Chinese mining area. CAS-NRC workshop of collaborating research in the field of Environment and Climate, Dec 1, 2009, Beijing CHINA

Transcription

1 Contamination ti of antimony (Sb) from a Chinese mining area Gudny Okkenhaug (PhD candidate) Norwegian Geotechnical Institute (NGI), Dep. Environmental Technnology University of Life Science (UMB), Dep. of plant and environmental sciences, CAS-NRC workshop of collaborating research in the field of Environment and Climate, Dec 1, 2009, Beijing CHINA

2 PhD working title: Binding mechanisms and solubility of antimony (Sb) in the environment Research stay at Center for Eco-Environmental Environmental Sciences (RCEES), CAS, Beijing (May October 2009) Soil science group, Prof. Yongguan Zhu Focus on antimony contaminated soil from Sbmining area

3 Antimony (Sb=Stibium) Stibium) Toxicity: Antimony is not an essential element for organisms Toxicity considered to be about the same as As Toxicity depends d on the redox state: Stibin (SbH 3 ) most toxic Sb(III) is more toxic than Sb(V) Defined as a Priority Pollutant (US-EPA, EU)

4 China the world wide largest producer of antimony Applications: Flame retardant Alloys (increases the hardness of lead) Batteries Glass, pottery Painting Anthropogenic sources: Mining activity Metal smelters Shooting ranges Road traffic (dust from brake linings and tires) Waste disposal and incineration rom Wikipedia

5 Sampling area in Xikuangshan, Lengshuijiang largest antimony mining i area in the world Hunan Agricultural University, Changsha

6 Xikuangshan antimony mining area Tailings Tailingdam

7 Soil sampling downstream antimony mining area

8 Laboratory work at RCEES, Beijing Soil from Sb mining area - Distribution and speciation of Sb in soil and plants Sb- contaminated paddy field soil (downstream) - Mobility and speciation in soil pore water - Uptake in rice plants - Effect of sorbent amendment (chemical stabilization)

9 Speciation and distribution of antimony in soil samples from Sb-mining i area Sequential extraction of antimony, distribution in soil Sb mainly associated to the LOC 10 oxalate extractable fraction LOC 9 (Considered as amorphous and LOC 8 crystalline Fe-oxides) and to LOC 7 the residual fraction LOC 6 LOC 5B Very high amount of LOC 5A leachable (bioavailable) Sb LOC 4 in soil. Exceed leaching LOC 3 limits for hazardous waste LOC 2 according to EU landfill directive Occurs mainly as Sb(OH) 6-0% 20% 40% 60% 80% 100% (NH4)2SO4 (NH4)H2PO4 NH4-oxalate buffer Redsidual (HNO3, HCl, HF)

10 Paddy field soil downstream Sb mining area High amount of leachable Sb (exceeds limits of hazardous waste) Significant increase in Sb concentration in soil pore 2500 water after flooding 2000 Probably due to ph increase after flooding 1500 Changes sorption surfaces of soil particles, Sb co oncentration in porewater (µg g/l) 1000 Reduces the anion sorption 500 capacity of Fe-(hydr)oxides which are important sorbents 0 for Sb in soil Sb in paddy soil pore water during flooding 0 weeks 2 weeks 4 weeks 6 weeks

11 Redox speciation of Sb in flooded d paddy field soil Sb occurs mainly as Sb(OH) 6- in porewater Slightly reducing conditions in pore water (Eh=30 mv). Thermodynamically Sb(OH) 3 should be stable Fe- oxides can catalyse the oxidation of Sb(III) Due to high total concentrations, the Sb(III) concentrations are high (Sb(III) most toxic) ter (µg/l) tion in porewat Sb concentrat weeks 2 weeks 6 weeks SbV SbIII

12 Strong sorption of Sb to iron plaque on rice roots Iron plaque (ferrihydrite) develops on rice roots. Sb has strong affinity to Fe-oxides and especially ferrihydrite High concentrations of Sb (120 µg/mgfe) in iron plaque BUT: No reduction of Sb- concentration in pore water Sb solubility may be governd Sb solubility may be governd by mineral phase: Ca[Sb(OH) ]

13 Effect of Fe-based soil amendments (olivine, hematite) on Sb in porewater ration in porew water (µg/l) Sb concent Sb in paddy soil pore water effect of olivine 0 weeks 2 weeks 4 weeks 6 weeks RN RNO tration in porew water (µg/l) Sb concent Sb in paddy soil pore water effect of Merox-Fe2O3 0 weeks 2 weeks 4 weeks 6 weeks RN RN Olivine (Fe,Mg) 2 SiO 4 ) Hematite (Fe 2 O 3 )

14 Shanghai Synchrotron Radiation Facility Advanced X-ray based analysis technique XANES (X-ray Absorption Near Edge Structure) Information about redox state t EXAFS (Extended X-ray analysis Fine Structure) Information about binding to nearest neighbor

15 Possible collaborating research in the field of Antimony Lack of research on behavior and effect of antimony in the environment Sb behavior in soil, groundwater, surface water Measures to reduce contamination Stabilization (amendments) Bioavailability Uptake in plants Uptake in organisms Ecotoxicity Human toxicity

16 Thanks' for your attention!

17

18 Environmental technology - NGI s expertise Environmental technology Groundwater and hydrogeology Geothermal energy Instrumentation t ti and monitoring i Numerical modelling Laboratory and model testing Geographical Information Technology

19 Relationship between soluble Sb concentrations in soils and plants Passive transport by convection with he stream of transpirational water into and through the plants? 1000 Sb concentratio on in plant (sho oot) mg/kg R² = (NH4)2SO4 extractable Sb in soil (mg/kg soil) From Tschan et al. Environ Chem 2009

20 Sb porewater concentration governd by Sb porewater concentration governd by solubility of Ca[Sb(OH)6]2?

21 nvironmental effects?

22 Effect of changes in Fe concentration in porewater? High concentration of Fe(II) in porewater (>> SI) ewater Precipitation of Fe-minerals inhibited due to DOC and PO4 on nucleation sites ntration in pore (µg/l) Once sufficient super saturation: rapid precipitation of solid phases (Fe(CO 3 ), Fe(OH) Fe(II) oxidation of NO3- due to changes in Eh Sb concen Sb in paddy soil pore water 0 weeks 2 weeks 4 weeks 6 weeks SH N Fe in paddy field pore water rewater Fe conce entration in po (mg/l) weeks 2 weeks 4 weeks 6 weeks S N

23 Effect of Phosphorus in porewater on mobility of Sb and As? In general: H 2 PO - 4 behaves as competing ion for the ligand exchange of Sb and As Porewater saturated with Ca-phosphates Increase in Sb and As concentration in porewater probably not due to ion exchange reaction with P P concentration in porewater (mg/l) P in paddy field porewater SH N weeks 2 weeks 4 weeks 6 weeks

24 Sb concentrations and speciation in plant root & shoot (0.1 M citric acid extraction) 700 Sb(III) and Sb(V) in root & shoot SbV µg/g g Sb3+ µg/g c 3: Boehmeria vea (L.)Gaudich Sb (µg/g g) Shoot Root Shoot Root Shoot Root Shoot Root Shoot Root Shoot Root Shoot Root Shoot Root Shoot Root Loc2 Loc3 Loc4 Loc5A Loc5B Loc6 Loc8 Loc9 Loc10 c 2: Phytolacca

25 Speciation of Sb in paddy field soil What would we expect thermodynamically? Eh (mv) Eh in paddy field porewater after 6 weeks SH N RN RNO RNM Eh in porewater: mv Thermodynamically: RNMO mainly Sb(OH) 3

26 Effect of amendments on Sb concentration in rice plant 600 Sb in rice root (citric acid extracted) 10 Sb in rice shoot (citric acid extracted) 9 entration in ric ce root (µg/g) Sb conc Sb conce entration in rice shoot (µg/g) RN RNO RNM RNMO 0 RN RNO RNM RNMO

27 Effect of rice plants on Sb and As in 2500 porewater 2000 porewater oncentration in (µg/l) Sb: No significant 500 differences in pots with 0 and without rice As: Significant reduction in pots with rice Sorption to iron plaque? Uptake in rice plants? Sb co /L) porewater (µg/ As con ncentration in Sb in paddy soil pore water 0 weeks 2 weeks 4 weeks 6 weeks As in paddy soil pore water N R N R