Enhancing copper and lead adsorption in water by in-situ generation of calcium carbonate on alginate/chitosan biocomposite surfaces

Abstract

Chitosan (CS) and sodium alginate (SA)-based biocomposites (CSA) were prepared with the in-situ generation of Calcium Carbonate (CSAX_Ca) through a simple, straightforward, economical, and eco-friendly procedure. Different drying conditions (X) were tested to achieve suitable structural and surface characteristics to enhance adsorption capacity: freeze-dried (L), vacuum-dried with methanol (M), and freeze-dried + vacuum-dried with methanol (LM). Temperature and adsorbent dosage effects on the adsorption capacity of Cu²⁺ or Pb²⁺ were examined. Results showed that the higher-yielding biocomposite (CSALM_Ca) exhibited rapid adsorption and good diffusion properties, achieving removal above 90 % within contaminant initial concentration ranges of 10-100 mg/L. At 35 °C, a pseudo-second-order kinetic and the Langmuir model effectively described kinetics and isotherms, revealing maximum adsorption (q_{e, max}) of 429 mgCu²⁺/L and 1742 mgPb²⁺/g. Characterization through FTIR, XRD, and SEM of the as-prepared adsorbents confirmed the presence of CaCO₃ in vaterite and calcite forms and the influence of drying conditions on the material morphology. Post-adsorption material characterization, in combination with adsorption findings, revealed chemisorption processes involving Ca²⁺ ion exchange for Cu²⁺ or Pb²⁺, resulting in surface-insoluble compounds. The best-performing material showed that after three reuse cycles, the removal of Cu²⁺ and Pb²⁺ decreased to 75 % and 62 %, respectively.

Keywords: Alginate/chitosan; Bio-adsorbents; Calcium carbonate; Copper adsorption; Heavy metal adsorption; Lead adsorption; Water treatment.