The lake of fire and brimstone is so frequently talked about in the Book of Mormon that it would be a mistake if the reader thought this phrase is used literally. The interpretation is figurative as the teachings of Joseph Smith clarify.
Joseph Smith
"A man is his own tormenter and his own condemner. Hence the saying, They shall go into the lake that burns with fire and brimstone. The torment of disappointment in the mind of man is as exquisite as a lake burning with fire and brimstone. I say, so is the torment of man." (Teachings of the Prophet Joseph Smith, p.357)