Research on the adsorption of Co2+ ions using halloysite clay and the ability to recover them by electrodeposition method

In environmental research, along with discovering methods for adsorbing heavy metals, it is essential to comprehend the processes of desorption and recovery of these heavy metals from adsorbent materials and their reuse. In this study, halloysite (HAL) clay, obtained from the Thach Khoan, Vietnam, was utilized for the removal of Co2+ ions from an aqueous solution, and the influence of different factors on the adsorption properties of Co2+ was investigated. Optimal conditions determined were 0.8 g HAL mass per 50 mL of solution, initial Co2+ concentration of 40 mg·L−1, contact time of 80 min, pH0 of 6.09, and room temperature of 30°C. Under these conditions, the adsorption efficiency and capacity obtained were 76.358 ± 0.981% and 1.909 ± 0.025 mg·g−1, respectively. The adsorption process followed the Langmuir adsorption isotherms, with a maximum monolayer adsorption capacity of 3.10206 ± 0.13551 mg·g−1, and exhibited a pseudo-second-order kinetic model. Desorption experiments were conducted using the electrochemical method with a deep eutectic solvent based on choline chloride and urea (reline). The results demonstrated that 94.11% of the Co metal could be recovered through electrodeposition after 5 h, using an applied current of 7.5 mA at 60°C. The HAL material was successfully regenerated following the desorption process.