Clay honeycomb monoliths for the simultaneous retention of lead and cadmium in water

Abstract

Natural illite–smectite and stevensite Moroccan clays were used for the simultaneous removal of lead and cadmium from aqueous medium. The clays were employed in raw state and extruded as honeycomb monoliths form without any additives, which confirms the novelty of this approach in water treatment. The experiments were done in batch conditions with continuous stirring and using a recirculated flow, respectively. In addition to a characterization of the clays by XRF, XRD, TGA, laser granulometry, N 2 physisorption, FTIR spectroscopy, SEM-EDS and evaluation of the cation exchange capacity, special attention was paid to the influence on the co-adsorption of variables such as adsorbent dosage, contact time and initial concentration of Cd 2+ and Pb 2 + . Pseudo-second order kinetics and good fitting to Redlich–Peterson model for both heavy metals were found. Our results also suggest that Pb 2 + and Cd 2 + uptake is controlled by chemisorption with predominance of Langmuir characteristics. No significant depletion of the metals retention attributable to competition was observed, particularly for the stevensite (maximum retention capacity of 1.2 mg Pb 2 + /g and 4.6 mg Cd 2 + /g) that showed higher specific surface area. For both clays, cadmium ions adsorption was relatively favoured in the bimetallic solution, and the honeycombs kept the powders performance. Honeycomb monoliths as a compact adsorbent offer a promising way of water treatment thanks to their stability and easy incorporation into dynamic processes avoiding the issues of pressure drop under wastewater circulation. • Natural illite–smectite and stevencite for lead and cadmium co-adsorption in water. • Metals competition does not reduce total response but relatively favours Cd 2+ ions. • Clays extruded without additives as honeycomb monoliths keep powders performance. • Structured design adds easy handling and prevents from sludge generation. • Great potential as low cost solution for water depollution in developing regions.