Comparative adsorption study of cationic yellow 28 and anionic congo red dyes using Tunisian natural chert

This study investigates the use of chert, a natural and previously unexplored adsorbent from Jebel el Âli (Kef Ensour) in the Gafsa region, for the first time in dye removal. Both raw (CH-br) and purified (CH-p) forms of chert were used to remove the anionic dye Congo Red (CR) and the cationic dye Cationic Yellow 28 (CY28). Structural and morphological characterizations were conducted using XRD, FTIR, SEM, BET, and TGA analyses, along with the determination of the zero point of charge (pHzpc). Batch experiments assessed the effects of contact time, adsorbent dosage, initial dye concentration, and pH on dye removal. The adsorption of CY28 and CR on chert was strongly influenced by pH and initial dye concentration. The Langmuir model best described the adsorption, with maximum capacities of 69.93 mg/g and 75.18 mg/g for CY28, and 112.35 mg/g and 123.45 mg/g for CR on CH-br and CH-p, respectively. Kinetic studies showed that CY28 followed a pseudo-second-order model, while CR adhered to a pseudo-first-order model. This research highlights chert as a novel, environmentally friendly, and cost-effective adsorbent for dye removal from wastewater.