Comparison of Cr(VI) Adsorption Using Synthetic Schwertmannite Obtained by Fe3+ Hydrolysis and Fe2+ Oxidation: Kinetics, Isotherms and Adsorption Mechanism.

Justyna Ulatowska,Izabela Polowczyk,Łukasz Stala

doi:10.3390/ijms22158175

Abstract

Good sorption properties and simple synthesis route make schwertmannite an increasingly popular adsorbent. In this work, the adsorption properties of synthetic schwertmannite towards Cr(VI) were investigated. This study aimed to compare the properties and sorption performance of adsorbents obtained by two methods: Fe3+ hydrolysis (SCHA) and Fe2+ oxidation (SCHB). To characterise the sorbents before and after Cr(VI) adsorption, specific surface area, particle size distribution, density, and zeta potential were determined. Additionally, optical micrographs, SEM, and FTIR analyses were performed. Adsorption experiments were performed in varying process conditions: pH, adsorbent dosage, contact time, and initial concentration. Adsorption isotherms were fitted by Freundlich, Langmuir, and Temkin models. Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and liquid film diffusion models were used to fit the kinetics data. Linear regression was used to estimate the parameters of isotherm and kinetic models. The maximum adsorption capacity resulting from the fitted Langmuir isotherm is 42.97 and 17.54 mg·g−1 for SCHA and SCHB. Results show that the adsorption kinetics follows the pseudo-second-order kinetic model. Both iron-based adsorbents are suitable for removing Cr(VI) ions from aqueous solutions. Characterisation of the adsorbents after adsorption suggests that Cr(VI) adsorption can be mainly attributed to ion exchange with SO42− groups.

Highlights

Environmental pollution is a constant struggle in our thriving society
This paper presents adsorption studies of Cr(VI) on synthetic schwertmannite sorbents obtained through two different synthesis methods: Fe2+ oxidation and Fe3+ hydrolysis
The sorption of Cr(VI) from aqueous solutions has been examined on two types of schwertmannite sorbents (SCHA and schwertmannite B (SCHB))

Summary

Introduction

Toxic metal ions present in certain process effluents, if discharged into surface water, are a threat to the environment [1,2] but directly to human health, as well [3]. Processing this metal leads to toxic chromium ions emissions into the environment with industrial wastewater Another source of chromium contamination is fumes from fossil fuel incineration [3]. Iron oxyhydroxides are known adsorbents of toxic chromium ions as weak acid oxyanions have a strong affinity towards their proton-specific surface sites [15]. Schwertmannite sorbents can remove a variety of contaminants including fluorides, toxic metal ions, oxyanions, and organic pollutants [23,24,25,26,27,28,29,30,31,32]. Zeta Zeta ppootteennttiiaallooffssyynnththeteictisccshcwhewrtemrtamnnainteniatdesaodrbseonrbtse(nStCsH(SACaHndA aSnCdHSB)CaHs Bfu) nasctfiounncotfion of pH

Effect of Adsorbent Dose

Effect of Contact Time

Materials and Methods

Characterisation of Schwertmannite

Adsorption Experiments

Conclusions