Effect of precipitation and complexation on nanofiltration of strontium-containing nuclear wastewater

The performance of nanofiltration (NF) with the addition of poly (acrylic acid) (PAA) for treatment of strontiumbearing nuclear wastewater was investigated using different NF membranes at various pH levels and PAA/Sr ratios. Greater Sr removal at elevated pH was attributed to the formation of SrCO3(s) due to the dissolution of atmospheric CO2. A substantial improvement in Sr removal was achieved with the addition of PAA that can make complexes with strontium ions and then be rejected by NF membranes. However, a rapid decrease in feed solution pH aggravated the fouling of a NF membrane, possibly because of the formation and the sorption of associated forms of PAA at the membrane surface.

The application of NF for selective removal of strontium from simulated nuclear liquid waste was investigated with and without PAA addition and the following conclusions could be drawn. 1 Higher Sr removal was achieved with tighter NF membranes having higher NaCl rejection efficiencies. 2. The formation of SrCO3 related to atmospheric CO2 gas was more responsible for greater Sr removal at higher pH, rather than that of Sr(OH)2. 3. When PAA with a molecular weight of 5,000 was added into the feed solution as a complexing agent, further strontium removal (>50% removal) was achieved at higher pH as the molar ratio of [COOH] to [Sr] increased from 0 to 27.