Adsorptive Removal of Fe (II) By NaOH Treated Rice Husk: Adsorption Equilibrium And Kinetics

The low cost adsorbents were prepared from raw rice husk (RRH) and NaOH treated rice husk (NRH). Then prepared materials were characterized by XRD, FTIR and surface area of rice husk adsorbent were determined by methylene blue adsorption method. XRD showed amorphous nature with low crystallinity of the material. The FTIR spectra showed the presence of oxygenated functional groups such as ester, phenol, carbonyl and silica on the material. The surface area of RRH and NRH were found to be 387 and 417 m2/g respectively. Thus, prepared adsorbents were used for the removal of Fe(II) ion from aqueous solution. The influence of various parameters like pH, adsorbent doge, and contact time were studied for the better adsorption of Fe(II) on rice husk adsorbents. Results revealed that the maximum efficiency was achieved at pH 3 for Fe(II). The adsorption process was found to be best fitted to Langmuir adsorption isotherm model controlled by pseudo-second–order kinetics with the rate constant value i.e. 0.0218 and 0.0235 g/(mg·min) for RRH and NRH respectively. The χ2 values of pseudo second order was found to be lower which confirmed chemisorption, involving ion exchange and valence forces through sharing or exchange of electrons between adsorbent and adsorbate. The maximum adsorption capacity for Fe(II) on RRH and NRH was found to be 2.9 mg/g and 5.6 mg/g respectively. The positive ∆G value represents the randomness of the system during adsorption process. The slope of the linear plot of Qt vs t0.5 was linear but not passed through the origin, which indicates that, the intraparticle diffusion was not only rate controlling step. Temkin value showed the maximum binding energy (KT) for NRH was 16.4 L/g and for RRH it was 12.2 L/g. Key word: Rice husk; Iron; Langmuir adsorption. INTRODUCTION Metals of having relatively high densities (> 5 g/cm3) and high atomic weights simply means heavy metals1. Copper, aluminium, iron, zinc, platinum, arsenic, chromium, etc are some of the examples. Heavy metals are either essential nutrients like iron, cobalt and zinc or relatively harmless such as ruthenium, silver and indium while other are highly poisonous such as arsenic, cadmium, mercury and lead1. Among the wide variety of heavy metals, iron i s one of the most common heavy metals that is found in nature. The magnetite [Fe3O4, 72.4 % Fe], hematite [Fe2O3, 69.9% Fe], goethite [FeO(OH), 62.9% Fe], limonite [FeO(OH).n(H2O)] or siderite [FeCO3, 48.2% Fe] are the most common ore of iron that is found in earth’s crust. Among them, hematite and magnetite are found in the form of rocks2 which during demineralization introduced in ground water by leaching and percolation. It also introduced from anthropogenic sources specially from industrial sector3. Heavy metals have become one of the major causes of concern for water pollution1. In ground water, iron exists in ferrous state and remains dissolved in water. Nonetheless when it is exposed to atmosphere, it gets oxidised to ferric ion. The iron in ferric state does not dissolved in water and forming reddish brown colour2. The relatively high content of iron levels in water can cause stains in plumbing, laundry and cooking utensils that can impart objectionable tastes and colours to foods3. Additionally, excessive Author for Correspondence: Armila Rajbhandari (Nyachhyon), Central Department of Chemistry, Tribhuvan University, Kirtipur, Nepal. E-mail: armila3@yahoo.com Received: 30 May 2020; First Review: 22 Sep 2020; Second Review: 23 Sep 2020; Accepted: 27 Sep 2020. Doi: https://doi.org/10.3126/sw.v14i14.34991