Honeycomb filters as an alternative to powders in the use of clays to remove cadmium from water

Abstract

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.