This investigation focused on the Congo red uptake, as the azo dye, from an aqueous environment. Herein, ash derived from sunflower seed pulp waste (SSPA) was used as an eco-friendly low-cost adsorbent. Based on the BET results, the specific active surface area of SSPA was approximately 102 m2/g. The effect of the initial analyte concentration (10–50 mg/L), the concentration of the adsorbent (1–5 g/L), and the processing time (10–240 min) on the rate of Congo red uptake was also evaluated and optimized. According to the results, the maximum dye removal from synthetic solution (91.89%) was achieved at a dye concentration of 50 mg/L, an adsorbent concentration of 3 g/L, and a processing time of 180 min. The maximum SSPA capacity for Congo red uptake from aquatic solution was 15.34 mg/g, achieving under optimized operational conditions. The adsorption process of SSPA also follows a pseudo-second-order kinetic model (qe = 15.85 mg/g; R2 > 0.99), considering the results of BET and FTIR, suggesting that the rate-controlling step in analyte removal is the chemical interaction between functional groups in SSPA and used dye. Finally, the SSPA washing with different solvents showed that the adsorbent treated with 1 M sodium hydroxide still performed well after his five reuses.
