M. Feki

Preparation of activated carbon from Tunisian olive-waste cakes and its application for adsorption of heavy metal ions

The present work explored the use of Tunisian olive-waste cakes, a by-product of the manufacture process of olive oil in mills, as a potential feedstock for the preparation of activated carbon. Chemical activation of this precursor, using phosphoric acid as dehydrating agent, was adopted. To optimize the preparation method, the effect of the main process parameters (such as acid concentration, impregnation ratio, temperature of pyrolysis step) on the performances of the obtained activated carbons (expressed in terms of iodine and methylene blue numbers and specific surface area) was studied. The optimal activated carbon was fully characterized considering its adsorption properties as well as its chemical structure and morphology. To enhance the adsorption capacity of this carbon for heavy metals, a modification of the chemical characteristics of the sorbent surface was performed, using KMnO(4) as oxidant. The efficiency of this treatment was evaluated considering the adsorption of Cu(2+) ions as a model for metallic species. Column adsorption tests showed the high capacity of the activated carbon to reduce KMnO(4) into insoluble manganese (IV) oxide (MnO(2)) which impregnated the sorbent surface. The results indicated also that copper uptake capacity was enhanced by a factor of up to 3 for the permanganate-treated activated carbon.

Heavy metal removal from aqueous solutions by activated phosphate rock.

The use of natural adsorbent such as phosphate rock to replace expensive imported synthetic adsorbent is particularly appropriate for developing countries such as Tunisia. In this study, the removal characteristics of lead, cadmium, copper and zinc ions from aqueous solution by activated phosphate rock were investigated under various operating variables like contact time, solution pH, initial metal concentration and temperature. The kinetic and the sorption process of these metal ions were compared for phosphate rock (PR) and activated phosphate rock (APR). To accomplish this objective we have: (a) characterized both (PR) and (APR) using different techniques (XRD, IR) and analyses (EDAX, BET-N(2)); and, (b) qualified and quantified the interaction of Pb(2+), Cd(2+), Cu(2+) and Zn(2+) with these sorbents through batch experiments. Initial uptake of these metal ions increases with time up to 1h for (PR) and 2h for (APR), after then, it reaches equilibrium. The maximum sorption obtained for (PR) and (APR) is between pH 2 and 3 for Pb(2+) and 4 and 6 for Cd(2+), Cu(2+) and Zn(2+). The effect of temperature has been carried out at 10, 20 and 40 degrees C. The data obtained from sorption isotherms of metal ions at different temperatures fit to linear form of Langmuir sorption equation. The heat of sorption (DeltaH degrees), free energy (DeltaG degrees) and change in entropy (DeltaS degrees) were calculated. They show that sorption of Pb(2+), Cd(2+), Cu(2+) and Zn(2+) on (PR) and (APR) an endothermic process. These findings are significant for future using of (APR) for the removal of heavy metal ions from wastewater under realistic competitive conditions in terms of initial heavy metals, concentrations and pH.

Electrochemical removal of Cr(VI) from aqueous media using iron and aluminum as electrode materials: Towards a better understanding of the involved phenomena

In the present work, electrocoagulation process with iron and aluminum electrodes was investigated to deepen the understanding of the mechanism of hexavalent chromium (Cr(VI)) removal. Electrocoagulation treatment efficiency was studied with regards to the abatement of Cr(VI) and the resulting species-namely Cr(III), Fe(II) and/or Fe(III). Unlike iron, aluminum electrodes were found to be unsatisfactory for Cr(VI) removal. To elucidate the removal mechanism of hexavalent chromium, different anode/cathode materials and configurations (Fe/Fe, Pt Ti (platinized titanium)/Fe, Al/Al and Pt Ti/Al) were considered. At nearly neutral pH and considering aluminum electrodes, both electrochemical reduction (Cr(VI) to Cr(III)) at the cathode surface and adsorption on Al(OH)(3) floc mechanisms were responsible for Cr(VI) exhaustion. However, the contribution of the two mechanisms to Cr(VI) removal was not discriminated. On the other hand, in the case of iron electrodes, even though electrochemical reduction may contribute to chromium removal, its influence seemed to be minor since the effect was confined to less than 5% of the removal efficiency. Hence, there was essentially one real root for the reduction of Cr(VI) by electrocoagulation with iron electrodes, and it was proven to be the chemical reduction by Fe(II) anodically generated. Moreover, the resulting Cr(III) was quickly removed from solution, via efficient precipitation as Cr(OH)(3) hydroxides. Besides, the electrodissolved iron remained at low level owing to the precipitation of Fe(OH)(2) and/or Fe(OH)(3). Although chemical reduction by Fe(II) predominantly governed the removal of Cr(VI), acidic pH media was found to promote electrochemical reduction of hexavalent chromium at the cathode and accordingly to enhance Cr(VI) removal efficiency. In contrast, a delay of Cr(III) precipitation and a contamination of the electrolyte by electrodissolved iron were observed under acidic conditions. The effect of supporting electrolyte (Na(2)SO(4) and NaCl) on chromium removal was also studied. No conspicuous disparity in the treatment efficiency was noted under the electrocoagulation conditions used.

Lead removal from aqueous solutions by a Tunisian smectitic clay.

The adsorption of Pb(2+) ions onto Tunisian smectite-rich clay in aqueous solution was studied in a batch system. Four samples of clay (AYD, AYDh, AYDs, AYDc) were used. The raw AYD clay was sampled in the Coniacian-Early Campanian of Jebel Aïdoudi in El Hamma area (South of Tunisia). AYDh and AYDs corresponds to AYD activated by 2.5 mol/l hydrochloric acid and 2.5 mol/l sulphuric acid, respectively. AYDc corresponds to AYD calcined at different temperatures (100, 200, 300, 400, 500 and 600 degrees C). The raw AYD clay was characterized by X-ray diffraction, chemical analysis, infrared spectroscopy and coupled DTA-TGA. Specific surface area of all the clay samples was determined from nitrogen adsorption isotherms. Preliminary adsorption tests showed that sulphuric acid and hydrochloric acid activation of raw AYD clay enhanced its adsorption capacity for Pb(2+) ions. However, the uptake of Pb(2+) by AYDs was very high compared to that by AYDh. This fact was attributed to the greater solubility of clay minerals in sulphuric acid compared to hydrochloric acid. Thermic activation of AYD clay reduced the Pb(2+) uptake as soon as calcination temperature reaches 200 degrees C. All these preliminary results were well correlated to the variation of the specific surface area of the clay samples. The ability of AYDs sample to remove Pb(2+) from aqueous solutions has been studied at different operating conditions: contact time, adsorbent amount, metal ion concentration and pH. Kinetic experiments showed that the sorption of lead ions on AYDs was very fast and the equilibrium was practically reached after only 20 min. The results revealed also that the adsorption of lead increases with an increase in the solution pH from 1 to 4.5 and then decreases, slightly between pH 4.5 and 6, and rapidly at pH 6.5 due to the precipitation of some Pb(2+) ions. The equilibrium data were analysed using Langmuir isotherm model. The maximum adsorption capacity (Q(0)) increased from 25 to 25.44 mg/g with increasing temperature from 25 to 40 degrees C. Comparative study between sulphuric acid activated clay (AYDs) and powder activated carbon (PAC) for the adsorption of lead was also conducted. The results showed that sulphuric acid activated clay is more efficient than PAC.

Electrochemical oxidation post-treatment of landfill leachates treated with membrane bioreactor

Integration of membrane bioreactor (MBR) with electrochemical process was investigated as treatment of stabilized landfill leachates, collected from Djebel Chekir (Tunisia). Results showed that at optimum conditions for the membrane and with organic loading rates of 1.9 and 2.7g COD L(-1)d(-1), MBR treated effluent is still colouring and contains high COD and ammonia concentrations. In order to reduce these high pollutant concentrations, electrochemical oxidation process using Ti/Pt, graphite and PbO(2) electrodes, was tested as effluent post-treatment. Ti/Pt electrodes showed the best performance. COD, ammonia and colours removals were affected by the current density (J) and treatment time (t). At optimal operational conditions (t=1h, J=4Adm(-2)), the final COD and total kjeldahl nitrogen concentrations (TKN) were 1000 and 86mgL(-1), respectively. The final treated wastewater COD, TKN, colours, pH meet the discharge standards in the sewer. The combination of MBR treatment process with electrochemical oxidation can be a technical suitable solution for stabilized landfill leachates treatment with an efficient reduction of different parameters, essentially COD (85%), TKN (94%), and colour(436) (99%).

Adsorption of a textile dye "Indanthrene Blue RS (C.I. Vat Blue 4)" from aqueous solutions onto smectite-rich clayey rock.

The adsorption of a textile dye, namely, Indanthrene Blue RS (C.I. Vat Blue 4) onto smectite-rich clayey rock (AYD) and its sulphuric acid-activated products (AYDS) in aqueous solution was studied in a batch system with respect to contact time, pH, and temperature. The adsorbents employed were characterized by X-ray diffraction, infrared spectroscopy and specific surface area, cation exchange capacity and point of zero charge were also estimated. The effect of contact time on dye adsorption showed that the equilibrium was reached after a contact time of 40 min for the both adsorbents. The optimum pH for dye retention was found 6.0 for AYDS and 7.3 for AYD. The equilibrium adsorption data were analysed using the Langmuir and Freundlich isotherms. The adsorption capacities (Q(m)) for AYD and AYDS were found 13.92 mg/g and 17.85 mg/g, respectively. The effect of temperature on the adsorption was also investigated; adsorption of Indanthrene Blue RS is an endothermic process. This study demonstrates that all the considered adsorbents can be used as an alternative emerging technology for water treatment.

Retention of nickel from aqueous solutions using iron oxide and manganese oxide coated sand: kinetic and thermodynamic studies

In this study, the removal of nickel ions from aqueous solutions using iron oxide and manganese oxide coated sand (ICS and MCS) under different experimental conditions was investigated. The effect of metal concentration, contact time, solution pH and temperature on the amount of Ni(II) sorbed was studied and discussed. Langmuir and Freundlich isotherm constants and correlation coefficients for the present systems at different temperatures were calculated and compared. The equilibrium process was well described by the Langmuir isotherm model: the maximum sorption capacities (at 29 K) were 2.73 mg Ni/g and 3.33 mg Ni/g of sorbent for ICS and MCS, respectively. Isotherms were also used to evaluate the thermodynamic parameters (ΔG°, ΔH°, ΔS°) of adsorption. The sorption kinetics were tested for the pseudo‐first‐order, pseudo‐second‐order and intra‐particle diffusion models. Good correlation coefficients were obtained for the pseudo‐second‐order kinetic model, showing that the nickel uptake process followed the pseudo‐second‐order rate expression.

Bioassay and use in irrigation of untreated and treated wastewaters from phosphate fertilizer industry

Wastewater from phosphate fertilizer industry that contains essentially a significant amount of both fluoride and phosphate was treated by separative precipitation of fluoride ions with hydrated lime. Thus, a phosphate-rich effluent with low content of fluoride was obtained. The microtoxicity of the treated wastewater was then monitored by LUMIStox and its phytotoxicity was investigated on tomato (Lycopersicon esculentum), wheat (Triticum aestivum), maize (Zea mays), ryegrass (Lolium perenne), and alfalfa (Medicago sativa) seed germination and plant growth. The cress (Lepidium sativum) was used as a standard species for the germination index and phytotoxicity evaluation. Seedlings of four species (namely wheat, maize, ryegrass, and alfalfa) were grown in pots, which were irrigated with untreated wastewater, treated wastewater, aqueous solution of triple superphosphate fertilizer (TSP) or with tap water as control. LUMIStox tests showed that lime treatment allowed a significant toxicity removal. The treated water displayed beneficial fertilizing effect on plants. An increase in the germination index from 100% to 119% was observed. However, the untreated wastewater inhibited the species germination even when diluted 10 times. Neither plants mortality nor growth inhibition was observed after 90 days of treated wastewater application. Moreover, an improvement in plant growth, leaf number and a root development were noticed in these plants when compared with those irrigated with tap water or with fertilizer. In contrast, leaf necrosis and growth inhibition were observed in plants amended with raw wastewater. The irrigation with treated wastewater also improved soil labile P content. Indeed, soils amended with treated wastewater had more a double labile P concentration (38.15 mg kg(-1)) in comparison with control soil (15.53 mg kg(-1)).

Study of the multicomponent system wet process phosphoric acid-methyl isobutyl ketone at 40 ◦ C phase equilibria and extraction performances

This work concerns the purification of wet process phosphoric acid (WPA) by solvent extraction with methyl isobutyl ketone (MIBK) at 40 ◦ C. For this purpose, an exhaustive study of the multicomponent extraction system WPA–MIBK was carried out. In a first step, the distribution of the main components (H3PO4 ,H 2O, MIBK) and the major impurities of WPA (Ca 2+ ,M g 2+ ,A l 3+ ,F e 3+ ,S O 4 2− ,F − ) between the conjugated phases was systematically studied. Then, expression of phase compositions in terms of H3PO4 ,H 2O and MIBK on an impurity-free basis enabled us to compute the characteristics of the H 3PO4 countercurrent multistage extraction using the Mac Cabe–Thiele method. Both as-received and water-saturated MIBK were considered as solvent. From graphical results, optimum conditions to conduct the extraction of H3PO4 from concentrated WPAs (53.5–58% P2O5) were determined. To validate experimentally the obtained results, continuous countercurrent extractions were performed on a laboratory-scale mixer-settler unit. A good agreement was observed.

Purification of Wet Process Phosphoric Acid by Solvent Extraction with Methyl Isobutyl Ketone: Systematic Study of Impurity Distribution

ABSTRACT This paper reports a study on the purification behavior of methyl isobutyl ketone (MIBK) for the major impurities of the phosphoric acid wet process (Ca2+, Mg2+ Al3+, Fe3+, SO, and F−). Distribution coefficients of phosphoric acid (PA) and impurities, as well as selectivity of MIBK for PA, have been studied as a function of the PA concentration (wt%) in the organic phase. Our results are compared to those obtained with other solvents (isoamyl alcohol, dibutyl ether, and dipropyl ether) described in the literature. MIBK seems to have the best selectivity for PA against SO, and it shows an intermediate behavior between those of isomyl alcohol and ethers with regard to metallic impurities.