Removal of Malachite Green, a hazardous dye from aqueous solutions using Avena sativa (oat) hull as a potential adsorbent

Abstract

Adsorptive potential of an agricultural waste, oat hull for the removal of a dye, Malachite Green from aqueous solutions was investigated. The adsorbent was characterized by FTIR, XRD, SEM, and BET. Batch adsorption experiments were conducted to examine the sorption behavior of MG at different adsorbent particle sizes, solution pH, initial dye concentration, contact time and temperature. Optimum conditions were investigated as adsorbent particle size ~150μm; initial pH, 8.0, contact time, 80min and at 313K. The study of sorption kinetics was found to be more consistent with pseudo second-order model and film diffusion mechanism was interpreted as rate limiting step. The adsorbate–adsorbent interaction as a function of temperature was assessed and the data fitted better in Freundlich model. The adsorption capacity increases with increasing temperature and maximum Langmuir's adsorption capacity was found to be 83mg/g at 313K. Thermodynamic studies indicated that the process of removal of MG was spontaneous in nature. The efficacy of the batch sorption process was further investigated by column experiments. Factors like effect of flow rate and bed depth were examined in column mode. The column sorption data was mathematically treated with bed depth service time (BDST) and Thomas models. The above findings recommend that oat hulls can be successfully used for the decoloration of MG contaminated wastewater.