Longhi, 63, is the former president and chief executive officer of United States Steel Corp. He served in that role for five years before retiring in June. He also had served as president and chief executive of Gerdau Ameristeel Corp. 

"We are very pleased to welcome Mario to our board of directors," said Harsco president and chief executive Nick Grasberger.  

"I have every confidence that, with his international experience, broad-based background and alignment with our values, Mario will make an enormous contribution as Harsco continues to execute its growth strategy," he said.