Sunset yellow (SY) FCF is a hazardous azo dye pollutant found in food processing effluent. This study investigates the use of diatomaceous earth with chitosan (DE@C) as a modified adsorbent for the removal of SY from wastewater. Fourier transform infrared spectroscopy results indicate the importance of functional groups during the adsorption of SY. The obtained N2 adsorption–desorption isotherm values accord well with IUPAC type II. Our calculations determined a surface area of 69.68 m2 g−1 for DE@C and an average pore diameter of 4.85 nm. Using response surface methodology, optimized conditions of process variables for dye adsorption were achieved. For the adsorption of SY onto DE@C, this study establishes mathematical models for the optimization of pH, contact time and initial dye concentration. Contact time plays a greater role in the adsorption process than either pH or initial dye concentration. According to the adjusted correlation coefficient (adj-R2 > 0.97), the models used here are suitable for illustration of the adsorption process. Theoretical experimental conditions included a pH of 2.40, initial dye concentration of 113 mg L−1 and 30.37 minutes of contact time. Experimental values for the adsorption rate (92.54%) were close to the values predicted by the models (95.29%).

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