Non-selective ion-exchange (IX) resins used to treat perchlorate (ClO4-) (often in combination with nitrate) must be regenerated using a brine solution, and this produces a concentrated waste stream.  Treatment or disposal of ClO4- containing brine is a challenge for water treatment plants. Most current chemical and biological treatment systems for ClO4- reduction are negatively influenced by concentrated salt solutions. In this study, ClO4- reduction activity with a Re-Pd/C bimetallic catalyst was evaluated in synthetic and waste IX brine solutions (6% NaCl), using H2 as the reductant at 25oC and 1 atm pressure. Catalytic activity in the synthetic brine was three times greater than the corresponding activity in DI water. However, catalytic activity in the waste IX brine was 65 times lower than in the synthetic brine. Both synthetic and real brines contained ClO4- at 100 mg/L. However, the real brine also contained nitrate (NO3-), at 2360 mg/L, which is also reduced by the catalyst. To explore the effects of nitrate on ClO4- reduction, nitrate was added to the synthetic brine, and the ClO4- reduction activity decreased by 20 times.  The extent of this decrease is much greater than expected based on simple sequential reduction. Hence, NO3- appears to deactivate the catalyst surface for ClO4- reduction. Pretreatment of NO3- in the real brine using a In-Pd/Al2O3 catalyst, and subsequent treatment of ClO4- using the Re-Pd/C catalyst resulted in ClO4- reduction rate constants that matched the NaCl-only synthetic brine. A sequential treatment of NO3- and ClO4- is proposed as a promising strategy for waste recycling, and could reduce costs and environmental impacts associated with brine production and discharges.

Treatment of perchlorate in waste ion-exchange regenerant brine with a Re-Pd catalyst

244th National Meeting (2012)

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