Acid leaching of LiCoO2 enhanced by reducing agent. Model formulation and validation.

In this work, a model has been formulated to describe the complex process of LiCoO2 leaching through the participation of competing reactions in acid media including the effect of H2O2 as reducing agent. The model presented here describes the extraction of Li and Co in the presence and absence of H2O2, and it takes into account the different phenomena affecting the controlling mechanisms. In this context, the model predicts the swift from kinetic control to diffusion control. The model has been implemented and solved to simulate the leaching process. To validate the model and to estimate the model parameters, a set of 12 (in triplicate) extraction experiments were carried out varying the concentration of hydrochloric acid (within the range of 0.5-2.5 M) and hydrogen peroxide (range 0-0.6%v/v). The simulation results match fairly well with the experimental data for a wide range of conditions. Furthermore, the model can be used to predict results with different solid-liquid ratios as well as different acid and oxygen peroxide concentrations. This model could be used to design or optimize a LiCoO2 extraction process facilitating the corresponding economical balance of the treatment.

Optimization of Ni (II) biosorption from aqueous solution on modified lemon peel.

The valorization of agricultural waste peels as a low-cost biosorbent is a promising approach to water treatment. In this work, the improvement of the adsorption capacity of lemon peel to remove Ni (II) from aqueous effluents was explored using several chemical modifiers: HNO3, HCl, H3PO4, CaCl2, NH3 and NaOH. The surface pretreatment using NaOH was selected as the best option because of the improvement of the maximum adsorption capacity. The maximum adsorption capacity was of 36.74 mg g-1 according to the Langmuir model at optimum conditions (pH = 5, S/L = 5 g L-1, 25 °C). The pseudo-first order model of biosorption kinetics provides the best fit for experimental data. From thermodynamic studies, it was concluded that Ni (II) biosorption by modified lemon peel was endothermic and spontaneous. After five consecutives adsorption-desorption cycles using 0.1 M of HNO3 and H2SO4, a recovery of 90% of Ni (II) was obtained. Regarding characterization of the biosorbent, the surface morphology was studied by Scanning Electron Microscopy while the functional groups responsible for Ni (II) adsorption were evaluated by Fourier transform infrared spectroscopy.

Biogas production from pear residues using sludge from a wastewater treatment plant digester. Influence of the feed delivery procedure.

Clear economic advantages may be obtained from the management of seasonal fruit wastes by codigestion at existing facilities which are working throughout the year with other residues. We have explored the biomethanization of pear residues in a 5L stirred reactor loaded with sludge from the anaerobic digester of a municipal wastewater treatment plant. Different organic loading rates (OLRs) of fruit waste were tested with two delivery procedures: a discontinuous one (fed once a day) and a pseudocontinuous one. For both procedures, as the OLR increases the pH of the digester drops to acidic values and large OLRs may cause the reactor failure. Nevertheless, the pseudocontinuous delivery allows the treatment of more residue, (10.5 versus 6.0 g of volatile solids per litre of reactor and day), maintaining the specific biogas production (0.44 L of biogas per gram of volatile solids), with some improvement in methane concentration (44% vs 39%).

Kinetics of the chemical reduction of nitrate by zero-valent iron.

The use of reactive barriers is one of the preferred remediation technologies for the remediation of groundwater contamination. An adequate design of these barriers requires the understanding of the kinetics of the reaction between the target contaminant and the solid phase in the barrier. A study of the kinetics between metallic iron and aqueous nitrate is presented in this paper. Published literature regarding this reaction indicates that researchers are far from a consensus about the mechanism of this reaction. This paper presents the results obtained from experiments performed at different constant pH values and iron dosages, together with a mathematical analysis of the kinetic results. We have found that an Eley-Rideal kinetic model yields a good explanation of the relatively complicated dependence between rate of nitrate reduction and the pH value of the solution.

[Impact of polymetallic mine (Zn, Pb, Cu) residues on surface water, sediments and soils at the vicinity (Marrakech, Morocco)]. / Impact des residus d'une mine polymetallique (Zn, Pb, Cu) sur les eaux de surface, les sediments et les sols avoisinants (Marrakech, Maroc).

Metal sulphide tailings present a potential risk for the environment because of their natural oxidability which leads to the production of acid mine drainage. The prospected site close to Marrakech includes zinc, lead and copper sulphide deposits. This site is located in an agricultural area near the Tensift River which is used for irrigation. In addition to the tailing leachates, underground mine waters are also discharged into the river. This represents a potential risk for the environment and human health. The aim of this study was to assess the tailings impact on surface water, sediments and soil qualities. Chemical analysis of surface water and sediments collected downstream of the mine revealed that, water and sediments present high concentrations of major ions and heavy metals. The analysis also revealed spatial as well as temporal changes in the chemical properties of the studied water and sediments. These changes are attributed to the rising phenomena. The soil near the mine presents high content of sulphate. Its Zn, Pb, Cu and Fe contents are respectively 38, 15, 11 and 1.6 times higher than non contaminated soils located far away from the site. The soil irrigated with underground mine waters shows concentrations of SO4(2-), Cu, Zn, Fe, Cd and Pb which are respectively 4, 10, 28, 2, 9 and 12 times higher than soils which are not irrigated with this mine water. This study also showed that there has been a change in the physicochemical characteristics of water and sediments in the sampling points downstream of the mine before its closure and after its activity renewal.

Biomethanization of mixtures of fruits and vegetables solid wastes and sludge from a municipal wastewater treatment plant.

The possible management of Fruit and Vegetable Solid Wastes (FVSWs) through their simultaneous digestion with the primary sludge of Municipal Wastewater Treatment plants is investigated. This alternative allows the recovery of energy and a solid product that can be used as an amendment for soils that generated the residue, while is not expensive. Results indicate that the ratio of FVSWs to sludge and the pH control are the main variables determining the methane production and concentration. NaHCO3 was selected to achieve the pH control. The results for a ratio of 50% sludge together with 10 g NaHCO3/kg of residue are among the best obtained, with a methane yield of about 90 L per kg of volatile solids, and a methane concentration of 40% (v/v) of the biogas. A 50% reduction of the total solids; 21% reduction of the volatile solids (in terms of total solids); and a pH value of the sludge, which is 6.9 indicate that the digested sludge can be a good material for soil amendment.

Modeling of electrodialytic and dialytic removal of Cr, Cu and As from CCA-treated wood chips.

A one-dimensional model is developed for simulating the electrodialytic and dialytic treatment of a saturated bed of wood chips containing chromium, copper and arsenic. The movement of Cr, Cu and As is mathematically modeled taking into account the diffusion transport resulting from the concentration gradients of their compounds and the electromigration of their ionic, simple and complex species during the operation. The model also includes the electromigration of the non-contaminant principal ionic species in the system, H(+) and OH(-), proceeding from the electrolysis at the electrodes, Na(+) and NO(3)(-) used as electrolyte solutions in the electrode compartments, and oxalate ions and protons incorporated with the oxalic acid solution during wood chips incubation. The model simulation also takes into account that OH(-) generated on the cathode, during electrodialytic remediation, is periodically neutralized by addition of nitric acid in the cathode compartment. The anion and cation-exchange membranes are simply represented as ionic filters that preclude the transport of co-ions (the cations and anions respectively) with the exception of H(+), which is retarded but considered to pass through the anion-exchange membrane.

Removal of organic contaminants from soils by an electrokinetic process: the case of atrazine. Experimental and modeling.

The atrazine behaviour in soils when submitted to an electric field was studied and the applicability of the electrokinetic process in atrazine soil remediation was evaluated. Two polluted soils were used, respectively with and without atrazine residues, being the last one spiked. Four electrokinetic experiments were carried out at a laboratory scale. Determination of atrazine residues were performed by enzyme-linked immunosorbent assay (ELISA). The results show that the electrokinetic process is able to remove efficiently atrazine in soil solution, mainly towards the anode compartment: Estimations show that 30-50% of its initial amount is removed from the soil within the first 24h. A one-dimensional model is developed for simulating the electrokinetic treatment of a saturated soil containing atrazine. The movement of atrazine is modelized taking into account the diffusion transport resulting from atrazine concentration gradients and the reversed electro-osmotic flow at acidic soil pH.

A column study of soil contamination by lead: influence of pH and carbonate content. II. Mathematical model.

A mathematical model is used for the interpretation of the results from earlier experimental studies in lab-scale columns on the contamination of a carbonatic soil with lead. Local equilibrium conditions suffice to reproduce the experimental curves for every pH value of the influent contaminant solution and carbonate content of the soils essayed, but heterogeneous contact between the aqueous and solid phase should be included. This heterogeneous contact is responsible for the important tailing effects observed, and is difficult to estimate even for the lab conditions. Then, important uncertainties should be accepted both for risk assessment and in situ remediation feasibility studies.

A column study of soil contamination by lead: influence of pH and carbonate content. I. Experimental results.

The influence of soil carbonate content on the fate of lead in soil was studied in a lab-scale column under different pH values of the contaminant solution. Results indicated that retention of this toxic heavy metal (up to 38% weight at pH = 5) occurred which was proportional to the total carbonate content. A decrease in the pH of the aqueous solution entering the column resulted in a decrease of the retention of lead in the soil. Furthermore, the concentration of lead in the effluent was increased dramatically. Concentrations of lead about 2.5 times higher than in the contaminant solution were measured at pH = 3. Knowledge of these phenomena is important for risk assessment and remediation feasibility studies.

Column study of the influence of air humidity on the retention of hydrocarbons on soil.

Inverse gas chromatography (IGC) is used for the analysis of the influence of air relative humidity on the retention of hexane, benzene, toluene and p-xylene in a sandy soil under experimental conditions similar to those typical of soil vapor extraction (SVE). The advantages of IGC over other techniques, are (a) an efficient use of lab resources, (b) a high sensitivity to low partitioning coefficients and (c) a closer reproduction of field conditions. In our procedure, experiments with only two samples of different mass are necessary to establish if linear isotherms can be used to describe the retention of the contaminants. This approach gives information necessary for analyzing the feasibility and design of remediation technologies with a laboratory effort significantly smaller than the adsorption/desorption cycle for isotherm determination. The retention coefficients of the contaminants decrease as humidity increases in a similar fashion for all of them, probably because the reduction in the number of the adsorption sites available for the organic compounds due to the presence of water is quite similar for all the contaminants studied. These retention coefficients may be related to those obtained for dry air conditions for all the contaminants through (R - 1)RH% = A(R - 1)dry air(B), where the parameter B is found to remain approximately constant (0.90), while the parameter A decreases linearly with the relative moisture.

Chemotaxis of pathogenic Vibrio strains towards mucus surfaces of gilt-head sea bream (Sparus aurata L.).

Vibrio anguillarum and Vibrio alginolyticus exhibited significant adhesion to and chemotactic abilities towards mucus collected from the skin, gills, and intestine of gilt-head sea bream. Quadratic polynomial models for chemotaxis designed to estimate the influence of temperature demonstrated a differential bacterial chemotaxis depending of the source of the mucus, with the chemotaxis towards intestinal mucus being the least influenced.

Cleanup of fractured rock aquifers. II. Effects of matrix diffusion and nonaqueous phase liquid.

Model calculations are used to explore the effects of the kinetics of diffusion of dissolved organic compounds into and out of low-permeability porous materials and of the rate of solution of nonaqueous phase liquid (NAPL) droplets (into the aqueous phase) on the rate of cleanup of contaminated aquifers. Two models are presented: (1) the flushing of organic compounds initially distributed as NAPL droplets in a fracture in a porous rock aquifer, and (2) the removal of organic compounds initially present as NAPL in an aquifer containing low-permeability porous clay lenses. NAPL droplet size is found to be of much less importance than the spacing of the fractures in the porous rock in the first model or the thickness of the clay lenses in the second.