Copper Ore Grade, Mining, and Tailings:
Ideas for Class Discussion

Copper occurs in Earth's crust (average) as 0.0058% by weight. A typical ore body has a grade of copper of 1-4% by weight. The concentration factor of copper in an economically viable ore body is about >80-100 times that of the average value of copper in the Earth's crust. The grade of copper required for mining to be viable changes with time as a result of variable demand for copper and new extraction and refining technologies. With only 1-4% of an ore body typically yielding copper, as much as 96-99% of the mined material is left behind as tailings. These tailings pose some of the most challenging environmental problems, as they typically are finely crushed and rich in sulfur and metals, leading to a potential abundance of acidic wastewater.

It is easy to draw parallels between mine tailings and acid wastewater in the real world and the waste products left behind in the demonstration. The acid extraction process in the demonstration is similar to heap-leaching of crushed ore placed on a pad at a mine operation (see upper photo at left). The solution in the beaker that has drained through the crushed malachite (ore mineral) contains copper ions and carbonic acid, whereas at a mine site the leachate is drained into a holding area (see lower photo at left). Point out to students that the malachite is a carbonate ore mineral, whereas copper sulfide ores can generate sulfuric acid in wastewater. The crushed ore mineral left behind in the filter paper in the funnel is equivalent to tailings left behind at a mine site.