The Canadian National Railway (TSX:CNR) train derailed on Friday afternoon 72 kilometres north of Lac La Biche.
Alberta Environment says a CN dangerous goods team contained the spill from three of the cars and continue to clean it up.
No one was hurt.
The government says molten sulfur doesn't pose a risk to human health or the environment unless it is heated to an extreme temperature.
CN says the rail line has since reopened.