*Rio Tinto to get about $520 mln from Cloud Peak IPO

*Sales at coal producer Cloud Peak rise, but demand wobbly

*Cloud Peak valuation is high compared to peers

By Phil Wahba and Clare Baldwin

NEW YORK, Nov 13 (Reuters) - Anglo-Australian miner Rio Tinto Plc (RIO.L: Quote, Profile, Research)(RIO.AX: Quote, Profile, Research) is hoping to raise $520 million by spinning off its U.S. coal business, but analysts cautioned that demand for the offering could be tepid.

The IPO is priced at a premium compared with competitors.

And Cloud Peak plans to issue $600 million in notes at the same time as the IPO, which will bring its total debt load to $760 million.

On top of that, global demand for coal has plummeted and the outlook is cloudy.

Rio Tinto is weighed with debt stemming from its 2007 acquisition of Canadian aluminum maker Alcan, and plans to take most of the initial public offering's proceeds.