Oct 14 (Reuters) - Shares of Walter Energy rose for a second day on Friday on reports that the U.S. coal mining company is the target of a takeover.The Australian newspaper reported that BHP Billiton , the world’s largest mining company, is considering a $6 billion bid for the company. It cited no sources.On Thursday, the British newspaper, The Independent, said BHP and other mining giants were interested in acquiring Walter, which has large reserves of steel-making metallurgical coal.BHP declined comment and there was no immediate comment from Alabama-based Walter.The company’s shares rose 12 percent on Thursday and were up 6 percent on Friday morning. In afternoon trading, they were up 3.2 percent at $77.61.Analyst Lucas Pipes, of Brean Murray Carret & Co, said the price rise was clearly linked to the market talk that Walter was a target.He noted U.S. coal producer Peabody Energy and European steelmaker ArcelorMittal had just received final approval to go ahead with their joint acquisition of Australian miner Macarthur Coal .”That indicates there’s still a lot of demand for met coal reserves and Walter falls into that category,” Pipes said.Other U.S. coal stocks rose on Friday on macro-economic issues, analysts said. Alpha Natural Resources was up 3.7 percent to $21.43, Arch Coal was 2.9 percent higher at $17.26 and Peabody Energy rose 2.7 percent to $39.28. The Dow Jones coal index was 3.6 percent higher.