Leaching of Copper Ore with Thiobacillus ferrooxidans

Introduction:

In any given year, approximately eleven percent of copper production of the United States is derived from low grade copper ore by microbiological leaching of these ores by Thiobacillus ferrooxidans.

The illustration is an aerial photograph of a large dump-leaching facility at the Bingham Canyon copper mine operation near Salt Lake City, Utah. Copper ore too low in copper to smelt directly is brought to the leaching pits by truck. The copper is extracted by spraying the middens with water. Bacteria, principally of the genus Thiobacillus which are ubiquitous in these ores grow on the surface of the copper bearing minerals. The copper is then typically extracted from the leachate by electrowinning or solvent extraction.

Photo courtesy of Kennecott Utah Copper, Salt Lake City, Utah.

The bacterium forms a biofilm layer associated with the copper mineral surface. Oxidation of Iron sulfide and other sulfide species with in the mineral results in the formation of ferrous sulfate, an oxidizing agent. This oxidant reacts with various species of copper sulfides (CuFeS2 [chalcopyrite], Cu2S [chalcocite], CuS, [covellite] and Cu5FeS4 [bornite], for example), oxidizing the mineral and releasing soluble CuSO4.

This page describes an exercise in which copper sulfate is leached from copper ore by the activities of Thiobacillus ferrooxidans.

Different descriptions of this exercise can be found in Hudson and Sherwood, 1997 and Lennox and Blaha, 1991. In the exercise by Lennox and Blaha (1991) a column is packed with sterile glass beads and crushed and sieved copper ore.

Any of the sulfide ores listed above will work and these can be obtained from a variety of sources. Some distributors will make available the chips left over from the production of hand specimens at a very reasonable cost.

The column drains into a three-necked boiling flask. The medium is a Thiobacillus medium consisting of basal salts (see appendix below). The medium is recirculated through the column by means of a peristaltic or diaphragmatic pump which carries the medium from the reservoir to the top of the column. At time zero, the column is charged with a culture of Thiobacillis ferrooxidans such as ATCC 13661. Samples are drawn at intervals and the copper concentrations determined.


Copper ion concentrations are measured with a Copper test kit such as those distributed by LaMotte Chemical or Hach.

Copper concentration can be plotted as a function of time.

After the leaching column has been running for a period of time, the presence of copper ion can be demonstrated directly by adding clean, oil free iron nails to the leachate solution. Within a short time one can observe the deposition of pure copper on the surface of the nails as the result of a single dispacement reaction between the iron and the copper sulfate in solution. This process is analogous to one of the techniques used industrially. Thus from ore too poor to process on can obtain pure copper with the aid of a very useful and versatile bacterium.

Appendix:

Thiobacillus Medium (after A.E. Torma, 1977) Basal salts

(NH4)2 SO4 3.0 g

K2HPO4 0.5 g

MgSO4.7H2O 0.5 g

KCl 0.1 g

Ca(NO3)2 0.01 g

Distilled Water 700 ml

10 N H2SO4 1.0 ml

For culturing Thiobacillus ferrooxidans an energy source must be added in the form of FeSO4.7H2O 300. Ml of a 14.74% wt/vol solution. Note: in the presence of the copper ores this additional energy source is not required.

References:

Brierley, Corale L. 1982. Microbiological Mining. Scientific American 248: 44-53.

Hudson, Barbara K. and Linda Sherwood, 1997. Explorations in Microbiology, A Discovery-Based Approach. Prentice Hall, Upper Saddle River, New Jersey.

Lennox, John E. and Thomas Blaha, 1991. Leaching of Copper Ore by Thiobacillus ferrooxidans. The American Biology Teacher, 53: 361-368.

Torma, A.E., 1977. The Role of Thiobacillus ferrooxidans in Hydrometallurgical Processes. Advances in Biochemical Engineering. IN: Ghose, Fletcher and Blackebrough, Eds., Springer-Verlag, Berlin.