No abstract

The pollution of water has been one of the greatest problems faced by the modern society, due to industrialization and urban growth. Rivers, lakes and seas have been continually suffering from the rising concentration of various pollutants, especially toxic elements. This study aimed to evaluate the use of cashew nut shell (Anacardium occidentale) (CNS), after chemical modification with H 2 O 2 , H 2 SO 4 and NaOH, as an new and renewable adsorbent material, for the removal of metals Cd 2+ , Pb 2+ and Cr 3+ in aqueous medium. The adsorbents were characterized by its chemical constitution, structure, infrared spectroscopy, morphology, by means of scanning electron microscopy, determination of the point of zero charge, thermogravimetrical analysis and porosimetry assessments. Tests were conducted to determine the optimal conditions (pH vs. adsorbent mass) for adsorption, by means of multivariate analysis using a central composite design. The adsorption kinetics was evaluated by models of pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion, while adsorption isotherms were linearized by Langmuir, Freundlich and Dubinin-Radushkevich. The effect of initial concentration, temperature and desorption was also performed. The adsorbents exhibited irregular, spongy and heterogeneous structure. FTIR analysis confirms the presence of hydroxyl, aliphatic, phenolic and carboxylic acid groups, which are favorable adsorption characteristics. The pH PZC of adsorbent is 4.35, 2.50 e 6.92, respectively, for CNS H 2 O 2 , H 2 SO 4 and NaOH. The optimum adsorption conditions were as follows: pH 5.0; relation of adsorbent mass/volume of water: 4 g L −1 ; 40 min of contact time for reaching the equilibration. Results suggest the predominance of chemisorption of Cd 2+ and Cr 3+ . Most of biosorbents exhibited good fit by Langmuir and Freundlich, suggesting the occurrence of adsorption on mono-and multilayers. The adsorbents of cashew nut shell exhibited high removal efficiency of Cd, Pb and Cr from waters.

Os rejeitos contendo metais pesados, originados de atividades industriais e mineradoras, podem ocasionar danos ao meio ambiente e à saúde humana. Mesmo o cromo, considerado um metal essencial, quando encontrado em altas concentrações, pode ser prejudicial, razão pela qual, o objetivo deste trabalho foi investigar a eficiência de tratamentos químicos em casca, bagaço e casca com bagaço de laranja, com o intuito de tratar efluentes aquosos contaminados por cromo (III). A modificação referese a alteração da estrutura química dos resíduos de laranja com hidróxido de sódio e ácido cítrico. Foram realizados ensaios em sistemas de batelada contendo cromo, sendo que as concentrações foram determinadas através da utilização de um espectrofotômetro de absorção atômica com chama. Analisouse a adsorção em função do pH, tempo de contato, concentração do metal, capacidade de dessorção e fatores termodinâmicos. As modificações foram constatadas no infravermelho pelo surgimento de um pico em 1730 cm-1 , o qual se refere aos grupos carboxilatos. O tempo necessário para o sistema de adsorção atingir o equilíbrio foi de cerca de 500 minutos e a cinética segue um comportamento descrito pela equação de pseudo-segunda ordem. Avaliou-se a adsorção em relação aos modelos de Langmuir e Freundlich, sendo o modelo de Freundlich o que se aplicou melhor ao processo. O valor da capacidade máxima de adsorção foi de 75,64 mg.g-1 para a casca modificada com NaOH. Além de aumentar as propriedades adsorventes, o sistema tornou-se mais espontâneo energeticamente após o tratamento químico, verificado pelos baixos valores da energia de Gibbs. Palavras-chave: Adsorção. Cromo. Resíduos de laranja. Modificação química.

No abstract

The effectiveness of Crambe abyssinica Hochst seeds by-product as a biosorbent for the removal of cadmium ions from wastewater was analyzed. The biomass of crambe was characterized by scanning electron microscopy, infrared spectroscopy and determining the point of zero charge. The optimum adsorption conditions obtained were 400 mg of biomass in a solution of pH 6.0 and contact time of 60 min to remove 19.342 mg g(-1) cadmium ions. The isotherms of adsorption were constructed and, according to the mathematical linearization, the best fitting followed the Freundlich and Dubinin-Radushkevich models, describing a multilayer adsorption and chemical interaction, also confirmed by the pseudo-second order model and enthalpy value. In the desorption process, about 79% of cadmium ions that had been adsorbed were recovered. The same conditions applied for studying the isotherms of adsorption and desorption were used for comparative study with activated carbon. It was concluded that the use of crambe by-product as biosorbent for cadmium removal in wastewaters was not only a viable alternative to activated carbon, but also required no previous treatment, so it represents a sustainable material with high applicability and low environmental impact.

Understanding the adsorption mechanisms of drugs on the surfaces of solid materials is important for determining the fate of these compounds in aqueous samples as water or wastewater treatment. A composite based on polyaniline (PAni), polypyrrole (PPy) and cigarette filters (CFs), PAni-PPy-CFs, was prepared, characterized by FTIR, TGA and SEM and applied in investigation of adsorption of a non-steroidal anti-inflammatory, phenylbutazone (PBZ), from aqueous solutions. A batch of experiments were conducted and four kinetic models and five isotherms models were used to describe the adsorption process. The experimental kinetic data were fitted very well with the second-order kinetic model, indicating that PBZ adsorption involves chemical adsorption in different binding sites, which could control the reaction rate. The equilibrium adsorption data were best fitted with the dual-site Langmuir-Freundlich isotherm, with maximum adsorption capacity of 100.22 mg g -1 , which recognizes the existence of two kinds of adsorption sites on the polymer composite surface. Finally, this composite might act as excellent adsorbents for environmental and analytical processes, for example, stationary phases in separation processes.

The assessment of vermicompost (VC) as a low-cost and alternative adsorbent for the removal of the pesticide methylparathion (MP) from an aqueous medium has been investigated by batch and column experiments. Parameters related to MP adsorption, i.e. equilibrium time (61.5 min) and adsorption pH (6.8) were optimized by using Doehlert design. The initial and final MP concentrations after adsorption assays were determined by square-wave adsorptive cathodic stripping voltammetry using an electrode composed of a multiwalled carbon nanotube dispersed in mineral oil. Batch adsorption experimental data were fitted to the Langmuir and Freundlich isotherm adsorptions, and a very good fit to the Langmuir linear model, giving a maximum adsorption capacity (MAC) of 0.17 mg g(-1). This result was very similar to that obtained with the column experiments. In order to evaluate the MP desorption from column packed VC, 100.0 ml of nitric acid solution (pH 3.0) has been percolated through material. No leaching of MP was observed, thus confirming the strong interaction between MP and VC. The satisfactory MAC obtained and low cost makes the VC a reliable natural material for the removal of MP from aqueous effluents.

No abstract