BHP, Vale CEOs visit Brazilian mine disaster site as toll mounts

By Stephen Eisenhammer and Marta Nogueira MARIANA, Brazil (Reuters) - The chief executives of BHP Billiton Ltd and Vale SA on Wednesday surveyed the devastation caused by burst dams at a Brazilian mine owned by the mining giants, as the human and environmental toll from the disaster mounted. Six people are confirmed killed and another 22 are missing as a result of the ruptures at an iron ore mine in the southeastern state of Minas Gerais nearly a week ago. Authorities in Minas Gerais and Espirit