Rusal will sell 1.61 billion shares at up to HK$12.50 (£1) a share to cut $14.9bn (£9.2bn) of debt in a float set to value Rusal at up to $24.3bn (£15bn).
Family-controlled Rothschild is said to be poised to earn tens of millions of pounds as adviser on the deal, believed to be the first major flotation this year and the first by a Russian firm in Hong Kong.
France's BNP Paribas and Switzerland's Credit Suisse will sponsor and co-ordinate the deal and will also act as book-runners with Bank of America Merrill Lynch, BOC International, Japanese bank Nomura, Renaissance Capital, Sberbank and VTB Capital.
The advisers are tipped to share fees of between $60m and $80m, based on typical commissions.
Separately, Nat Rothschild, a close friend of Deripaska and descendant of the bank's founder Nathan Mayer Rothschild, is said to be planning to inject $100m (£61.8m) into Rusal as one of four cornerstone investors in the flotation.
More than five global investment funds, including BlackRock and an unnamed Chinese fund are understood to have provisionally agreed to take part in the IPO.
Rusal is the flagship of Deripaska's business empire and helped its majority owner to top Russia's rich list before the economic crisis slashed the aluminum from its Siberian smelters.
The planned valuation is set to make Rusal the world's most expensive aluminum firm, against rival Alcoa's $15.6bn market capitalisation.
Rusal is believed to be planning a road-show on January 11 with pricing expected on January 21.
After the placement, Deripaska's EN+ will have 47.6 per cent of Rusal shares; Onexim Group of tycoon Mikhail Prokhorov will hold 17.1 percent; SUAL Partners, controlled by tycoons Viktor Vekse£erg and Len Blavatnik, will have 15.9 per cent; and Swiss-based commodities trader Glencore will hold 8.65 per cent.