After the Civil War Hanna invested in a Great Lakes steamer and built a petroleum refinery (he was a high-school classmate of John D. Rockefeller, who remained a friend).

By 1867, the ship had sunk, and the refinery had burned down without insurance, but his father-in-law recognized Hanna's potential and took him into Rhodes & Company as a partner before he retired.

Hanna also acquired interests in mineral companies in Latin America as well as beginning the mining of nickel in Oregon and silicon in Washington.

By the early 1970s, Hanna Mining was the world's second-largest producer of iron ore with United States Steel being the largest.

[3] During the 1980s under CEO Martin D. Walker, M. A. Hanna began acquiring plastic and polymer companies while divesting itself of mining and energy property.