Financial investor Rhone Group is close to a deal to buy the Carbon Black unit of unlisted German chemical maker Evonik, a source close to the deal said on Thursday.

The sale is expected to fetch just over €900 million ($1.3 billion), and could be signed as soon as Friday, the person said. Evonik declined to comment.

Carbon Black was originally derived from soot, and more than 60% of world's production is used to make tyres more durable. It is also used for laser printers and photocopier toners.

Market researcher Freedonia expects the global Carbon Black market to rise 4.3% per year until 2013, driven mainly by tyre demand in Asia.

Evonik, which said last year that it has hired an investment bank to manage the sale of the unit, has said it plans to use the proceeds to expand its core specialty chemicals business.

Evonik is majority owned by a government-controlled trust that bears the long-term liabilities of Germany's wound-down coal mining industry.

Private equity firm CVC Capital Partners bought a 25% stake in Evonik in 2008.