Environmental Geochemistry Lab

Environmental Geochemistry Lab Name:______

Lab 2 Acid Mine Drainage & Oxidation Reduction

Part 1 Acid Mine Drainage.

Why does acid mine drainage form?

In many areas, acid drainage forms naturally when certain minerals come into contact with water, air and bacteria. This contact and the chemical reactions that take place are part of the weathering process. The weathering of the rocks and minerals in the creek slowly releases the acids, salts, metals and sulfates into creeks, rivers, lakes and wetlands. Weathering is a natural process, but many times human activities interfere and can increase the amounts of contaminants. When too much of these acids enter creeks, they become polluted and can support only extreme bacteria.

Instructions:

In the green tray you should find 4 jars containing 100ml of de-ionized water in equilibrium with the atmosphere. The pH of these containers has been measured. The pH of the water in these jars should be:

______.

You should also have 3 different rocks or minerals in the tray. You should add each to one of the jars. This should give you one jar with water and pyrite, one with water and coal and one with water and limestone. (One jar should remain with water only. This is your control.)

Over the next week you will need to check the pH of each container and determine if there has been any change.

Sample / pH day 1 / pH day 2 / DpH
Water w/ pyrite
Water w/ coal
Water w/ CaCO3
Control water

Questions:

1.  What materials lowered the pH of the water?

2.  What materials raised the pH of the water?

3.  How long did it take an acid to form?

4.  What else did you observe?

5.  Which sample would be a better buffer and what does this imply?

Part 2 Oxidation-Reduction reactions

Some metals that when combined with a different metal in solution, will have the tendency to gain or lose electrons. This type of reaction is called an oxidation – reduction or redox reaction. We are going to examine what happens when Copper and Iron are combined. This is the basic idea behind a simple battery. (Keep in mind the idea of metal reclamation from open pit waste rock left after ore processing.)

Materials required:

Experiment derived from Ward’s Natural Science Establishment Exploring Mine Pollution and Reclamation (1992)

25 ml 20% cupric sulfate solution

50 ml de-ionized water

3 iron nails

3 glass jars

Litmus test strips

Forceps

Gloves

Safety glasses

Experiment derived from Ward’s Natural Science Establishment Exploring Mine Pollution and Reclamation (1992)

Procedure:

·  Please use caution when near the 25 ml of cupric sulfate. This solution is toxic, so you should avoid contact with your skin. Wash your hands thoroughly after use and contact Prof. Weeden immediately should a spill occur.

·  Record the color of the solution in the data table below and test with litmus paper. Contrast the litmus paper test color from the solution with a litmus test of water. Record your litmus test results in the data table.

·  Place 3 iron nails in the solution and allow to stand overnight. The following day remove the nails with the forceps and let them drain on a paper towel. Examine the nails and the remaining solution and record your observations in the data table.

·  Test the leftover cupric sulfate solution, water and untested cupric sulfate with litmus paper once again and record your observations.

·  Carefully pour liquid in waste container in sink.

Data Table

Solution / Color / Litmus Test / Observations
CuSO4 day 1
H2O day 1
CuSO4 day 2
H2O day 2

Questions:

1) Write the redox reaction that you have observed in this experiment.

2) Which of the metals was the oxidizing agent and which was the reducing agent?

3) Referring to the last question, how do you know?

4) What is the DGR for the redox reaction and what is the electromotive force?

5) Does this experiment represent a possible method for reclaiming precious metal? If so, how?

6) What might happen if large amounts of leftover solution from this reclaiming process were allowed to runoff into nearby streams?

7) Any additional thoughts?

Sources: http://clevergreen.co.za/2010/12/01/acid-mine-drainage-explained/http://craddock_t.tripod.com/amd_experiments-html.htm#Why

Experiment derived from Ward’s Natural Science Establishment Exploring Mine Pollution and Reclamation (1992)