There are two things that are important for a silver kill coil - surface area and purity of silver. The coils normally used for water cooling are flat strips of silver which provides a relatively large surface area, then bent into a coil shape to reduce the size to a convenient level, without reducing the surface area. Typical kill coils are 99% or more silver.
The wire you have sounds like it is silver plated on a copper core. The plating is probably sterling silver, so around 90% silver and 10% other metals to improve the strength of the silver.
However, assuming the silver plating is reasonably thick, theres no reason why it shouldn't work as a kill coil. The wire you have, being circular, won't have a great surface area meaning you would need to use a longer length than a standard coil to get the same effect.
The one problem you might have is corrosion, depending on the other metal alloyed with the silver. This might cause it to tarnish over time, thereby forming an oxide layer which would block the silver and preventing the biocide properties.
