Baohua Gu and Gilbert M. Brown

Transcription

1 Efficient Removal of Perchlorate (ClO 4 ) From Contaminated Water by Highly Selective, Regenerable Bifunctional Resins Baohua Gu and Gilbert M. Brown Environmental Sciences Division Chemical and Analytical Sciences Division Oak Ridge National Laboratory Oak Ridge, TN

2 Background Perchlorate (ClO 4 ) contamination is a widespread problem and has been detected in ground or surface water in 14 states (Urbansky 1998; Damian and Pontius, 1999). ClO 4 exceedingly mobile and stable in underground aquifers and surface water. Remediation technologies are limited.

3 Comparison of Treatment Technologies Bioremediation Technology Conventional Ion Exchange Reverse Osmosis Chemical Reduction Chemical Precipitation Effective Advantages Practical and economical Effective for treatment at relatively high concentrations (e.g., above 10 mg/l) Effective and able to remove ClO 4 below detection limit (<4 ppb) Fast reaction and simple operation Can be operated at a high flow rate A possible alternative May work well with highly concentrated ClO 4 in a small volume May work well with highly concentrated ClO 4 in a small volume (e.g., nitron and K + ) Fast reactions Disadvantages Need a highly reducing environment and a continual feed of nutrients Other electron acceptors in groundwater and soil Not suitable for treatment of water plumes with only slightly contaminated ClO 4. Slow reactions and living microorganisms Competition by other anions (e.g., NO 3, Cl, SO 4 =, HCO 3 ) Large quantities of waste brine generation Remineralization may be needed Regeneration problems with selective resins Fouling of the membranes Remineralization may be needed High capital cost and impractical Relatively slow reduction process Addition of chemicals May generate toxic byproducts Addition of chemicals Impractical for largescale treatment Reference: Urbansky 1998, Biorem. J. 2:8195; Damian and Pontius 1999, Environ. Prot. pp

4 Treatment by Highly Selective, Regenerable Resins Under DOE sponsorship, bifunctional anion exchange resins developed for pertechnetate (TcO 4 ) removal at ppt levels. Bifunctional resins consist of quaternary ammonium groups with both large (C 6 ) and small (C 2 ) alkyl groups resulting in high selectivity and good exchange kinetics. Demonstrated to be highly Paducah Groundwater efficient in removing lowlevels of TcO 0.03 Purolite A520E Flow rate changed 4 from 0.02 groundwater at Paducah, Bifunctional resin KY (with an initial TcO RO concentration ~ 0.1 ppb (or 0.00 ~0.7 nmol/l) C/C Bed Volume (x10 3 )

5 Treatment by Highly Selective, Regenerable Resins Perchlorate (ClO 4 ) behaves similarly as pertechnetate (TcO 4 ) both are large, poorly hydrated anions. Bifunctional resins were also demonstrated to be highly effective in removing lowlevels of ClO 4 from groundwater in northern California (with an initial ClO 4 concentration ~ 50 ppb). C/C Purolite A520E Column flowthrough experiment Bifunctional D3696 resin Bed Volume Bifunctional resins can be regenerated using the innovative sequential chemical displacement technique (patent pending).

6 Objectives Selective sorption (or partitioning) of ClO 4 on bifunctional resins and the treatment processes. Column flowthrough experiments and field evaluation. Regeneration of bifunctional resins (loaded with ClO 4 ) theory and experimental results.

7 Synthetic Resins Bifunctional resins (or BiQuat): RO02119 with trihexylamine/triethylamine functional groups; Synthesized at the Univ. of Tennessee, Knoxville. D3696 with trihexylamine/triethylamine functional groups; Scaleup version by Purolite International, Inc. Commercial monofunctional resins: Purolite A520E with triethylamine functional groups (by Purolite International). Sybron SR6 with tributylamine functional groups (by Sybron Chemicals, Inc.).

8 Experimental Batch Sorption Experiments Sorption and selectivity coefficient: K d = ClO 4 sorbed on resin (mg/g) ClO 4 in solution (mg/ml) (ml/g) Initial ClO 4 concentration: 1, ,000 ppb (or mg/l). Column FlowThrough Experiments Flow rate: ~17 BV/min in laboratory; ~2 BV/min in field. Resin column Influent ClO 4 concentration: 1,000 or 10,000 ppb in lab; ~50 ppb in field. 3way valve HPLC pump ClO 4 input solution

9 Experimental (water chemistry) Property Cl (mg/l) F (mg/l) NO 3 (mg/l) SO 4= (mg/l) HCO 3 (mg/l) ClO 4 (µg/l) ph Synthetic water (lab test) ,000 10, Groundwater (field test) ~50 6.9

10 ClO 4 Sorption on Synthetic Resins ClO 4 Adsorbed (mg/g) Equilibrated 24 hours Bifunctional, RO02119 Purolite A520E ClO 4 in Solution (mg/l)

11 Perchlorate Selectivity Coefficients (K d ) on Synthetic Resins (C 0 = 10 mg/l ClO 4 ) RESIN 1h Kd (ml/g) 24h Kd (ml/g) 168h Kd (ml/g) Bifunctional anion exchange resins RO ,000 >3,330,000 >3,330,000 Purolite D3696 * 164,800 1,877,000 1,842,000 Commercial anion exchange resins Purolite A520E 97, , ,000 Sybron SR6 65, , ,000 * Purolite D3696 is a scaleup version of ORNL bifunctional resin made by Purolite International, Inc.

12 ClO 4 Breakthrough in Laboratory Column FlowThrough Experiment 0.09 Synthetic Test Solution (C 0 = ~1100 m g/l ClO 4 ) 0.06 C/C Sybron SR6 Purolite A520E Bifunctional resin, RO Bed Volume

13 Field Evaluation Groundwater Treatment Flow: ~200 ml/min (~2 BV/min) Influent ClO 4 = ~50 ppb

14 Treatment of ClO 4 Contaminated Groundwater in Northern California Initial ClO 4 ~50 ppb Purolite A520E Treated ~110,000 bed volumes of groundwater in ~40 days. C/C Bifunctional D3696 resin Less than 10% breakthrough of ClO 4 occurred. Flow rate ~ 2 bed volumes min 1. No pretreatment is necessary. Bed Volume

15 Resin Regeneration Conventional Regeneration Washing with a brine (~12% NaCl) for nonselective resins. ClO 4 loading often less than 0.5% of the exchange capacity on nonselective resins because of the competition and partitioning by other anions (Loading K d *C). Regeneration questionable because >99.5% of the exchange sites loaded with other anions (HCO 3, NO 3, Cl, SO 4= ). A mass balance must be obtained to evaluate the regeneration efficiency. Regeneration by brine is ineffective for selective resins such as Purolite A520E and bifunctional resins.

16 Regeneration by Tetrachloroferrate (FeCl 4 ) (Patent pending) FeCl 4 formed in ferric chloride solutions (FeCl 3 + Cl FeCl 4 ). FeCl 4 is also a large, poorly hydrated anion and strongly sorbed by selective anion exchange resins. FeCl 4 effectively displaces ClO 4 sorbed on resins. However, FeCl 4 readily dissociates in dilute HCl solutions: FeCl 4 FeCl 3 + Cl FeCl 4 FeCl Cl Positivelycharged Fe species are readily eluted off the resin bed by electrostatic repulsion, whereas Cl remaining on the resin bed by charge balance, thereby regenerating the resin to its original state.

17 Regeneration Efficiency and MassBalance Analysis of Displaced ClO 4 by FeCl 4 (mm) Effluent ClO Effluent ClO Bed Volume 100 ClO 4 desorbed 0 ClO 4 Desorbed (%)

18 Resin Performance After Repeated Regeneration C/C C 0 = 10 mg/l ClO 4 Initial Breakthrough Regeneration1 Regeneration2 Regeneration3 Regeneration4 Regeneration5 No decrease in resin performance after repeated ClO 4 loading and regeneration cycles (7 cycles). Performed with D 0.2 Regeneration6 Regeneration resin column (10x22 mm), Flow = 17 BV/min, and Initial ClO 4 = mg/l. Bed Volume

19 Comparison of IonExchange Treatment Technologies Conventional Ion Exchange (Nonselective resin, brine regeneration) Effective and able to remove ClO 4 below detection limit (<4 ppb). Inefficient (ClO 4 loading <0.5%) because of the Competition by other anions (e.g., NO 3, Cl, SO 4 =, HCO 3 ). Less effective at low ClO 4 concentration levels in groundwater. Require frequent regeneration. Generate large quantities of secondary waste brine (with ClO 4 ). Remineralization may be needed. High operational and waste disposal costs. Conclusion: Unattractive (Urbansky 1998, 1999; Damian and Pontius 1999; Batista et al. 2000) New Technology (Highly Selective, Regenerable Resins) Effective and able to remove ClO 4 below detection limit (<4 ppb). Efficient because of its high selectivity (ClO 4 loading capacity ~ K d *C ). No changes in groundwater chemistry, and no remineralization is needed. Last longer and require less regeneration cycles. Particularly effective in removing low levels of ClO 4 (at ppb levels). Effective regeneration by FeCl 4 with a good mass balance and recovery of ClO 4. Regenerant solution can be reused and FeCl 3 can be precipitated out for waste minimization. ClO 4 can be coprecipitated out from the highly concentrated regenerant solution with KOH. Reduced overall operational and waste disposal cost.

20 Summary Bifunctional resins were demonstrated to have superior selectivity for perchlorate sorption in both laboratory and field tests. A singlestep treatment process (because of its high selectivity); No pretreatment (e.g., carbon or nanofilter) is necessary. Bifunctional resin is particularly effective in removing ClO 4 at low or trace concentrations. New regeneration technology has been developed for selective anion exchange resins (for reduced operational and waste disposal costs). Can be operated at a high flow rate, typically at 2 4 BV/min (e.g., a 6x4 ft treatment column may be operated at gpm). A combination of highly selective anion exchange resins and the new regeneration technology may offer a promising treatment technology for remediating ClO 4 contaminated water.