Extracting copper from an ore

Saturday, November 23, 1996

Ron Benson, Helena High School, Helena, MT

This article is reprinted from the November 1994 issue of our sister publication Chem 13 News produced for high school chemistry teachers by the Chemistry Department of the University of Waterloo.

While participating in a Chemistry Institute last summer at the University of Washington, I developed a demonstration to show the way that chemistry is used to extract copper from an ore. The demonstration will fit nicely into Earth Science or Chemistry curriculums. You will need a small piece of malachite, a green mineral whose formula can be written as Cu2CO3(OH)2 or CuCO3*Cu(OH)2. This can be purchased through most science supply companies (10 pieces for under $10.) As with most copper ores, the malachite ore does not contain pure copper (native copper) and will contain other minerals besides the malachite. Malachite, one of several minerals mined to obtain copper is mined primarily in Arizona, the leading copper producing state in the United States. As is the case at most real mines, the first thing you will need to do is crush the ore. Take the lid cut from a coffee can, bend it in half, place the malachite ore between the halves, and then place them in a sandwich "baggie." Place the baggie on the sidewalk or other sturdy surface and gently pound with a hammer until the ore is crushed. At an actual mine site the ore may be put into a ball mill, a huge rotating cylinder containing steel balls that roll around, crushing the ore. At your demonstration site, set up a ring stand with a funnel, containing filter paper in the funnel. Next you will need two 250 mL beakers, one containing 75-125mL of 1 M H2SO4. Position the empty beaker beneath the funnel and then pour the acid over the crushed ore. Once it has leached through, switch the beakers and repeat the process one or two more times until the leachate becomes sky-blue. The blue colour is due to the presence of Cu2+ ions which go into solution as the acid reacts with the malachite. Part of what happens is:

Cu(OH)2 + H2SO4 -> 2H2O + CuSO4 

Next remove the solution from beneath the funnel and put the empty beaker in its place to catch the remaining drops. Finally, take several iron nails that have been cleaned with steel wool and place them into the leachate solution. You will want your students to be close by as you do this so that they will observe the nails as they become coated with copper. Use forceps to lift them out of the solution and show the brilliant copper colour. The mining industry uses scrap iron such as discarded cars for this process. Chemically, the copper ions are "stealing" electrons from the iron atoms as shown in this ionic equation:

Fe + Cu2+ -> Fe2+ = Cu