Rio Tinto's (NYSE:RIO) Canadian iron ore project is still looking for a new owner and today three potential buyers were scratched off that list.

Private equity firms Apollo and Blackstone and miner Glencore are out of the bidding process after putting in offers "well below the mining group's a targets," Reuters reports.

The firm has been very "ambitious on price" – estimating the value of the sale about about $3.5 to $4 billion – according to an industry adviser interviewed by Reuters.

By selling its 59% stake in the Iron Ore Company of Canada (IOC), Rio will be able to focus on its Australian iron ore projects. Lately the miner has been pumping cash into the Australian mines as it works on increasing production by 21% this year. Iron-ore accounts for four-fifths of Rio's earnings.

In June, state-owned metals giant China Minmetals Corp announced that it was considering buying the shares; Reuters reports that one of the remaining bidders, in addition to Canada's Teck, "could be a consortium of Chinese buyers." Earlier this year, the world's third largest integrated miner began a "blowout sale" of its assets as it attempts to tackle its $19 billion debt.

Most recently, Rio announced the sale of its Australian NorthParkes copper mine to China Molybdenum for $820 million. In 2012, a Chinese firm also bought the miner's shares in the South African Palabora Mining company.

Rio may also be close to offloading one of its three diamond mines: Rumours swirled in July that Toronto's Harry Winston Diamond (NYSE:HWD) was in "advanced talks" to buy Rio's 60% stake in the Canadian Diavik Mine.