Mosaic Co. CEO Jim Prokopanko will return to work after a medical leave, the fertilizer company said Thursday, as it reported quarterly results that showed some new momentum from pressure that developed a year ago.

Prokopanko has been on medical leave since June 1 recovering from cancer surgery. He will resume work on Monday.

Mosaic said its profit fell 42 percent to $248.4 million, or 64 cents a share, in the second quarter. Sales fell 7 percent to $2.4 billion.The year-ago period was the last before the global fertilizer market was upended when the world's leading potash producer, Russia's OAO Uralkali, backed out of a marketing agreement with partner Belaruskali. That move sent fertilizer prices plummeting, which hurt Plymouth-based Mosaic and others.

Prices began to stabilize near the end of 2013 and Mosaic's results have improved since. It second quarter profit was 14 percent higher than in the first, and sales were 23 percent higher.

"Mosaic's business momentum accelerated from the first quarter to the second quarter," Larry Stranghoener, interim CEO, said in a statement. "Very strong global demand for phosphates pushed prices higher, while potash demand exceeded even our high expectations."

Before taking the interim CEO position, Stranghoener had been Mosaic's CFO and planned to retire at the end of 2014. With Prokopanko returning, Mosaic said Stranghoener will become executive vice president of strategy and business development until the end of the year.

Mosaic shares were down 2.3 percent in midday trading.

Mosaic's sales for the first six months ended June 30th were $4.4 billion, down 10.2 percent from a year ago. Net earnings were $466 million, or $1.18 per share, down from $809.6 million, or $1.90 per share, a year ago.