No abstract

ResumoA ativação ácida de uma argila tem por finalidade aumentar as suas propriedades adsortivas e catalíticas. Nesse estudo, uma amostra de argila bentonítica, proveniente da Província de Mendoza (Argentina), foi ativada com diferentes concentrações (4 e 8 N) por ácido sulfúrico e clorídrico. Para verificar a influência das concentrações e do tipo de ácido usado na ativação da argila, utilizou-se técnicas de difração de raios X, análise térmica diferencial e termogravimétrica e análise química. Os resultados mostraram que houve modificação na estrutura do material argiloso após o ataque ácido. O tratamento com ácido sulfúrico e clorídrico sobre uma mesma bentonita originou produtos com diferentes características estruturais.Palavras-chave: ativação ácida, argila, bentonita. AbstractThe clay acid activation has the purpose of increasing its adsorbent and catalytic properties. In this study, a bentonite clay sample from Mendoza (Argentine) was activated in different concentrations (4 N and 8 N)

Adsorption processes have been investigated and successfully applied in the removal of dyes from textile plant wastewaters. Activated carbon is one of the most commonly used adsorbents, due to its excellent characteristics and relatively low cost. However, its dye removal efficiency depends on several parameters, notably the chemical nature of the carbon surface. To enhance the adsorption capacity, different methods have been proposed in the literature, chemical modification using acidic agents being one of the most commonly used. In this study, the performance of samples of activated carbon chemically modified with nitric and phosphoric acid in the adsorption of Basic Yellow 28 is evaluated. The physical and chemical structure of these adsorbents was investigated using electron microscopy, X‐ray spectrometry, and infrared spectroscopy, revealing significant modifications depending on the agent used. Adsorption tests were conducted at three different temperatures and the adsorption kinetics and isotherms were evaluated. Comparing the experimental data and results obtained with models reported in the literature showed that in both cases the pseudo‐second order kinetics model and the Freundlich isotherms provided the closest fits. The samples modified with nitric acid presented better overall performance, particularly due to pore collapse observed for the samples treated with phosphoric acid, which caused a significant reduction in the surface area and total pore volume. These results indicate that the chemically‐modified activated carbon can be employed in the removal of basic dyes from textile effluents, allowing the reuse of the effluent.

Nineteen fungal strains were isolated from a chicken slaughterhouse effluent and within those, only one showed high values of lipolytic activity in submerged cultures. This fungus was identified as Trametes hirsuta. The crude extract was immobilized in chitosan/clay beads, with an immobilization yield of 80.9%. The analyses of the crude extract and the immobilized derivative at different temperatures, pH (s), solvents, metallic ions and storage showed that the immobilization process increased the enzyme life span. Ethyl esters were obtained in solvent free systems using chicken viscera oil and the enzyme crude extract. For effective comparison, a reaction using viscera oil and commercial lipase Novozym 435 was carried out. The result revealed 35% and 28% esters conversion in the reactions containing chicken viscera oil, using Novozym 435 and the crude extract respectively. The extract was also used in a reaction with soybean oil, traditionally used as starting substrate for biodiesel production.

A natural bentonite sample from Argentina was activated by sulfuric acid in different concentrations (20 and 40 wt%) and different contact time (120 and 210 min), at the same temperature (90°C) . The ratio of the mass of clay to the volume of acid solution was 1:10 (w/v). These materials were tested to verify its bleaching (decolorization) capacity of soybean oil, which was compared to a standard commercial bleaching material Fulmont Premiere. Differential thermal analysis and thermogravimetric techniques, infrared spectrometry and chemical analysis showed that the acid activation modified the clay material structural properties. Bleaching capacity was found to be dependent on the acid concentration and treatment time used. The activated Argentine material showed superior bleaching performance compared to the commercial clay used by vegetable oil refiners.