Descoloração de efluentes de tinturaria por oxidação electroquímica

Os efluentes provenientes da indústria tê xtil apresentam, de um modo geral, forte coloração, pH altamente variável e elevado teor em matérias oxidáveis, traduzido pelos significativos valores de C.Q.O. (Carência Química em Oxigénio). Devido a estas características e à variável composição destes efluentes, o seu tratamento através de métodos mais tradicionais (combinação de processos físicos, químicos e biológicos) nem sempre é o mais eficaz. Uma das principais características dos efluentes de tinturaria é a presença de corantes, altamente visível. Dependendo do tipo de corante usado, a cor do efluente pode variar diariamente ou várias vezes por dia. A utilização de diferentes corantes pode conduzir, também, a uma variação significativa do valor do pH (de 2 a 12, por exemplo). O trabalho apresentado teve, como objectivo, a utilização de um processo electroquímico no tratamento de um efluente têxtil simulado, cuja composição traduzisse a situação real de tingimento com um corante de base antraquinóica. Os resultados obtidos permitiram concluir que o método aplicado conduziu a uma redução significativa dos valores de C.Q.O. (eliminação de matérias oxidáveis), assim como a uma completa descoloração do efluente

Effect of CO2 laser radiation on surface properties of synthetic fibres

Chemical treatment methods are most often used in the present for polymer surface modification; however, these methods are frequently “environmentally unfriendly”. So, new technologies are now considered, especially in physical treatment methods. This is the case of laser technologies, like CO2 laser radiation. Morphological modifications can be produced on the surface of polymers, resulting in changes in the physical and chemical properties of the materials. In this study, different experimental conditions were applied in CO2 laser irradiation of polyamide (PA 6.6) fibres. Resulting morphological modification of surface and possible crystallinity variation were investigated. SEM (scanning electron microscopy) and DSC (differential scanning calorimetry) analysis were used

CO2 laser modification on synthetic fibres:effect on dyeing properties

Infrared lasers, like CO2, appear to be advantageous due to their large beam size, high efficiency, easy operation, use of non-toxic gases and low cost. However, they have been less used than others for the surface treatment of polymers, likely due to the thermal damage effects caused by infrared radiation. This shortcoming can be overcome by use of pulsed lasers. CO2 pulsed laser can be considered as a non-contact and environmentally friendly treatment technique for modification of surface of polymers. Morphological modifications can result in changes on physical and chemical properties of the materials, such as water absorption and dyeing. In this work, polyester (PES) and polyamide (PA 6.6) fabrics were treated with a CO2 pulsed laser and then dyed with different commercially available dyes. Dyeing properties were investigated, as changes in the dye ability of laser treated fibres are expected, namely an improvement in those properties. In fact, laser treatment creates a certain roughness on the fibre surface, resulting in an increase of the overall surface area and a subsequent enhance of dye adsorption

Electrochemical degradation of C.I. reactive orange 16 in the presence of H2O2/Cu+ Ions

The aim of the present study was to investigate the electrochemical degradation of a vinylsulphone reactive dye, C.I. Reactive Orange 16, in the presence of hydrogen peroxide and copper ions. The reaction between these two species leads to the generation of hydroxyl radicals, causing dye oxidation and degradation. The efficiency of dyebath decolorization and dye degradation was evaluated by color removal and COD variation. With a two-electrode electrochemical system it was possible to optimize experimental conditions in order to achieve color removal of simulated dyebaths over than 90% after 30-90 min of electrolysis.Fundação para a Ciência e Tecnologia (FCT

C.I. Reactive Black 5 degradation by advanced electrochemical oxidation process, AEOP

In the last decades, an increasing number of procedures to remove pollutants from wastewater have been reported. Advanced oxidation processes (AOPs) are one of those technologies used for this purpose, namely, for textile wastewater treatment. AOPs are environmentally friendly methods based on chemical, photochemical or photocatalytical production of hydroxyl radical (HO•). This strong oxidant can react with most organic compounds present in wastewater, as dyestuffs. In this paper, an Advanced Electrochemical Oxidation Process (AEOP) is discussed concerning the electrochemical degradation of a vinylsulphone reactive dye, C.I. Reactive Black 5, in the presence of hydrogen peroxide and copper ions. The reaction between H2O2 and electrochemically generated Cu+ ions leads to the production of hydroxyl radicals, causing dye oxidation and degradation. The efficiency of the process is followed by evaluation of dyebath decolorization (measured by color removal), Chemical Oxygen Demand (COD) variation, among other parameters. Simulated dyebath were prepared and diluted to 5 and 20% of initial concentration. Experimental results confirmed the effectiveness of the procedure in C.I. Reactive Black 5 degradation.Fundação para a Ciência e a Tecnologia (FCT)

Electrochemical degradation of reactive blue 19 dye in textile wastewater

Textile wastewater is notoriously known to contain strong colour, a highly fluctuating pH and significant COD (Chemical Oxygen Demand) values. Because of these characteristics, treatment of these effluents has been rather difficult. Traditional methods for dealing with textile wastewater consist of various combinations of biological, physical and chemical methods. Because of the large variability of the composition of textile wastewaters, most of these traditional methods are becoming inadequate. The aim of this work was to use an electrochemical procedure to treat used dyebaths and cyclic voltammetry (CV) technique for dye degradation study. Electrolysis can be an adequate process for colour removal as well organics pollutants and CV is an important tool for redox reactions interpretation. Electrochemical treatment results show significant decrease on COD values, for the different values of dye concentration and several applied potentials. Progressive colour removal and dye degradation can be achieved for different values of dye concentration. Depending on electrolysis time and applied potential, total decolouration can be attained

Application of cyclic voltammetric technique on dye concentration control in aqueous solutions

This communication follows a previous work concerning indirect electrochemical reduction of dyes [1] and its application on dyeing control with sulphur dyes. The study concerns the cathodic peak intensity variation with sulphur dye C.I. Leuco Sulphur Black 1 (Black Diresul RDT liq.) concentration, in the presence of a mediator, iron/triethanolamine (FeIII/TEA), in alkaline media

Tingimento com novos corantes sulfurosos: Contribuição para uma tecnologia mais limpa

Os corantes sulfurosos constituem um exemplo dos problemas encontrados no sector têxtil. Os processos com este tipo de corante apresentam um elevado teor em sulfuretos e carga poluente. Associadas a estes salientam-se as dificuldades na quantificação de corante rejeitado. Nesta comunicação, pretende-se apresentar um contributo à alteração da situação exposta, quer pela substituição dos corantes tradicionais por corantes sulfurosos pré-reduzidos, com baixo teor em sulfuretos e sua quantificação, quer pela aplicação do tingimento com redução electroquímica indirecta

Voltammetric study and electrochemical degradation of reactive dyes

The aim of this study was, in a first stage, to investigate the voltammetric behavior of two reactive dyes, C.I.Reactive Orange 16 and C.I.Reactive Blue 19. Cyclic voltammetry technique (CV), on a glassy carbon electrode, was used for this purpose in order to identify the electrochemical activity of the chromophore group in each case, in the present experimental conditions. A second part of the study was to investigate the electrochemical degradation of the dyes, in the presence of hydrogen peroxide and copper ions. The reaction between the two species leads to the generation of hydroxyl radicals, which causes the oxidation and degradation of the organic compounds. The efficiency of dye degradation and ecolorization were evaluated by color removal and COD values. Depending on electrolysis time, applied potential, hydrogen peroxide concentration and dye concentration, different stages of color removal were attained

Aplicação da técnica de voltametria cíclica na selecção de material de eléctrodo para o sistema mediador FeIII/TEA

Enquadrada num trabalho mais amplo sobre a redução electroquímica indirecta de corantes, a presente comunicação teve, como objectivo, a selecção de um material de eléctrodo adequado ao complexo de ferro e trietanolamina (FeIII/TEA), em meio básico, usado como mediador redox. A análise dos resultados experimentais e dos voltamogramas obtidos permitiu concluir que, dos diferentes materiais testados (aço, ferro e cobre), o cobre parece ser o que permite uma transferência electrónica de maior reversibilidade