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Copper Mining Lab
Mining is the extraction of metals or minerals from the Earth. Commercial mining has gone on in many regions of the United States since the middle of the 19th century. Most of the copper mines use the open pit method of extracting ore (a piece of Earth’s crust that contains a profitable amount of metal) which is a type of surface mining. This 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.
Copper is mined from deposits of native copper (Cu2), cuprite (Cu2O) azurite [Cu3(CO3)2(OH)2], malachite [(Cu2CO3(OH)2)], and chalcopyrite (CuFeS2). Modern mining involves three steps: extraction of the rock, mineral processing, and metal purification. Before this can happen, the overburden which is the top layer of soil and rock, are moved away from the rock 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 elements. The metal ore proceeds to the purification process while the nonmetal waste, called tailings, are 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 precipitate the copper from the nonmetal components of the mineral.
Ecosystems surrounding mines are often adversely affected by the tailing and spoil piles, which contain sulfur. As precipitation such as rain or snow falls onto the tailing and spoil piles, the water seeps through the pieces of rock. Species of sulfur-loving bacteria, water and oxygen react to create sulfuric acid. Because the solubility of metals increases with a decrease in pH the sulfuric acid solution leaches metals, such as iron, copper, lead and nickel or arsenic from the tailing and spoiling piles. The metal containing sulfuric acid solution, called acid mine drainage, travels to nearby streams, ponds and lakes, and often enters groundwater. 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 benthos 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 plastic liner on the ground. A sulfuric acid solution is applied (often by spraying) 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:
Fe + CuSO4 (aq) FeSO4 (aq) + Cu (s)
The sulfate ion has a greater affinity for the iron than copper. This change is observable because copper sulfate is blue while iron sulfate is colorless. Shiny copper metal forms, while the iron metal leaches into the solution.
Copper Ore sample (Azurite)
Neutralization (Part 2): 0.5 M FeSO4, 3M NaOH, buret
Procedure: Part 1: The purpose of Part 1 of the experiment is to simulate heap leach extraction of copper from copper ore. Copper metal will be recovered using two chemical reactions. The basic technique for copper extraction will involve the following steps:
Record exact mass of ore used. Mass an Erlenmeyer Flask and measure mass of sample in the flask. Measure out approximately 3 g of small-sized pieces of copper ore and subtract the mass of flask.
Add 8 mL 3 M H2SO4 to the flask, allowing the sulfuric acid solution to leach copper from the ore until no more evidence of reaction (bubbling) occurs. This could take 10 minutes. Periodically swirl the flask
Decant the copper sulfate solution from the tailings into a small beaker and add approximately 1.5 g of iron. Let the Erlenmeyer dry overnight before you determine the mass of tailings
Measure the pH of the iron sulfate solution
Label and mass a piece of filter paper; fold it, place it in a funnel and filter iron sulfate solution. When complete, remove filter paper and place under hood to dry.
Calculate the final mass of copper in the ore
Calculate the theoretical percent copper in the ore you used and the experimental percent copper.
Procedure: Part 2 (Demonstration): The purpose of Part 2 is to neutralize the acid mine drainage for disposal.
Dispense 30 mL solutions of 0.5 M Iron II sulfate into 250 mL flasks; dilute with DI water to 50 mL
Fill a buret with 50 mL each of NaOH
Measure the pH of solutions and record
Titrate each solution with the base, recording the pH and color after each 2 mL addition. Continue titrating until 1) there is no more color change 2) you see a dark green endpoint 3) pH jumps to 11-14iling and spoiling piles. The metal containing sulfuric acid solution, called acid mine drainage, travels to nearby streams, ponds and lakes, and often enters groundwater. Acid mine drainage can be extremely corrosive, causing tissue damage and death to many plant and animal species surrounding the mine.
The sulfate ion has a greater affinity for the iron than copper. This change is observable because copper sulfate is blue whi