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

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.

Investigation of the influence of crosslinking activation methods on the physicochemical and Cu(II) adsorption characteristics of cellulose hydrogels

“…The third segment at t 0.5 > 17.32 min 0.5 (t > 300 min) refers to the equilibrium step in which the solute immigrates slowly to micropores in the inner matrix of the adsorbent, thus causing a slow (nearly zero) adsorption rate. A similar phenomenon was reported in other studies related to adsorption kinetics [58,64,[66][67][68]. The rapid adsorption rate at the first segment occurs since the adsorbent has high vacant sites initially, and the solute concentration gradient in bulk and on the adsorbent surface is very high.…”

Adsorption Behaviors and Mechanism of Phenol and Catechol in Wastewater by Magnetic Graphene Oxides: A Comprehensive Study Based on Adsorption Experiments, Mathematical Models, and Molecular Simulations

“…If the R L value is greater than 1, it is unfavorable for adsorption. When the R L value is equal to 1, the adsorption isotherm is linear or equal to zero, and the adsorption is irreversible. , …”

“…When the R L value is equal to 1, the adsorption isotherm is linear or equal to zero, and the adsorption is irreversible. 50 , 51 …”

“…When the R L value is equal to 1, the adsorption isotherm is linear or equal to zero, and the adsorption is irreversible. 50,51 The adsorption isotherms of phenol and catechol on magnetic graphene oxide obtained by Langmuir-type isotherm equation fitting are shown in Figure 7, and the fitted data are shown in Table 1. It can be seen that temperature has a significant effect on the maximum equilibrium adsorption capacity: the maximum equilibrium adsorption capacity of MgO for phenol is 27.60 mg/g (318 K) < 113.44 mg/g (298 K) < 125.71 mg/g (308 K); the maximum equilibrium adsorption capacity of MgO for catechol is 117.90 mg/g (318 K) < 177.69 mg/g (298 K) < 186.89 mg/g (308 K).…”

Impact of Fulvic Acid and Acidithiobacillus ferrooxidan Inoculum Amount on the Formation of Secondary Iron Minerals

“…For example, schwertmannite possesses hydroxyl groups, sulfate groups, and a large specific surface area. It has been reported in the literature that the adsorption capacity of As by schwertmannite has a good adsorption effect on both As and Cr [ 17 , 18 ]. Cu 2+ and Pb 2+ also exist in the form of ternary complexes on the surface of schwertmannite [ 19 ], which plays an important role in the migration of heavy metals and has a potential application value.…”