Antimony (V) removal from water by zirconium-iron binary oxide: performance and mechanism X.M. Dou, X.H. Li, Y.S. Zhang College of Environment Science and Technology, Beijing Forestry University, Beijing P. R. China 2 nd International workshop on antimony, Jena
Outline Background; Zr-Fe binary oxide adsorbent preparation and characterization; Evaluation of Sb(V) removal performance: batch tests Investigation on adsorption mechanisms using multiple techniques Conclusion.
Sb production in China World production of Sb in 2005-2009 World total: 179 000 tonnes China: 166 200 tonnes 93% of world supply. (British Geological Survey, 2011) Sb resources in China 12 provinces; the 3 most abundant places including: Guangxi province Hunan province Yunnan province Large mines in China Xikuangshan mine, Hunan Dachang mine, Guangxi (www.chinamining.org, 2006) (http://www.antimonynet.com/., 2011)
Antimony pollution in China (He et al., 2011) Heavy pollution was reported in mine areas in Yangtze River area, China (He et al, 2011) up to 29.4 mg L 1 in water; High potential of Sb contamination in source drinking water through water cycle up to 1163 mg kg 1 in sediments; 3.92-143.7 mg kg 1 in 34 species of ferns; 29.5-255 mg m 3 in fly ash
Antimony removal technologies USEPA and EEA have set Sb and its compounds as priority pollutants Regulation guide value for Sb in water 6 μg/l, USEPA; 6 μg/l, EEA 5 μg/l, Ministry of Health, China Technologies used for Sb removal Adsorption; simple, low cost, easy to operate Coagulation; Membrane separation; Electrodialysis; etc. Few work addressed Sb removal in engineering practice, such as in drinking water treatment plant (DWTP). Commonly investigated geomaterials showed insufficient performance goethite, hametite, montmorillonite, bentolite, gibbsite, etc., In present study, incorporation of Zr to Fe oxides, Zr-Fe binary oxide (Zr-Fe) was investigated
Procedure of adsorbent preparation NaOH Separation FeSO 4 + Zr(SO4) 2 Co-precipitation Aging Fabrication Grinding Drying
Characterizations of Zr-Fe adsorbent Zr-Fe oxide powder XRD pattern FE-SEM Pore size dis. Micro-scale powder; nanoscale grains; amorphous structure;
Comparison of Zr-Fe with Fe/Zr oxide Isotherm Parameters Zr-Fe ZrOx FeOOH Langmiur q m,l (mg/g) 60.368 55.036 18.530 model k L (L/mg) 3.483 1.013 0.343 R 2 0.963 0.942 0.920 Freundlich k F (g/mg L) 41.751 7.351 22.705 model 1/n 0.186 0.272 0.391 R 2 0.896 0.869 0.852 Zr-Fe>FeOOH>Zirconium oxide Sb(V) adsorption followed pseudo-second order rate law 51 mg-sb/g-adsorbent at ph 7.0, with initial concentration of 10 mg/l
Comparison with reported adsorbents Adsorbent ph C initial of Sb(V) (mg/l) Dose (g/l) Capacity (mg/g); t eq (h); temp. ( o C) Reference Zr-Fe 7.0 10 0.2 51; 24; 25 Present study goethite 3.0 24.35 0.5 17.6; 168; 25 Leuz et al., 2006 kaolinite 6.0 3 25 0.059; 24; 25 Xi et al., 2010 bentonite 6.0 1 25 0.5; 24; 25 Xi et al., 2010 montmorillonite 2025 (antimony acetate) 5 40.75; 6; 120 Zhao et al., 2010 Zr-Fe has a higher capacity than some reported adsorbents in removal of Sb(V).
Thermodynamic: effect of temperature Thermodynamic parameters of Sb(V) adsorption on the Zr-Fe T ( o C) ΔG o (kj/mol) Δs o (kj/(mol K)) Δh o (kj/mol) 15-6.127 0.175 47.674 25-4.503 35-2.636 Sb(V) adsorption on Zr-Fe was an endothermic process Adsorption of Sb(V) enhanced with increasing temperature
Understanding of adsorption mechanism Research questions: Surface complexes after Sb(V) adsorption? Role of active surface sites, Fe-OH or Zr-OH or both? Role of contained sulphate?
Effect of ph and ion strength No obvious change of ph edge curve with an increase of IS from 0.001 to 0.01 M; Obvious increase of adsorption with an increase of IS from 0.01 to 0.1 M at ph above 8.0 Indicating formation of inner-sphere surface complexes
Surface complexes: zeta potential test No obvious shift of phiep and zeta potential curve with increasing surface loading of Sb(V) from 0 to 1 mg/l; Obvious negative shifts of phiep and zeta potential curve were observed with surface loading up to 5 mg/l; which also indicated inner-sphere complexes formed after adsorption.
Active surface sites I: XPS measurement Sb(V) chemsorbed; Broad scan O1s+Sb3d Peak positions of O1s and Fe2p negatively shifted Fe2p Zr3d Peak intensities of Zr3d and Fe2p weakened; Both Fe-OH and Zr-OH sites interacted with Sb(OH) 6-, contributing to Sb(V) adsorption
Active surface sites II: Raman spectra Goethite, hematite, maghemite Sb-O a) Peaks at 390 and 1002 cm-1 weakened; Goethite b) New peak at 621 cm-1 appeared; Indication of the interaction of Fe-OH sites with Sb(V)
Role of sulphate: FTIR and SO 4 2- release FTIR observations SO 4 2- release test 1206, 1130, 1062 and 988 cm -1 declined; Sb-O band was not observed; 0.33 mmol SO 4 2- released when 1 mmol Sb adsorbed; Ion exchange between contained SO 4 2- and Sb(V) was observed An minor role in adsorption of Sb(V)
Conclusions Zr-Fe adsorbent was prepared, which has higher capacity than FeOOH, ZrOx and many reported adsorbents. Inner-sphere surface complexes formed after Sb(V) adsorption; Interaction of active Fe-OH and Zr-OH sites on Zr-Fe with Sb(V) played a major role in the adsorption process; Ion exchange between contained SO 2-4 and Sb(V) also contributed and played a minor role in adsorption.
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