The firm, which was acquired by Warburg Pincus in 2008 for 565 million pounds ($695.57 million) could fetch around 640 million pounds, including debt, at a multiple of around eight times core earnings, two of the sources said.

Warburg Pincus and Goldman Sachs declined to comment.

Safetykleen Europe had earnings before interest, taxes, depreciation and amortisation (EBITDA) of 60 million pounds in 2015, when its debt was 635 million pounds.

One of the sources said core earnings were expected to reach 70 million pounds in 2016 and 80 million pounds in 2017, helped by a rebound of the industrials unit's business.

Warburg Pincus owned 295 million pounds of the debt at end-2015 though preference shares and subordinated debt which has to be paid back in case of a sale. It obtained returns of 60 million pounds on those instruments in 2015.

The sale was likely to attract bids from Europe, the United States and China, the source also said, adding that Britain's vote to leave the European Union had potentially played a role as Warburg had invested in Safetykleen from a dollar fund and the value of the pound was a concern.

Safetykleen Europe has 1,500 staff working in 70 locations in Europe, Turkey, Brasil, China and Hong Kong.

(Editing by Julien Toyer and Louise Heavens)

By Andrés González and Arno Schuetze