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25.3 Metallurgical Processes
In this section, we look at several processes.
The first step in processing metal-Containing ores is crushing.
Magnets can separate minerals if they are magnetic.
polar minerals can be separated from nonpolar gangue by static forces.
Sometimes solutions separate the minerals from the gangue.
The air forms bubbles and a froth.
The minerals are attached to the wet agent and can be collected.
The solution is separated by the gangue.
The minerals attach to the froth in a bubbled solution with the help of a wet agent.
Different techniques can be used to achieve this separation.
Different heating conditions affect the mineral.
Section 3.5 states that hydrated compounds can drive off water.
It is important to roast sulfide ores.
The ores are heated in the presence of oxygen to convert the sulfide into oxide and sulfur dioxide.
In some cases, a flux must be added to the mixture to separate the two materials.
The liquid metal and liquid slag have different densities.
The more dense liquid can flow out of the lower tap holes and the less dense liquid can flow out of the higher tap holes.
A hydrometallurgy process is used.
Small particles of gold are mixed with other substances.
Many streams and rivers have been contaminated with cyanide due to the practice of quenching.
New alternatives using the thiosulfate ion are being investigated.
Acid, base, and salt solutions can be used to separate metal-bearing minerals.
Under high pressure, the bauxite is heated in a concentrated NaOH solution.
Reduction of the aluminum out of the aluminum oxide is done by lysis.
The electrolysis is not carried out on molten Al2O3 because it is at a high temperature.
In the Hall process, the Al2O3 is dissolved into molten cryolite (Na3AlF6) and graphite rods are used to carry out the electrolysis in the liquid mixture.
The dissolved oxygen ion in the molten salt oxidizes the carbon that composes the electrodes.
Reducing agents are achieved by the use of graphite electrodes.
The refining of copper is an example of metallurgy.
The CuFeS2 is the most abundant copper source.
The chalcopyrite is roasted to convert it to CuS.
The iron forms oxides and sulfides.
The iron silicate is removed after it is formed.
The metal is not very pure because it reacts with oxygen to form sulfur dioxide gas and copper metal.
The copper is refined using lysis.
The copper is refined.
Pure metal is formed on the cathode.
The anode and the cathode are made of copper in the cell used to refine copper.
The impure copper needs to be refined, and the thin sheet of pure copper is the cathode.
As the current flows through the cell, the copper from the anode oxidizes and is dissolved in a copper sulfate solution.
It goes out as pure copper.
Even though the more active metals oxidize from the anode, they stay in solution and do not plate out on the cathode, because the copper anode is separate from the copper during electrolysis.
The less active metals do not oxidize and fall to the bottom of the cell as the copper is dissolved.
The sludge at the bottom of the cell contains precious metals.
About 25% of the silver produced in the US is recovered from the copper refining process.
Under high pressures, metal particles are pressed together to form a component.
The metal particles are fused together at a temperature high enough to strengthen them and increase their density.
Iron powder from mill scrap was once used in powder metallurgy.
The iron oxide in the scrap would fall off as it was being processed.
The iron oxide dust was heated in a hydrogen atmosphere.
Water atomization, a new method for the development of powdered metal, was introduced in the 1960s by the A. O. Smith Company.
The molten metal is melted and a small stream of liquid is allowed to flow from the bottom of the container.
A high-pressure blast of cold water breaks a stream of metal into small droplets that quickly solidify.
The metal products made in this way are more dense and smooth than the sponge powder made by powder metallurgy.
Many copper, bronze, carbide, and brass parts are made with powder metallurgy processes.
The part can be pressed directly into the desired shape, so waste is almost eliminated.
The press can be designed with intricate teeth on gears and multiple holes.
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