Acidic modification of natural stone for Remazol Black B dye adsorption from aqueous solution- central composite design (CCD) and response surface methodology (RSM)

This study investigated the adsorption capacity of Remazol Black B (RBB) from aqueous solutions using a pumice stone as a cheap, high-frequent, and available adsorbent. The raw pumice was modified using five acids: Acetic, Sulfuric, Phosphoric, Nitric, and Hydrochloric acid. Fourier transform infrared spectrograph (FTIR), x-ray fluorescence (XRF), and scanning electron microscopy (SEM) were used to analyze the morphological and chemical properties of raw and modified adsorbents. The adsorption capacity equilibrium was investigated using the Langmuir, Freundlich, Temkin, and Dubinin – Radushkevich isotherms. The results indicated that the data are well-fitted with Langmuir isotherm. The maximum adsorption capacity was observed when pumice modified with H2SO4 (qm = 10.00 mg/g) was used, and the RBB removal efficiency was higher than that for raw pumice (qm = 5.26 mg/g). Also, the results were best fitted with pseudo-second-order kinetic. The experiments indicated that increasing the RBB concentration reduces the efficiency of adsorbents while increasing the contact time and adsorbent doses improved the RBB removal efficiency. Accordingly, it can be concluded that pumice stone modified with various acids can be considered a cheap adsorbent with high efficiency in removing RBB from industry effluent.