Elution profile of cationic and anionic adsorbate from exhausted adsorbent using solvent desorption

Area of Science:

• Environmental Science
• Materials Science
• Chemical Engineering

Background:

• Adsorbent materials derived from natural sources like Gulmohar (Delonix regia) leaf powder (GLP) and Neem (Azadirachta indica) leaf powder (NLP) are increasingly explored for pollutant removal.
• Understanding the elution profile of adsorbed anionic and cationic compounds is critical for efficient adsorbent regeneration and sustainable wastewater treatment.
• Previous studies have focused on sorption, but comprehensive elution studies from exhausted natural adsorbents are less explored.

Purpose of the Study:

• To investigate the elution profile of anionic (Congo Red dye, Carbonate ion) and cationic (Methylene blue dye, Cadmium metal) compounds from exhausted GLP and NLP adsorbents.
• To evaluate the impact of various eluents (acids, alkaline solutions, solvents) and pH on desorption efficiency over multiple sorption-desorption cycles.
• To assess the performance of column elution for selected pollutants and adsorbents, and analyze kinetic and life cycle data.

Main Methods:

• Batch elution studies were conducted using exhausted GLP and NLP with various concentrations of acids, alkaline solutions, and solvents.
• Kinetic models including Pseudo First-order, Pseudo Second-order, Intra-particle diffusion, and Elovic equation were applied to batch data.
• Column elution experiments were performed for Congo Red from NLP and Cadmium from activated charcoal derived from NLP (AC-NLP) using optimized eluents.

Main Results:

• Desorption efficiency was found to be predominantly dependent on the pH of the eluent, with specific pH ranges favoring the removal of anionic and cationic species.
• Multiple sorption-desorption cycles demonstrated the potential for adsorbent regeneration, although efficiency varied with eluent and pollutant type.
• Kinetic modeling provided insights into the mechanisms governing the elution process, aiding in the selection of optimal eluents and conditions.
• Column studies confirmed the feasibility of eluent-based regeneration for specific pollutant-adsorbent combinations.

Conclusions:

• The pH of the eluent is the most significant factor controlling the desorption of anionic and cationic compounds from exhausted GLP and NLP adsorbents.
• Natural adsorbents like NLP show promise for regeneration and reuse, enhancing the economic viability and environmental sustainability of adsorption processes.
• Further research into tailored eluent formulations and process optimization can improve the regeneration efficiency and extend the lifespan of these bio-adsorbents.