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Home , Ion exchange, Radium, Reverse osmosis

Fundamentals of Radium and Removal from Drinking Supplies

Dennis Clifford University of Houston Important Radium

Radium Half Life Primary Decay Emission Series 226Ra 1600 y Alpha Uranium

228Ra 5.7 y Beta

224Ra 3.64 d Alpha Thorium Important Uranium Isotopes

Isotope, Natural Half Life Specific Relative Emission Abundance yr Activity Activity % pCi/µg % 238U, α 99.276 4.51 x 109 0.333 47.33

235U, α/γ 0.7196 7.1 x 108 2.144 2.21

234U, α 0.0057 2.47 x 105 6189.0 50.51

Natural abundance and half life from Lange's Handbook, 1973, p. 3-108 Specific activity and relative activity calculated from isotope mass, half life and . If present at natural abundance 1µg U = 0.67 pCi Chemical and Physical-Chemical Behavior of Isotopes

• Although possessing differing decay rates and modes of decay, the chemical and physical- chemical behavior of all isotopes is the same. • 95% removal of 226Ra is also 95% removal of 228Ra when they are present together regardless of the ratio of their initial activities. • 95% removal of 238U is also 95% removal of 235U when they are present together regardless of the ratio of their activities. Radium and Uranium Speciation in Ground Water as a Function of pH

pH Range Predominant Predominant Species Species Charge All Ra2+ a divalent cation 2+ < 5 UO2 a divalent cation

0 5 to 6.5 UO2CO3 a neutral

2- 6.5 to 7.6 UO2(CO3)2 a divalent anion

4- 7.6 UO2(CO3)3 a tetravalent anion

-2 pCO2 = 10 atm, CT,U = 2.38 mg/L, 25 °C Above pH 10.5, positively charged uranyl complexes are dominant. Radium-Removal Methods

• Cation Exchange Softening (BAT) 2+ 2 RNa + Ra R2Ra + 2 Na+ • (BAT) • Reverse (BAT)

• onto MnO2 (HMO) • Precipitation with BaSO4 (by adding BaCl2) 2+ 2- – (Excess)Ba + (Trace)Ra + SO4 = Ba(Ra)SO4 • Sorption onto BaSO4-Impregnated Media 2+ 2+ – Media●BaSO4 + Ra = Media●Ba(Ra)SO4 + Ba • POU Radium-Removal Methods

• (BAT) • Cation Exchange Softening 2+ 2 RNa + Ra R2Ra + 2 Na+

• Sorption onto MnO2-impregnated fibers or filters, e.g., DE or granular media.

• Sorption onto BaSO4-Impregnated Resin or Activated Alumina Radium removal by - exchange softening with bypass blending of . Resins for Radium Removal

Resin Ionic Capacity Designation Description Form meq/mL Strong Acid Cation Standard SAC resin, Na+ 1.9 exchange resin for polystyrene-DVB matrix, - radium removal: —SO3 exchange groups Amberlite IR-120+, Duolite C20, Purolite C100, Dowex HCR-S , and radium breakthrough curves for ion-exchange softening.

If feed water contains 10 pCi/L, the resin contains ~20 pCi/g at steady state operation. Waste contains ~600 pCi/L Alternatively,

BaCl2 may be added to precipitate BaSO4(s)

Process flow schematic for radium removal by

onto preformed MnO2 For 50% removal in water with 10

pCi/L, Residual dry MnO2 (s) contains 21,000 pCi/g

Radium Removal as a function of MnO2 dose. Houston GW with 120 mg/L hardness and pH = 7.5 Feed Ra = 8.7 pCi/L

For single-column operation with 10 pCi/L in feed, spent dry resin contains 510 pCi/g

Radium breakthrough curve for Dow Radium Selective Complexer (RSC), a BaSO4(s) loaded cation resin. For single-column operation with 10 pCi/L in feed, spent dry AAl contains 220 pCi/g

Radium breakthrough curves for plain and BaSO4-loaded activated alumina. EBCT = 3 min. Feed Ra = 8.7-11.3 pCi/L Uranium-Removal Methods

• Anion Exchange (BAT) 4- 4 RCl + UO2(CO3)3 4- - R4UO2(CO3)3 + 4Cl • Lime Softening (BAT) • Enhanced Coagulation / (BAT) • Reverse Osmosis (BAT) • Activated Alumina Adsorption • Electrodialysis POU Uranium-Removal Methods

• Anion Exchange 4- 4 RCl + UO2(CO3)3 4- - R4UO2(CO3)3 + 4Cl • Reverse Osmosis • Activated Alumina Adsorption Coagulation for Uranium Removal

For 50% removal of 40 µg U/L, the dry contains

800 pCi/g Fe(OH)3(s)

Effect of pH and coagulant on uranium removal by coagulation with 25 mg/L dose. (Sorg 1990; Lee & Bondietti, 1983) Lime Softening Above pH 10.6, for added Mg2+ Uranium improves U Removal removal.

For 90% removal of 40 µg U/L, the dry sludge contains

135 pCi/g CaCO3(s)

Effect of pH (and lime dose) on uranium removal by lime softening. (Sorg 1990; Lee & Bondietti, 1983) Ion-Exchange Resins for Uranium Removal

Resin Ionic Capacity Designation Description Form meq/mL Strong- Anion Type 1, macroporous, SBA Cl- 1.0 exchange resin for resin, polystystrene-DVB + uranium removal matrix, —N(CH3)3 Ionac A-642 exchange groups Purolite A-500 Amberlite IRA 900 Anion Exchange for Uranium Removal

Effluent uranium levels during anion exchange with macroporous SBA resin at pH 8. If feed water contains 40 µg U/L, Waste brine contains ~80,000 pCi/L for a 30,000 BV run length. Effect of uranium, sulfate, and concentrations on BV to uranium exhaustion. Processes for Radium Removal

Treatment Removal Comment Method IX Softening >95% Operate to hardness (Na+, SAC) breakthrough, NaCl Regen.

Ba(Ra)SO4 50-95% Add BaCl2 to feed water Precipitation before filtration.

MnO2 50-95% Use preformed MnO2 or Adsorption MnO2-coated filter media. RO >99% Effective but expensive Processes for Uranium Removal

Treatment Removal Comment Method Coagulation 50-90% Effective at pH near 6 and 10 w Fe/Al Lime 80-99% Higher pH = greater removal. Softening Mg2+ helps at pH > 10.6. Anion >95% Regenerate with 2-4 M NaCl Exchange after 10,000-50,000 BV RO >99% Effective but expensive Residuals • The more effective the coagulant or adsorbent, the higher is the radioactivity in the residuals. Ion Exchange Softening 600 pCi/L spent brine for Radium Removal 20 pCi/g dry resin

Coag-Filt w MnO2(s) for 21,000 pCi/g dry MnO2(s) Radium Removal

Fe(III) Coag-Filtration 800 pCi/g Fe(OH)3(s) for Uranium Removal Anion Exchange for 80,000 pCi/L spent brine Uranium Removal (30,000 BV run length)