Rio Tinto's largest shareholder, Aluminum Corporation of China (Chinalco), has taken full part in a $US15.2 billion rights issue from the Anglo-Australian miner.

Chinalco on Thursday confirmed its participation in the issue, following speculation that it may not do so after Rio Tinto last month abandoned a $US19.5 billion ($A24.09 billion) deal with the Chinese company.

Instead, Rio announced a $US116 billion ($A143.31 billion) tie-up with rival BHP Billiton on the companies' Western Australia iron-ore operations.

But, in a statement on Thursday, Chinalco said it had chosen to fully participate in the rights issue from Rio Tinto plc, the UK-listed entity of the miner.

"Chinalco can confirm that it has taken up all its rights in Rio Tinto plc," the statement said.

"This was an economically rational decision as it prevented the dilution of our ownership in Rio.

"Chinalco believes in the long-term prospects of the industry and will continue to explore opportunities to advance its strategic objectives.

"Chinalco will, as the company's current largest single shareholder, continue to monitor developments at Rio," the company said.

The Chinese company owns a 12 per cent stake Rio Tinto Plc, representing a 9.3 per cent holding in the Rio Tinto group.

It has no shares in the Australian-listed Rio Tinto Ltd.

After taking up the rights issue, Chinalco is understood now to have a $US15 billion ($A18.53 billion) total investment in Rio.