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This study describes the selective removal of cobalt (II) and nickel (II) from hydrometallurgical effluent using modified clinoptilolite. X-ray fluorescence (XRF), x-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis were used to characterize the natural and modified clinoptilolites with dialkylphosphinic acid. In a batch experiment, the influence of different variables such as initial concentration, pH, particle size, clinoptilolites dosage, temperature, and contact time was evaluated. Higher removal efficiency was obtained at initial concentration of 600 mg/L, pH 6, particles size of 1000-1400 μm, dosage of 10 g/100 mL, a temperature of 25 C, and contact time of 300 minutes. The experimental data fit satisfactorily to the pseudo-second order kinetic and to the Langmuir isotherm model. Thermodynamic parameters like Gibb's free energy (ΔG o ), enthalpy (ΔH o ), and entropy (ΔS o ) were also evaluated. The results revealed that modified clinoptilolite with dialkylphosphinic acid could be successfully employed for the selective removal of cobalt (II) and nickel (II) from hydrometallurgical effluent. K E Y W O R D Sclinoptilolite, cobalt (II) and nickel (II) selective removal, dialkylphosphinic acid, ion-exchange

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The steam extraction was used to investigate the process parameters important in the extraction of essential oils from the leaves of the Eucalyptus tree. The diffusion process and the application of Fick's law, as well as the temperature dependence of the diffusion coefficient were exhibited. This has enabled the setting up of a model that takes account of the initial amount of oil in the leaves and the effect of temperature. From the literature, it can be seen that the oil collected after an extended time represents all the oil that is present in the material initially. The research conducted indicates that the extraction temperature has a significant effect on the percentage of the initial oil that is eventually extracted, with the amount of oil extracted apparently decreasing for lower temperature. This effect could, however, be modelled accurately by simply considering the temperature dependence of the diffusion coefficient. This model can lead to the design of an optimum steam extraction plant.L'extraction par vapeur aété utilisée pourétudier les paramètres importants du processus de l'extraction des huiles essentielles des feuilles de l'eucalyptus. Le processus de diffusion et l'application de la loi de Fick, ainsi que la dépendance par rapportà la température du coefficient de diffusion ontété montrés. Ceci a permis la mise en place d'un modèle qui prend en compte la quantité initiale d'huile dans les feuilles et l'effet de la température. Le coefficient de diffusionétabli dans cetteétude de recherche tombe dans l'intervalle des valeurs rapportées par la littérature pour les huiles essentielles.À partir de la littérature, on peut voir que l'huile collectée après une période prolongée représente la totalité de l'huile présente initialement dans le matériau. L'étude présente indique que la température d'extraction a un effet significatif sur le pourcentage de la quantité initiale d'huileéventuellement extraite, la quantité extraite diminuant apparemment pour les températures plus basses. Cet effet pourrait cependantêtre modélisé exactement en considérant simplement la dépendance par rapportà la température du coefficient de diffusion. Ce modèle peut conduireà la conception d'une usine d'extraction optimaleà la vapeur.

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Solar illuminated reactors have been used by several researchers for photocatalytic wastewater treatment. In this work, the light distribution in a solar illuminated slurry bubble column reactor was investigated using the Monte Carlo method. The model was validated using total refracted radiation (TRR) measurements at the unilluminated reactor wall. A fairly good agreement between the simulated and experimental TRR measurements was achieved. Bubbles were shown to affect the transmission of direct light much more than that of diffuse light. While the solar diffuse fraction and bubbles strongly affected the TRR at low catalyst loadings, they had a negligible effect on the overall light absorption. The catalyst significantly affected the light distribution with an optimal catalyst loading of 0.15 g/L being deduced from the simulation. An analysis of the local volumetric rate of energy absorption (LVREA) revealed fairly uniform light absorption along the axial direction. The radial LVREA profiles were nonuniform with the region of highest LVREA shifting from the unilluminated side of the reactor at low catalyst loadings to the illuminated side at high catalyst loadings. This study highlighted the rigor, accuracy, and utility of the Monte Carlo method for simulation of the solar light distribution.