Naturally occurring iron-aluminum oxides and oxy-hydroxides coated sand for removing cationic dyes from contaminated water
摘要
The potential application of naturally occurring iron-aluminum oxides and oxy-hydroxides-coated sand-rich soil, known as red earth, as a filter medium to remove Methylene Blue and Rhodamine 6G dyes from aqueous media was investigated. Batch experiments were conducted to determine the optimal conditions (initial concentration, pH, contact time, adsorbent dosage, and temperature) for achieving maximum sorption efficiency. According to the surface response methodology performed using Box–Behnken design, the maximum Methylene Blue removal (100%) and Rhodamine 6G removal (99.06%) were achieved at initial concentrations of 46.63 and 38.03 mg/L, pH 10.54 and 3.31, dosages of 24.63 and 27.04 g/L, temperatures of 326.35 K and 318.67 K, and contact times of 84.43 and 88.33 min, respectively. Considering the interactive effect, time and initial dye concentration strongly affect Methylene Blue adsorption, whereas pH, dosage, and time mainly influence Rhodamine 6G adsorption. As depicted by adsorption isotherms, kinetic and thermodynamic models, monolayer electrostatic attraction followed by chemisorption is identified as the Methylene Blue adsorption mechanism by red-earth with the adsorption capacity of 1.6 mg/g at 298 K. Weak π-π interactions, which occur as multilayer adsorption on heterogeneous surfaces, are suggested as the mechanism for Rhodamine 6G adsorption with an adsorption capacity of 3.8 mg/g at 298 K. According to Fourier Transform Infrared spectroscopic analysis, the involvement of O–H groups of Al and Fe oxy-hydroxides and Si–O groups of red-earth in Methylene Blue adsorption, and O–H groups in Rhodamine 6G adsorption is confirmed. The data suggested the potential application of natural red earth as a filter medium for cationic dyes.