Magnetic Fixed-bed Column for Cr(VI) Removal from Aqueous Solution Using Schwertmannite

Abstract

The fine particles of schwertmannite as an iron oxyhydroxide adsorbent has been suggested as a novel and strong Cr(VI) sorbent for treatment of Cr-contaminated industrial wastewater. The removal process was conducted in both batch and continuous trials. As a result of the batch experiments, the maximal adsorption capacity of the schwertmannite was obtained as 178 mg/g which was quite high amount in comparison with the usual applied Cr(VI) sorbents in the literatures. The continuous removal process involved a combination of a fixed bed column with a high gradient magnetic field which was firstly introduced as a novel designation of a fixed bed column to overcome the difficulties accompanied with the application of some especial fine particle adsorbents through the fixed-beds. The experimental results revealed that the magnetization force had a great function in this process to control the shape and the fitness of the bed during the sorption test as well as to simplify the experimental set-up.KEY WORDS: magnetic fixed bed column; Cr removal; high magnetic field; schwertmannite; wastewater treatment; electromagnetic processing of materials.tion, however, has some inherent limitations to be utilized as a continuous filtering system because of time-dependent plugging and saturation of its matrix.The most optimal configuration for continuous-flow sorption is the packed-bed column which gets gradually saturated from the feed to the solution exit end. High-quality fixed-bed column hardware is the subject of several US patents. In our study work, the experimental trials of the process have been conducted for many times by directly packing the column with the fine particle size of schwertmannite as the most strong Cr adsorbents. Extremely fine particles and mud like properties of the adsorbent, however, has caused a verity of problems to the system such as high pressure drop, mass transfer resistance and so on. To solve the problems dealing with the system, a magnetic fixed-bed column, as a novel designation of the fixed-bed columns, has been presented in this study. Moreover, the batch Cr(VI) adsorption data containing equilibrium models using the schwertmannite adsorbent and also the effect of pH on the adsorption to predict the sorption characteristics of the adsorbent have been given. Materials and MethodsAll chemicals used were of high purity and analytical grades. The schwertmannite powder as the chemical adsorbent of Cr(VI) in these experiments was made by homogenous hydrolysis of iron ferric salt (Fe 2 (SO 4 ) 3 · nH 2 O) according to the methods mentioned in our pervious work. 14)Stock solution of 130 mg/L of Cr(VI) for use in the fixed column experiment was prepared by dissolving of a known amount of K 2 Cr 2 O 7 in dionized water. In the batch mode adsorption trials, 50 mL of the solution with desired concentrations of Cr and the adsorbent were mixed in a bottle of 100 mL and shaken for about 5 h to reach to the equilibrium state. Then the yielded solution was filtered through a paper filter and then chromium c...

Cr(VI) removal by biogenic schwertmannite in continuous flow column

“…The piercing points at pH 2 (initial conditions) and 4 were at approximately 50 and 90 min, respectively; however, it took approximately 100 min for the piercing point to appear at pH 8, earlier than that observed at pH 6. This increase in Cr(VI) removal over the pH span 2-6 was inconsistent with the results reported by Eskandarpour et al (2008) and Antelo et al (2012); however, it was confirmed by Chen and Zhou (2006), who reported that the maximum saturated adsorption amounts of Cr(VI) by schwertmannite in batch trials were obtained in the pH et al, 2011), and 7.0 (Antelo et al, 2012). The schwertmannite used in this study was obtained by a biological process, whereas studies by Eskandarpour et al (2008) and Antelo et al (2012) employed schwertmannite prepared by chemical processes.…”

“…This increase in Cr(VI) removal over the pH span 2-6 was inconsistent with the results reported by Eskandarpour et al (2008) and Antelo et al (2012); however, it was confirmed by Chen and Zhou (2006), who reported that the maximum saturated adsorption amounts of Cr(VI) by schwertmannite in batch trials were obtained in the pH et al, 2011), and 7.0 (Antelo et al, 2012). The schwertmannite used in this study was obtained by a biological process, whereas studies by Eskandarpour et al (2008) and Antelo et al (2012) employed schwertmannite prepared by chemical processes. Based on the fact that the maximum adsorption capacity of Cr(VI) was obtained at pH 6 (i.e., the schwertmannite surface is negatively charged), it can be concluded that anion exchange between HCrO 4 -and SO 4 2-dominated the adsorption process in the present system.…”

“…Therefore, Cr(VI) reduction methods for remediating Crcontaminated sites have been actively investigated, including conventional chemical reduction (Lan et al, 2005(Lan et al, , 2006Li et al, 2007); photocatalytic reduction (Gaberell et al, 2003;Sun et al, 2009;Tian et al, 2010); electrochemical reduction (Lakshmipathiraj et al, 2008;Olmez, 2009); and bioreduction (Cheung and Gu, 2007;Patra et al, 2010;Contreras et al, 2011). Cr(III), the product of Cr(VI) reduction, is subsequently removed from 2006; Zhou et al, 2007); however, the extremely fine particle sizes of schwertmannite render it very difficult to be utilized in combination with traditional filtration techniques in practice, i.e., solid-liquid separation (Eskandarpour et al, 2008). The fixed-bed column is regarded as an alternative approach to overcome the above limitations.…”

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

“…Chemical oxidation yields schwertmannite with a specific surface area of 4–14 m 2 ·g − 1 [ 30 ], 2.06–16.3 m 2 ·g − 1 [ 44 ], 48.2 m 2 ·g − 1 [ 27 ], and even 130.9 m 2 ·g − 1 [ 45 ]. In contrast, rapid hydrolysis enables the synthesis of schwertmannite with a specific surface area several times greater, e.g., 165 m 2 ·g − 1 [ 46 ], 199.4 m 2 ·g − 1 [ 47 ], 206.1 m 2 ·g − 1 [ 29 ], and even 325.5 m 2 ·g − 1 [ 48 ]. The density of SCH A and SCH B was determined using a pycnometer, and amounts to 3.54 and 3.75 g·cm − 3 , respectively.…”

Schwertmannite: occurrence, properties, synthesis and application in environmental remediation

“…The pI value order (called pH zpc in most reported references) is as follows: 7.2 (AMD) 45 > 5.4 (bio-ferrooxidation) 59 > 5.1 (chem. oxidation) 34 > 4.2 (fast hydrolysis) 60 > 3.7 (fast hydrolysis) 61 > 3.05 (fast hydrolysis). 62 According to the above order, natural Sch may have a higher pH zpc value, and Sch obtained using fast hydrolysis may have the lowest pH zpc value.…”