Effluent Treatment - Copper
June 19, 2002

Introduction

Copper, as with most heavy metals can be removed from acidic waste streams by precipitation as relatively insoluble metal hydroxides at alkaline pH.  Lime is generally used to adjust the pH due to its low cost and reaction to form the metal hydroxide.

Copper hydroxide solubility is a minimum around pH 9.0 to 10.3.  A maximum solubility of 0.01 mg/l has been reported at a pH of 10.  This can be considered as a theoretical minimum effluent level which can be obtained by precipitation.   However, in practice this level is difficult to obtain due to slow reaction rates, pH fluctucations, influence of other metal ions and poor settling of colloidal precipitates.  Above pH 10, the solubility of copper hydroxide begins to increase again.

Effluent levels of copper below 0.5 mg/l are consistently and easily achieved by lime precipitation with proper pH control and good filtration or settling of the precipitate.

The reaction between copper and lime is as follows:

Cu SO₄ + Ca(OH)₂ => Cu(OH) + CaSO₄

Recovery of copper from the resulting sludge is more attractive than some other metals due to its higher value.