Sumitomo and SC hold the minority 20%, while Rio Tinto owns 80% but in late July Rio announced plans to sell its stake to China Molybdenum for $US820 million ($A910.9 million).
The waiving of the rights over the stake paves the way for China Molybdenum to complete the buy.
China Molybdenum said it looked forward to closing the deal and working with Sumitomo for the long-term benefit of both parties.
Last month, China Molybdenum received approval from the National Development and Reform Commission of China for the deal.
Luoyang Mining Group Co and Cathay Fortune Corporation, which hold a controlling 69% of China Molybdenum, also approved the purchase.
The buy is expected to be completed by the end of the year.