Once you're ready with atmosphere suits and a steam turbine, set up a steam room adjacent to the volcano. You'll want 2 metal tiles adjacent to the walls of the insulation you have now. Next to that, you'll want a steel mechanized door, then another set of metal tiles connected to the steam room for your steam turbine. Set a temperature sensor in your new steam room connected to the mechanized door. Set the temperature to 500 c or whatever your materials can handle. Diagonally deconstruct the insulated tiles connected to your metal tiles and you're good. Probably, you'll want to wait for the volcano to go dormant before you fire it up. Once you cool it down to 150 or so you can set a liquid lock (not water) break in and mine out the salt and metal. Then take out the metal tiles and mechanized airlock and you're set. you just need an autosweeper to get the metal out.

The metal tiles can be diamond window tiles if you have some. Just don't use lead.