Industrial Coin Cleaner

If you check with the tab at the top for SEARCH, you may find numerous stories about cleaning coins, coin cleaning, Acetone, etc. For you problem I'd sart with dipping in Acetone. If that fails, try Laquer Thinner, Mineral Spirts, Tomato Juice, Lemon or Lime Juices too. Like I said if you check here you would also find how many swear by Olive Oils, battery acids, baking soday and wate and on and on and on.
Way back when I was a kid my Dad had a gas station where they also did tires for trucks. One trick they used to use to free those tires from the rims after being on the road a long time was Coke. Yes a bottle of Coke. Try it. From what you disctibe for those coins you have little to loose.

Welcome to CC!

Just toss them into your mixer with water and laundry detergent. That should work good enough.

because these coins were cemented togetheer in the presence of water, water based solvents aren't going to do a good job of uncementing them.

are you sure it's just gum and grease? If so I suspect tumbling them in a diesel bath will take care of that.

I wouldn't be suprised if you also had some of the coins cemented together with calcium carbonate. This is one of the main components of hard water.

If after the diesel they're still stuck together you might try an acid bath. Swimming pool supply stores sell muratic acid in 5 gallon buckets. Muratic works wonders on calcium. However after an acid bath be sure to rinse them in water as acid will dissolve most coinage.