D. Lambert, J. Pareizs, D. Click
2010 unpublished
A 3-L PUREX sludge sample from Tank 7 was characterized and then processed through a series of inhibited water washes to remove oxalate, sodium, and other soluble ions. Current plans use Tank 7 as one of the feed sources for Sludge Batch 7 (SB7). Tank 7 is high in oxalate due to the oxalic acid cleaning of the sludge heels from Tanks 5 and 6 and subsequent transfer to Tank 7. Ten decant and nine wash cycles were performed over a 47 day period at ambient temperature. Initially, seven decants and
more » ... , seven decants and seven washes were completed based on preliminary estimates of the number of wash cycles required to remove the oxalate in the sludge. After reviewing the composition data, SRNL recommended the completion of 2 or 3 more decant/wash cycles to ensure all of the sodium oxalate had redissolved. In the first 7 washes, the slurry oxalate concentration was 12,300 mg/kg (69.6% oxalate removal compared to 96.1% removal of the other soluble ions). After all ten decants were complete, the slurry oxalate concentration was 3,080 mg/kg (89.2% oxalate removal compared to 99.0% of the other soluble ions). The rate of dissolution of oxalate increased significantly with subsequent washes until all of the sodium oxalate had been redissolved after seven decant/wash cycles. The measured oxalate concentrations agreed very well with LWO predictions for washing of the Tank 7 sample. Highlights of the analysis and washing of the Tank 7 sample include: • Sodium oxalate was detected in the as-received filtered solids. 95% of the oxalate was insoluble (undissolved) in the as-received slurry. • No sodium oxalate was detected in the post-wash filtered solids. • Sodium oxalate is the last soluble species that redissolves during washing with inhibited water. In order to significantly reduce the sodium oxalate concentration, the sludge must be highly washed, leaving the other soluble anions and cations (including sodium) very low in concentration. • The post-wash slurry had 1% of the soluble anions and cations remaining, with the exception of sodium and oxalate, for which the percentages were 2.8% and 10.8% respectively. The post-wash sodium concentration was 9.25 wt% slurry total solids basis and 0.15 M supernate. • The settling rate of slurry was very fast allowing the completion of one decant/wash cycle each day. • The measured yield stress of as-received (6.42 wt% undissolved solids) and post-wash (7.77 wt% undissolved solids) slurry was <1 Pa. For rapidly settling slurries, it can be
doi:10.2172/979691 fatcat:5trn37s52fa43dpt2bcdpqjiju