Immobilization of antimony (Sb) in shooting range soil by soil amendments

Transcription

1 Immobilization of antimony (Sb) in shooting range soil by soil amendments Espen Mariussen Arnljot Strømseng Norwegian Defence Research Establishment (FFI)

2 - Metal accumulation in small arms shooting ranges Stop butt Surface run-off Pb Metals Zn Cu Sb Leachate Ground water surface Bedrock

3 Antimony in shooting ranges Lead bullets contain Sb as an alloy Used as an hardening agent For the years 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

4 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

5 Reactive sorbents tested 1. Hydroxyapatite (Ca 5 (PO 4 ) 3 (OH)): Used as an amendment to stabilize Pb and Cu in soil 2. Finely grounded olivine (Mg 2 Fe 2 SiO 4 ): 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 (Fe 2 O 3 ) from Merox Charged surface groups that can form complexes with both cations and anions 4. Zero-valent iron (Fe 0 ) a) (Fe 0 )-grit (0.3-1mm) and (Fe 0 )-powder (< 150 µm) Oxidize into amorphous Fe-oxides with high sorption capacity to both cations and anions.

6 Experimental 2-4% sorbent (w/w) mixed in soil Tractor mixer and cement mixer

7 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

8 Leakage of Sb from butt soil -Column study with simulated precipitation -Leakage from the reference soil Treshold limit for hazardous waste Treshold limit for non-hazardous waste Treshold limit for inert waste Evjemoen soil Rena soil Sessvoll soil Ulven soil

9 Leakage of Cu, Sb and Pb from butt soil -Column study with simulated precipitation -Leakage from the reference soil Evjemoen 2 soil Steinsjøen soil 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

10 Results Effects of the soil amendments

11 Hydroxyapatite as sorbent Evjemoen soil Rena soil Sessvoll soil Ulven soil Increased leakage of Sb Anion exchange with PO3- Suitable for Pb and Cu, but not in combination with Sb

12 Olivine as sorbent Evjemoen soil Rena soil Sessvoll soil Ulven soil Increased leakage of Sb Anion exchange with PO 3 - or carbonates?? Suitable as a leakage barrier but not as soil amendment

13 Iron oxides as sorbent; Merox Fe 2 O 3 Evjemoen soil Rena soil Sessvoll soil Ulven soil 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

14 Zerovalent iron as sorbent; Fe 0 -powder Evjemoen soil Rena soil Sessvoll soil Ulven soil

15 Zerovalent iron as sorbent; Fe 0 -grit Evjemoen 2 soil Steinsjøen soil 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 Fe 2 O 3 nh2o and iron(iii) oxide-hydroxide FeO(OH) Fe(OH) 3

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

17 Iron oxides as soil stabilizing agent Iron oxides creates surface complexes with both anions and cations ( FeO, FeOH 0, FeOH 2+ ). 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

18 Iron and iron oxides as sorbents for Sb depend on several factors Iron oxide-hydroxide (Fe 2 O 3 nh2o or Fe(O)OH)) probably better than the iron oxides (Fe 2 O 3, Fe 3 O 4 ). 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, FeOH 2+ ) 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 Fe 2 O 3 nh2o and iron(iii) oxide-hydroxide FeO(OH) Fe(OH) 3

19 Thank you for your attention?