The growth of anthropogenic actions, especially industrial development and urbanization, has increased the release of heavy metals in the environment, including hexavalent chromium, Cr (VI), requiring, as a matter of urgency, new processes for pollutants removal, among which are the adsorption processes, which are the focus of this work. Biosorption is an efficient, economical, high selectivity and low energy consumption technique. The main objective of this work was the production of a biosorbent from the crop residues of Cocos nucifera, enhancing it with superparamagnetic properties, as a viable technical and economical alternative, able to adsorb hexavalent chromium ions, Cr (VI), applicable to the treatment of industrial wastewater, expanding pollution control strategies and minimizing environmental impacts. Thus, low concentration coprecipitation routes for the synthesis of nanoparticle (NPs) were proposed, conveying magnetic property to the Cocos nucifera biomass. During the biosorption of hexavalent chromium ions, Cr (VI), the saturation conditions (equilibrium) and the kinetic parameters were evaluated to determine the maximum removal capacity and equilibrium time for the biosorption, besides the optimum conditions for pH, initial concentration, biosorbent content, particle size (grain size), stirring velocity and temperature, providing the fitting of equilibrium models and kinetic constants determination. The biosorbents were characterized by scanning electron microscopy techniques with dispersive energy spectroscopy (SEM/EDS), Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (EDX), X-ray fluorescence with dispersive energy (FR-X/WD), thermogravimetric analysis (TGA), magnetization measurements, zero load point analysis (pCZ), and specific surface analysis through the Brunauer, Emmet and Teller (BET) method. The leachate effluent obtained in the production of the magnetized fibers was characterized through the parameters biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC) and pH. The characterization of biosorbents and the determination of kinetic and equilibrium parameters provided the main mechanisms of the biosorption process, giving arise to a possible application on an industrial scale, helping to solve serious environmental problems. / O crescimento das atividades antrópicas, sobretudo o desenvolvimento industrial e o crescimento das cidades têm como consequência o aumento do descarte de metais pesados no ambiente com destaque para o cromo hexavalente, Cr(VI), demandando, urgentemente, novos processos para remoção destes poluentes, dentre os quais os processos adsortivos, que são o foco do presente trabalho. A biossorção tem se destacado como uma técnica eficaz, econômica, de alta seletividade e baixo consumo energético. O objetivo principal desse trabalho é a produção de um biossorvente a partir de rejeitos agrícolas de fibra de Cocos nucifera com propriedades superparamagnética, capaz de adsorver íons de cromo hexavalente, Cr(VI), facilmente aplicável as indústrias, como uma alternativa técnica e econômica viável, ampliando as estratégias de controle de poluentes e minimizando os impactos ambientais. Com essa finalidade foram propostas rotas de síntese de coprecipitação de nanoparticulas (NPs) de magnetita, em baixas concentrações, promovendo propriedade magnética à biomassa das fibras do Cocos nucifera. No processo de biossorção dos íons cromo hexavalente, Cr(VI), foram avaliadas as condições de saturação (equilíbrio) e os parâmetros cinéticos para determinar a capacidade máxima de remoção e o tempo de equilíbrio da biossorção, além das condições ótimas de pH, concentração inicial e carga dos biossorventes, tamanho das partículas (granulometria), velocidade de agitação e temperatura, definindo os modelos de equilíbrio e as constantes cinéticas. Os biossorventes foram caracterizados pelas técnicas de microscopia eletrônica de varredura com espectroscopia de energia dispersiva (MEV/EDS), espectrometria de infravermelho por transformada de Fourier (FT-IR), difratometria de raios-X (EDX), fluorescência de raios-X por energia dispersiva (FR-X/WD), análise termogravimétrica (TGA), medidas de magnetização, análise do ponto de carga zero (pCZ) e análise superficial especifica pelo método de Brunauer, Emmet e Teller (B.E.T). O lixiviado, efluente obtido na produção das fibras magnetizadas, foi caracterizado pelas determinações da demanda bioquímica de oxigênio (DBO), demanda química de oxigênio (DQO), carbono orgânico total (COT) e pH. Como resultado da caracterização dos biossorventes e dos cálculos dos parâmetros cinéticos e de equilíbrio, foi possível sugerir os principais mecanismos do processo de biossorção, facilitando uma possível aplicação em escala industrial, remediando sérios problemas ambientais.

The issue of Hexavalent chromium toxicity to Portland cement hydration is a very actual these days. It takes much effort to obtain a cement containing Cr(VI) less than 2 ppm. The primary objective of this diploma theses is to find appropriate reducing substances and specify their efficiency, as well as to make an attempt to optimize their dosage. As reducing substances there were plumbed sulphites and tin(II) salts. The influence of reducing substances applied to the hydration and cement properties were validated by strenght tests, the calorimetric measurement and the volume-variation measurement. And also the changes in hydration products microstructure of Portland clinker after the gypsum replacement by sulphite ions were plumbed. The study of microstructure is based on SEM and XRD methods.

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Water scarcity due to limited resources and pollution of the little available water by organic and inorganic contaminants remains as one of the critical issues of the 21st century. Several treatment methods have been developed, with some being used successfully at industrial scale but many challenges including secondary sludge generation, high operation costs, high maintenance costs and high energy input were observed. In this study, the adsorption process was explored as an effective means for the removal of Cr(VI) ions from aqueous solution due to its economic feasibility and use of abundantly available adsorbents. Amongst the many available adsorbents, this work focused on exploring functionalized activated carbons (ACs) as adsorbents for Cr(VI) ions due to their favorable adsorption characteristics which involve large surface area, high porosity, and high radiant stability. The iron oxide functionalized polyethyleneimine activated carbon-silica composites were prepared through co-precipitation of Fe(II) and Fe(III) over Macadamia activated carbon to form the AC-Fe3O4 co-shell which was reacted with tetraethylorthosilicate (TEOS) and the polyethyleneimine (PEI). The different adsorbents prepared were labelled AC-Fe3O4, AC-Fe3O4-SiO2 and AC-Fe3O4-SiO2-PEI. The adsorbents were further characterized using elemental analysis (CHNS), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), transmission electron spectroscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FTIR displayed successful attachment of Fe3O4 and SiO2 with bands at 404 and 786 cm-1 being assigned to the asymmetric vibration of Fe-O and Si-O-Si while the asymmetric stretch of Si-OH is observed at 1066 cm-1. XRD showed the presence of magnetite particles in the adsorbents confirmed by the JCPDS 00-019-0629. EDS revealed the presence of Fe, Si, and N atoms which can relate to successful incorporation of the desired functional groups. Each of these materials were evaluated for their Cr(VI) ion removal through batch adsorption experiments where one parameter at a time was varied while all others were fixed. The parameters investigated included the effect of pH, contact time, initials Cr(VI) concentration, adsorbent dosage concentration and temperature. The optimum conditions were obtained at pH 3, initial concentration 2.5 mg/L, contact time of 120 min for AC-Fe3O4-SiO2-PEI. The optimization of each parameter was done in order to determine the conditions in which the adsorbents work best in the uptake of Cr(VI). All the three studied adsorbents showed acceptable adsorption performance for the removal of Cr(VI) from aqueous solutions. Adsorption isotherms studied confirmed that the adsorption data in all the three adsorbents fitted well into the Langmuir isotherm, demonstrating a homogeneous monolayer coverage. Regarding the kinetic studies, the adsorption data were best described by the pseudo-second order rate model with R2 values of 0.974, 0.974 and 0.962 for AC-Fe3O4, AC-Fe3O4-SiO2 and AC-Fe3O4-SiO2-PEI, respectively. The adsorption capacity observed from the present study (6.62, 3.92 and 5.48 for AC-Fe3O4, AC-Fe3O4-SiO2 and AC-Fe3O4-SiO2-PEI, respectively) were satisfactory and suitable as compared to those reported in literature. Thermodynamics data of the adsorption processes revealed a feasible spontaneous endothermic adsorption process which also confirmed that the reaction process occurred through chemisorption.