Application d’argiles locales du nord du maroc pour le traitement des effluents liquides contaminés par les colorants organiques et les métaux lourds

Abstract

This work focuses on the valorization of natural clays from the northern region of Morocco by means of their use in the treatment of wastewater contaminated by organic dyes and heavy metals. It is part of a sustainable local development perspective, which consists of implementing effective approaches to preserve water quality and protect the environment against pollutants on the one hand, and to develop abundant mineral resources on the other. The first step was the detailed physico-chemical characterization of the clay powders used as raw materials by means of different techniques such as X-ray diffraction with Rietveld analysis for an in-depth interpretation of the results, thermal analysis employing both thermogravimetry and mass spectrometry, quantitative analysis using ICP-AES and XRF, SEM-EDS electron microscopy, FTIR spectroscopy, and textural analysis by laser granulometry and nitrogen physisorption. Secondly, a complete study of the clays adsorption capacity with regard to a model dye, methylene blue, and two heavy metals, lead and cadmium, in aqueous solution was performed. The tests in batch mode included the analysis of the influence on the adsorption process of different experimental parameters which are usual in this type of experiments such as adsorbent amount, contact time, pH of the medium, pollutant initial concentration and temperature. On the other hand, it should be highlighted the use of atomic absorption spectroscopy as analytical tool which provided the adequate sensitiveness and accuracy for the concentration level of the studied metallic ions. In a third stage, integral clay honeycomb monoliths could be prepared following Casagrande´s methodology, which was initially employed for the extrusion of other ceramics. This technique is based on the prediction of the extrudability of a paste through simple rheological properties estimate in order to avoid an expensive and tedious trial and error procedure. The adsorptive performance of the filters prepared in this way was also studied against methylene blue, lead and cadmium present in water. In this case, the experiments were carried out using a dynamic setup which included a flow recirculation through the clay structured filters. The general output of this study allowed concluding that the clays denoted as O (illite-smectite) and ST (stevencite) are easily extrudable in the form of honeycomb monoliths, showing a remarkable efficiency to retain lead (2 mg/g) and cadmium (4 mg/g), respectively. In addition, the study of the methylene blue adsorption also evidenced a good affinity of the O clay towards this pollutant (100 mg/g). According to the results obtained, the honeycomb monoliths prepared from natural clays have demonstrated an enormous potential for the retention of pollutants in aqueous solution. Moreover, these structured filters add significant advantages to the process of water purification, without losing the adsorption properties of starting clay powders. Therefore, the here proposed materials and design open up new alternatives to combat the problem of water pollution by heavy metals and organic dyes, and by doing so their valorization has been reached.