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The Hartford FerrocyanideTask Team is addressingissues involving ferrocyanideprecipitatesin single-shell waste storage tanks (SSTs), in particularthe storage of waste in a safe manner. This Task Team, composed of researchersfrom Westinghouse HartfordCompany (WHC), Pacific Northwest Laboratory(PNL), and outside consultants, was formed in response to the need for an updatedanalysis of safety questionsabout the Hanfordferrocyanide tanks. The FerrocyanideSafety Project at PNL is partof the Waste Tank Safety Programled by WHC. The overall purpose of the WHC program, sponsored by the U.S. Departmentof Energy's Tank Farm Project Office, is to 1) maintainthe ferrocyanidetanks with minimal risk of an accident, 2) select one or more strategies to assure safe storage, and 3) close out the unreviewed safety question (USO). This annualreportgives the results of the work conducted by PNL in FY 1993 on Task 3, FerrocyanideAging Studies, which deals with the aging behavior of simulated ferrocyanide wastes. Aging processes include the dissolution and hydrolysis of nickel ferrocyanides in high pH aqueous solutions. Investigatedwere the effects of pH variation; ionic strength and sodium ion concentration; the presenceof anions such as phosphate, carbonate, and nitrate; temperature;and gamma radiation on solubility of ferrocyanide materials includingIn-Farm-lA, Rev. 4 flowsheet-prepared Na2NiFe(CN)6. Vendor-preparedNa2NiFe(CN)6dissolves in aqueousbase to give primarily insoluble Ni(OH)2 and soluble Na4Fe(CN)6. The rate of dissolution of Na2NiFe(CN)6 in aqueous base increases with increasingpH. At pH 14, 95% dissolution is observed after 0.5 h. Addition of sodium ion in the form of Na2SO4 or NaNO3 suppressesdissolution at pH 13. However, 1 M Na+ in the form of Na2CO 3, Na3PO, t, or SST simulant salts (mixed sodium salts of phosphate,carbonate, nitrate, nitrite, sulfate, and hydroxide) results in an enhancementof the rateof solubflization. At pH 14 these effects are not seen, dissolution being rapideven in the presence of 4 M sodium ion. The rate of dissolution is influenced most by base concentration. Cesium nickel ferrocyanideis not easily dissolved. A materialcontaining a Cs2NiFe(CN)6 phase (2.3 moles Cs/moles ferrocyanide) was found to be insoluble in up to 4 M NaOH after stirringfor 144 h. ln-Farm-lA, Rev. 4 0F-1A), containing4.51 x 10-2 moles Cs/mole ferrocyanide, dissolved more slowly than the vendor material under identical conditions at both pH 13 and pH 14. The inhibition of IF-1A dissolution may be due to concentrationof an insoluble (or less soluble) Cs2NiFe(CN)6 phase at the particle surface as Na2NiFe(CN)6dissolves. Studies of the hydrolysis of IF-1A in 4 M NaOH at 90°C were initiated. Experimentswere conducted in the gamma pit with identical controls outside the gamma field. Gamma promotes ferrocyanidehydrolysis. Over 42 % of the cyanide ions were hydrolyzed in the radiationfield III comparedwith 4.8% in the control. Similar experimentsat pH 10 and 60°C indicatedIF-IA was insoluble outside of the gamma pit and only very...

This annual report gives the results of the work conducted by the Pacific Northwest Laboratory in FY 1994 on Task 3 of the Ferrocyanide Safety Project, Ferrocyanide Aging Studies. Waste aging refers to the dissolution and hydrolysis of simulated Hanford ferrocyanide waste in alkaline aqueous solutions by radiolytic and chemical means. The ferrocyanide simulant primarily used in these studies Savannah River Operations Office PO. Box A

"_i_eHanford Ferrocyanide Task Team is addressing issues involving ferrocyanide precipitates in single-shell waste storage tanks (SSTs), in particular the storage of waste in a safe manner. This Task Team, composed of researchers from Westinghouse Hanford Company (WHC), Pacific Northwest Laboratory (PNL), and outside consultants, was formed in response to the need for an updated analysis of safety questions about the Hanford ferrocyanide tanks. " The Ferrocyanide Safety Project at PNL is part of the Waste 'Tank Safety Program led by WHC. The overall purpose of the WHC program, sponsored by the U.S. Department of Energy's Tank. Farm Project Office, is to 1) maintain the ferroeyanide tanks with minimal risk of an accident, 2) select one or more strategies to assure safe storage, 3) close out the unreviewed safety question (USQ), and 4) identify ultimate disposal options to be used when waste is removed from the tanks. This annual report gives the resu!t_ of the work conducted by PNL in FY 1992 on Subtask 3.4, Aging Studies, which is part of Task 3, Chemical Nature of Ferrocyanide in Wastes. Subtask 3.4 deals with the aging behavior and solubilization of ferrocyanide tank waste sludges in a basic aqueous environment. Investigated were the effects of pH variation, ionic strength, salts present in SSTs, and gamma radiation on solubilization of vendor-prepared Na_NiFe(CN)6. Vendor-prepared Na_NiFe(CN)6 dissolves in aqueous base to give primarily insoluble Ni(OH)2 and soluble Na4Fe(CN)6. Precipitation of Ni(OH)2 apparently drives the ferrocyanide dissolution. From the gamma pit experiments, the in_,_uble solids contained more than one iron cyanide species, yet to be identified. The rate of dissolution of Na2NiFe(CN)6 in aqueous base increases with increasing pH. At pH 14, 95% dissolution is observed after 0.5 h. Addition of 1 M Na + ions in the form of Na2SO4 suppresses dissolution at pH 13, presumably because of a common ion effect. However, 1 M Na + in the form of SST simulant salts (sodium salts of phosphate, carbonate, nitrate, nitrite, sulfate, and hydroxide) resulted in an enhancement of the rate of solubilization most likely arising from buffering of the solution by phosphate. Even when the solution is not stirred, dissolution is relatively rapid. Approximately 40% of the Na_NiFe(CN)6 dissolves in 24 h in an unstirred solution containing SST salts. Gamma radiation does not appear to greatly affect the dissolution reaction. Similar rates were observed in unstirred irradiated and control solutions. A more complex mixture of iron cyanides in the insoluble fraction of the gamma radiation experiments is obtained, suggesting the possibility that an iron cyanide species re-precipitates from solution. Further work is needed to determine the identity of this species. Solubilization work will continue next fiscal year. In addition, cyanide and ferrocyanide hydrolysis studies will be conducted.