Jordi Poch

Determination of the effective diffusion coefficient of Zn(II) on a macroporous resin XAD-2 impregnated with di-2-ethylhexyl phosphoric acid (DEHPA): Influence of metal concentration and particle size

Abstract In this work the experimental and numerical techniques employed to estimate the diffusion coefficient, D e , of Zn(II) adsorption on a macroporous resin XAD-2 impregnated with di-(2-ethylhexyl) phosphoric acid (DEHPA) have been reported. The influence of initial metal concentration and particle size on the D e has been studied. In the studied initial metal concentration range (37–248 mg/dm 3 ), D e was found to vary when increasing the initial feed concentration from 2.30×10 −13 to 14.05×10 −13 m 2 /s for the particle size 840–630 μm, and from 1.63×10 −13 to 7.32×10 −13 m 2 /s for the particle size 630–400 μm. When comparing the effect of particle size, the values of D e and k f corresponding to the biggest size showed a clear correlation with the step governing the adsorption, liquid film mass transfer or intraparticle diffusion.

Chromium (VI) uptake by grape stalks wastes encapsulated in calcium alginate beads: equilibrium and kinetics studies

Abstract The removal of hexavalent chromium from aqueous solution using grape stalks wastes encapsulated in calcium alginate (GS–CA) beads was investigated. Cr(VI) sorption kinetics were evaluated as a function of chromium initial concentration and grape stalks (GS) content in the calcium alginate (CA) beads. The process follows pseudo second-order kinetics. Transport properties of hexavalent chromium on GS–CA beads was characterised by calculating chromium diffusion coefficient using the Linear Absorption Model (LAM). Langmuir isotherms, at pH 3.0 were used to describe sorption equilibrium data as a function of GS percentage in the CAbeads. Maximum uptake obtained was 86.42 mmol of Cr(VI) per L of wet sorbent volume. Results indicated that both kinetic and equilibrium models describe adequately the adsorption process.

A teaching/learning support tool for introductory programming courses

In This work we present a Web-based tool developed with the aim of reinforcing teaching and learning of introductory programming courses. This tool provides support for teaching and learning. From the teachers perspective the system introduces important gains with respect to the classical teaching methodology. It reinforces lecture and laboratory sessions, makes it possible to give personalized attention to the student, assesses the degree of participation of the students and most importantly, performs a continuous assessment of the students progress. From the students perspective it provides a learning framework, consisting in a help environment and a correction environment, which facilitates their personal work. With this tool students are more motivated to do programming.

Modeling of kinetics of Cr(VI) sorption onto grape stalk waste in a stirred batch reactor.

Recently, Cr(VI) removal by grape stalks has been postulated to follow two mechanisms, adsorption and reduction to trivalent chromium. Nevertheless, the rate at which both processes take place and the possible simultaneity of both processes has not been investigated. In this work, kinetics of Cr(VI) sorption onto grape stalk waste has been studied. Experiments were carried out at different temperatures but at a constant pH (3+/-0.1) in a stirred batch reactor. Results showed that three steps take place in the process of Cr(VI) sorption onto grape stalk waste: Cr(VI) sorption, Cr(VI) reduction to Cr(III) and the adsorption of the formed Cr(III). Taking into account the evidences above mentioned, a model has been developed to predict Cr(VI) sorption on grape stalks on the basis of (i) irreversible reduction of Cr(VI) to Cr(III) reaction, whose reaction rate is assumed to be proportional to the Cr(VI) concentration in solution and (ii) adsorption and desorption of Cr(VI) and formed Cr(III) assuming that all the processes follow Langmuir type kinetics. The proposed model fits successfully the kinetic data obtained at different temperatures and describes the kinetics profile of total, hexavalent and trivalent chromium. The proposed model would be helpful for researchers in the field of Cr(VI) biosorption to design and predict the performance of sorption processes.

Determination of the effective diffusion coefficient for gold(III) on a macroporous resin XAD-2 impregnated with triisobutyl phosphine sulfide

Abstract In this work the experimental and numerical techniques employed to estimate the diffusion coefficient of gold(III) in a macroporous particle of resin XAD-2 impregnated with triisobutyl phosphine sulfide (TIBPS) have been described. Batch and column experiments were performed in order to get the necessary experimental results to determine the effective diffusion coefficient, D e . In the studied initial metal concentration range (39.3–196 mg/dm 3 ), D e was found to increase with increasing the initial feed concentration from 1.28×10 −8 to 6.40×10 −8 m 2 /h.

Grape Stalks Wastes Encapsulated in Calcium Alginate Beads for Cr(VI) Removal from Aqueous Solutions

Abstract In this study, a low‐cost effective adsorbent based on grape stalks encapsulated in calcium alginate beads was investigated as a possible sorbent for the removal of Cr(VI) from aqueous solution. The present paper deals with the procedure for the preparation of calcium alginate beads and the encapsulation of grape stalks powder into calcium alginate beads, the characterization of these beads and the study of their behavior on Cr(VI) adsorption from aqueous solutions. The influence of grape stalks powder concentration in the calcium alginate beads, metal solution pH, sodium chloride, and metal concentration on metal removal has been studied. Uptake showed a pH‐dependent profile. Maximum Cr(VI) sorption was achieved at pH 3.0. High NaCl concentrations significantly reduce the mechanical resistance of the beads, however, this does not have a significant effect on metal removal. Langmuir and Freundlich isotherms were used to describe sorption equilibrium data. The experimental data were fitted better by the Langmuir adsorption isotherm. The Langmuir adsorption capacity for calcium alginate beads containing 2% (w/v) grape stalks powder was found to be 71.98 10−3 mg/bead (≈225 mg Cr(VI)/g grape stalks).

A web-based e-learning tool for UML class diagrams

The paper presents a web-based tool designed to give support to teaching and learning of UML class diagrams. The proposed UML environment is capable to correct automatically UML class diagrams exercises providing feedback to the student immediately. The tool is part of a more general framework, denoted ACME, which provides the main functionalities of an e-learning platform. The tool has been used in a first experimental group of an introductory database course.

An automatic correction tool for relational database schemas

A Web-based tool developed to automatically correct relational database schemas is presented. This tool has been integrated into a more general e-learning platform and is used to reinforce teaching and learning on database courses. This platform assigns to each student a set of database problems selected from a common repository. The student has to design a relational database schema and enter it into the system through a user friendly interface specifically designed for it. The correction tool corrects the design and shows detected errors. The student has the chance to correct them and send a new solution. These steps can be repeated as many times as required until a correct solution is obtained. Currently, this system is being used in different introductory database courses at the University of Girona with very promising results.

Expansion of adsorption isotherms into equilibrium surface: Case 1: solvent impregnated resins (SIR)

In this work, the adsorption of Au(III) and Zn(II) by impregnated resins has been studied in batch and column experiments. In batch experiments successive contacts for each metal concentration were made until saturation was reached. Equilibrium points corresponding to each contact brought a different isotherm. By introducing a new variable it was observed that all the equilibrium points fitted a surface that we call the equilibrium surface. Once the equilibrium surface was determined it was found that the different isotherms, obtained in batch and column experiments, were fitted on the surface. Traditional isotherms and the equations of the equilibrium surfaces for zinc(II) and gold(III) adsorption with impregnated resins have been compared and discussed. The equilibrium surface equation proposed in this work has been proven to be a good tool for modelling adsorption by impregnated resins in batch and column experiments.

A model to describe Cr(VI) kinetics biosorption.

In this work, the effect of pH control on kinetics of Cr(VI) sorption onto grape stalks has been studied. A set of experiments were performed at a constant pH 3+/-0.1 which was assured by means of a Programmable Logic Controller (PLC). In a second set of experiments the initial pH was adjusted to pH 3 and then pH was allowed to freely evolve during the sorption process. Both sets of experiments were carried out at different temperatures within the range 5-50 degrees C. Constant temperature was assured by water recirculation from a thermostatic bath. Results demonstrated that pH has high influence on kinetics only at the lowest temperatures studied. A model based on a complex reaction sequence which takes into account Cr(VI) sorption, reduction of Cr(VI) to Cr(III), sorption of the formed Cr(III) which includes the pH variation during the sorption process has been proposed to model Cr(VI) kinetics sorption onto grape stalk waste. Furthermore, the robustness of the model has been tested.