Effective adsorption of cadmium and nickel ions in mono and bicomponent systems using eco-friendly adsorbents...

The work investigates the potential of peanut shells, an abundant agro-industrial waste, to serve as an adsorbent precursor for the effective and simple treatment of effluents loaded with cadmium and nickel ions. Among the adsorbents prepared, carbonized peanut shell (C_Carb), due to its higher adsorption capacity, proved to be the most effective compared to carbonized and activated peanut shell (C_ATQ). The carbonization process led to structural changes, which resulted in an increase in surface area (around 6 times more in C_ATQ) and pore volume (around 3 times more in C_ATQ). Even so, the amount of H⁺ acid sites due to acid activation produced unfavorable effects for adsorption. Hydroxyl, carboxyl and carbonyl groups were identified on the adsorbent surface which presented favorable charges for metal adsorption. This improvement propels the carbonized variant to the forefront, demonstrating the highest adsorption capacity and reaching equilibrium in less than 90 and 60 min for cadmium and nickel ions, respectively. In both monocomponent and bicomponent systems concentrations greater than 40 ppm signify an increase in adsorption capacity for Ni²⁺. The experimental data best fit the Freundlich model, showing maximum adsorption capacities of 17.04 mg g^-1 for cadmium and 31.28 mg g^-1 for nickel. Despite the antagonistic effect observed in the bicomponent system, this study concludes by underlining the promise of activated carbon from peanut shells to harmonize technical and environmental concerns.