Modificação superficial de argila caulinítica: oclusão de agentes tensoativos

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Química, Florianópolis, 2013.As argilas são compostas, no geral, de silicatos hidratados de alumínio ou argilominerais que comumente atingem certa plasticidade quando umedecidas. O que diferencia uma argila de outra é o tipo de estrutura e as substituições que podem ocorrer dentro desta estrutura do alumínio, por magnésio ou ferro, e do silício, por alumínio ou ferro, principalmente. A argila caulinítica possui partículas de caulinita formadas normalmente por placas hexagonais. A maioria das partículas grandes tende a formar empilhamentos de partículas menores. Além disso, as argilas cauliníticas possuem baixa capacidade de troca catiônica e menor plasticidade comparativa entre às argilas, devido à forte ligação entre as camadas de clivagem. A modificação estrutural das argilas cauliníticas, pela intercalação de agentes tensoativos, visa estudar/entender a capacidade de dispersão em pastas/soluções aquosas. Os agentes tensoativos são substâncias orgânicas que ficam intercaladas nas lamelas da argila, que aumentam o espaçamento basal entre elas. Essas substâncias químicas tensoativas foram incorporadas na argila de duas formas, a primeira foi misturar o tensoativo à argila e, em seguida, acrescentá-la à pasta, na segunda forma, o tensoativo modificou a argila por um processo de adsorção. Embora o espaçamento das lamelas da argila seja limitado, foi possível a intercalação de partículas serem formadas entre as lamelas com o tratamento dos tensoativos. Os agentes tensoativos conferiram um aumento do espaçamento basal das argilas, o que foi confirmado nos testes de difração de raios-X, espectroscopia de absorção na região do infravermelho e microscopia eletrônica de varredura, mostrando que a capacidade da argila de intercalar substâncias orgânicas depende da composição química de sua superfície. Além do mais, a intercalação de agentes tensoativos na argila diminuiu a cristalinidade da caulinita, relacionada a um menor espaço para as vibrações e estiramentos de seus grupos de átomos e ligações. Desta maneira foi possível relacionar que as moléculas dos tensoativos interagem com estas hidroxilas The clays are generally composed of hydrated aluminum silicates or clay minerals that commonly affect certain plasticity when moist. What differentiates a clay is another type of structure and substitutions that may occur inside the structure of aluminum magnesium or iron and silicon to aluminum or iron mainly. The kaolinite has particles usually formed by hexagonal plates. The majority of large particles tend to form stacks of smaller particles. Furthermore, kaolinitic clays have low cation exchange capacity and lower plasticity clays between due to the strong link between the layers of cleavage. Structural modification of kaolinitic clays by intercalation of surfactants aims to study/understand the dispersal capacity in folders/aqueous solutions. The surfactants are intercalated organic substances in the clay lamellae, increasing the basal spacing between them. These chemicals have been incorporated in the clay surfactant in two ways. The first way was to mix the surfactant to the clay and then add the pasta. The second surfactant forms the clay modified by an adsorption process. Although the spacing of the lamellar clay is limited, it was possible to merge particles are formed between the lamellae of the surfactant treatment. The surfactants conferred an increased basal spacing of the clays, making methods on the practical and attractive environment. Analyses of X-ray diffraction, absorption spectroscopy in the infrared and scanning electron microscopy showed that the capacity of the clay interlayer organic substances depends on the chemical composition of its surface. Furthermore, interleaving surfactants in clay decreased the crystallinity of kaolinite, related to the shortest and stretching vibrations of its atoms and groups of links, to relate this way it was possible that molecules of these surfactants interact with hydroxyl groups

UTILIZAÇÃO DE SUBPRODUTOS DA CADEIA PRODUTIVA DO ARROZ COMO ADSORVENTES PARA A REMOÇÃO DE COBRE EM UMA SOLUÇÃO SINTÉTICA

A casca de arroz é um subproduto obtido nas primeiras etapas de beneficiamento do arroz. Geralmente é destinada para a geração de energia através da sua incineração, dando origem a um novo resíduo, a cinza de casca de arroz. Indústrias de diversos segmentos (processamento de metais) produzem grande quantidade de efluentes contendo teores de cobre superior à concentração permitida pela legislação, fazendo-se necessário o estudo de técnicas para a sua remoção, como a adsorção. Neste trabalho, casca de arroz tratada (CAT) e cinza da casca de arroz (CCA) foram utilizados como materiais adsorventes para a remoção de íons cobre em efluente sintético. Os espectros de infravermelho para a CAT e para a CCA sugerem a presença de celulose, lignina e hemicelulose e silicatos, respectivamente. Verificou-se que, para a CAT e CCA, a adsorção é favorecida em pHs variando entre 4 a 6, uma vez que pH superiores a 6, tende a formar precipitados insolúveis de cobre, e em pHs muito ácidos, os íons hidrogênio (H+) tendem a competir com o cobre pelo sítio ativo do adsorvente. A cinética predominante ao modelo foi de pseudo-segunda ordem, e o modelo de isoterma de Langmuir. Ademais, a CAT apresentou maior percentual de remoção de cobre, 91,59 1,93%, quando utilizado 5 g.L-1 de adsorvente

Vinasse treatment using a vegetable-tannin coagulant and photocatalysis - doi: 10.4025/actascitechnol.v35i1.11011

The large volume of sugar cane vinasse generated by alcohol distillation motivated current treatment to reduce vinasse volume by a concentration process and to eliminate pollutants in the wastewater. The vinasse concentration by the coagulation/flocculation process favored the use of the thickened sludge either for fertilizing purposes or for biogas production. The photocatalysis treatment of the clarified vinasse mineralized pollutants and reduced toxicity, with subsequent water reuse. The first series of coagulation/flocculation experiments were carried out in a jar-test apparatus at room temperature with samples of 200 mL and several coagulant concentrations. In the second series of experiments, photocatalysis tests were performed on the clarified vinasse obtained by coagulation/flocculation under conditions optimized in the first series of experiments. The photocatalysis tests were performed for five consecutive days with UV irradiation, using TiO2-P25 as photocatalyst. Significant reduction of toxicity, consistent with the reduction in chemical oxygen demand (COD), was found when the photocatalysis treatment subsequent to coagulation/flocculation process was employed. Further, 98% reduction of turbidity and 87% reduction of color were obtained by the coagulation/flocculation process. Coupled to the photocatalysis process, significant reductions in absorbance, toxicity and COD (80%) were also achieved.

Marine macroalgae Pelvetia canaliculata (Phaeophyceae) as a natural cation exchanger for cadmium and lead ions separation in aqueous solutions

This work aims to add value to marine brown macro-algae Pelvetia canaliculata (Linnaeus) Decaisne and Thuret through its use as cation exchanger for separation and recovery of cadmium and lead ions in aqueous solution, as a cost effective and environmental friendly process. Raw algae was established as a cation exchanger, in which cadmium and lead ions present in the solution exchange with Na+, K+, Ca2+ and Mg2+, bound to the negatively functional groups existing on the algae surface, with a stoichiometric ratio of 1:1 between ions of the same charge and 2:1 between monovalent and divalent ions. Batch equilibrium and kinetic experiments were conducted at different pH values using Na-loaded algae. The main functional groups present on the surface of the algae responsible for binding metals, as determined by Fourier Transform Infrared (FTIR) analysis, are weakly acidic carboxylic groups and strongly acidic sulfonic groups. Considering the potentiometric titration and biomass esterification results, the amount of sulfonic and carboxylic groups is 1.0 mmol/g and 1.5 mmol/g, respectively, which is in agreement with the total amount of Na+ present at the surface of Na-loaded biomass (2.5 mEq/g) and total amount of light metals present at the surface of raw biomass (2.5 mEq/g). Maximum biosorption capacity of Pb2+ at pH 4.0 was 1.25 mmol/g (2.5 mEq/g; 259 mg/g) and for Cd2+ at pH 4.5 was 1.25 mmol/g (2.5 mEq/g; 140 mg/g). The mass action law for the ternary mixture was able to predict the equilibrium data, with the selectivity coefficients alpha(Cd)(Na) = 337 and alpha(Pb)(Na) = 941 for carboxylic and alpha(Cd)(Na) = 38 and alpha(Pb)(Na) = 1695 for sulfonic groups, revealing a higher affinity of the biomass towards lead ions. A mass transfer model, considering equilibrium given by the mass action law, and a linear driving force model for intraparticle diffusion, was able to fit well the batch kinetic data

Ion exchange prediction model for multi-metal systems obtained from single-metal systems using the macroalga Pelvetia canaliculata (Phaeophyceae) as a natural cation exchanger

The aim of this study was to investigate the cation exchange capacity of the macroalga Pelvetia canaliculata (Linnaeus) Decaisne & Thuret in a multi-metal system containing Cd2+, Pb2+, Cu2+ and Zn2+. The Naloaded alga was established as a cation exchanger, in which cadmium, lead, copper, zinc and hydrogen ions present in the liquid phase exchange with sodium ions bound to the functional groups on the algal surface, mainly weakly acidic carboxylic groups and strongly acidic sulfonic groups. A mass action law for the senary system (Na+/H+/cd(2+)/Pb2+/Zn2+) was able to predict the equilibrium data using the selectivity coefficients determined for the single-metal systems. Multi-metal equilibrium results, in agreement with the selectivity coefficients, showed a higher preference (affinity) of the biomass toward lead ions followed by copper, cadmium and zinc ions. A mass transfer model, considering equilibrium given by the mass action law, and a linear driving force model for intraparticle diffusion, was able to fit well the batch kinetic experimental data for all chemical species in the liquid and solid phase. The results indicate that the biomass of P. canaliculata is an efficient natural cation exchanger for multi-metal systems

Ion-exchange breakthrough curves for single and multi-metal systems using marine macroalgae Pelvetia canaliculata as a natural cation exchanger

In this study, single and multi-metal ion-exchange systems, Na+/H+/Cd2+, Ne+/H+/Pb2+, Na+/H+/Cu2+, Na+/ H+/Zn2+ and Na+/H+/Cd2+/Pb2+/Cu2+/Zn2+, were studied in continuous mode using a fixed-bed column packed with Na-loaded macroalgae Pelvetia canaliculata as natural cation exchanger. Breakthrough curves were obtained for all the systems operating at inlet metal concentrations of 20 mg/L. For the single metal ion-exchange systems, the service capacity obtained was 329, 107, 120 and 184 bed volumes for Zn2+, Cu2+, Cd2+ and Pb2+, respectively. Desorption, using 0.1 M HNO3 as eluent, was fast and near to 100% of effectiveness, using only 10 bed volumes of eluent, achieving maximum metal concentrations at the column outlet of 2.8 3.8, 1.5 and 1.8 g/L for Cd2+, Pb2+, Cu2+ and Zn2+ ions, respectively. In the multi-metal sorption process, Cd and Zn break through the column faster than Cu and Pb due to its lower affinity for the biosorbent. An overshoot in the Cd and Zn outlet concentrations was observed for the multi-metal system and explained by the competitive uptake with Pb and Cu ions. Biosorption of Cd2+, Pb2+, Cu2+ and Zn2+ by P. canaliculata pre-loaded with sodium is based on an ion-exchange mechanism accompanied by the release of Na+ into the liquid phase. A mass transfer model, including the mass balances to the packed bed column and thin plate algal particles, assuming a LDF model, and complementary equations (as mass action law equilibrium relations, initial and boundary equations), was able to fit well the experimental data. Finally, an ion-exchange pilot plant was tested for the treatment of a multi-metal synthetic solution using the natural macroalgae