Materials Included In Kit

Additional Materials Required

Prelab Preparation

Cut sandpaper into 3" x 3" squares.

Safety Precautions

Sulfuric acid solution is corrosive to eyes, skin, mucous membranes and other tissues. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Crushing rock is an eye and hand hazard. Wear protective eyewear and be aware of hand position when striking the rock. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The waste solution will be acidic, check the pH and, if necessary, neutralize with a base as described in Flinn Suggested Disposal Method #24b. The solid waste may be disposed of in the regular trash according to Flinn Suggested Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of three or for 10 groups of students. This laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab, and the data calculations and questions may be completed the day after the lab.
• Test the pH of the waste solution and relate the results to the Prelab Questions.

Teacher Tips

• Make this laboratory quantitative by recording the exact mass of dry azurite before and after treatment with the sulfuric acid. Assuming that only copper has gone into solution, the mass lost is equal to the mass of copper in solution. The amount of copper recovered can be determined by massing the nail before and after exposure to the copper sulfate. The reaction is complete when the solution appears colorless. Filter and dry the nail and copper metal before determining its final mass. The copper metal will oxidize quickly as it dries so the final mass is an approximation of the true amount of copper metal recovered. Stoichiometry can be used to calculate the actual amount recovered.
• Other copper containing minerals available from Flinn Scientific such as chalcopyrite, AP4905, malachite, AP4924, or native copper, AP4907, can be treated with sulfuric acid and the results compared to the azurite used in this activity.
• Convert this activity to a guided inquiry activity using various concentrations of sulfuric acid, different copper minerals, other sources of iron, or varying the temperature of the acid.
• The Internet has many links to information about working copper mines and mines that have been abandoned. Researching copper mines such as the Berkeley Pit Copper Mine, Kennecott Copper Mine, and the Chuquicamata Copper Mine make a great extension to this activity.

Answers to Prelab Questions

1. Many old pit mines have gradually filled with water from precipitation and underground springs. The water in these pit mines is often very acidic. Discuss the potential environmental benefits of reclaiming metal and minerals such as sulfur from the acid mine drainage in these pit mines.

   If sulfur was extracted from pit mines, it would result in several environmental benefits. Sulfur’s main use is in making chemicals for fertilizers and refining petroleum.

2. Discuss the potential environmental problems of reclaiming minerals from the acid mine drainage in the old pit mines.

   Reclaiming minerals from old pit mines may lead to a delay in the cleanup of these sites. The delays will prevent native species from returning to the habitat resulting in fewer numbers of these species. The lack of habitat may lead to genetic drift or extinction of some species.

Sample Data

Azurite Rock Observations
The azurite rock contains blue, yellow and green domains. Areas of the rock are soft and transfer when rubbed.

Reaction Observations
The solution becomes a cloudy bluish green as parts of the azurite break apart. Nail observations As the liquid drips onto the nail, the nail becomes coated with copper metal.

Solution Observations
A clear, blue solution drips from the funnel.

Answers to Questions

1. What happened to the azurite rock when the sulfuric acid was added?

   The blue and green areas of the azurite rock gradually dissolved leaving only gray solid to be filtered out of the solution.

2. Based on the information in the Background section, speculate about the metal composition of the nail. Cite any specific evidence that led you to this conclusion.

   The sulfuric acid reacts with the copper to produce copper sulfate. The copper sulfate undergoes a single replacement reaction with the iron in the nail to produce iron sulfate and free copper metal. The nail must contain iron because it is gradually etched away while copper plates onto it.

3. Speculate how the solution would change over time if the nail was allowed to sit in the solution over night.

   Eventually the solution will become colorless as the copper plates out as copper metal and the reaction produces iron sulfate.

References

Skousen, Jeff, Hilton, Tiff, and Faulkner, Ben. Overview of Acid Mine Drainage Treatment with Chemicals. West Virginia University Extension Service. http://www.wvu.edu/~agexten/landrec/chemtrt.htm (accessed April 2008).

Woods, Ronald, “Extracting Metals from Sulfide Ores.” Electrochemistry Encyclopedia, revised November 2004; http://electrochem.cwru.edu/ed/encycl/art-m02-metals.htm (accessed April 2008).

Introduction

Mining is the extraction of metals or minerals from the Earth. Mining done above ground is called surface mining, and mining below ground is called subsurface mining. All types of mining pose environmental challenges. This activity focuses on surface mining of copper.

Concepts

• Surface vs. subsurface mining
• Acid mine drainage

Background

Copper is mined from deposits of native copper (Cu₂), cuprite (Cu₂O), azurite [Cu₃(CO₃)₂(OH)₂], chrysocolla [(Cu,Al)₂H₂Si₂O₅(OH)₄•nH₂O] and chalcopyrite (CuFeS₂). In ancient times, nuggets of native copper were collected in streams or found lying on the ground. The native copper collected in this way was essentially pure copper metal. Simply heating these copper nuggets at a high temperature was enough to melt the metal so that it could be cast or formed into jewelry, weapons or household objects. Native copper was also found projecting out of the ground in what is known as veins. This discovery led to surface and crude subsurface shaft mining of the ore. Surface mining involves scraping or digging to remove the layers of soil and rock that cover the vein of metal or mineral. Subsurface mining involves digging long holes, or shafts, from an above ground entrance to very deep levels underground. Gradually, the large veins of native copper were mined to completion causing less pure forms of copper, such as cuprite, azurite, malachite and chalcopyrite, to become the most common source of copper. These copper minerals are often found close to the surface, making surface mining the most common type of copper mine. Some of the largest surface mines in the world are copper mines.

Three steps are involved in mining—extraction of the rock, mineral processing, and metal purification. In surface mining, the top layers of soil and rock, called overburden or gangue, is moved away from the ore vein and heaped into spoil piles. The ore is extracted from the vein and moved to a processing plant. At the processing plant the metal ore is separated from naturally occurring nonmetallic minerals in a process called benefication. The metal ore proceeds to the purification process while the nonmetallic waste, called tailings, is heaped into piles similar to the spoil piles. High quality metal ore can be initially refined by smelting. Smelting involves heating the metal ore in a kiln-like oven in a reducing environment to “release” the copper from the nonmetal components of the mineral.

Ecosystems surrounding mines are often adversely affected by to the tailing and spoil piles. Many of the copper minerals or the surrounding minerals contain sulfur. As precipitation such as rain or snow falls onto the tailing and spoil piles, the water seeps through the pieces of rock (see Figure 1). Species of sulfur-loving bacteria, water and oxygen react to create sulfuric acid. The solubility of metals increases with a decrease in pH. The sulfuric acid solution leaches metals, such as iron, copper, lead, nickel or arsenic from the tailing and spoil piles. The metal containing sulfuric acid solution, called acid mine drainage, travels to nearby streams, ponds, lakes and even groundwater, changing the pH of the water. Acid mine drainage can be extremely corrosive, causing tissue damage and death to many plant and animal species surrounding the mine.

Bedrock surrounding a stream or lake near a mine contains minerals which act to neutralize the acid environment making it basic. If the water becomes sufficiently alkaline (basic), metals will precipitate out of the solution coating the bottom of the stream or lake. Bottom feeding animals ingest small amounts of the metal-laden sediment. Other species may bioaccumulate the metal as they feed on the bottom-feeding species or on plants that have absorbed small amounts of metal.

The chemical process behind acid mine drainage has led to the development of a process for low quality mineral ore called heap leach extraction. In heap leach extraction, crushed tailings and spoil piles are piled into a tank or onto a plastic liner on the ground. A sulfuric acid solution is sprayed onto the pile of ore. The solution permeates through the ore pile and dissolves metals from the rock. The amount of metal recovered using the heap leach extraction process can be greatly increased by the addition of specific bacteria to the mineral pile. Acidophilic, thermophilic or chemolithotrophic bacteria thrive in the harsh conditions created in the heap leach piles. Chemolithotrophic bacteria derive energy by oxidizing inorganic compounds such as nitrogen, sulfur, hydrogen or metals. The resulting copper sulfate solution, an acidic blue liquid, is collected into vats for refining.

Several different refining techniques are used to capture the copper from the copper sulfate solution. One of the simplest methods is to add iron metal to the solution. The following reaction occurs:

CuSO₄(aq) + Fe(s) → Fe₂SO₄(aq) + Cu(s)

The sulfate ion has a greater affinity for iron than copper. This change is observable because copper sulfate is blue while iron sulfate is colorless. Shiny copper metal plates onto the iron, while the iron metal leaches into the solution. Eventually the copper metal builds up enough to either stop the reaction or it may fall off the iron substrate allowing the reaction to continue. This is an example of a single replacement reaction often studied in chemistry.

Experiment Overview

The purpose of this experiment is to simulate heap leach extraction of copper from copper ore. Copper metal will be recovered using a single replacement reaction.

Materials

Prelab Questions

1. Many old pit mines have gradually filled with water from precipitation and underground springs. The water in these pit mines is often very acidic. Discuss the potential environmental benefits of reclaiming metal and minerals such as sulfur from the acid mine drainage in these pit mines.
2. Discuss the potential environmental problems of reclaiming minerals from the acid mine drainage in the old pit mines.

Safety Precautions

Sulfuric acid solution is corrosive to eyes, skin, mucous membranes and other tissues. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Crushing rock is an eye and hand hazard. Wear protective eyewear and be aware of hand position when striking the rock. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Closely observe a piece of azurite rock. Record the observations on the Copper Mining Worksheet.
2. Wrap the piece of azurite in several sheets of paper towel.
3. Place the wrapped azurite onto a hard durable surface and pulverize the rock with the hammer into pea-size or smaller pieces.
4. Using a balance, weigh out 1 g of the pulverized azurite and place the azurite into a clean test tube.
5. Using a graduated cylinder, measure and add 10 mL of 2 M sulfuric acid solution to the test tube. Observe and record the reaction between the sulfuric acid and azurite.
6. Allow the sulfuric acid solution to leach copper from the azurite for 20 minutes, stirring occasionally with a glass stirring rod.
7. Using the sandpaper, sand the surface of the nail. Carefully place the nail point side down into a clean test tube.
8. Place a funnel into the top of the clean test tube with the nail.
9. Fold the filter paper in half and then in half again. Tear off a small corner of the filter paper.
10. Place the folded piece of filter paper into the funnel (see Figure 2).
    {10906_Procedure_Figure_2}
11. Carefully pour the sulfuric acid–azurite mixture into the filter paper. Closely observe the drops of copper sulfate solution as it drips through the filter paper and onto the sanded nail. Record the observations on the Copper Mining Worksheet.
12. Observe the color of the solution as it drips from the filter paper. Record the observations on the Copper Mining Worksheet.
13. Complete the Post-Lab Questions on the Copper Mining Worksheet.
14. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

10906_Student1.pdf