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Résumé: As the exploitation of industrial waste has regained interest in recent years for economic and environmental reasons, the valorization of by-products is now part of the sustainable development. This makes it possible to enhance the ethical image of companies and establish commitment towards nature and society. Replacing some chemicals by recovered waste can help in solving the problem partially. Thus, the present work studies the use of metallurgical waste FeSO4 ·7H2 O as a catalyst in the degradation of the black azo dye eriochrome T (EBT) by the electro-Fenton process. The powder of the FeSO4 ·7H2 O waste was characterized by X-ray diffraction and scanning electron microscopy. The study of the effect of operating parameters on the efficiency of the EF revealed optimal values for catalyst dose (0.038 g·L–1), supporting electrolyte concentration (8 × 10–3 M) and current density (15 mA·cm–2). The 60 min treatment of 50 mg·L–1 EBT solution under optimal operating conditions led to a color and COD removal efficiency of 86.79% and 83.01%, respectively. The results obtained were promising and are of great interest for the use of FeSO4 ·7H2 O metallurgical waste as a catalyst in the electro-Fenton process. Keywords: Electro-Fenton; Wastewater treatment; Electrochemical advanced oxidation process; Organic persistent pollutants

Résumé: The Advanced Oxidation Processes (AOPs) are promising environmentally friendly technologies for the treatment of wastewater containing organic pollutants in general and particularly dyes. The aim of this work is to determine which of the AOP processes based on the Fenton reaction is more effective in degrading the methyl orange (MO) dye. The comparative study of the Fenton, photo-Fenton (PF) and electro-Fenton (EF) processes has shown that electro-Fenton is the most efficient method for oxidizing Methyl Orange. The evolution of organic matter degradation was followed by absorbance (discoloration) and COD (mineralization) measurements. The kinetics of the MO degradation by the electro-Fenton process is very rapid and the OM degradation rate reached 90.87% after 5 min. The influence of some parameters such as the concentration of the catalyst (Fe (II)), the concentration of MO, the current density, the nature and the concentration of supporting electrolyte was investigated. The results showed that the degradation rate increases with the increase in the applied current density and the concentration of the supporting electrolyte. The study of the concentration effect on the rate degradation revealed optimal values for the concentrations 2.10−5 M and 75 mg L−1 of Fe (II) and MO respectively. Keywords: advanced oxidation processes; dye degradation; persistent organic pollutants mineralization; water treatment

Résumé: This study was undertaken to enhance the selectivity and the removal efficiency of Cd2+ from a mixture solution containing Cd2+ and Na+ using continuous electropermutation (EP) with alginate-modified resin (MR). The surface of the MR was characterized via scanning electron microscopy and Fourier transform infrared. The use of the MR in EP process has improved the efficiency and the selectivity for Cd2+ removal from Cd2+ (88, 46%), Na+ (81, 41%) to Cd2+ (96, 98%), Na+ (51, 47%). The effect of current density and concentration of the electro-regeneration electrolyte on the Cd2+ removal efficiency was investigated.

Résumé: The degradation of the herbicide fenuron was investigated using a new porous bifunctional electrode where the electrooxidation takes place on one side and the photocatalysis on the other side. The characterization of the synthetized bifunctional electrode (PbO2/SnO2-Sb2O3/Ti//Ti/TiO2) was performed by scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction analysis and showed that the anodic side (Ti/SnO2-Sb2O3/PbO2) is covered with a tetragonal β-PbO2 film and that the photocatalytic side (Ti/TiO2) consists of an anatase phase of TiO2. The single application of electrooxidation achieved 87.8% fenuron degradation and 84.1% chemical oxygen demand (COD) removal while heterogeneous photocatalysis resulted in only 59.2% and 39.7% fenuron concentration decay and COD removal, respectively. On the other hand, the photocatalytically-assisted electrooxidation (photo-electrooxidation) performed on the bifunctional electrode provided higher performances of fenuron degradation (97.5%) and mineralization (97.4%). Investigation of operating parameters highlighted the positive effect of increase in current density. Conversely, an increase in fenuron concentration led to a decrease in degradation rate and COD removal. It was also found that the COD removal and mineralization efficiency are higher in a neutral medium.

Résumé: In this work, the electrochemical degradation efficiency of synthetic azo dye, methylene blue, at positive electrode PbO2 of lead-acid battery was investigated. The structure and morphology of the electrode was investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectrometry. The influence of several operating parameters on electro-oxidation of 100 mL of methylene blue solution 100 mg/L was studied. Results indicated that lead-acid battery electrode is effective for removing color and chemical oxygen demand (COD). It is found that current density, the stirring speed, and the supporting electrolyte concentration have a positive effect on decolorization and mineralization, and no significant effect of the distance between the electrodes on methylene blue degradation and COD removal was observed. By contrast, the percentage of color and COD removal decreases with increasing of pH. Kinetic analysis of the results revealed that the COD removal follows a pseudo-first-order kinetics.

Résumé: Phosphate rock is a valuable material that is used for the production of large phosphorus chemicals. However, this natural material usually contains some toxic elements such as cadmium (Cd). Cd is a non-nutritive metal regarded as harmful to both humans and the environment. The main toxic effects of Cd on human health are the kidney and renal cortex diseases. Other effects were observed on pulmonary, cardiovascular, and musculoskeletal systems, in addition to including Cd as a human carcinogen. In order to reduce the cadmium content in the phosphate ore, an original method was studied and consists of coupling both leaching and electrodialysis. The effects of process parameters, such as reaction time, nature, and concentration of the extracting agent, liquid/phosphate ore ratio, pH, temperature, and current density, were investigated. The obtained results show that the cadmium extraction from phosphate ore using simple batch leaching does not reduce the cadmium content to the required level. However, the application of leaching- electrodialysis coupled method at optimum current density of 10 mA cm−2 increases the cadmium extraction efficiency up to 84.3%. This synergetic process could be applied to the treatment of phosphate ore containing cadmium.

Résumé: This study discusses the operating variables for removal of cadmium from phosphate ore using Na2EDTA. These variables include the reaction time, Na2EDTA concentration, liquid/phosphate ore ratio, number of extractions and microwave extraction. Na2EDTA induced a two-step extraction process including a rapid extraction within the first hour, and a subsequent gradual release that occurred over the following hours. The cadmium extraction efficiency increased progressively with the increasing of Na2EDTA concentration. The extraction efficiency of cadmium increased with increasing liquid/phosphate ratio in the 5–200 range. Consecutive extractions using low concentrations were more effective than a single soil extraction with concentrated Na2EDTA. Microwave was beneficial to improve the removal in soil washing, and using microwave could partly substitute for agitation.

Résumé: Phosphate rocks are a vital and non-renewable resource which is crucial for agricultural uses. However, this raw material contains various contaminants such as Pb, Cr, Cu, Ni and Zn. Among these elements, chromium is considered as an essential micronutrient at low intake levels. Its occurrence in industrial products at higher concentration can cause a potential risk to plants, animals and human health. The objective of this work was to select a chemical reagent capable of efficiently extracting chromium from phosphate ore in order to reduce its content. The study of chromium speciation in phosphate ore allows us to evaluate its mobility and therefore its potential toxicity. To this end, the test and selection of the specific chemical reagent for efficient chromium extraction from phosphate ore were studied. The effects of some parameters were taken into consideration and optimized. The results show that the chromium content was reduced to approximately 30% in natural phosphate using citric acid as extracting solution. Sequential extractions proposed by the European Communities Bureau of Reference method were used to assess the distribution of chromium before and after chemical extraction. The results indicate that the distribution of chromium in the residual fraction is dominant.

Résumé: The objective of this work was to correlate the separation process of the metallic cations (M(II)) by electropermutation (EP) of multications solution with the affinity of ion-exchange materials (IEMs). The obtained results show that the affinity order is similar for all tested IEMs and is as follows: Pb(II)>Cd(II)>Zn(II)>Mg(II). Furthermore, the order of the transfer flux (J) of metallic cations obtained with different tested cation-exchange membranes (CEMs) is identical to that encountered for the affinity order. Further analysis of the results demonstrated that the affinity of IEMs and the transfer flux change in reverse order of hydration ionic radius (r) of metallic cations: rMg(II)>rZn(II)≥rCd(II)>rPb(II). During the EP, the order of metallic cations transfer is as established previously when using different electro-regeneration cations (H+, Na+, NH4+) and different co-ions (NO3−, Cl−, SO42−). However, the extent of the transfer flux as a function of the nature of electro-regeneration cation follows the order: JM(II)(H+)>JM(II)(NH4+)>JM(II)(Na+). The removal rates of metallic cations vary in the range 89−99%. This work shows that the orders of the IEMs affinity and the transfer are mainly determined by the properties of metallic cations such as the hydration ionic radius. Nevertheless, the importance of the fixation and the transfer of metallic cations depend on the IEMs’ nature

Résumé: During the chromic plating of parts, the baths become more and more poor in chromic acid and rich in metallic impurities such as Cu2+, Zn2+, Fe3+ and Cr3+ which makes the bath useless. Also, the water used to rinse parts contains chromic acid and metallic impurities. As it is known that chromic acid is relatively expensive and very toxic, so its recovery has double interest: economic and environmental. Its reuse is possible after removal of metallic impurities. In this work, we studied the possibility of metallic impurities elimination from the chromic acid. The influence of the current density and the circulating solution flow rate on the process efficiency has been studied. The elimination rates obtained in the presence of ion exchange textile are superior to those obtained in the absence of textile. The analysis of the results showed that for the three metallic impurities studied (Cu2+, Fe3+ and Zn2+), the purification rate increases versus the applied current density and solution flow rate. The importance of the elimination of the three metal cations is as the following order: Cu2+ >Zn2+ >Fe3+.

Résumé: The analysis of wastewater from a factory of painted steel tiles showed a high pollution degree. The pollution load (organic and mineral) of these waters generates degradation or even an eutrophication of the receiving environment (river and sea). The objective of this study was to reduce this pollution by applying an appropriate pretreatment that takes into account the industrial effluent standards, opportunities and interests of the company. The pretreatment of clarification chosen was the coagulation–flocculation where we have used two coagulants such as aluminum sulphate and ferric chloride and two types of flocculant: anionic and cationic. Clarification tests by jar-test showed that the mixture of aluminum sulphate/cationic flocculant gives the best results. However, the sludge volume remains high despite its decline to 290 cm3 after 24 h of settling. By comparing the results of analysis of wastewater before and after treatment, we can deduce that the method used is satisfactory.

Résumé: This paper discusses the extraction of cadmium from phosphate ore by the washing method. Various parameters were investigated for the cadmium extraction from phosphate ore. The results from extraction tests showed that cadmium extraction depends on the nature and concentration of the extracting agent, the liquid/phosphate ore ratio, the temperature and the solution pH. The effi ciency of the nine extracting agents for removing cadmium from phosphate ore was found to be in the order: Na2EDTA > citric acid > tartric acid > ammonium citrate > calcium chloride > ammonium acetate > ammonium chloride > oxalic acid > ammonium hydroxide. In this study cadmium extraction kinetics was best described by the product layer diffusion control model.

Résumé: According to World Bank projections, world population will reach 7 billion in 2020. This impressive population must be accommodated, clothed and most importantly it must be fed. It keep into this challenge an increase in the agricultural production must reach 90% of the already cultivated land. It is clear that mineral fertilizers will continue to play an important role in improving agricultural production. A fertilizer is by definition ”any product containing at least 5% of the three major plant nutrients: N, , and . The most common fertilizers are nitrogen, phosphate, potassium, magnesium and sulphur fertilizers. They can be simple, single or complex nutrients. Currently, phosphate fertilizers are by far the most prevalent. However, the fertilizers produced from phosphate ores still contain heavy metals that are harmful to human health. These heavy metals are transferred through processing to phosphoric acid: the main intermediary between the rock and phosphate fertilizers. Among these heavy metals, cadmium seems to be the most harmful and toxic element. The occurrence of such element in the fertilizer products causes a serious danger to both human health and environment. Most of the phosphate-bearing rocks contain large Cd amounts that are often above acceptable levels. Phosphate ore industry usually tends to improve the quality of product by eliminating this toxic element. The aim of this study is to present an accurate and less expensive method by which cadmium in phosphate ore would be reduced to lower rates. The method uses ammonium acetate salt, diamine tetra-acetic and hydrochloric acids as extracting agents of cadmium in phosphate. The influence of some parameters was taken into consideration, such as the volume/mass ratios, the extracting agent concentration and the temperature. The results analyses were based on the amount of cadmium extracted and P2O5 loss, and the efficiencies of extracting agents.

Résumé: The aim of this work is to highlight the coupling efficiency of electrodialysis and ion-exchange processes for treating water containing heavy metal ions at low concentrations. This hybrid technique called electropermutation (EP) or also continuous electroregeneration. The effects of various physico-chemical parameters on the efficiency of the coupled process such as pH, flow rate of feed solution circulation, density of the applied current and initial concentration of Cd(II) in the solution have been studied. The results obtained show that the removal and transfer of Cd(II) ions decreases with the increase of the flow rate of feed solution and with pH increasing. Furthermore, the increase of the current density enhances the elimination and therefore the transfer of this ion until a density value of 10 mA.cm−2. The EP on resin remains effective until a 224.8 mg.L−1 of Cd(II) ions in the feed solution. Overall, under the optimal operating conditions determined, the hybrid technique of EP removes about 98% of Cd(II) from a dilute solution.

Résumé: l'acide chromique et des impuretés métalliques telles que Cu2+, Zn2+, Fe3+ et Cr3+. Sachant que l'acide chromique est relativement cher et très toxique, sa récupération s’impose et présente un intérêt double, économique et environnemental. Dans ce travail, nous avons étudié la possibilité d’éliminer les impuretés métalliques de l’acide chromique et de reconcentrer ce dernier par électrodialyse. La concentration, la conductivité, le pH et la différence de potentiel ont été suivis pendant l’opération de l’électrodialyse. L’analyse des résultats a montré que pour les trois impuretés métalliques étudiées (Cu2+, Zn2+ et Fe3+), le taux d’épuration augmente avec la densité de courant appliquée et le débit de circulation de la solution à traiter. L’importance de l’élimination des trois cations métalliques suit l’ordre suivant : Cu2+ > Zn2+ > Fe3+. La reconcentration de l’acide chromique est également favorisée par l’augmentation de la densité de courant et le débit de circulation de la solution. Cependant, à cause de la fuite en proton, cette reconcentration reste limitée.

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