Removal of dissolved copper and iron at the freshwater-saltwater interface of an acid mine stream

The King River, Tasmania, contains elevated levels of heavy metals, in particular copper, a result of the discharge of mine tailings and acid mine water from the Mt Lyell copper mine, which operated until late 1994. Samples were collected from the lower King River in July 1994, over a 48-h period, during which time the power station at the head of the river was off for the first 24 h. Saline water was observed in the delta region during this low flow period, and dissolved iron and copper were found to exhibit nonconservative behaviour with salinity. Removal of dissolved copper, as the river enters the harbour, was confirmed by laboratory experiments. The removal mechanism appears to be dependent on rapid pH increases and the formation of amorphous iron flocs which occur in the estuary, and results in a significant proportion of dissolved copper being removed from solution.