Adsorption of dye removal from aqueous solutions using natural bitter orange waste: An isotherm and kinetic processes study with efficiency evaluation under optimum conditions

In this study, the practical use of natural bitter orange peels (NBOP) from waste for adsorption-based quinoline yellow (QY) dye removal from an aqueous medium was investigated. Variations in pH (3–8), contact time (0–160 min), initial QY dye concentration (25–75 mg/L), and temperature (16–36°C) were used to test the adsorption process. The adsorption capacity ( q e ) was found to be strongly dependent on pH, increasing with decreasing pH value. The equilibrium was reached in 80 min due to the rapid adsorption process. Three isotherm models (Langmuir, Freundlich, and Temkin) were used to test the equilibrium data and the intraparticle diffusion equation. According to the isothermal data, the Langmuir model provides a good description of the adsorption process. Under optimal conditions of pH 4, 24 °C, and initial concentration 55 mg/L, at a dosage of 2.0 g/L, with a shaking speed of 250 rpm after 80 min of contact time, the maximum NBOP adsorption for QY dye was 49.285 mg/g. The best-fitting model for the adsorption process was determined to be the pseudo-second-order model, which showed that the adsorption process is mainly chemical adsorption and that QY dye is adsorbed uniformly onto monolayer NBOP sites. Qy dye adsorption onto NBOP was shown to be exothermic and spontaneous by thermodynamic parameters. Furthermore, after five consecutive cycles, the NBOP can be recovered with only a 16.93% decrease in adsorption ability. A Box Behnken design (BBD) in conjunction with response surface methodology (RSM) was utilized to identify the optimum parameters, including shaking speed, contact time, and adsorbent dosage. The highest removal efficiency of over 87% was obtained under the most optimum circumstances (dosage of 0.2 g/100 ml, contact time of 80 min, and shaking speed of 250 rpm). With an R 2 value of 99.4%, the BBD-RSM-based analysis of variance (ANOVA) showed a good fit between the experimental data and the quadratic model results' predictions. Thus, the study findings showed that NBOP is effective in removing QY dye.