Adsorption in an Aqueous Multimetal System Using a Mineral–Biological Composite: A Kinetic and Isotherm Study

Anthropogenic activities generate waste that negatively impacts the environment, especially water resources, due to the accumulation of heavy metal ions. Several adsorption methods have been developed, including the use of natural materials such as algae and activated clay. This study aimed to evaluate the effect of pH on batch adsorption of heavy metal ions using Nostoc sphaericum hydrocolloid (HA)/activated nanoclay (NR) composites. The NR/HMB-HA and NR/HUT-HA composites were prepared with a 2:8 mass ratio of HA and NR, using types of clay with code HMB and HUT, previously activated with 1 M NaCl and acid treatment. The adsorption capacity was evaluated using batch tests at pH 4.5 and 5.5, analyzing the removal percentage, adsorption kinetics, adsorption isotherms, and regeneration cycles for unimetal and multimetal systems. The composites present a load point close to 5.1. The FTIR analysis showed changes in the intensity of functional groups following adsorption, confirming the interaction with metallic ions. Both composites showed high affinity in multimetallic systems, especially at pH 5.5, with high selectivity for Pb2+ (≈99% removal), followed by As, Cd, and Zn, from an initial concentration of 10 ppm for each metal ion. Equilibrium is reached in approximately 90 min, allowing adsorption of up to 69.9% after five regeneration cycles in a multimetal system. The kinetic study showed that multimetal absorption at equilibrium is governed by chemisorption processes in the order Pb > As > Zn > Cd, with qe values between 0.392 and 0.058 mmol/g and diffusivity from 15.506 × 1011 to 1.692 × 1011 m2/s. Likewise, the isotherms study indicated a favorable process with maximum adsorption (qmax) between 16.696 and 5.223 mmol/g at pH 5.5. Altogether, the developed composites show high potential for the removal of heavy metals in contaminated waters, in addition to their high reuse capacity.