Adsorption of ferric ions onto natural feldspar: kinetic modeling and adsorption isotherm

The removing of ferric ions (Fe3+) from aqueous solution using natural feldspar (NF) has been studied in a batch operation mode. The factors affecting of the sorption equilibrium, such as contact time, initial concentration of the ferric ions (Fe3+), feldspar dosage concentration and temperature, were investigated. The maximum removal is 93 % (approx.) using low-level concentration of Fe3+ ions (30 mg L−1) and high dosage concentration (40 g L−1). The adsorption equilibrium is achieved during the first 90 min. Freundlich model has successfully analyzed the equilibrium of isotherms with R2 = 1. The adsorption mechanism of aqueous ferric ion on NF follows Freundlich isotherm models (R2 = 0.997). The capacity (Kf) and intensity (1/n) of Freundlich adsorption are 1.70 and 0.621, respectively. The results reveal that the adsorption mechanism of ferric ion on NF is chemisorptions, heterogeneous multilayer and spontaneous in nature (ΔG = −19.778 kJ mol−1). Adsorption reaction kinetic models, such as pseudo-first order and pseudo-second order, and adsorption diffusion model, such as Weber–Morris intraparticle diffusion model, have been used to describe the adsorption rate and mechanism of the ferric ion onto NF surface. Adsorption of ferric ion on the NF has achieved Lagergren pseudo-second-order model (R2 = 1.0 approx.) more than Lagergren pseudo-first-order model. The kinetic parameters, rate constant and sorption capacities have been calculated. The new information in this study suggests that NF could be used as a novel filtering materials for removing ferric ions from water.