Waste materials as adsorbents for heavy metals removal from water: Comparative analysis of modification techniques

This study aims to investigate the effect of alkalization and chemical coupling methods on the surface and adsorption properties of waste cotton and cotton/polyester yarns. The simple and cheap alkali treatment was performed using 10% and 18% NaOH solution, while the chemical coupling method involved combining cotton and cotton/polyester yarns and fly ash, using sodium carboxymethyl cellulose and sodium alginate as binders. Morphological and surface characteristics of unmodified and modified cotton and cotton/polyester yarns were analyzed by scanning electron microscopy and Fourier transform infrared spectroscopy, while adsorption properties were assessed by the removal of lead and cadmium ions from aqueous solution. It was found that chemical modification with 18% NaOH solution positively affected the adsorption properties of only cotton yarns, increasing the removal efficiency of lead ions up to 75%. On the other hand, modification with fly ash improves the adsorption properties of both, cotton and cotton/polyester yarns, increasing the efficiency in removing lead ions by using sodium carboxymethyl cellulose, and cadmium ions by using alginate as a binder. Using the chemical coupling method, effective adsorbents are obtained starting from waste yarn, which gives it added value, the amount of non-degradable waste material can be reduced and the criteria of a cleaner environment and circular economy can be met.