PNNL has developed a method for the production of high-purity 90Y from 90Sr stocks. The method was designed such that it could be fully automated. The objective of the development work was to devise a process that could purify multi-Ci levels of 90Y. As this level of radiation would require the use of hot cells for production, automation is a highly desirable feature. Also, since the radiotoxicity of 90Sr is so great (bone seeker, 30 year half-life), the degree of chemical purity of the 90Y is immense ( >/= 1x10^6 degrees of purity). Therefore, PNNL designed a tandem column purification process, which allows the 90Y to be purified across two columns placed in tandem. PNNL surveyed a wide range of inorganic sorbents for use in the 90Y purification process. In previous research (Lynntech project and associated PNNL patent (attached)), we found that an antimony silicate resin possessed good properties for holding up 90Sr while allowing 90Y to pass through (though inefficiently) in a HCl matrix. However, for multi-Ci levels of 90Y production, a generator system with 90Sr affixed to the inorganic sorbent would degrade quickly due to radiolysis. Hence, PNNL developed a new type of generator, wherein the 90Sr is contained in a "liquid cow" versus a "column-bound cow". In this manner, the radioactivity would be stored outside of the purification system, thus minimizing radiolytic degradation of the system. Tandem column generator -- PRIMARY COLUMN LOAD: A recent Chinese publication (attached) described a method wherein antimony silicate nanocrystals could be formed. The researchers then characterized the 90Sr sorption properties onto these nanocrystals in HCl media. Since nanocrystals cannot be used in a generator column, PNNL extrapolated that basic premise of the reaction and used it to co-form antimony silicate nanocrystals into / onto a silica gel support (which could be used in a column format). Through parametric optimization of the synthesis process, we determined that an antimony silicate resin could be formed without incorporation of these nanocrystals on the Si gel surface. Rather, we were able to form an antimony silicate complex directly on the Si gel surface structures. This approach yielded the best separation factors for 90Y from 90Sr. Furthermore, PNNL needed to use the antimony silicate resin in "reverse" of the configuration that was used in the earlier patent (and also described in the recent Chinese publication). Instead of 90Sr being bound to the resin and 90Y passing through, we needed a process wherein the 90Sr would pass through the resin and temporarily retain the 90Y (this is necessary to avoid extreme radiolysis of multi-Ci 90Sr sources). We found that in concentrated formic acid, 90Sr has no affinity for the resin and 90Y has a good affinity for it. Therefore, a 90Sr stock solution can be passed through the resin column to extract all the 90Y, and the 90Sr stock solution can be cycled back to its storage container. Tandem column generator -- PRIMARY COLUMN TRANSFER TO SECONDARY COLUMN: PNNL determined that a dilute solution of HCl was effective in removing the sorbed 90Y from the antimony silicate column. Additionally, we determined that a tiny column of HDEHP-impregnated chromatography resin (sold as Ln Resin by Eichrom Technologies) would adsorb 90Y in dilute HCl. Therefore, the dilute HCl solution could be used to "transfer" 90Y from the primary column to the secondary column. Importantly, any trace / residual 90Sr that would pass to the secondary column would not be retained on the secondary column. Hence, the method has two degrees of purification. Tandem column generator -- SECONDARY COLUMN ELUTION: PNNL determined that stronger HCl (1 to >6 M) was highly effective at eluting 90Y from the secondary column. Virtually all the 90Y could be eluted from the secondary column in <1 mL of 6M HCl. This small volume, in turn, can be quickly evaporated so the 90Y can be redissolved in a solution amenable to radiolabeling or microsphere incorporation. <p>Attached is a powerpoint presentation that outlines the initial development work and performance of the primary, secondary columns and the combined tandem purification process.</p>