Patrick, silver is used as a reactor catalyst in the EO process [4% to 17% depending on the research at the time]. As time goes by, its activity decays and it has to be reactivated externally, say every two years. Once this has been done, it can be reused with only a small loss. I managed the design of the Dow EOEG process at Dow's Fort Saskatchewan plant in the early 80s. I expect the silver being used therein today is still the same silver George Scott, Project Mgr, traded with the Hunts in the mid 60s in Texas ... and made an ROI even before our plant was designed.