During HB-Line Pu-239 operations, plutonium (Pu) is precipitated as Pu(IV) oxalate (Pu(C2O4)2) using oxalic acid (H2C2O4). Following the removal of precipitate by filtration, the H2C2O4 must be removed from solution before the filtrate can be discharged to H-Canyon under one criticality-control strategy. HB-Line uses sodium permanganate (NaMnO4) solution to oxidize H2C2O4 to carbon dioxide (CO2) and water. Excess NaMnO4, which reacts to form manganese dioxide (MnO2) solids, is converted to soluble manganese via a reaction with sodium nitrite (NaNO2). HB-Line Engineering requested the Savannah River National Laboratory (SRNL) to verify the quantities and addition rates of NaMnO4 and NaNO2 required to react excess oxalic acid and MnO2 solids without over-pressurization of the reaction vessel. According to the literature, the oxidation of H2C2O4 by permanganate involves three concurrent chemical reactions. The net effect of the three reactions is that there is an observed incubation period at the outset of the process chemistry. However, as the reaction progresses, the reaction rate accelerates until the end point is reached. The end point is visibly identified by the formation of brown MnO2 solids. Four titration experiments at 1.0-6.0 M HNO3 confirmed that the H2C2O4 oxidation reaction proceeds by both the kinetics and stoichiometry reported in the literature. The data show that as NaMnO4 is added the Na and Mn concentrations increased while the H2C2O4 concentration decreased. However, once the H2C2O4 was below detectable limits, the addition of NaMnO4 caused the soluble Mn concentration to decrease (from the formation of MnO2 solids) while the Na concentration continued to increase.
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