Analysis of Leachates in Activated Char from Textile Sources: Implications for Their Use as Adsorbents

Textile waste management remains a critical environmental challenge. Valorization through thermochemical routes such as pyrolysis offers a sustainable pathway within the circular economy. In this study, carbonaceous materials were obtained from the pyrolysis of 100% cotton textile residues and subsequently activated with sodium thiosulfate (Na2S2O3). The physicochemical and leaching behaviors of the activated (CA) and non-activated (C) chars were assessed in aqueous solution under controlled pH conditions (3, 7, and 11). Activation significantly increased the specific surface area (from 90 to 975 m2 g−1). Leaching tests revealed that acidic conditions (pH = 3) enhanced the release of major elements following the order Na > Ca > K for C and S > Ca > Na for CA. Despite this, all concentrations of major and trace metals remained well below regulatory discharge limits. Anionic species (Cl−, SO42−) increased slightly after activation but also stayed within safe thresholds, and chemical oxygen demand (COD) values were low (0–9 mg O2 L−1), indicating negligible organic leaching. Overall, the findings show that the structural quality of textile-derived chars was improved by Na2S2O3 activation without compromising their environmental stability, validating their applicability as effective and safe adsorbents for wastewater treatment applications.