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[en] OBTAINING CHROMIUM OXIDE FROM FINE FECR HIGH-CARBON ALLOY / [pt] OBTENÇÃO DO ÓXIDO DE CROMO A PARTIR DE FINOS DE UMA LIGA FECR-ALTO CARBONOWALTER EDUARDO LAZO MALAGA 23 March 2010 (has links)
[pt] O trabalho tem como motivação principal conciliar a crescente demanda de
cromo em aplicações específicas com o aproveitamento de um resíduo industrial
que está na forma de finos de baixo valor agregado. Desta forma, se estuda a
possibilidade de recuperar o cromo, na forma de óxido, que está contido em finos
da liga Fe-Cr Alto Carbono. Inicialmente, foi estudado o efeito das variáveis
relevantes (temperatura, proporção dos reagentes) sobre a ustulação da liga com
os hidróxidos de Na e Mg. Os resultados foram baseados na solubilização do
produto ustulado e a subseqüente obtenção de uma solução rica em cromo
separada de um composto rico em ferro. A etapa final envolve a precipitação do
óxido de cromo. Os materiais envolvidos foram caracterizados por análise
química, difração de raio-X e microscopia eletrônica de varredura. Os resultados
qualitativos indicam a viabilidade do processo, mas, condições otimizadas devem
ser identificadas visando uma maior eficiência do mesmo. / [en] The investigation main motivation is to combine the growing chromium
demand for specific applications with the reuse of a low value Cr-Fe-carbon
alloy. Thus, it has been studied the possibility of recovering chromium, in the
oxide form, from fines generated in the production of Fe-Cr High Carbon.
Initially, the effect of relevant variables (temperature, ratio of reactants) on the
alloy roasting with Na and Mg hydroxides, were studied. Then, the chromate
solubilization followed by the chromium oxide precipitation have been carried
out. The materials involved in the work have characterized by chemical analysis,
DRX and MEV/EDS. The qualitative results indicated that the method can be
applied but further experiments has to be carried out to optimize the process.
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[en] EFFECTS OF THE RESIDUES CONTAINING CHROMIUM CO-PROCESSING ON THE CLINKERIZATION REACTION / [pt] EFEITOS DO CO-PROCESSAMENTO DE RESÍDUOS CONTENDO CROMO SOBRE A REAÇÃO DE CLINQUERIZAÇÃOCAROLINA TURON WAGNER 21 March 2005 (has links)
[pt] O presente trabalho surge da crescente preocupação a
respeito das práticas de
disposição de resíduos industriais de forma a propiciar um
desenvolvimento sustentável. A
impossibilidade ou falta de opção de tratamento de um
determinado resíduo e o desejo de
eliminação de um passivo ambiental de risco conduz à
escolha de diversas técnicas. Entre
elas o co-processamento em fornos de cimento se destaca
como um importante recurso a ser
utilizado pelas empresas geradoras de resíduos.
O co-processamento é a técnica que aproveita as condições
operacionais dos fornos de
clínquer (matéria-prima básica do cimento) para reciclar
resíduos industriais, aproveitando o
seu poder calorífico e/ou matérias-primas neles contidas,
inerentes ao processo de fabricação
normal do cimento.
Há a necessidade, no entanto, de compreender com uma maior
base científica o
impacto de componentes menores no processo de produção do
clínquer e nas propriedades do
mesmo, tais como a prioridade de se produzir cimento com
propriedades equivalentes, o
compromisso de diminuir emissões e a garantia de manter a
qualidade ambiental do clínquer.
O trabalho pretende, portanto, investigar o efeito do
cromo - contaminante comumente
presente em diversas fontes de resíduos co-processados em
fornos de cimento - sobre a
cinética da reação de clinquerização e nas fases do
clínquer de cimento Portland produzido -
C3S-alita, C2S-belita, C3A-aluminato tricálcico e C4AF-
ferro aluminato tetracálcico.
Para tal, foi incorporado óxido de cromo nas proporções de
0,1%, 0,5% e 1% à farinha
e foram realizados os seguintes testes: Fluorescência de
Raios-X, Difração de Raios-X,
Microscopia Eletrônica de Varredura com o dispositivo de
EDS e Análise Térmica
Diferencial (DTA). Para avaliar quantitativamente as fases
presentes, utilizou-se ainda o
Método de Rietveld. Dentre os resultados obtidos, pôde-se
observar que a incorporação de
cromo à farinha inibe a formação de alita. / [en] This work arises from the growing concern about the
practices in industrial
waste disposal to reach a sustainable development. One
important technique to be
considered by the waste generating companies is co-
processing of residues in rotary
cement kilns.
The co-processing technique takes advantage of the cement
kiln operational
conditions to recycle industrial wastes. It also utilizes
residue´s calorific power and/or
the raw material that is eventually enclosed on it.
Although, it´s necessary to understand the impact of the
minor and secondary
elements in the clinker production process and on its
proprieties, like the preference
to produce cement with equivalents proprieties, the
commitment to decrease pollution
gas emissions and the guarantee to support clinker´s
environmental quality.
The purpose of this work is to investigate the effect of
chromium - an usual
element found on several sources of co-processed residues -
at the kinetics of the
clinkerization reaction and in the clinker´s phases - C3S-
alite, C2S-belite, C3Atricalcic
aluminate and C4AF-tetracalcic iron aluminate.
Chromium oxide at the proportions of 0,1%, 0,5% e 1% was
incorporated at the
raw material of clinker production and some testes were
realized: X-Ray Diffraction,
Scattering Electronic Microscopy with EDS and Differential
Thermal Analysis. To
quantitatively evaluate the phases, the Rietveld Method was
utilized. Among the
obtained results, it could be observed that chromium
inhibits the formation of alite.
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[en] KINETICS ASPECTS OF CHROMIUM (III) REMOVAL BY PRECIPITATE FLOTATION / [pt] ASPECTOS CINÉTICOS DA REMOÇÃO DE CROMO (III) POR FLOTAÇÃO DE PRECIPITADOSBELENIA YANETH MEDINA BUENO 22 December 2003 (has links)
[pt] Metais pesados contidos em efluentes industriais são
fontes
de grande potencial de degradação ambiental; visto que
eles
produzem alterações físicoquímicas na qualidade da água.
Estas alterações têm um impacto direto na mortandade da
flora e fauna afetando indiretamente a saúde dos seres
humanos.
Esta dissertação refere-se ao estudo dos aspectos
cinéticos
da remoção de cromo (III) por flotação de precipitados a
partir de cloreto de cromo hexahidratado, utilizando
dodecilsulfato de sódio (DSS) como coletor aniônico.
Para este estudo, foram realizadas medidas de potencial
zeta, bem como ensaios de flotação do cromo (III) para
determinar os parâmetros adequados de operação: vazão de
ar, concentração de coletor e concentração de espumante.
Medições de potencial zeta das partículas de hidróxido de
cromo na presença de eletrólito indiferente KCl,
indicaram
ponto isoelétrico (PIE) em pH em torno de 8,5. A presença
do coletor aniônico (DSS) no sistema hidróxido de
cromo-água indicou uma redução do potencial zeta, para os
três níveis de concentrações investigados. Havendo um
deslocamento do PIE na direção de valores de pH mais
inferiores, atribuindo tal comportamento à adsorção do
coletor sobre o Cr(OH)3 através de interação
eletrostática.
Com relação aos resultados dos ensaios de flotação de
precipitados do cromo (III), obtiveram-se remoções de
aproximadamente 96,2%, conseguindo-se chegar a valores
inferiores ao estabelecido pela norma do CONAMA (20/86),
ou
seja, [Cr3+]£0,5 mg/L.
O estudo da cinética da flotação mediante as análises
integral e diferencial evidenciaram que o processo de
remoção do precipitado de hidróxido de cromo
segue um modelo de primeira ordem. / [en] Heavy metals contained in industrial effluents are sources
of great potential environmental degradation, since their
presence produce physicochemical alterations harming in the
quality of the water. These alterations have a direct
impact in the mortality of the flora and fauna affecting
indirectly the human health.
This dissertation refers to the study of the kinetic
aspects of chromium (III)removal by precipitate flotation
from chromium chloride (CrCl3.6H2O), using
sodium dodecylsulfate (SDS) as anionic collector.
For this study, measurements of zeta potential were
accomplished as well as chromium (III) tests of flotation
to determine the appropriate parameters operation: gas flow
rate, concentration of collector and frother.
Measurements of zeta potential of the particles of chromium
(III) hydroxide in the presence of indifferent electrolyte
KCl, indicated an isoelectric point (PIE)in pH around 8,5.
The particles of chromium (III) hydroxide in the presence of
anionic collector (SDS) showed a decrease in module of the
zeta potential, for the three levels of concentrations
investigated, as well as a displacement of the PIE in
the direction of the more inferior pH values. This behavior
can be attributed to the adsorption of the anionic
collector on Cr(OH)3 due to the electrostatic attraction.
Chromium (III) removals of 96,2% were obtained by
precipitate flotation.
Residual values of chromium reached are lower than the
standards values established by the CONAMA (20/86), that
mean [Cr3+]£0,5 mg/L.
The kinetic flotation study showed that the removal of
chromium (III)hydroxide precipitates followed a first order
model.
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[en] SYNTHESIS OF NANOSTRUCTURED FE0-NI0/SIO2 PARTICLES FOR THE REDUCTION OF HEXAVALENT CHROMIUM TO TRIVALENT CHROMIUM / [pt] SÍNTESE DE PARTÍCULAS NANOESTRUTURADAS DE FE0-NI0 /SI02 PARA REDUÇÃO DO CROMO HEXAVALENTE PARA CROMO TRIVALENTETHIAGO OLIVEIRA FERREIRA CORREIA 09 January 2019 (has links)
[pt] 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. / [en] 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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[en] DETERMINATION OF NICKEL AND CHROMIUM IN GEOLOGICAL SAMPLES BY ISOTOPE DILUTION USING INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY. / [pt] DETERMINAÇÃO DE NÍQUEL E CROMO POR DILUIÇÃO ISOTÓPICA EM AMOSTRAS GEOLÓGICAS UTILIZANDO ESPECTROMETRIA DE MASSA COM PLASMA INDUTIVAMENTE ACOPLADOLAIS NASCIMENTO VIANA 15 July 2020 (has links)
[pt] Os metais estão presentes em diversos materiais e muitos deles, como o níquel e o cromo, possuem papeis significativos em diversos setores industriais. A quantificação desses metais é importante tanto para obtenção de informações relevantes a respeito desses materiais, como para avaliação de possíveis contaminações ambientais. No presente trabalho, foram desenvolvidos métodos analíticos para a determinação de níquel e cromo em amostras de asfalto, brita e CAP por espectrometria de massa com plasma indutivamente acoplado usando calibração externa e diluição isotópica. Para a avaliação da exatidão dos métodos foram utilizados os materiais de referência certificados NIST 1084a e NBS 688. Como métodos de preparo de amostra, foram estudadas a decomposição ácida em bloco digestor, e a diluição em uma mistura de xileno/butanol na proporção 60:40 v:v (para amostras de óleo). Para a correção da interferência da espécie 40Ar12C positivo sobre o isótopo de 52Cr foi utilizada a célula de reação dinâmica com introdução de CH4 como gás de reação, o que reduziu de forma significativa o sinal de fundo característico para o isótopo de cromo. Os métodos desenvolvidos se mostraram eficientes na determinação dos metais. As recuperações obtidas para os SRMs se encontram entre 80-120 porcento. As concentrações médias, em mg kg-1 , encontradas para Ni pelos diferentes métodos nas amostras de CAP, brita e asfalto foram, respectivamente 39,9 mais ou menos 0,6, 6,7 mais ou menos 0,5 e 11,2 mais ou menos 0,8, enquanto para Cr as concentrações foram 1,8 mais ou menos 0,1, 15,3 mais ou menos 0,3, 16,6 mais ou menos 0,4. O sucesso da aplicação da diluição isotópica em amostras dissolvidas em solvente orgânico mostrou-se muito promissor, pois elimina a necessidade da decomposição ácida das matrizes tornando o preparo das amostras mais rápido e menos trabalhoso. / [en] Metals are present in several samples and many of them, such as nickel and chromium, have significant roles in several industry sectors. The quantification of these metals is important both for obtaining relevant information regarding these materials, and for evaluating possible environmental contaminations. In the present work, analytical methods were developed for the determination of nickel and chromium in asphalt, crushed stone and CAP samples by inductively coupled plasma mass spectrometry using both external calibration technique and isotopic dilution. To evaluate accuracy of the method, the certified reference materials NIST 1084a and NBS 688 were used. Two different methods of sample preparation were
employed, block digestion and direct dilution in a xylene / butanol mixture using a 60:40 v:v ratio (for the oil samples). For the interference correction imposed by 40Ar12C over 52Cr, the dynamic reaction cell was used with CH4 as the reaction gas, which significantly reduced the characteristic background signal of the chromium isotope. The methods developed proved to be efficient in the determination of the metals in question. The recovery values obtained for the SRMs were between 80-120 percent. The average concentrations, in mg kg-1 , found for Ni by the different methods in CAP, crushed stone and asphalt samples were, respectively, 39,9 more or less 0,6, 6,7 more or less 0,5 and 11,2 more or less 0,8, while for Cr the concentrations were 1,8 more or less 0,1, 15,3 more or less 0,3, 16,6 more or less 0,4. The successful application of isotope dilution in samples dissolved in organic solvent is very promising because it eliminates the need for acid digestion, making the sample preparation faster and less labor intensive.
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[en] HEXAVALENT CHROMIUM REMEDIATION USING CALCIUM POLYSULFIDE: STUDY CASE: RIO DE JANEIRO / [pt] REMEDIAÇÃO DE CROMO HEXAVALENTE UTILIZANDO POLISSULFETO DE CÁLCIO: ESTUDO DE CASO: RIO DE JANEIRORAFAEL FERREIRA GODOY 10 August 2015 (has links)
[pt] Esta dissertação apresenta os resultados obtidos no processo de remediação de uma área contaminada por cromo hexavalente por meio da técnica de remediação química in situ (ISCR). A área de estudo localiza-se na
cidade do Rio de Janeiro e foi ocupada por uma fábrica de vidros por cerca de quarenta anos e comprada para construção de condomínios residenciais. A área de estudo passou um processo de gerenciamento ambiental que contemplou diversos estudos ambientais para aquisição de dados e delimitar a contaminação, horizontal e verticalmente. O teste de bancada realizado com o reagente químico polissulfeto de cálcio demonstrou ser eficiente para reduzir as concentrações de cromo hexavalente em solo e água subterrânea. Com base nos
dados adquiridos neste teste foi possível calcular a dose de injeção do polissulfeto de cálcio. Foram realizados setenta pontos de sondagem, pela técnica direct push, para injetar duzentos e cinquenta e dois mil e trinta litros de solução de polissulfeto de cálcio e água, sendo aproximadamente três mil e quinhentos litros por ponto de injeção. Os resultados após a injeção demonstraram que o polissulfeto de cálcio conseguiu remover o cromo hexavalente que estava adsorvido ao solo e reduziu a concentração de cromo hexavalente na água subterrânea entre quarenta e seis e sessenta e sete e noventa e nove e noventa e cinco por cento , após dezenove meses da injeção. Dessa forma, comprovou a eficiência deste reagente químico para remediação de áreas contaminadas por cromo hexavalente, assim como foi observado nos artigos técnicos de estudos de casos nos Estados Unidos e Europa. / [en] This dissertation presents the results obtained in the remediation process
remediation of a contaminated area by hexavalent chromium applying the
technology in situ chemical remediation (ISCR). The study area is located in
the Rio de Janeiro city and was occupied by a glass factory for forty years and
purchased for construction of residential condominiums.
This dissertation presents the results obtained in the remediation process
remediation of a contaminated area by hexavalent chromium applying the
technology in situ chemical remediation (ISCR). The study area is located in
the Rio de Janeiro city and was occupied by a glass factory for forty years and
purchased for construction of residential condominiums.
Chromium is an important metal for the industry and is used in various
products and processes, such as electroplating, leather treatment, pulp, wood
preservation, and refractory manufacturing. The trivalent chromium is essential
from a nutritional point of view, non-toxic and poorly absorbed in the body,
acting in the maintenance of some functions. Cr(III) is the most common being
found and occurs naturally, since the element Cr(VI) can occur naturally, but in
low concentrations, if the groundwater has geochemical conditions the Cr (III)
can be oxidize to Cr (VI). The hexavalent chromium is the most dangerous
valence state and, according to ATSDR (two thousand and twelve), have greater mobility in the
groundwater, being carcinogenic by inhalation of high doses of soluble
chromate salts. The mobility of hexavalent chromium is high in soil and
groundwater because it is not adsorbed by the soil in that valence state, on the
other hand when it is in trivalent form is strongly adsorbed by the soil, forming
insoluble precipitates, having low mobility in soil and groundwater.
The hexavalent chromium remediation by in situ chemical reduction
using calcium polysulfide has been the subject of several field studies
documented in the literature, both for soil and groundwater from the Chromite
Ore Processing Residue (COPR) (Storch, et al., two thousand and two; Graham, et al., two thousand and six ;
Charboneau, et al., two thousand and six ; Wazne, et al., two thousand seven a; Wazne, et al., two thousand seven b;
Chrysochoou, et al., two thousand and ten ; Chrysochoou & Ting, two thousand and eleven ; Pakzadeh & Batista,
two thousand and eleven ; Chrysochoou, et al., two thousand and twelve ).
Calcium polysulfide is a fertilizer to soil and commercially available and
has been used in some remediation studies cases for reducing hexavalent
chromium in soil and groundwater. Being commercially available and used as
fertilizer, it is a relatively cheap chemical reagent in comparison with other
chemical compounds exclusively developed for this purpose.
The stoichiometric demand and the chemical kinetics of the reduction of
Cr (VI) by the calcium polysulfide in aqueous solution was studied by Graham
et al. (two thousand and six) from the chromite ore processing residue (COPR). With this study
it was reported that a molar ratio of a point sixty-six is required (close to the theoretical
value of one point five) and a first-order kinetics with an initial concentration of twenty-six eight point
mg/L and pH of the CPS solution around eleven point five, with the presence of oxygen.
Thus, the hexavalent chromium is reduced to chromium hydroxide, slightly
water soluble compound which is precipitated to the soil. The trivalent
chromium has low solubility, toxicity, mobility, reactivity and is considered
stable.
There are various application techniques of chemical reagents in the
underground environment, and choosing the most appropriate method for each
area depends on the type of contaminant, geological environment, groundwater
and surface interference, depth, thickness and size of the contaminated area. As
described by Suthersan (mil novecentos ninety-six), the injection of chemical reagents has to
achieve two objectives: (one) creating and maintaining an ideal redox
environment and other parameters such as pH, presence or absence of
dissolved oxygen, etc.; and (two) the delivery and distribution of the necessary
reagents for a homogeneous way throughout the injection area, both
horizontally and vertically. Thus, it is essential that the conceptual model of the
study area is very detailed, so there is no doubt in the choice of chemical
reagent application methodology.
Although there are numerous laboratory studies on hexavalent chromium
remediation using calcium polysulfide, there are few reports in the literature on
the field application, especially case studies in Brazil, therefore, this case study
becomes a demonstration applying calcium polysulfide as a remediation
technique for hexavalent chrome, with geochemical data, which are important
for monitoring chemical reduction. This case study shows the effectiveness,
dosage and concentration of the study area, and may apply to other hexavalent
chromium remediation projects.
Materials and Methods
A former glass factory (the Site ) operated in the North Zone of Rio de
Janeiro / RJ, Brazil from the mid-thousand nine hundred and fifty s to two thousand and five. A portion of the facility was
used to store raw material to produce glass, including arsenic oxide, and
another portion of the Site was used to conduct industrial plating using
hexavalent chromium (Cr(VI)) in the glass molds. In two thousand and nine, the Site was
purchased for mixed use redevelopment, demanding an environmental
assessment and subsequent remediation.
Between two thousand and nine and two thousand and twelve several phases of site investigation was
conducted. The results of the investigation indicated that Cr(VI) was present in
soil at concentrations up to approximately twenty one mg/kg and in groundwater at
concentrations up to approximately thirty mg/L. These concentrations exceeded
regulatory criteria of three hundred mg/Kg for soil and zero point zero five mg/L for groundwater. A
phased remedial approach was developed consisting of the following: (a)
excavation and off-site disposal of two and four hundred ton of Cr(VI) impacted soil from the
source area, performed in the unsaturated and saturated zone soils in the Cr(VI)
source area; (b) post-excavation monitoring of the groundwater conditions; and
(c) groundwater treatment following the excavation program. Hexavalent
chromium concentrations in groundwater decreased significantly following the
excavation, however, additional reduction of concentrations of Cr(VI)
contaminant in groundwater was required.
Then was designed and implemented a set of bench-scale treatability
tests in order to evaluate groundwater remediation alternatives. Several
proprietary and non-proprietary reductants for co-treatment of Cr(VI) were
evaluated. Calcium polysulfide were selected to treat Cr(VI).
To reduce residual Cr(VI) concentrations in the groundwater plume
located downgradient of the former excavated source area, dois e seven hundred cubic meters
were targeted for active treatment. The groundwater remediation approach
consisted of the injection of thirty liters of CPS (twenty nine percent) diluted in two hundred and twenty
liters of water, yielding a total of two hundred and fifty liters of solution injected using direct
push technology into seventy two locations.
Groundwater Monitoring
As part of chemical reagent injection stage was performed the baseline
monitoring with collection of soil and groundwater samples. The soil sampling
was performed by direct push technique using PVC liner with two inches in
diameter, to analyze the total and hexavalent chromium concentrations.
Six months after the injection were installed sixteen monitoring wells, eight
shallow wells (five meters) and eight deep wells (nine meters) spread upstream, side,
middle and downstream of the injection area.
Groundwater geochemical parameters (i.e., temperature, total solids
dissolved, specific conductance, pH, oxidation-reduction potential, and
temperature) were measured at the time groundwater samples were collected.
Groundwater samples were collected and analyzed for total and dissolved
chromium, hexavalent chromium, iron, arsenic, manganese, calcium, sulfate,
and sulfide. Samples were field-filtered with disposable zero point forty-five μm polyethylene
filter capsules prior to collecting samples for dissolved metals.
Results and Discussion
Dose calculations for the reduction of hexavalent chromium have been
performed with the data obtained in the bench-scale treatability test and
resulted in a stoichiometric demand of four mlCPS/kg soil to the treatment of the
study area. Therefore thirty liters of solution was used containing twenty-nine percent
calcium polysulfide and approximately two hundred and twenty two liters to perform their mixture,
totaling two hundred and fifty-two thousand and thirty liters of solution.
For solution injection were performed seventy two soil borings with eight point five meters
deep, and the product was injected range between two point five and eightpoint five meters. The
depth of injection was from two point five mbgl covered any change in water level due to
seasonal variation.
In each soil boring was injected chemical reagent solution comprised four hundred and seventeen
liters of calcium polysulfide diluted in tree and eighty-three liters of water for a total volume
of tree and a half liters of solution injected per point.
The comparative analysis results of the third monitoring campaign ( eighteen
months post-injection) with the baseline campaign (september/two thousand and twelve) indicated
reduction of hexavalent chromium concentrations between forty-six point sixty-seven and ninety-nine and ninety-five percent.
Regarding the second monitoring campaign (twelve months post-injection),
the hexavalent chromium concentrations reduced between twenty-three point ninety-nine and ninety nine point seventy-nine percent in
five of the fifteen monitoring wells that were sampled. In three of the fifteen
monitoring wells the hexavalent chromium concentrations remained below the
quantitation limit used by the analytical laboratory method. There was no
increase in hexavalent chromium concentration, compared the results of the
third and second monitoring campaign.
The evaluation of the Eh and pH values measured in the monitoring
campaigns showed that the pH value was in the acidic range (about four ) and after
removal of contaminated soil with hexavalent chromium pH raised to between
five and six, after the chemical reagent injection pH increased to the basic range
(above seven point five). In the second and third campaign the pH reduced to acid range
(below six point five), which can be regarded as the pH value of the area background.
The Eh has inversely proportional behavior, increasing between the first and
third campaign, and in the third campaign the measured values are in the
ranges considered as moderately reducing (hundred to four hundred mV) and oxidizer (> four hundred
mV).
The pH variation also showed a relationship between increased
concentrations of calcium, iron, manganese and sulfate (in some monitoring
wells). There were also reductions in hexavalent chromium concentrations in
monitoring wells.
Conclusion
This case study indicates that the use of different remediation techniques
when applied together (excavation and chemical reduction), reducing the time
required for remediation of a contaminated site without impacting the final cost
of remediation. The chemical reduction of hexavalent chromium using calcium
polysulfide was effective to reduce the concentration to less than the
quantification limit of the analytical method used.
Therefore, as presented it is necessary to carry out several studies to
detail the hexavalent chromium concentration in the site, as well as understand
the geochemistry of groundwater and performing bench-scale tests to evaluate
the effectiveness of the chemical reagent in the site study hydrogeological
environment and calculate the required dose.
The treatability test with calcium polysulfide demonstrated the feasibility
of using this chemical reagent by In Situ Chemical Reduction (ISCR) to reduce
the hexavalent chrome concentration in soil and groundwater. The test resulted
in a stoichiometric demand of four mlCPS /kg soil to the treatment of the study
area.
Soil samples collected six months after injection showed that the calcium
polysulfide could desorb hexavalent chromium from the soil, since,
contaminant concentrations were not detected in the samples.
neteen months after the injection of the chemical reagent the groundwater
concentrations of hexavalent chromium reduced from forty-six point sixty-seven to ninety-nine and ninety-five percent in
relation to baseline campaign. And, of the fifteen monitoring wells in just three
wells hexavalent chromium concentrations were detected.
This demonstrates the effectiveness of using calcium polysulfide to
remediate hexavalent chromium in soil and groundwater, confirming the
studies by Storch et al. (two thousand and two), Graham et al (two thousand and six), Charboneau et al. ( two thousand and six),
Wazne et al. (two thousand and seven a), Wazne et al. (two thousand and seven b), Chrysochoou et al. (two thousand and ten),
Chrysochoou & Ting (two thousand and eleven), Pakzadeh & Batista (two thousand and eleven), Chrysochoou et al
(2012) in several areas in United States and Europe.
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