The removal rate of Cr(VI) from water by using granular activated carbon (GAC) supported nanoscale zero-valent iron (nZVI) composites (GAC-nZVI) was studied through batch experiments. The GAC-nZVI composites were synthesized from Fe2+ aqueous solution by traditional liquid-phase reduction technique with NaBH4 as a reducing agent. The composites were characterized by SEM. The effects of pH value, reaction temperature, GAC-nZVI composites addition and initial Cr(VI) concentration on the removal rate of Cr(VI) were studied. The removal processes were analyzed by a pseudo first-order kinetic model. The results showed that granular activated carbon supports could effectively prevent nanoscale zero-valent iron particles from aggregating together. Synthesized GAC-nZVI composites was efficient in removing Cr(VI) from water, 99.4% of Cr(VI) was removed from water containing 50 mg/L Cr(VI) within 5 min using 3.0 g/L GAC-nZVI composites at pH 2.0 and 40℃. The total Cr concentration in treated water was below 1 mg/L at pH 2.0?4.0, suggesting that little Cr(III) was residue. When pH was 1.0, the removal rate of Cr(VI) reached 98.8% within 2 min, but the total Cr concentration in water after reaction was 32.506 mg/L. The removal rate of Cr(VI) decreased with the increase of pH value and initial Cr(VI) concentration, and increased with the increase of reaction temperature and GAC-nZVI composites addition. Pseudo first-order kinetic model was suitable for describing the removal process of Cr(VI), and the fitting correlation coefficients R2 were all over 0.98 (except R2=0.9367 with GAC, R2=0.9277 when pH=3.0). The reaction rate constant (k) of GAC-nZVI composites was 0.19797 min?1, it was 86 times of original granular activated carbon (0.0023 min?1) at the same experimental conditions. The reaction rate constant increased with decreasing the initial pH value or increasing the reaction temperature and GAC-nZVI composites addition.
[1] Dong H R, Zeng Y L, Zeng G M, et al. EDDS-assisted reduction of Cr(VI) by nanoscale zero-valent iron [J]. Sep. Purif. Technol., 2016, 165: 86-91.
[2] Sheng G D, Hu J, Li H, et al. Enhanced sequestration of Cr(VI) by nanoscale zero-valent iron supported on layered double hydroxide by batch and XAFS study [J]. Chemosphere, 2016, 148: 227-232.
[3] Fu R B, Yang Y P, Xu Z, et al. The removal of chromium (VI) and lead (II) from groundwater using sepiolite-supported nanoscale zero-valent iron (S-NZVI) [J]. Chemosphere, 2015, 138: 726-734.
[4] Ponder S M, Darab J G, Mallouk T E. Remediation of Cr(VI) and Pb(II) aqueous solutions using supported nanoscale zero-valent iron [J]. Environ. Sci. Technol., 2000, 34(12): 2564-2569.
[5] Calabro P S, Moraci N, Suraci P. Estimate of the optimum weight ratio in zero-valent/pumice granular mixtures used in permeable reactive barriers for the remediation of nickel contaminated groundwater [J]. J. Hazard. Mater., 2012, 207-208: 111-116.
[6] Li X Q, Zhang W X. Sequestration of metal cations with zerovalent iron nanoparticles-A study with high resolution X-ray photoelectron spectroscopy (HR-XPS) [J]. J. Phys. Chem. C, 2007, 111(19): 6939-6946.
[7] Chang D Y, Chen T H, Liu H B, et al. A new approach to prepare ZVI and its application in removal of Cr(VI) from aqueous solution [J]. Chem. Eng. J.,2014, 244: 264-272.
[8] Kanel S R, Greneche J, Choi H. Arsenic (V) removal from groundwater using nano scale zero-valent iron as a colloidal reactive barrier material [J]. Environ. Sci. Technol., 2006, 40(6): 2045-2050.
[9] Kanel S R, Manning B, Charlet L, Choi H. Removal of arsenic(III) from groundwater by nano scale zero-valent iron [J]. Environ. Sci. Technol., 2005, 39(5): 1291-1298.
[10] Wei Y T, Wu S C, Yang S W, et al. Biodegradable surfactant stabilized nanoscale zero-valent iron for in situ treatment of vinyl chloride and 1,2-dichloroethane [J]. J. Hazard. Mater., 2012, 211-212: 373-380.
[11] Petala E, Dimos K, Douvalis A, et al. Nanoscale zero-valent iron supported on mesoporous silica: Characterization and reactivity for Cr(VI) removal from aqueous solution [J]. J. Hazard. Mater., 2013, 261: 295-306.
[12] Kim S A, Kamala-Kannan S, Lee K J, et al. Removal of Pb(II) from aqueous solution by a zeolite–nanoscale zero-valent iron composite [J]. Chem. Eng. J., 2013, 217: 54-60.
[13] Zhang X, Lin S, Lu X Q, et al. Removal of Pb(II) from water using synthesized kaolin supported nanoscale zero-valent iron [J]. Chem. Eng. J., 2010, 163(3): 243-248.
[14] Kerkez D V, Tomasevic D D, Kozma G, et al. Three different clay-supported nanoscale zero-valent iron materials for industrial azo dye degradation: A comparative study [J]. J.Taiwan Inst. Chem. E, 2014, 45(5): 2451-2461.
[15] Diao Z H, Xu X R, Chen H, et al. Simultaneous removal of Cr(VI) and phenol by persulfate activated with bentonite-supported nanoscale zero-valent iron: Reactivity and mechanism [J]. J. Hazard. Mater., 2016, 316: 186-193.
[16] Kumar A, Jena H M. Adsorption of Cr(VI) from aqueous phase by high surface area activated carbon prepared by chemical activation with ZnCl2 [J]. Process Saf. Environ., 2017, 109: 63-71.
[17] Wang W Q. Chromium(VI) removal from aqueous solutions through powdered activated carbon countercurrent two-stage adsorption [J]. Chemosphere, 2018, 190: 97-102.
[18] AL-Othman Z A, Ali R, Naushad M. Hexavalent chromium removal from aqueous medium by activated carbon prepared from peanut shell: Adsorption kinetics, equilibrium and thermodynamic studies [J]. Chem. Eng. J., 2012, 184: 238-247.
[19] Huang L H, Zhou S J, Jin F, et al. Characterization and mechanism analysis of activated carbon fiber felt-stabilized nanoscale zero-valent iron for the removal of Cr(VI) from aqueous solution [J]. Colloid. Surface. A, 2014, 447: 59-66.
[20] Tseng H H, Su J G, Liang C. Synthesis of granular activated carbon/zero valent iron composites for simultaneous adsorption/dechlorination of trichloroethylene [J]. J. Hazard. Mater., 2011, 192(2): 500-506.
[21] Shi L N, Zhang X, Chen Z L. Removal of Chromium (VI) from wastewater using bentonite-supported nanoscale zero-valent iron [J]. Water Res., 2011, 45(2): 886-892.
[22] Wang W, Zhou M H, Mao Q, et al. Novel NaY zeolite-supported nanoscale zero-valent iron as an efficient heterogeneous Fenton catalyst [J]. Catal. Commun., 2010, 11(11): 937-941.
[23] Fu F L, Ma J, Xie L P, et al. Chromium removal using resin supported nanoscale zero-valent iron [J]. J. Environ. Manage., 2013, 128: 822-827.
[24] Xu C H, Zhu L J, Wang X H, et al. Fast and Highly Efficient Removal of chromate from aqueous solution using nanoscale zero-valent iron/activated carbon (NZVI/AC) [J]. Water Air Soil Poll., 2014, 225: 1845-1858.
[25] Aravindhan R, Fathima A, Selvamurugan M, et al. Adsorption, desorption, and kinetic study on Cr(III) removal from aqueous solution using Bacillus subtilis biomass [J]. Clean Technol. Envir., 2012, 14: 727-735.
[26] Li W X, Ye Y X. Modified wool as adsorbent for the removal of Cr(III) from aqueous solution: adsorption properties, isotherm and kinetics [J]. Res. Chem. Intermediat., 2015, 41: 803-812.
[27] Zhou X B, Lv B H, Zhou Z M, et al. Evaluation of highly active nanoscale zero-valent iron coupled with ultrasound for chromium (VI) removal [J]. Chem. Eng. J., 2015, 281: 155-163.
[28] Liu T Y, Wang Z L, Zhao L, et al. Enhanced chitosan/Fe0-nanoparticles beads for hexavalent chromium removal from wastewater [J]. Chem. Eng. J., 2012, 189-190: 196-202.
