Removal of Cr(VI) from Wastewater by a Novel Adsorbent of Magnetic Goethite: Adsorption Performance and Adsorbent Characterisation

Abstract

A novel adsorbent of magnetic goethite was prepared by neutralisation hydrolysis and employed for Cr(VI) adsorption from aqueous solution. The magnetic goethite adsorbent was characterised by using scanning electron microscopy (SEM), X‐ray diffractometer (XRD), vibrating sample magnetometer (VSM), fourier transform infrared (FTIR), brunauer‐Emmett‐Teller (BET) and X‐ray photoelectron spectroscopy (XPS) method. VSM showed that the prepared adsorbents are super‐paramagnetic iron hydroxide. FTIR spectra revealed that magnetic goethite have ‐OH and other functional groups. The effects of various factors, including pH, adsorbent dosage, initial concentration, and ion concentration, were evaluated. Under the conditions of pH 3, 4 g/L magnetic goethite, 20 mg/L Cr(VI) concentration, and 0.01 mol/L NaNO3, the removal efficiency of Cr (VI) reached 88.2% and the adsorption capacity of the adsorbent reached 4.32 mg/g. The adsorption kinetic tests showed that the adsorption of Cr(VI) on the adsorbent matched well with pseudo‐second‐order kinetics, indicating the occurrence of chemisorption. The fitting of the Langmuir isotherm model showed that the adsorption of Cr(VI) on magnetic goethite was monolayer adsorption. On the other hand, thermodynamic studies conjectured that the adsorption processes of magnetic goethite for Cr(VI) was endothermic and spontaneous. These results suggest that magnetic goethite has great potential for the removal of heavy metals from wastewater.

Synthesis of Mg-Al Hydrotalcite Clay with High Adsorption Capacity

“…The isotherm constants of the Langmuir and Freundlich isotherms, presented in Table 4 , were calculated from the slope and intercept of the linear plot obtained in Figure 12 a,b respectively. The correlation coefficient values obtained for the Langmuir isotherm were all above 0.99, indicating that the Langmuir model was more qualified to explicate the adsorption isotherm of sulfonated lignite by filter paper-templated Mg-Al metal oxides, and hence that the adsorption of sulfonated lignite by metal oxides may be monolayer adsorption [ 37 ]. The maximum adsorption capacity determined from the Langmuir model was 1189.29 mg/g for a temperature of 303 K. It is known that the constant R L in the Langmuir equation is an important index for measuring the stability of the adsorbent/adsorbate complex.…”

Structural elucidation of hexavalent Cr adsorbed on surfaces and bulks of Fe3O4 and α-FeOOH

“…54 The Cr 2p 3/2 exhibited the characteristics of Cr 3+ in Cr 2 O 3 (576.6 eV), CrO(OH)/Cr(OH) 3 (577.7 eV) and Cr 6+ in CrO 3 (579.9 eV). 7,42,44,50–54 Those characters were similarly found in Cr@Fe 3 O 4 and Cr@FeOOH. However, the area ratio of Cr 2 O 3 /CrO(OH) in Cr@FeOOH was higher than that in Cr@Fe 3 O 4 .…”

“…† The Cr 6+ adsorption behaviors of a-FeOOH and Fe 3 O 4 obeyed the Langmuir model (higher regression coefficient (R 2 )) indicating that adsorption takes place at a specic homogeneous site, and monolayer coverage was formed on the adsorbent surface. [42][43][44] A low b value implied a strong binding ability. 28 Therefore, the lower b value of Fe 3 O 4 indicated its stronger Cr 6+ adsorption ability than that of a-FeOOH.…”

Clay/MgFe2O4 as a Novel Composite for Removal of Cr (VI) From Aqueous Media

“…[3] These metals at high concentrations cause to poisoning, cancer and brain injuries. [4,5] Among the heavy metals, the removal of chromium from aqueous media has been extensively studied due to the high toxicity. Chromium ion in water has two forms: Cr (III) and Cr (VI), which Cr (VI) has a much higher toxicity (500-1000 times).…”

“…Also, this adsorbent can be quickly separated from the suspension by a magnet due to its magnetic property. [13,14] There are various types of adsorbents, nano-adsorbents, and bio-adsorbents in the literature, which are applied to remove Cr (VI) from wastewater including magnetic Goethite, [4] clay, clay@ MnFe 2 O 4 , [6] Fe 3 O 4 nanoparticles, [9] MgO/Fe 3 O 4 , [15] activated carbon prepared by lotus leaf , [16] magnetite nanospheres, [17] activated carbon/CoFe 2 O 4 , [18] etc.…”