Natural Moroccan phosphate for Astrazon Orange G dye removal: Performance analysis and breakthrough curves modeling

This research paper presents the first experimental results obtained using Moroccan Phosphate Rock (MPR) as adsorbent for the removal of Astrazon Orange G (AOG) from wastewater in a fixed-bed column adsorption. Firstly, the MPR was characterized by different techniques, namely Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Nitrogen sorption analysis shows that the BET specific surface area and pore volume of the sample are 18 m².g⁻¹ and 0.11 cm³.g⁻¹, respectively. The effects of operating parameters on the fixed-bed column performance are examined, including initial AOG concentration (10–39 mg.L^-1), flow rate (5–30 mL.min⁻¹), and bed height (3.8–15 cm). Experimental data showed that the adsorption column’s maximum capacity varied between 1.44 and 3.00 mg.g⁻¹, the rather than its removal efficiency was found to be varied from 20.01 to 38.8 %. Additionally, residence time distribution (RTD) analysis highlighted the influence of flow rate on axial dispersion and flow uniformity, confirming that higher flow rates reduce residence time heterogeneity and shift the system toward more plug-flow-like behavior. Dynamic adsorption models, including the Thomas, Bohart-Adams, Yoon-Nelson, Bed Depth Service Time (BDST), and their corresponding modified logarithmic models were applied to predict the asymmetric breakthrough curves obtained from the fixed-bed column adsorption tests. According to the results, MPR fixed-bed column for AOG removal was well fitting logarithmic models. It can be concluded that the low specific surface area, heterogeneous particle size distribution, weak intraparticle, and surface diffusion of MPR were responsible on the asymmetrical curves. In addition, the bed regeneration was conducted at room temperature using acetic acid (0.1 N), and the results showed that the MPR could be efficiently reused for four consecutive cycles. Finally, the natural Moroccan phosphate rock could be employed as a potential adsorbent to remove azo dyes from wastewater.