@ Steambike: Check out this post for an alternative to flap-discs on an Angle-Grinder. I use mine all the time & it's well worth the investment. viewtopic.php?f=81&t=12130&p=66267&hilit=flex+burnisher#p66267
Media Blasting will lead you to the poor-house. It takes too long (waaaaay too long) and it leaves a matte finish, which then has to be brightened up, so you've gained nothing. Disclaimer: The FLEX® Burnisher is not a good option for removing mill-scale. It's better than a flap-disc or an AVOS® Disc, but the abrasive will "load-up" with the mill-scale, which is just a bunch of oxides & scale that's actually harder than the carbon steel beneath it. Have you ever puked?
You know that burning sensation in your throat, mouth & nasal passages? It's muriatic acid. Technically, it's hydrochloric acid, which is the same thing as muriatic acid. Hydrochloric Acid is the main component of a human's stomach. It's not that dangerous if handled respectfully. There's a LOT Worse Acids out there, and muriatic acid is a necessary evil when dealing with heavy rust on older steel or Mill-Scale on new HR Steel. Once you've mixed it 1:1 with water, there is no appreciable odor, (I can't smell it at all at that ratio). The main thing to remember is this: Keep Your Tank Covered!!
The off-gassing of the hydrochloric acid will lay down a rust film on any ferrous metal within 50 feet! If you don't have a cover or don't want to make one, buy a few hundred ping-pong balls and cover the entire surface of liquid, one-layer thick. You can find 'em online really cheap. That will prevent >90% Off-Gassing. They make special HDPE Plating Tank Balls, but they're really expensive. Any hollow ball (with the exception of wiffle balls), that's made of any plastic will work. Styrofoam balls won't work...too porous. The smaller the balls (spheres) that you use, the better, as the smaller balls minimize negative space. Bubble wrap would work, but may tend to bunch up and shift in a breeze. You could thread some tie-wire through the edge to make the bubble-wrap sheet more rigid.
At some point, maybe now...you're realizing that the old saying, "Time is Money" is really true, and you will try muriatic acid and wonder why you waited so long. Don't buy the unscented variety of muriatic acid. Too expensive & too weak.
btw...my tank is a Rubbermaid® HDPE, heavy-wall, 250 Gallon Water Trough, Oval in shape. I only have about 4"-8" of liquid in it, I don't fill it to capacity. I started using that because I could fit my larger pieces in it. You could make a nice tank from 4"X4" lumber & a shower liner or 'in-ground' water-feature liner. Those liners are not too expensive & are totally impervious to the acid. Pond Liners are so heavy that you could actually cut a piece for the top/cover, too. When your acid bath gets crusty and gross (and it will), add some water & tip it over in the dirt. It won't harm groundwater, as hydrochloric is actually a gas, suspended in water. It will "disappear" in a few minutes. Don't empty your tank on concrete, though...unless you want the 'rusted concrete look'. (Some folks pay a LOT to get their concrete stained)!! And, no need to neutralize with CaCO3 (Calcium Carbonate), a.k.a Lime
or NaHCO3 (Sodium Bicarbonate a.k.a Baking Soda
You may see a few posts where guys are dipping their steel pieces in a baking soda/water bath after removing from the acid bath. Totally unnecessary. Absolute Waste of Time. ZERO (0%) Acid will remain on your steel after rinsing with water. Zero!
Just remove your steel pieces one at a time, rinse both sides w/ plain water & immediately force-dry with clean, dry, oil-free compressed air & set aside, ready to be shined up. If you're using a rusting patina, there's no need to shine the steel, just as long as it's good & clean, you're 'good to go'.. Thanks! Hope this info helps a little.