# Presentation: 018421

## Fundamentals of Radium and Uranium Removal from Drinking Water Supplies

- Dennis Clifford
- University of Houston

## Important Radium Isotopes

| Radium Isotope | Half Life | PrimaryEmission | Decay Series |
| --- | --- | --- | --- |
| 226Ra | 1600 y | Alpha | Uranium |
| 228Ra | 5.7 y | Beta | Thorium |
| 224Ra | 3.64 d | Alpha | Thorium |

## Important Uranium Isotopes 

| Isotope, Emission | NaturalAbundance 
% | Half Life 
yr | Specific Activity
pCi/μg | Relative Activity 
% |
| --- | --- | --- | --- | --- |
| 238U,  | 99.276 | 4.51 x 109 | 0.333 | 47.33 |
| 235U, / | 0.7196 | 7.1 x 108 | 2.144 | 2.21 |
| 234U,  | 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 natural abundance.
- If present at natural abundance 1g 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 Species | Predominant Species Charge |
| --- | --- | --- |
| All | Ra2+ | a divalent cation |
| < 5 | UO22+ | a divalent cation |
| 5 to 6.5 | UO2CO30 | a neutral molecule |
| 6.5 to 7.6 | UO2(CO3)22- | a divalent anion |
| 7.6 | UO2(CO3)34- | a tetravalent anion |

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

## Radium-Removal Methods

*** *****Cation Exchange Softening (BAT)****    *****2 RNa + Ra******2+****** ************ R******2******Ra  +  2 Na+***
**Lime Softening (BAT)**
**Reverse Osmosis (BAT)**
**Sorption onto MnO****2**** (HMO)**
**Precipitation with BaSO****4**** (by adding BaCl****2****)**
**(Excess)Ba****2+**** + (Trace)Ra + SO****4****2-**** = Ba(Ra)SO****4**
**Sorption onto BaSO****4****-Impregnated Media**
**Media****●****BaSO****4**** + Ra****2+**** = Media****●****Ba(Ra)SO****4 ****+ Ba****2+**
**Electrodialysis**

## POU Radium-Removal Methods

**Reverse Osmosis (BAT)**
*** *****Cation Exchange Softening *****2 RNa + Ra******2+****** ************ R******2******Ra  +  2 Na+***
**Sorption onto MnO****2****-impregnated fibers or filters, e.g., DE or granular media.**
**Sorption onto BaSO****4****-Impregnated Resin or****	****Activated Alumina**

## Radium removal by ion-exchange softening with bypass blending of raw water.

## Ion Exchange Resins for Radium Removal

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

## Magnesium, calcium 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 brine contains ~600 pCi/L*

## Process flow schematic for radium removal by adsorption onto preformed MnO2

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

*For 50% removal in water with 10 pCi/L, Residual dry MnO**2** (s) contains 21,000 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 resin contains 510 pCi/g*

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

*For single-column operation with 10 pCi/L in feed, spent dry AAl contains 220 pCi/g*

## Uranium-Removal Methods

**Anion Exchange (BAT)**
***	******	******4 RCl + UO******2******(CO******3******)******3******4-****** ************ ******	******	******	******	******	******	******R******4******UO******2******(CO3)******3******4-****** + 4Cl******-***
**•  ****Lime Softening (BAT)**
**Enhanced Coagulation /Filtration (BAT)**
**Reverse Osmosis (BAT)**
**Activated Alumina Adsorption**
**Electrodialysis**

## POU Uranium-Removal Methods

**Anion Exchange *****4 RCl + UO******2******(CO******3******)******3******4-****** ************ ******	******	******	******	******	******R******4******UO******2******(CO3)******3******4-****** + 4Cl******-***
**Reverse Osmosis**
**Activated Alumina Adsorption**

## Effect of pH and coagulant on uranium removal by coagulation with 25 mg/L dose. (Sorg 1990; Lee & Bondietti, 1983)

- Coagulation for Uranium Removal

*For 50% removal of 40 ****g U/L, the dry sludge contains **800 pCi/g Fe(OH)**3**(s)*

## Effect of pH (and lime dose) on uranium removal by lime softening. (Sorg 1990; Lee & Bondietti, 1983)

- Lime Softeningfor Uranium Removal

- Above pH 10.6, added Mg2+ improves U removal.

*For 90% removal of 40 ****g U/L, the dry sludge contains **135 pCi/g CaCO**3**(s)*

##  Ion-Exchange Resins for Uranium Removal

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

-  Ion-Exchange Resins for Uranium Removal

## Effluent uranium levels during anion exchange with macroporous SBA resin at pH 8.

- Anion Exchange for Uranium Removal

*If feed water contains 40 ****g U/L, Waste brine contains ~80,000 pCi/L for a 30,000 BV run length.*

## Effect of uranium, sulfate, and chloride concentrations on BV to uranium exhaustion.

## Processes for Radium Removal

| Treatment Method | Removal | Comment |
| --- | --- | --- |
| IX Softening(Na+, SAC) | >95% | Operate to hardness breakthrough, NaCl Regen. |
| Ba(Ra)SO4Precipitation | 50-95% | Add BaCl2 to feed water before filtration. |
| MnO2 Adsorption | 50-95% | Use preformed MnO2 or MnO2-coated filter media. |
| RO | >99% | Effective but expensive |

## Processes for Uranium Removal

| Treatment Method | Removal | Comment |
| --- | --- | --- |
| Coagulation w Fe/Al | 50-90% | Effective at pH near 6 and 10 |
| Lime Softening | 80-99% | Higher pH = greater removal. Mg2+ helps at pH > 10.6. |
| Anion Exchange | >95% | Regenerate with 2-4 M NaCl 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 for Radium Removal | 600 pCi/L spent brine20 pCi/g dry resin |
| --- | --- |
| Coag-Filt w MnO2(s) for Radium Removal | 21,000 pCi/g dry MnO2(s) |
| Fe(III) Coag-Filtration for Uranium Removal | 800 pCi/g Fe(OH)3(s) |
| Anion Exchange for Uranium Removal | 80,000 pCi/L spent brine(30,000 BV run length) |