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


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


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


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


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


Hydroxyapatite as sorbent


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



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




Zerovalent iron as sorbent; Fe0-powder


Evjemoen soil

Rena 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



Iron oxide-hydroxide as sorbent; Kemira® Fe(O)OH



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


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


Thank you for your attention

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Immobilization of antimony (Sb) in shooting range soil by