Radium-enriched barite (barium sulfate [BaSO4]) is arguably the dominant form of Naturally Occurring Radioactive Material (NORM) associated with certain radioactively impacted wastes, including those from mining and milling efforts. The very low solubility of barite, under oxic and sulfate-bearing environments, combined with its well crystalline form results in the effective physical encapsulation of radium isotopes (226Ra and 228Ra) during their co-precipitation with the barite mineralization. Within oxic and sulfate-bearing conditions, such as those in surficial environments, the dispersion of barite is dominantly by physical hydrodynamic processes. However, when barite is exposed to a geochemically reducing environment sufficient to result in the bacterially-mediated depletion of sulfate the subsequent dissolution of barite may allow for the dissolution of previously encapsulated radium. Geochemical modeling will help establish the limits of barite stability and the geochemical conditions conductive to its destabilization and dissolution and the release of co-precipitated radium and the factors that can lead to a sufficiently reducing geochemical environment will be discussed.

1. 1 February 2014
The Behavior of Radium-Enriched Barite
in Geochemically Reducing Conditions
Aids in Understanding Radium
Anomalies
Richard Murphy, Ph.D.
Don Carpenter
ARCADIS U.S., Inc.
Society for Mining,
Metallurgy, and Exploration
2014 Meeting

2. 2 February 2014
THIS PRESENTATION WILL SYSTEMATICALLY
ADDRESS THE FOLLOWING ITEMS:
Occurrence of Radium
Incorporation of Radium into Barite
Destabilizing Geochemical Conditions
Reprecipitation of Radium
Discussion of Findings

3. 3 February 2014
Decay of Naturally Occurring Uranium and Thorium
Generates Radioactive Progeny and NORM
Radium isotopes
are produced
within each
decay chain
Comparatively short
half-life of Radium-
228 results in rapid
natural attenuation

4. 4 February 2014
Radium Occurs Naturally in Groundwater Systems
Throughout US

5. 5 February 2014
Precipitation of Alkaline Earth Sulfates can
Co-Precipitate Radium Sulfate forming a NORM
Ba+2 + SO4
-2 → BaSO4
Ba+2 + (Ra+2) + SO4
-2 → Ba(Ra)SO4
Acid insoluble
Low (“insolubility”) of Barite
causes Radium and decay
products to be largely
retained within crystalline
structure

6. 6 February 2014
Radium and Mining/Milling
NORM occurrence in copper ore
Uranium soluble at acid and alkaline pH
Acid leaching (sulfuric acid) will liberate uranium however high sulfate concentrations
limit radium dissolution
At alkaline pH, radium less soluble
Radium present naturally in groundwater systems at mines
due to geochemically-reducing systems (where present)

7. 7 February 2014
Typically Instability of Barite is the Least of the NORM-
Related Problems its Presence May Engender
Present as dispersed ,potentially
non-actionable material, at many
sites:
Mines, Mills, Smelters, Tailings,
Slag

8. 8 February 2014
The Insolubility of Barite Under Geochemically Oxidizing
Conditions Prevents its Chemical Removal
pH (oxidizing
conditions)
Dissolved Barium
(mg/L)
Dissolved Sulfate
(mg/L)
4 0.32 5.1
7 0.30 5.1
9 0.30 5.1

9. 9 February 2014
Precipitation of Alkaline Earth Sulfates can
Co-Precipitate Radium Sulfate forming a NORM
Ba+2 + SO4
-2 → BaSO4
Ba+2 + (Ra+2) + SO4
-2 → Ba(Ra)SO4
Precipitation Reaction Documents:
1) Importance of Barium ion activity
2) Importance of Sulfate ion activity

10. 10 February 2014
This Chemical Behavior is Leveraged for Removal of
Both Dissolved Barium and Radium
Best Demonstrated Available Technology [BDAT]
1) Addition of Sodium Sulfate [Na2SO4]
2) Addition of Barium Chloride [BaCl2]
BaSO4 readily passes
Toxicity Characteristics Leaching Procedure (TCLP)

11. 11 February 2014
Stability of Barite (and Radium) is a Function of Both
Dissolved Barium and Sulfate Ion Activity
BaSO4 = Ba+2 + SO4
-2
log_k -9.97
aBa+2 * aSO4
-2 = 10-9.97
Note that any process that results in removal of
one of these results in destabilization of the
barite
Linear relationship (i. e., remove one, dissolve
the other)

12. 12 February 2014
Modeling Results Also Document Relationship
Between Barium and Total Dissolved Solids
Empirical
relationship has
been noted between
NORM formation and
Total Dissolved
Solids (and depth)
Barium solubility can
be shown to be a
function of chloride
concentration
(activity)
0
10
20
30
40
50
Barium (brine) Barium (chloride-free)
Barium Solubility (ppm) – 81° C

13. 13 February 2014
Barite Solubility Increases at High Ionic
Strength due to Thermodynamics
Rosenberg et al., 2011

14. 14 February 2014
Sulfate Reducing Bacteria can Quantitatively Remove
Sulfate in the Presence of Sufficient Organic Carbon
2CH2O + SO4
-2  2HCO3
- + H2S
60.0 g CH2O + 96.1 g SO4
-2  122.0 g HCO3
- + 34.1 g H2S
Consequently, any environment where solid phase
metabolizable organic carbon as a ratio approaching 60% of
the available dissolved phase sulfate can lead to depletion of
the dissolved sulfate
Dissolution of previously solid phase sulfates (e. g., Barite)
may occur

15. 15 February 2014
Geochemically-Reducing Systems
Liberate Radium
Szabo et al., 2012

16. 16 February 2014
Radium Release from Dissolving Barite can Result in an
Important Increase in Dissolved Radium Activity
500 mg of Barium per Kilogram of Soil
850 mg of Barite per Kilogram of Soil
5 pCi of Radium per Milligram of Barite
4,250 pCi of Radium per Kilogram of Soil

17. 17 February 2014
Dissolution of only a Comparatively Small Amount of
Radium-226 can Exceed the Drinking Water Standard
4,250 pCi/Kg of Soil of Radium
5 pCi/L is Drinking Water Standard
Consequently, Dissolution of Barite within 1 Kilogram of
Soil can impact 850 Liters of Water

18. 18 February 2014
Geochemical Leading to Reducing Conditions Can
Result in Adverse and Unexpected Radium
Release of a bacteriological organic substrate (petroleum,
biological wastes, etc.)
Elevated Radium typically found with predictable co-
contaminants
Cr+3
As+3
Ba+2
H2S
Fe+2

19. 19 February 2014
The Optimum Modes of Control, if Necessary, Relate
Back to the Initial Dissolution Reaction
Ba+2 + SO4
-2 = BaSO4
Oxygenate system (H2S → SO4
-2)
Add a more readily soluble sulfate (Na2SO4, MgSO4)
Radium can re-incorporate into
barium, strontium, and calcium
minerals through co-precipitation
Rosenberg et al., 2011

20. 20 February 2014
Radium Co-precipitate with Calcium and
Strontium
Ca+2 + SO4
-2 + 2H2O → CaSO4 * 2H2O
Ca+2 + (Ra+2) + SO4
-2 + 2H2O →
Ca(Ra)SO4 * 2H2O
Ca+2 + (Ra+2) + SO4
-2 → Ca(Ra)SO4
Acid Soluble – HCl
Less adherence of the scale
More readily removed
Potential release of radium

21. 21 February 2014
Instability of Radium-Enriched Barite
The Insolubility of Barite Under Geochemically Oxidizing Conditions
Prevents its Chemical Removal
Precipitation of Alkaline Earth Sulfates can
Co-Precipitate Radium Sulfate forming a NORM
Stability of Barite is a Function of Both Dissolved Barium and Sulfate Ion
Activity
Sulfate Reducing Bacteria can Quantitatively Remove Sulfate in the
Presence of Sufficient Organic Carbon
Dissolution of only a Comparatively Small Amount of Radium can Exceed
the Drinking Water Standard

22. 22 February 2014
Imagine the result
Contact:
Donald Carpenter, PG
ARCADIS
Donald.Carpenter@arcadis-us.com