UPDATE 2-Rio Tinto mulls sale of Energy America unit

(Adds more analyst comment, company value)

JOHANNESBURG/NEW YORK, Nov 8 (Reuters) - Mining group Rio Tinto (RIO.L: Quote, Profile, Research, Stock Buzz) (RIO.AX: Quote, Profile, Research, Stock Buzz) said on Thursday it was considering selling its Energy America unit, the second-largest U.S. coal producer by tonnage.

The move had been widely expected because Rio previously hinted that it might sell the coal business after its purchase of aluminum group Alcan. That deal closed on Wednesday.

"As part of the groupwide strategic review announced at the time of the acquisition of Alcan, Rio Tinto has decided to explore options for the sale of some or all of Rio Tinto Energy America," the company said in a statement.

Energy America, formerly called Kennecott Energy Co, produced about 125 million tons of coal last year, or about 6 percent of the fuel used for U.S. power generation, second only to Peabody Energy Corp (BTU.N: Quote, Profile, Research, Stock Buzz).

The business was estimated to be worth about $4 billion, according to Jeremy Sussman, analyst with Natixis Bleichroeder.

While a number of international coal players have the cash to afford Energy America, better opportunities are available outside the U.S., leaving U.S. companies as the most likely acquirers, he said.

But even among its U.S. peers, several would face tough antitrust scrutiny because they already have significant operations in the Powder River Basin, a region in Montana and Wyoming where Energy America's five mines are located.

Those companies include Peabody, Arch Coal Inc (ACI.N: Quote, Profile, Research, Stock Buzz) and Foundation Coal Holdings Inc (FCL.N: Quote, Profile, Research, Stock Buzz), said analyst Pearce Hammond of energy investment firm Simmons & Co in Houston.