Removal of copper from an industrial wastewater stream

Abstract

Two alternative ways to process a wastewater that contains Cu(I) and Cu(ll) were investigated experimentally on a laboratory scale: ion exchange and hydrometallurgical extraction. The Cu(I) and a small fraction of the Cu(II) are present in the wastewater in the form of negatively charged halogenide complexes due to the high chloride and bromide content (4kmol/m³) of the water.

Anion exchange resins were chosen to remove the copper from the solution. none of the resins that were tested gave fully satisfactory results. The ion exchange alternative was rejected.

Hydrometallurgical extractions of solutions of Cu(I) or Cu(ll) containing NaCl and NaBr were carried out using a mixture of oleic acid and cyclohexa-noneoxime dissolved in toluene as extractiot. The experiments showed that the extraction efficiency increases with increasing pH of the water solution and with decreasing chloride and bromide concentration. The extraction efficiency for Cu(II) is very high at pH = 5. The copper can be stripped from the organic phase by means of 1N sulfuric acid even if CuSO₄.5H₂O crystals develop in the latter phase.

The extraction efficiency of Cu(I) from the salt solution proved to be poor. A search for other extractants for the Cu(I) ions was unsuccessful. Therefore the Cu(I) in the wastewater had to be oxidized to Cu(II) which can then be extracted.

The above leads to a copper removing process which consists of the following steps:

• 1.

  1. Removal of the methanol that is also present in the wastewater in a continuous distillation column.

• 2.

  2. oxidation of Cu(I) to Cu(II) with air.

• 3.

  3. Hydrometallurgical extraction of Cu(ll) by oleic acid in toluene in a three stage countercurrent extractor. The remaining copper concentration in the waste stream is reduced to a few ppm. Crystals of CUSO₄.5H₂O are obtained in the subsequent stripping of the organic phase.

A cost estimate of the process is presented.