Q:  I’m running a lithium extraction process where a mineral called spodumene is roasted in a mixture of sulphuric acid (95-97%) at at about 150°C to form lithium sulfate. I’ve to use Hastelloy C276 for some process equipment but I’m still experiencing corrosion. Please help.

A:  Hastelloy C276 bolts typically work well in sulfuric acid but not at this temperature and concentration. Normally the max operating temperature for Hastelloy C276 at with H2SO4 at 97% concentration would be around 70C. For these conditions of sulfuric acid, I would suggest to go with tantalum metal fasteners. Tantalum is the most corrosion resistant option available to industry. It is very capable of handling sulfuric acid at any concentration 150C.

Q: I was planning on using Hastelloy C276 in hot sulfuric acid. It would be approximately 50% concentration around 100F +/- 10 degrees. Will this be okay? I’m just concerned because I read that it cannot handle strong oxidizing environments and I’ll be using it in an application where its exposed to air? Does Hastelloy C276 need to be in a vacuum? What does an oxidizing environment mean?

A: All grades of Hastelloy can handle air environments. C276 is also fine in moderately oxidizing environments. What is meant by a strong oxidizer is when it is exposed to oxidizing chemicals like ferric chlorides or highly concentrated nitric acid. This is due to it’s lower chromium content than say Hastelloy C22 which can handle these types of strong oxidizers. Air is not considered a strong oxidizer so you  will be perfectly fine using C276 in sulfuric acid at these concentrations and temperatures. For additional corrosion information on using C276 in sulfuric acid reference the C276 / Sulfuric Acid Iso-Corrosion chart.