Towards zero-waste processes: Waste wool derivatives as phosphate adsorbents and auxiliaries for textiles’ natural dyeing

The textile industry is a pillar of the manufacturing sector worldwide, but it still represents a significantly polluting production sector since it is energy-, water- and natural resource-intensive. Herein, waste wool that did not meet the technical requirements to be used for yarns and fabrics was recovered first to prepare materials for wastewater remediation, specifically for phosphate removal. The wool underwent an alkaline treatment, eventually saturated with FeCl₃ and then left at room temperature or thermally treated to induce crosslinking/stabilisation, obtaining adsorbent panels. The main characterisation findings concerned the impact of alkaline treatment on morphology and structure; additionally, the samples with iron displayed a behaviour attributable to a crosslinking effect operated by Fe³⁺. Batch experiments showed that only samples with iron were efficient in phosphate adsorption, with a high removal percentage obtained in a wide pH range. Adsorption isotherms and kinetics were investigated, suggesting a complex system of interactions. Moreover, during the alkaline treatment necessary to prepare such wool-derived adsorbent panels, a significant amount of wool hydrolysates left in the solution was produced. These substances, in view of zero-waste procedures, were isolated and re-employed as dyeing auxiliaries. Preliminary results demonstrated that the wool hydrolysates enabled the dyeing of cotton with natural dyes, which is generally a tricky process.