I think you need to be a little more specific. Do you want a full hood and exhaust outside, or trap the fumes in filter/chemical media? Or, do you just want to get it out of the work zone and diluted?
The most volatile toxic metal that could be encountered in soldering (or brazing) would be Cd, I think. Hg would not be in solders, but any spillage would be a problem. If such spillage is likely, keep a jar of flowers (dust) of sulfur on hand to help trap the vapors - just sprinkle it on generously. Cd should be fairly stable but easy to vaporize at elevated temperatures (like soldering), so you don't want that hanging around. Once things cool down, you'll have particles of the metals like Cd and the ubiquitous Pb (and its oxide) in the form of toxic dust - that's a good thing to trap out in filters. Any Hg around will eventually evaporate away and bind with O2 or S. The sulfide is fairly benign, unless you cook it out.
Ed
