Search

Different natural Moroccan clays were used as adsorbents for the removal of lead from aqueous solution. The study was performed not only employing the starting clays in the form of powder but also after their extrusion as honeycomb monoliths, this representing the major novelty of this work respect to the current state-of-art. The experiments were done in batch conditions with continuous stirring and using a recirculated flow, respectively. In addition to an exhaustive characterization of the clays by means of X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, laser granulometry, N2 physisorption, infrared spectroscopy, SEM-EDS and evaluation of the cation exchange capacity, special attention was paid to the influence on the lead adsorption of variables such as adsorbent dosage, pH, contact time with the adsorbate and initial concentration of lead. Considering the cheap and abundant character of the raw materials, their easy processing (no additives were required for their extrusion) and the time and energy save due to no need for further modification through chemical/thermal activation, the obtained results (with retention over 90% for 30 ppm of lead) demonstrated the potential of the proposed design as low cost solution that may be competitive versus other technologies for water depollution, especially in developing regions.

Sewage sludge valorization must be the favored solution of management for a residue that does not present the desired improvement in terms of wastewater treatment. The objective of this research work was to study the dye fixation capacity of the adsorbents produced from sewage sludge. The dried sewage sludge (DSS) was used as an adsorbent to remove a cationic dye, methylene blue (MB), from an aqueous solution in a batch system, as a function of contact time, pH, temperature and initial concentration. The proposed adsorbent was characterized using several techniques such as scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The adsorption equilibrium of MB was described using Langmuir, Freundlich and Sips equations. The equilibrium is perfectly adapted to the Langmuir model with a maximum adsorption capacity of 44.39 mg g−1 on a single layer. In order to study the adsorption mechanisms, first- and second-order kinetic models were used. The adsorbent produced from the sludge was capable of absorbing MB from the solution, with the expression of the second-order rate being preferred to that of the first order. In addition, the thermodynamic parameters were evaluated, demonstrating that the adsorption process is spontaneous and endothermic. Thus, this study convinced that the DDS proved to be an alternative, attractive, effective, economic, and environmentally friendly adsorbent for MB dye removal from aqueous solution. Schematic illustration of the prepared dried sewage sludge adsorbent for the removal of methylene blue from aquatic samples

natural Moroccan illite–smectite was used as an adsorbent for the removal of methylene blue (MB) from aqueous solutions. The clay was characterized by FTIR spectroscopy, TGA, SEM–EDS, X-ray fluorescence, XRD and N2 physisorption. The influence of pH, temperature and time on the MB adsorption by the clay was investigated. The maximum equilibrium adsorption capacity was 100 mg g−1 at 45 °C. The kinetic behavior and the isotherms better-fitted with the pseudosecond- order and Langmuir models, respectively. Clay honeycomb monoliths (50 cells cm−2) were obtained by means of extrusion from the starting material without any additive except water. The structured filters exhibited better performance under dynamic conditions than the powdered clay, adding value to the application of this low-cost adsorbent.

Clay honeycomb monoliths were manufactured from a natural montmorillonite and used for CO2 adsorption, their performance being compared with that of the same clay but in the form of powder. Volumetric adsorption isotherms, thermogravimetric studies, temperature-programmed desorption experiments and transient kinetic analysis, the two latter followed by mass spectrometry, were employed to investigate the interaction of the samples with CO2, both under static and dynamic conditions, and at different temperatures. This research demonstrated that the honeycomb monoliths kept the adsorptive properties of the starting material in terms of capture capacity (around 15 mg/g), Henry constant, heat of adsorption and activation energy. Most of retained CO2 was weakly adsorbed, the temperature needed for its release being 130 °C, an appropriate value which is sufficiently high to avoid undesirable desorption while being low enough to minimize the costs derived from controlled regeneration for further CO2 reuse. The kinetics of the CO2 uptake over the monolith (though of second order like over the powder) was slightly different, allowing a wider operative window for a highly efficient CO2 removal. These results suggest the potential of the honeycomb monolithic design for an even more competitive use of clays as low cost CO2 filters.

Two natural Moroccan clays, an illite-smectite (O) and a stevensite (ST), were used to manufacture honeycomb monoliths for the removal of cadmium from aqueous solution. This goal was based on their easy extrudibility without additives and good performance for organic dyes and lead removal in previous studies. First, the influence of adsorbent dosage, time, pH and initial Cd(II) concentration was studied through batch experiments with the clay powders. Then, flow recirculation tests with the clays conformed as structured filters were performed. These confirmed the kinetics and adsorptive model, pseudo-second order and Langmuir, respectively, no matter the linear or non-linear character of the regression followed to fit the experimental data. With both experimental and sample designs, ST exhibited better performance than O. This could not be attributed to an exchange with Mg(II) overlapping the adsorption, despite its greater content in this element. Clay honeycombs behaved also better than packed columns charged with the same amount of powdered clay in similar experiments. Their maximum adsorption capacity (4 mg/g) ensures complete depuration of a solution containing 150 ppm of Cd(II) after recirculation through a 10 cm long and 3 cm-diameter monolith with the help of a centrifugal pump for less than 10 h.