Adsorption of Methylene Blue onto Raw Wastes of Argan, Date, and Olive: Study of Kinetics and Isotherms

Most textile industrial wastewater contains Methylene Blue (MB), a dangerous organic dye. In the present work, its adsorption on a concentration of 1 g/L of raw argan nut shells (ANS), date stones (DS), and olive hulls (OH) was studied. The adsorbents were characterized by X-ray diffraction and Fourier Transform Infrared Spectroscopy. Both the kinetics and isotherms were compared with the mathematical models. DS had the highest MB elimination rate with 86.45%, followed by ANS and OH. The pseudo-second-order fitted the best kinetics data, indicating that the adsorption process was controlled by chemisorption. The Langmuir model described the adsorption equilibrium data. The monolayer adsorption capacity was the highest for DS with 55.27 mg/g, followed by ANS and OH with capacities of 49.26 and 45.66 mg/g, respectively. The optimal time to adsorb a dye concentration of 15 mg/L was 50, 90, and 120 min for DS, ANS, and OH, respectively. Compared with other potential adsorbents, the three raw adsorbents offered great efficiency in MB adsorption from wastewater without any treatment or chemical activation, promoting, therefore, these abundant, low-cost, and ecological-friendly biomasses.