Organic dye removal from aqueous media by using acid modified Clinoptilolite

Dyes are an important class of pollutants which when discharged into water resources can be toxic to the aquatic environment and cause serious problems for public health. Various treatment technologies such as adsorption are in use. For this reason, clinoptilolite was used as a low-cost adsorbent to remove color from aqueous solution. Clinoptilolite was modified with sulfuric and phosphoric acids in order to adsorp aqueous direct red 23. The batch adsorption experiments used dye concentrations ranging from 50 to 200 mg/L. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier transform infrared spectra (FTIR) were used to determine properties of clinoptilolite. To evaluate the experimental data, adsorption isotherms and kinetics were studied. The results showed that experimental data followed both Langmuir and Freundlich isotherms, with a correlation coefficient of 0.95–0.99. Kinetic studies showed that adsorption followed pseudo first-order kinetics. The adsorption results showed that acid-modified clinoptilolite with maximum adsorption capacity of 0.0009 mmol/g was a superior adsorbent compared with unmodified clinoptilolite, according to Langmuir equation. It caused adsorption efficiency in terms of Si/Al ratio 7.5 after 200 min of contact of between 31% to 60%. According to the Dubinin-Radushkevich isotherm model, mean free energy of adsorption (8.2–8.9 kJ/ mol) means that adsorption might follow a weak chemisorption mechanism. We conclude that adsorbing properties of clinoptilolite, a cheap and abundant adsorbent, can be improved and used for removing dyes from wastewater.