I think this is the early gorget from the start of Belgium as an independent kingdom in 1831. Gorgets were worn round the neck as the last vestige of armour and an indication of officer rank. They were worn in the Belgian army throughout most of the 19th century, normally only by infantry. Cavalry did not wear these, for instance.
The later Belgian gorgets are rather different, as far as the central device is concerned, having the cypher of the monarch on a shield, clutched by a rampant lion. There's an outside chance that it could be that of the Belgian Legion, which lasted from 1789-1814 in the French service.
This has most of its original silvered finish on a brass base, together with the bulk of its red Morocco leather lining on the reverse. The lions at the corners are loose - I have deliberately left them this way so that they can be easily removed for cleaning the rest of the gorget, which I have not cleaned as the silver plate is thin. The badge elements of the gorget are struck in gilding metal with a thin gilt wash, which is now somewhat polished on the highlights.