated complex remained stable for a period of 4 days even when subjected to acidic conditions.
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Franco, Debora Vilela. "Tratamento redutivo de solo e agua subterranea contaminados com cromo hexavalente." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249653.
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Orientador: Wilson de Figueiredo JardimTese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
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Resumo: A redução química do cromo hexavalente, Cr(VI), presente em solo e água subterrânea contaminados, foi investigada empregando-se diferentes agentes redutores (batelada e semi-batelada) para avaliar a extensão da redução do Cr(VI) e da imobilização (precipitação) do cromo trivalente, Cr(III). O estudo comparativo envolvendo o uso de diferentes agentes redutores evidenciou que as espécies Fe(II) e FZVcol (nanopartículas estabilizadas com carboximetilcelulose) apresentaram os resultados mais promissores para a remoção do Cr(VI), visto que houve uma redução quantitativa desta espécie com sua concomitante imobilização. A aplicação do Fe(II) e FZVcol nas razões molares 1[Cr(VI)]:20[Fe(II)] e 1[Cr(VI)]:4[FZVcol] resultou na conversão redox superior a 98% e na imobilização das frações de Cr(VI) lábil e trocável. Foi verificado para o Fe(II), que o aumento da velocidade do fluxo volumétrico (G) resulta na diminuição do número de volume de poro para o tratamento do solo e da quantidade de Cr(VI) residual. O estudo hidrodinâmico teórico da coluna recheada com solo (meio poroso) permitiu mensurar o grau de dispersão do redutor na coluna frente ao modelo pistonado de escoamento em função de G mediante o cálculo do coeficiente de dispersão mássica volumétrico (kDV), o qual foi calculado a partir da modelagem da curva de saturação experimental. Foi verificado em todos os casos que a cinética do processo redox Cr(VI)/Cr(III) segue uma lei empírica de velocidade de pseudo-primeira ordem. A complexidade cinética do processo redox foi evidenciada pela dependência da constante de velocidade global de pseudo-primeira ordem (k*) com o tempo de reação, G e a concentração inicial do redutor. Um modelo cinético fenomenológico foi proposto para se obter uma expressão representativa de k* nas diferentes situações experimentais investigadas, bem como nos casos limites previstos. Um esquema reacional global foi proposto para representar os diferentes processos elementares envolvendo as espécies Cr(VI) e Cr(III) na matriz porosa (solo/água subterrânea). Um ensaio de tratamento em escala piloto foi realizado in situ tendo-se como balizadora as condições experimentais mais promissoras obtidas nos estudos realizados em escala laboratorial
Abstract: Chemical reduction of the hexavalent chromium, Cr(VI), present in contaminated soil and groundwater was investigated using several different reductants (batch and semi-batch) in order to evaluate the extension of Cr(VI) reduction and the immobilization (precipitation) of trivalent chromium, Cr(III). A comparative study concerning the use of different reductants revealed that Fe(II) and ZVIcol (nanoparticles stabilized with carboximethylcellulose) present the most promising findings for the Cr(VI) removal, since it was found that a quantitative reduction of this specie is accompanied by its immobilization. Application of Fe(II) and ZVIcol using the 1[Cr(VI)]:20[Fe(II)] and 1[Cr(VI)]:4[ZVIcol] molar ratios resulted in a redox conversion degree higher than 98% and in the immobilization of the labile and the exchangeable Cr(VI) fractions. It was verified for Fe(II) that increasing the volumetric flow rate (G) both the pore volume necessary for the redox treatment and the residual Cr(VI) decrease. The theoretical hydrodynamic study concerning the packed column reactor containing soil (porous medium) permitted to evaluate the reductant dispersion degree inside the column in relation to the plug-flow model as functions of G by measuring the volumetric mass dispersion coefficient (kVD), which was calculated from simulation of the experimental saturation curve. In all cases, it was found the kinetics of the Cr(VI)/Cr(III) redox process follows a pseudo-first order rate law. The complexicity concerning the kinetic process was evidenced by the dependence of the overall pseudo-first order kinetic rate constant (k*) on reaction time, G and the initial concentration of the reductant. A phenomenological kinetic model was proposed in order to obtain a relation capable to represent k* for the different experimental conditions investigated, as well for the possible limit cases. An overall reaction scheme was proposed in order to describe the different elementary processes concerning the Cr(VI) and Cr(III) species, which take place inside the porous soil matrix (soil/groundwater). A pilot scale test was carried out in situ taking into account the best experimental scenario obtained in laboratory.
Doutorado
Quimica Analitica
Doutor em Ciencias Quimicas
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Kabeche, Tanina. "Procédé de traitement in situ des sites pollués par réduction chimique à l'aide de micro et nanoparticules de fer zérovalent." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0034/document.
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Dans cette thèse, nous avons déterminé les mécanismes qui régissent l'efficacité des particules de fer zérovalent (ZVI) dans la dépollution des sols et des eaux souterraines. Dans les milieux contaminés par des polluants accepteurs d'électrons, le ZVI est injecté in situ sous forme de suspensions de particules micro et/ou nanométriques. La première étude a porté sur la caractérisation de poudres industrielles et de particules synthétisées au laboratoire à partir de thé vert. Afin de comparer la réactivité de l'ensemble des particules, un test en milieu fermé a été mis en oeuvre avec une solution de nitrate. Ce test a permis de différencier les particules en mettant en évidence des mécanismes réactionnels et des cinétiques de réduction qui dépendent du type de poudre utilisé. La seconde étude a porté sur la dégradation du chrome hexavalent (dans une matrice sol et eau) en combinant le ZVI à du thiosulfate de sodium. Les résultats ont été probants et ont mené au dimensionnement d'un pilote sur un site de Soléo Services. Enfin, deux cas de remédiation de sites pollués aux solvants chlorés ont été étudiés. Des expériences de laboratoire ont été menées pour expliquer l'impact des conditions opératoires sur l'efficacité du traitementThis thesis aims at a better understanding of mechanisms governing the efficiency of zerovalent iron (ZVI) particles in soil and groundwater remediation. In these processes ZVI is injected in situ as micro and/or nanoparticles slurry in areas contaminated by electron acceptor pollutants. At first, we characterized industrial powders and particles synthetized with green tea in the laboratory. In order to compare the reactivity of all the particles, a batch test has been carried out with nitrate solution. Differences in pathways and kinetic reduction have been exhibited. Secondly, we combined ZVI with sodium thiosulfate to investigate hexavalent chromium degradation (soil and water matrices). The results are conclusive and were used to design a pilot on a Soléo Services site.Finally, remediation cases of sites contaminated by chlorinated solvents have been investigated. Lab experiments have been run to explain the influence of operating conditions on the treatment efficacy
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Mončeková, Miroslava. "Úloha síranu železnatého jako regulátoru tuhnutí a redukčního činidla portlandského slínku." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2016. http://www.nusl.cz/ntk/nusl-256551.
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In 2003, the European Community Obligation (directive 2003/5C/EC) regulates a maximal value of soluble hexavalent chromium to 0.0002 % (per weight of dry cement). This limitation leads to modifications of the regular Portland cement by using of suitable reduction agents. Therefore, the possibilities of chromium reduction become a very actual topic. The primary goal of this work is a basic research of the ferrous sulphate influence on hexavalent chromium reduction and also its influence on Portland clinker hydration process. The reduction ability was determined by UV/VIS method. The mechanism and ferrous sulphate influence on Portland clinker hydration process was observed by isothermal calorimetry and mechanical strength tests. XRD method, SEM-EDS analysis and Raman microscopy were used for identification of formed hydration products. Study of hydration mechanism occurring in this system was focused on the divergence observations from the regular Portland cement hydration. Pore solution analysis provided significant information about chromium behavior during the hydration process (substitution and releasing). Chromium incorporation into structure of hydration products during the reduction process was also studied in the pure tricalciumaluminate system with targeted Cr6+ content. This work suggests the possible substitution of the trivalent and hexavalent chromium into structure of monosulphate (AFm) phase.
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Xu, Xiangrong. "Reductive detoxification of hexavalent chromium and degradation of methyl tertiary butyl ether and phthalate esters." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B31636196.
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Xu, Xiangrong, and 徐向榮. "Reductive detoxification of hexavalent chromium and degradation of methyl tertiary butyl ether and phthalate esters." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B31636196.
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Moura, Alex Anderson de Oliveira. "Influência de campo eletromagnético aplicado no biotratamento de efluente de cromo hexavalente." Universidade Federal de Uberlândia, 2012. https://repositorio.ufu.br/handle/123456789/15187.
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Fundação de Amparo a Pesquisa do Estado de Minas GeraisThis work was to study the influence of the magnetic field on the reduction of hexavalent chromium, removal of COD and total chromium, addition of cell growth in batch (batch reactor), using a mixed culture from located in a tanning city of Franca-SP (AMCOA). The influence of static magnetic field generated by a device that produces an electric current through a conductor, producing a magnetic field around the conductor, like a magnet. This equipment produces a magnetic field pulsed square wave of constant intensity and frequency. In the first step of adjusting the mixed cultures of chromium VI obtained a promising response. Thereafter, a preliminary test was performed to analyze the behavior of the influence of the magnetic field in the reduction of chromium VI and diameter of the reactor, obtaining 71% reduction of chromium VI with a larger diameter, without the presence of magnetic field has seen a reduction of 53%, with an initial concentration of 100 mg/l of chromium and a time of 4 hours of process. In other stages of the project, performing the tests with different frequencies of the magnetic field (1,2,5 and 10 Hz) and doing an analysis related to cell death of micro-organisms, showed that for frequencies of 10 Hz, there was cell death presents some cultures, which was confirmed in a lower frequency. The results were satisfactory when used in a magnetic field frequency of 5 Hz, maximal reduction of chromium VI reducing the time about 4 hours of processing, better removal of COD and total chromium using a volume of 500 ml and concentration of 100 mg/l initial chromium. Checking the influence of different frequency magnetic field, the initial effluent volumes (300 and 1000 ml) and initial concentration of chromium VI (50, 150 and 200 mg/l). The higher the initial concentration the lower the chromium reduction of chromium VI, larger volumes and a reduction of chromium VI and removal of COD and total chromium is not as significant as the use of smaller volumes.
Neste trabalho foi realizado o estudo da influência do campo magnético sobre a redução de cromo hexavalente, remoção de cromo total e DQO, além do crescimento celular em modo descontínuo (reator batelada), utilizando-se de uma cultura mista proveniente do curtume AMCOA localizado na cidade de Franca-SP. Foi avaliada a influência de campo eletromagnético estático gerado por um equipamento que produz uma corrente elétrica, passando por um condutor, produzindo um campo magnético ao redor do condutor, como se fosse um ímã. Este equipamento produz um campo magnético pulsante com onda quadrática de intensidade e frequência constantes. Na primeira etapa de adaptação das culturas mistas ao cromo VI obteve-se uma resposta promissora. Posteriormente, foi realizado um teste preliminar para analisar o comportamento da influência do campo magnético na redução de cromo VI e diâmetro de reator, obtendo 71% de redução de cromo VI com um maior diâmetro, sem a presença de campo magnético obteve uma redução de 53%, com uma concentração inicial de 100 mg/L de cromo e com um tempo de 4 horas de processo. Nas outras etapas do projeto, realizando os testes com diferentes frequências de campo magnético (1, 2, 5 e 10 Hz) e fazendo uma análise relacionada à morte celular dos micro-organismos, mostrou-se que para frequências de 10 Hz, havia morte celular de algumas culturas presentes, o que não foi verificado em uma frequência menor. Os resultados foram satisfatórios quando se utiliza uma frequência de campo magnético de 5 Hz, com máxima redução de cromo VI reduzindo o tempo em torno de 4 horas de processo, com melhor remoção de cromo total e DQO, utilizando um volume de 500 mL e concentração de 100 mg/L de cromo inicial. Verificando a influência de diferentes frequências de campo magnético, volumes iniciais de efluente (300 e 1000 mL) e concentrações iniciais de cromo VI (50, 150 e 200 mg/L). Quanto maior a concentração inicial de cromo menor foi a redução de cromo VI, e em volumes de efluentes maiores a redução de cromo VI e remoção de cromo total e DQO não foram tão significativas quanto em se aplicar volumes menores.
Mestre em Engenharia Química
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"Hexavalent Chromium Removal Using Ultraviolet Photocatalytic Reactor." Master's thesis, 2013. http://hdl.handle.net/2286/R.I.20986.
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abstract: Hexavalant chromium (Cr(VI)) poses an emerging concern in drinking water treatment with stricter regulations on the horizon. Photocatalytic reduction of Cr(VI) was investigated as an engineering scale option to remove hexavalent chromium from drinking or industrial waters via a UV/titanium dioxide (TiO2) process. Using an integrated UV lamp/ceramic membrane system to recirculate TiO2, both hexavalent and total chromium levels were reduced through photocatalytic processes without additional chemicals. Cr(VI) removal increased as a function of higher energy input and TiO2 dosage, achieving above 90% removal for a 1g/L dose of TiO2. Surface analysis of effluent TiO2 confirmed the presence of chromium species.Dissertation/Thesis
M.S. Engineering 2013
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Lokothwayo, Robson Bhekisisa. "Hexavalent chromium analysis, reduction and stabilization in cement and concrete." Thesis, 2008. http://hdl.handle.net/10539/4649.
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Abstract
Hexavalent chromium is one of the toxic contaminants unavoidably widespread in the
environment that exists in cement and concrete. Cement producers need to determine and
control the content of hexavalent chromium, hence this study investigated the effect of
environmental parameters on the leachability, stability and reduction of Cr(VI) in
different types of concrete. Concrete cubes were made with different cement mixtures,
and in some cases, reducing agents were added. The bulk and designed surface leaching
experiments that simulated different environmental conditions were devised for leaching
of Cr(VI). The Cr(VI) content in cement and concrete leachate solution was determined
using optimized Adsorptive Stripping Voltammetry method which proved to be very
sensitive and selective. Parameters like addition of MnO2, aging of concrete, increase of
temperature, UV variation and decrease in pH enhanced the leachability of Cr(VI).
Cement type also affected the Cr(VI) stabilization. Attempts to stabilize Cr(VI) included
addition of humic acid which proved to be not effective while the addition of ferrous
sulfate was successful in reducing and stabilizing Cr(VI) in concrete.
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Ochola, Charles E. "Utilization of reclaimed limestone residual (RLR) for the reduction of hexavalent chromium Cr (VI) /." Diss., 2002. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3073987.
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"Removal of Hexavalent Chromium from Groundwater Using Stannous Chloride Reductive Treatment." Master's thesis, 2019. http://hdl.handle.net/2286/R.I.53764.
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abstract: Mineral weathering and industrial activities cause elevated concentration of hexavalent chromium (Cr(VI)) in groundwater, and this poses potential health concern (>10 ppb) to southwestern USA. The conversion of Cr(VI) to Cr(III) – a fairly soluble and non-toxic form at typical pH of groundwater is an effective method to control the mobility and carcinogenic effects of Cr(VI). In-situ chemical reduction using SnCl2 was investigated to initiate this redox process using jar testing with buffered ultrapure water and native Arizona groundwater spiked with varying Cr(VI) concentrations. Cr(VI) transformation by SnCl2 is super rapid (<60 seconds) and depends upon the molar dosage of Sn(II) to Cr(VI). Cr(VI) removal improved significantly at higher pH while was independent on Cr(VI) initial concentration and dissolved oxygen (DO) level. Co-existing oxyanions (As and W) competed with Cr(VI) for SnCl2 oxidation and adsorption sites of formed precipitates, thus resulted in lower Cr(VI) removal in the challenge water. SnCl2 reagent grade and commercial grade behaved similarly when freshly prepared, but the reducing strength of the commercial product decreased by 50% over a week after exposing to atmosphere. Equilibrium modeling with Visual MINTEQ suggested redox potential < 400 mV to reach Cr(VI) treatment goal of 10 ppb. Kinetics of Cr(VI) reduction was simulated via the rate expression: r=-k[H+]-0.25[Sn2+]0.5[Cr2O72-]3 with k = 0.146 uM-2.25s-1, which correlated consistently with experimental data under different pH and SnCl2 doses. These results proved SnCl2 reductive treatment is a simple and highly effective method to treat Cr(VI) in groundwater.Dissertation/Thesis
Masters Thesis Civil, Environmental and Sustainable Engineering 2019
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Yeh, Chih-Jung, and 葉致榮. "A Study of Microwave Accelerated Reduction of Hexavalent Chromium by Zero-Valent Iron." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/29574702597562062201.
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碩士淡江大學
水資源及環境工程學系碩士班
98
A simple system for hexavalent chromium removal by iron powder in the wastewater treatment using microwave to replace the conventional treatment method is proposed. The goal of this study is to accelerate the rate of the reaction which hexavalent chromium reacts with the acid-washed iron powder in a home-made microwave oven combined with oscillator. This method consists of a small test tube (10 mL) where the iron powder and chromium solution were added and oscillated while microwave heating. The detection of chromium and trivalent chromium were carried out by atomic absorption spectrophotometer and colorimeter, respectively. In order to estimate the optimum levels and determine the relative magnitude of the effect of various factors, a number of experiments were performed. The microwave heating parameters for optimization were as follows: microwave power 575 W, reaction time 20 seconds, hexavalent chromium concentration 100 ppm and mole ratio (Fe/Cr) 500. The results showed that the hexavalent chromium removal by iron powder was 95 % (n = 10), relative standard deviation 5 %.
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Shang-ShingWu and 吳尚興. "Renewable Sunlight- or Visible Light-Driven Reduction of Hexavalent Chromium Photocatalyzed by Graphene Oxide." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/3qcm7u.
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Azizian, Mohammed F. "Experimental evaluation and chemical modeling of hexavalent chromium adsorption, desorption, and reduction in a natural soil /." 1993. http://hdl.handle.net/1957/9421.
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Huang, Yu-Chi, and 黃昱綺. "Amine-modified Zinc-based Metal Organic Framework for Photocatalytic Reduction of Hexavalent Chromium from Water." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/25g5rc.
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碩士中原大學
化學工程研究所
106
Among common industrial wastewater containing organic dyes, heavy metal ions and other contaminants, hexavalent chromium (Cr(VI)) is one of the most toxic and carcinogenic species to the environment and human. For industrial wastewater treatments, membrane filtration, ionic exchange, adsorption method, and photocatalytic reduction are widely used. In the past decades, photocatalytic reduction method can be regarded as the most harmless and effective approach to remove heavy metal ions in the wastewater. Zeolitic imidazolate frameworks (ZIFs), a typical structure of metal organic frameworks (MOFs), have high porosity and specific surface area that can serve as a promising candidate for photocatalytic hexavalent chromium reduction. In this study, amine-modified and ZnO-coupled ZIF-8 were used in an attempt to extend the visible light absorption, and hence the photocatalytic activity to reduce hexavalent chromium. Moreover, ZnO-coupled ZIF-8 with amine modification exhibited photocatalytic reduction activity to remove hexavalent chromium under light irradiation. In summary, ZnO-coupled ZIF-8 showed the highest photocatalytic activity among these samples that can be attributed to its high crystallinity, enhanced visible light absorption, and high surface area.
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Chien-YunLin and 林謙妘. "Sunlight-responsive Bio-based Alginate Aerogel: Reduction of Hexavalent Chromium and Hydroxyl Radical Induced Oxidation." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/y8h4h6.
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Mtimunye, Phalazane Johanna. "A steady-state model for hexavalent chromium reduction in simulated biological reactive barrier : microcosm analysis." Diss., 2011. http://hdl.handle.net/2263/28130.
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Biological remediation of Cr(VI) contaminated soil and groundwater is an emerging field. In this study, the in situ bioremediation technology for treating Cr(VI) contaminated groundwater aquifers was evaluated using a laboratory microcosm system. The study was conducted using columns with five equally spaced intermediate sampling ports along the length to facilitate finite difference modelling of the Cr(VI) concentration profile within the column. Cr(VI) concentration was continuously measured in the influent, in five equally spaced intermediate ports within the column and in the effluent port. The change or the shift in microbial community within the inoculated column was also monitored due to exposure to toxic conditions after seven weeks of operation using the 16S rRNA genotype fingerprinting method. The effect of introducing a natural carbon source (sawdust) in inoculated columns in comparison with the performance of sterile controls under various loading conditions was also evaluated. Near complete Cr(VI) removal was achieved in an inoculated carbon source reactor, whereas only 69.5% of Cr(VI) removal was achieved in an inoculated column without an added carbon source after 4 days of operation at 20 mg/L. In a sterile control reactor less than 2% of Cr(VI) was removed after 4 days of operation at 20 mg/L. Experimental cores demonstrated a successful Cr(VI) reduction process in the simulated microbial barrier system that was evaluated internally. The model that simulates Cr(VI) removal and transport in the subsoil environment was developed. The Cr(VI) mass balance model across the reactor that accounts for the flow characteristics and biological removal mechanism successfully captured the trends of Cr(VI) response profiles under quasi-steady state conditions for different loading conditions. This study demonstrate the potential of applying effective Cr(VI) reducers in the reactive barrier systems to contain or attenuate the spread of Cr(VI) contaminant in groundwater aquifer systems. The finite difference model developed in this study to evaluate the behaviour of Cr(VI) in the reactor could contribute towards improved designs of future in situ bioremediation systems that can be implemented for remediation of Cr(VI) on site.Dissertation (MSc)--University of Pretoria, 2011.
Chemical Engineering
unrestricted
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Chen, Tai-Yu, and 陳泰宇. "Comparison of Zero-Valent Iron and Bimetallic Iron-Aluminum on the Reduction of Aqueous Hexavalent Chromium." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/32429452237965149507.
Full textAbstract:
碩士國立屏東科技大學
環境工程與科學系
94
Due to the rapid industrial development, many pollutants were produced in recent years. Chromium is a raw materials and often used in the industrial manufacturing process such as pigment, paint, fireproofing materials, electroplating, metal processing, and tanning, etc. Chromic compounds, which are toxic to human health, are considered to be the teratogenic and carcinogenic substances. Electroplating wastewater accounts for about 5 to 10 percent volumes of all industrial wastewater. If the wastewater is not properly handled and processed, it may bring about enormous impairments to the environment. In this study, zero-valent iron (Fe0) including micro-scale and nano-scale iron, and bimetallic iron-aluminum (Fe-Al) were utilized to reduce the hexavalent chromium (Cr6+) to the trivalent chromium (Cr3+) which is a less toxic from of chromic compound. The parameters concerned in this study included initial pH value, particle size of Fe0 and Fe-Al, pretreatment of acid-washing process, dosage ratio between Fe0 and Cr6+ (Fe/Cr6+), dosage ratio between Fe-Al and Cr6+ (Fe-Al/Cr6+), and iron contents of Fe-Al. The result shows that acid-washing pretreatment could remove the impurities which were adsorbed by iron particle, and then enhanced the reaction rate. From the characteristic analysis, the surface area of Fe0 was reciprocally proportional to particle size but was directly proportional to the adsorption efficiency, while the surface area of the Fe-Al was directly proportional to particle size and adsorption efficiency. As for the particle sizes, micro-scale Fe was the biggest while the nano-scale Fe was the smallest. The dosage of nano-scale Fe and Fe-Al applied to reduce the same concentration of Cr6+ was only one half of that of micro-scale Fe. As for the final reduction efficiency, Fe0 and Fe-Al could reach to more than 95% with less reactive time as compared with the micro-scale iron. The variation ranges of pH, oxidation-reduction potential (ORP), and dissolved oxygen (DO) were the lowest for Fe-Al and the highest for nano-scale Fe. The reasons for Cr6+ reduction efficiency of Fe-Al better than that of nano-scale Fe were summarized as follows: (1) the variation range of pH of Fe-Al was minimal so as to avoid Cr3+ transforming to Cr6+ during the reduction process, (2) the variation ranges of ORP and DO of Fe-Al were small that favored the follow-up treatment process, (3) the particle size of nano-scale Fe was too small to be recycled. This study shoes micro-scale Fe0 with acid-washing pretreatment, nano-scale Fe0, and Fe-Al can effectively reduce the aqueous Cr6+ and this techinique can be referred as an alternative for treatment of wastewater and remediation of aquifer as well as soil contaminated with chromium.
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Wang, Yong-jhong, and 王雍中. "Study on Exposure Reduction and Internal Dose of Hexavalent Chromium for Workers with Usage of Hand Cream." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/4596r9.
Full textAbstract:
碩士長榮大學
職業安全與衛生學系碩士班
98
Electric plating and construction industries are the representative professions of hexavalent chromium (Cr6+) exposure. How to prevent the workers in these industries from health hazards due to Cr6+ exposure is an important issue of occupational health. Because dermal exposure is one of the main route of Cr6+ exposure, the objective of this study is to explore the effectiveness of usage of hand cream with vitamin C on the reduction of Cr6+ exposure for the workers. Ten workers were recruited from an electroplating plant and a construction workplace in the study. Each worker was asked to apply the hand cream before and during the work on every day for five consecutive days. Normally a worker applied the hand cream about six times on a workday. The urine samples of the workers were collected before, during and after the work shifts in five consecutive days. In order to make a comparison, the urine samples of the workers without using the hand cream on other workdays were also collected before and after the work shifts for 2~3 days. Air samples were taken in the workplaces to measure airborne exposure. Skin wiping samples were also taken on 2~3 days before the workers using the hand cream to assess the workers’ hands exposure to Cr6+. The amount of Cr6+ of the skin wiping samples were analyzed by ultra violet-visible spectroscopy (UV/Vis). The concentration of total chromium of the urine samples were analyzed by atomic absorption spectrometer (AA). Based on the measurements of the total chromium in the urine samples from the workers with Cr6+ exposure who used the hand cream with vitamin C on about ten continuous days in the electroplating plant and the construction workplace, the concentration change of the total chromium in the urine samples showed that the hand cream with vitamin C tended to reduce the skin absorption of Cr6+ and had the effectiveness of protection from Cr6+ exposure. However, when a worker did not have a high cumulative dose of Cr6+ and only had a low concentration exposure to Cr6+, the effectiveness of total chromium reduction became not significant. Because the sample sizes of this study was small and the exposure concentration of Cr6+ was not high enough, the power of the study results was not sufficient. More research on the reduction of Cr6+ exposure for the workers using the hand cream with vitamin C will be necessary.
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Zeleke, Misganaw Alemu, and Misganaw Alemu Zeleke. "Synthesis of Oxy-Sulfide Catalysts and Their Application for Reduction of Hazardous Hexavalent Chromium under Visible Light Illumination." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/pyecev.
Full textAbstract:
博士國立臺灣科技大學
材料科學與工程系
107
Human beings are dependent on the environment for stable survival and sustainable development. However, human being-environment interaction is causing many environmental devastations which caused excessive negative impacts on the inhabitants. Industrialization is among the human activity where illegal waste disposal is mostly practiced. The waste disposed to the environment comprises many toxic pollutants including carcinogenic and mutagenic heavy metals. Hexavalent chromium is among the heaviest metal contaminants which cause serious health problems to living organisms. Hence, photocatalysis is the promising green technology to detoxify it. For this purpose, bimetallic (In,Ga)2(O,S)3 oxy-sulfide nanoflower catalyst with different Ga contents was successfully synthesized at a low temperature of 150 oC via a facile method. The oxy-sulfide catalysts were systematically characterized and the catalyst with InCl2-4H2O:Ga(NO3)3-8H2O at 1:0.50, designated as SA-2, revealed 100% Cr(VI) reduction at 4 min under visible light irradiation. The Cr(VI) reduction reaction rate constant was 13.8 fold higher than that of Ga-free In2(O,S)3 catalyst. The photoexcited electrons and H+ ions played crucial roles in the reduction of Cr(VI). The photocatalytic activity of the bimetallic oxy-sulfide nanoflower catalyst was further enhanced via composite formation with V2O5. The oxy-sulfide based V2O5@(In,Ga)2(O,S)3 nanocomposite catalyst, at different weight percentages of V2O5, was successfully synthesized via a simplistic procedural route. The two pure catalysts were intimately allied and used for enhanced visible light-assisted reduction of Cr(VI). The nanocomposite catalysts were characterized to observe the effects of V2O5 on crystal phase, morphology, light absorption, catalytic activity, and electrical properties. Compared to all, 40% V2O5 loaded nanocomposite catalyst, designated as VOS-2, exhibited the best-reducing capability. It completely reduced toxic Cr(VI) in 2 min under visible light irradiation, where its rate constant was increased by a factor of 3.6 compared to the pure (In,Ga)2(O,S)3 nanoflower catalyst. The plausible mechanism of charge transfer process across the interfacial region indicates the diminished recombination probability of photogenerated charge carriers. Therefore, the single phase (In,Ga)2(O,S)3 nanoflower catalyst and V2O5@(In,Ga)2(O,S)3 nanocomposite catalyst are promising for enhanced reduction of Cr(VI) in the Cr-based industrial activities, which is significantly relevant for environmental remediation.
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Kaimbi, L. A. (Lapaka Albertina). "Remobilization of trivalent chromium and the regeneration of in situ permeable reactive barriers during operation." Diss., 2014. http://hdl.handle.net/2263/43365.
Full textAbstract:
Chromium exists largely in two oxidation states, namely hexavalent chromium (Cr(VI))
which is carcinogenic, mutagenic to living organisms including humans and trivalent
chromium (Cr(III)) which is known to be 1000 times less toxic than Cr(VI). It is therefore
desirable in most cases to reduce Cr(VI) to Cr(III). Various studies have been conducted on
the Cr(VI) reduction process either in situ or ex situ. However in situ bioremediation using
permeable reactive barrier system appears as a potential and attractive technology compared
to other in situ technologies. This study was conducted to evaluate the reduction of Cr(VI) to
Cr(III) in the short term and regeneration of the biological reactive barrier to achieve
continuous long term operation. It was observed from the study that the chromium hydroxide
Cr(OH)3(s) precipitated and thus affected the porosity and hydraulic conductivity of the
barrier system. It was therefore proposed to implement a regeneration process involving
remobilization of precipitated Cr(OH)3 using a dilute acid (0.1% HCl) and recover Cr(III) by
electrokinetics.
Lowering the pH in the reactor introduced harsh conditions which necessitated the evaluation
of a possible culture shift during the regeneration phase. Microbial culture composition
during bioremediation and after soil washing was evaluated using a 16S rRNA finger printing
method. The microbial barrier was initially inoculated with indigenous bacterial species from
dried sludge. The results presented in the phylogenic tree diagrams confirm that, after
microbial barrier system operation, the well-known Cr(VI) reducers Bacillus mycoides, Lysinibacillus fusiformis and Micrococcus lylae were the predominant species in the
microbial community of the barrier.
The microbial barrier system successfully achieved near complete removal of Cr(VI),
whereby approximately 75% Cr(VI) removal was achieved within 63 days of operation. The
formation of Cr(OH)3(s) was observed in the second week of operation. After 4 weeks of
operating the mesocosm under soil washing with 0.1% HCl and electrokinetics remediation
with a DC voltage of 50-150 V an increase in total chromium (73%) was observed suggesting
that the trapped chromium species in the mesocosm was effectively remobilized with the
assumption that Cr(III) had attached to the cathode forming a white-yellow precipitate layer
around the cathode. Additionally more than 95% Cr(VI) was transformed to lower toxicity
Cr(III) during electrokinetics and soil washing remediation. However, one of the limitations
of electrokinetics is near anode focusing effect whereby a layer of precipitate is formed
around the anode that lead to the reduction of efficiency of the technology.Dissertation (MSc)--University of Pretoria, 2014.
lk2014
Chemical Engineering
MSc
Unrestricted
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Alves, Ana Rita Ribeira. "Bioremediation : validation of spectroscopic methods for the analysis of Cr 6+ internalisation and reduction of Cr 6+ to Cr 3+ by Pseudomonas alcaliphila." Master's thesis, 2015. http://hdl.handle.net/10451/26746.
Full textAbstract:
Trabalho Final de Mestrado Integrado, Ciências Farmacêuticas, Universidade de Lisboa, Faculdade de Farmácia, 2014Hexavalent chromium is a toxic by-product of several industries. Contamination of soil and water with Cr(VI) is prevalent all over the world, but conventional processes used to remove heavy metals from the environment are expensive and often not as effective as desired. Bioremediation with heavy metal-resistant microorganisms is a cheaper and promising approach to removal of toxic metals from soil and water. In this thesis the Cr(VI)-reducing capabilities of Pseudomonas alcaliphila were tested by analysing surnatant samples of P. alcaliphila exposed to 3900 ppm and 7800 ppm of K2CrO4 for 24 hours. Analysis was done by F-AAS and UV techniques and required devising calibration methods for both techniques that fit changing experimental conditions. Results from several samples were largely inconclusive for both methods but seemed to suggest that Cr(VI) removal from the medium by P. alcaliphila might occur by different mechanisms and that one might be prioritised over the others by the bacteria. Results also seemed to suggest that those mechanisms might be employed cyclically. Although further investigation into Cr(VI)-removal mechanisms of P. alcaliphila is required, this species is a possible candidate for hexavalent chromium bioremediation.
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Μιχαηλίδης, Μιχαήλ. "Βιολογική αναγωγή εξασθενούς χρωμίου." Thesis, 2015. http://hdl.handle.net/10889/8650.
Full textAbstract:
Το χρώμιο (Cr) αποτελεί έναν από τους σημαντικότερους ρύπους του φυσικού περιβάλλοντος. Η ευρεία βιομηχανική χρήση του χρωμίου έχει ως αποτέλεσμα την απελευθέρωση μεγάλων ποσοτήτων του μετάλλου στο περιβάλλον κυρίως με τη μορφή του εξασθενούς χρωμίου (Cr(VI)). Το εξασθενές χρώμιο, μία από τις σταθερές μορφές του χρωμίου στο περιβάλλον, είναι ευδιάλυτο, υψηλά τοξικό, καρκινογενές και μεταλλαξιγόνο.
Οι σύγχρονες μέθοδοι επεξεργασίας του εξασθενούς χρωμίου χρησιμοποιούν μικροοργανισμούς, στηριζόμενες στη μεταβολική και κυτταρική τους δράση. Πρόκειται για διεργασίες πιο ανταγωνιστικές, αποτελεσματικές και οικονομικές έναντι των συμβατικών φυσικοχημικών μεθόδων (χημική αναγωγή, ανταλλαγή ιόντων, διήθηση, ηλεκτροχημική επεξεργασία, προσρόφηση σε ενεργό άνθρακα, αντίστροφη όσμωση και μεμβράνες) καθώς παρουσιάζουν μικρές ενεργειακές απαιτήσεις, χαμηλό πάγιο και λειτουργικό κόστος και τέλος μικρότερη παραγωγή τοξικής λάσπης. Η βιολογική αναγωγή του εξασθενούς χρωμίου απαιτεί την παρουσία ενός δότη ηλεκτρονίων. Το ρόλο αυτό παίζει ο οργανικός άνθρακας, ο οποίος είναι απαραίτητος για την πραγματοποίηση της διεργασίας αυτής.
Στην παρούσα διδακτορική διατριβή μελετήθηκε η επεξεργασία υγρών χρωμικών βιομηχανικών αποβλήτων, με ταυτόχρονη εκμετάλλευση/αξιοποίηση αγροτοβιομηχανικών παραπροϊόντων/αποβλήτων (μελάσα - χαμηλού κόστους και ορρός γάλακτος – μηδενικού κόστους), χρησιμοποιώντας βιολογικές μεθόδους. Αρχικά, πραγματοποιήθηκαν πειράματα για τη βελτιστοποίηση του ρυθμού αναγωγής των μεικτών αερόβιων γηγενών καλλιεργειών σε αντιδραστήρες αιωρούμενης ανάπτυξης. Στη συνέχεια χρησιμοποιήθηκε η μεικτή καλλιέργεια για τη μελέτη της βιολογικής αναγωγής του εξασθενούς χρωμίου σε αντιδραστήρες σταθερής κλίνης πιλοτικής κλίμακας με πλαστικό πληρωτικό υλικό, σε διάφορες λειτουργικές συνθήκες, στοχεύοντας στην μέγιστη απόδοση των συστημάτων και την αποφυγή λειτουργικών προβλημάτων.
Το βιολογικό σύστημα που χρησιμοποιήθηκε στην παρούσα διδακτορική διατριβή, αποτελεί μία πολύ αποτελεσματική μέθοδο επεξεργασίας βιομηχανικών αποβλήτων επιβαρυμένων με το τοξικό εξασθενές χρώμιο, χρησιμοποιώντας οικονομικές πηγές άνθρακα όπως η μελάσα και ο ορρός γάλακτος. Η μέθοδος αυτή είναι πολλά υποσχόμενη, συνδυάζοντας υψηλά ποσοστά απομάκρυνσης με εξαιρετικά χαμηλές δαπάνες λειτουργικού κόστους.Chromium is one of the most serious pollutants of natural environment. The widespread industrial use of chromium leads to the release of large quantities of this metal in the environment, mainly in the form of hexavalent chromium. The hexavalent chromium, one of the most stable forms that we can notice in the environment, is soluble, highly toxic carcinogenic and mutagenic. Contemporary water processing techniques of hexavalent chromium use micro-organisms, based on their metabolic and cellular activity. These procedures are more competitive, more effective and certainly financially affordable over the conventional physicochemical methods (chemical oxidation or reduction, ion exchange, filtration, electrochemical treatment, activated carbon adsorption, reverse osmosis and membrane technologies) as they show low energy demands, low maintenance cost and a smaller production of toxic mud. The biological reduction of hexavalent chromium requires the presence of an electron donor. This part is covered by organic carbon that is essential for carrying out the process. The present thesis studied the treatment of liquid industrial chromate waste and the exploitation/utilization of agroindustrial byproducts/wastewaters (molasses - low cost and cheese whey- zero cost), using biological methods. At the beginning, experiments were conducted to optimize the reduction rate of mixed aerobic indigenous cultures in suspended growth reactors. Subsequently, the mixed culture was used for the biological reduction of the hexavalent chromium, in laboratory pilot scale fixed bed reactors, with plastic media, in various functional conditions targeting to the maximum system performance and the prevention of functional problems. The biological system used in the present thesis constitutes a very effective method of processing industrial wastewater polluted with the toxic hexavalent chromium, by using affordable sources of carbon, such as molasses and cheese whey. This is a quite promising method, combining high removal rates with extremely low operating expenditure.
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Shen, Ying-Shuian, and 沈盈嬛. "Sorption and reductive transformation of hexavalent chromium on coconut-shell-derived black carbon." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/84244213088814901872.
Full textAbstract:
碩士國立中興大學
土壤環境科學系所
97
Coconut shell (CS) is a waste by-product from agriculture. In this study, CS was converted to carbonized materials by pyrolysis at different temperatures. The extent and rate of Cr(VI) sorption of CS and CS-derived carbons were studied as a function of pH, contact time, and initial Cr(VI) concentration. The structures of sorbed Cr species on the sorbents were determined using X-ray absorption spectroscopy. XPS and FT-IR spectra were obtained for the sorbents before and after reaction to identify the functional groups responsible for sorption and reduction of Cr(VI) on the surfaces of the CS-derived carbon. The Cr(VI) sorption of CS-derived carbons was primarily dependent on the surface area and porosity of the sorbents. Upon decreasing solution pH, the Cr(VI) sorption on CS-derived carbon increased due to increasing positive charges on the surfaces of the sorbents. In addition, the reduction of Cr(VI) to Cr(III) became more significant at lower pH, which also contributed to the Cr(VI) removal from solutions. The removal of Cr(VI) by CS-derived carbons are dependent on their pyrolysis temperature. CS and CS-250 were better than other carbon materials in terms of the Cr(VI) removal rate. As the pyrolysis temperature was increased to 350°C and above, the removal of Cr(VI) decreased. The surface properties of CS-derived carbon, in particular the surface functional groups, may play a a significant role in Cr(VI) sorption and reduction. The functional groups involving in Cr(VI) reduction would be the phenolic, carboxylic and oxygen substituted aromatic functional groups(-OCH and –OH).
27
HSu, Nai-Hua, and 許乃樺. "Sorption and reductive transformation of hexavalent chromium by black carbon derived from rice straw." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/55763547325968696369.
Full textAbstract:
碩士國立中興大學
土壤環境科學系所
96
Black carbon (BC) is produced by incomplete combustion of various organic material including fossil fuels and vegetation. In rice paddy soils, the major source of black carbon is burning rice straw. Burning rice straw is a common post-harvest practice of rice production. Because black carbon is resistant to decomposition, a long-term rice production may result in the accumulation of BC in rice paddy soils to a considerable extent with respect to determining the fates of contaminants in soils. In this work, Cr(VI) sorption and reductive transformation on BC derived from rice straw were investigated. Rice straw was burned in the air and the resulting ash was treated with HCl/HF solution to remove soluble salts and silica. Sorption of Cr(VI) on BC was investigated under various pHs, Cr(VI) concentrations and ion strengths. After sorption experiments, the residual sorbents were analyzed by X-ray photoelectron spectroscopy(XPS) and Cr K-edge X-ray absorption near-edge structure (Cr K-edge XANES) to determine the structures of sorbed Cr. The results of Cr K-edge XANES and XPS revealed that Cr(VI) was sorbed and reduced to Cr(III) on BC. Thus, BC derived from rice straw is an effective sorbent and reductant for Cr(VI) and may play an important role in determining the fate of Cr(VI) in soils.