Aluminosilicate-based adsorbent in equimolar and non-equimolar binary-component heavy metal removal systems

Cadmium (Cd) and lead (Pb) are toxic heavy metals commonly used in various industries. The simultaneous presence of these metals in wastewater amplifies the toxicity of wastewater and the complexity of the treatment process. This study has investigated the selective behavior of an aluminosilicate-based mesoporous adsorbent. It has been demonstrated that when equimolar quantities of the metals are present in wastewater, the adsorbent uptakes the Pb2+ ions selectively. This has been attributed to the higher electronegativity value of Pb2+ compared to Cd2+ which can be more readily adsorbed on the adsorbent surface, displacing the Cd2+ ions. The selectivity can be advantageous when the objective is the separation and reuse of the metals besides wastewater treatment. In non-equimolar solutions, a complete selectivity can be observed up to a threshold Pb2+ molar ratio of 30%. Below this threshold value, the Cd2+ and Pb2+ ions are uptaken simultaneously due to the abundance of Cd2+ ions and the availability of adsorption sites at very low Pb2+ molar ratios. Moreover, the total adsorption capacities of the adsorbent for the multi-component system have been shown to be in the same range as the single-component system for each metal ion which can be of high value for industrial applications.