Immobilization of antimony (Sb) in shooting range soil by ...
Transcript of Immobilization of antimony (Sb) in shooting range soil by ...
Immobilization of antimony (Sb) in shooting range
soil by soil amendments
Espen Mariussen
Arnljot Strømseng
Norwegian Defence Research Establishment (FFI)
- Metal accumulation in small arms shooting ranges
Helsinki 21-22. May 2013
Stop butt
Ground water surface
Bedrock
Metals
Cu
Pb Sb
Zn Surface
run-off
Leachate
Antimony in shooting ranges
• Lead bullets contain Sb as an alloy
– Used as an hardening agent
• For the years 2004-2008
– Annually input of approximately 14 metric ton of Sb
– Both in stop-but zones and heterogeneously spread
• Sb is readily mobilized from the bullets during weathering
– Elevated concentrations in run-off water (5-20 µg/L)
• Sb is a particular problem when contaminated soil is to be deposited at
waste disposal sites.
• Often categorized as hazardous waste due to the high mobility of Sb.
• Increase considerably the cost of remediation projects
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Stabilization of elements in soil
• Reactive sorbents added to the soil may adsorb and reduce leakage
of hazardous metals.
– Less spread into environment from stop butts
– Safer and more economical feasible waste disposal
• The sorbents should adsorb both cationic (Pb and Cu) and anionic
species (Sb).
• The goal is:
– Identify sorbents with high capacity and ability of sorption
– Identify sorbents that are economical feasible
– Identify sorbents that are easy to handle
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1. Hydroxyapatite (Ca5(PO4)3(OH)):
– Used as an amendment to stabilize Pb and Cu in soil
2. Finely grounded olivine (Mg2Fe2SiO4):
– Used in the field as a leakage barrier to reduce leakage of metals from
disposed shooting ranges
– Contain Fe and Mg oxides with presumed binding properties to both cations
and anions
3. Iron oxides
a) Ferric oxyhydroxide (Fe(O)OH) from Kemira®
b) Ferric oxide (Fe2O3) from Merox®
• Charged surface groups that can form complexes with both
cations and anions
4. Zero-valent iron (Fe0)
a) (Fe0)-grit (0.3-1mm) and (Fe0)-powder (< 150 µm)
• Oxidize into amorphous Fe-oxides with high sorption capacity
to both cations and anions.
Reactive sorbents tested
Experimental
• 2-4% sorbent (w/w) mixed in soil
– Tractor mixer and cement mixer
Experimental • PVC columns (~75 L) prepared with soil and connected to a vacuum pump
– 6 different soil types from stop-butt were tested
• Regularly addition of rainwater by a sprinkler system (3-5L each application)
• Collection of soil water
Helsinki 21-22. May 2013
Leakage of Sb from butt soil
-Column study with simulated precipitation
-Leakage from the reference soil
Evjemoen soil Rena soil
Sessvoll soil
Ulven soil
Treshold limit for hazardous waste
Treshold limit for non-hazardous waste
Treshold limit for inert waste
• All soils had Sb-leakage above the threshold limit for non-hazardous
waste
• Four of the soils have Sb-leakage above the threshold limit for
hazardous waste
– Waste disposal of hazardous waste involves high cost
Helsinki 21-22. May 2013
Leakage of Cu, Sb and Pb from butt soil
-Column study with simulated precipitation
-Leakage from the reference soil
Evjemoen 2 soil Steinsjøen soil
Results
• Effects of the soil amendments
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Hydroxyapatite as sorbent
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Rena soil
Ulven soil
Evjemoen soil
Sessvoll soil
Increased leakage of Sb
•Anion exchange with PO3-
•Suitable for Pb and Cu, but not in combination with Sb
Olivine as sorbent
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Evjemoen soil Rena soil
Sessvoll soil Ulven soil
Increased leakage of Sb
•Anion exchange with PO3- or carbonates??
•Suitable as a leakage barrier but not as soil amendment
Iron oxides as sorbent; Merox® Fe2O3
• Reduced leakage of Sb
• Three of the soils below threshold for hazardous waste
• Not adequate performance compared to hydrated iron oxides
• Non-hydrated iron oxide with higher proportion of crystalline Fe-forms may
implicate less sorption sites
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Evjemoen soil Rena soil
Sessvoll soil Ulven soil
Zerovalent iron as sorbent; Fe0-powder
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Evjemoen soil
Rena soil
Sessvoll soil Ulven soil
Zerovalent iron as sorbent; Fe0-grit
• Reduced leakage of Sb >95%
• Three of the soil types below threshold limits for inert waste
• One of the soils still above threshold limit for hazardous waste
• Crusting and compaction of the soil due to oxidation of the iron
• Zerovalent iron is a very promising product as a soil stabilizing agent
• Zerovalent iron oxidizes to rust, which consists of hydrated iron(III) oxides Fe2O3·nH2O
and iron(III) oxide-hydroxide FeO(OH)·Fe(OH)3
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Evjemoen 2 soil Steinsjøen soil
Iron oxide-hydroxide as sorbent; Kemira® Fe(O)OH
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Evjemoen 2 soil Steinsjøen soil
Reduced leakage of Sb >95%
•Well below threshold limits for inert waste
•Very promising product as a soil stabilizing agent
Iron oxides as soil stabilizing agent
• Iron oxides creates surface complexes with both anions and cations
– ( FeO−, FeOH0, FeOH2+).
• Adsorption is governed by pH and the iron oxides iso-electric point.
– At low pH, predominantly positive charge which will favour sorption of anions
(such as Sb and As)
– At high pH, predominantly negative charge which will favour sorption of cations
(such as Pb and Cu)
• High surface area of the sorbent will increase the number of sorption
sites
• Amorphous forms of the sorbent will favour sorption compared to
crystalline forms
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Iron and iron oxides as sorbents for Sb depend
on several factors
• Iron oxide-hydroxide (Fe2O3·nH2O or Fe(O)OH)) probably better
than the iron oxides (Fe2O3, Fe3O4).
– More sorption sites due to an amorphous state with a high surface area
– Crystalline properties of the iron oxides will reduce sorption
• pH dependency
– The surface charge properties (-FeOH-, -FeOH, FeOH2+) varies
depending on pH
• Acid conditions should favor Sb-adsorption
• Anarobic or aerobic conditions
– Aerobic conditions will increase oxidation of zerovalent iron which
probably will increase the sorption capacity.
– Zerovalent iron oxidizes to rust, which consists of hydrated iron(III)
oxides Fe2O3·nH2O and iron(III) oxide-hydroxide FeO(OH)·Fe(OH)3
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Thank you for your attention
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Helsinki 21-22. May 2013