Electrolytic refining of copper: composition, formulas and reactions

Copper refining is the process of refining metal through electrolysis. Electrolysis purification is the easiest way to achieve a purity of 99.999% in copper. Electrolysis improves the quality of copper as an electrical conductor. Electrical equipment often contains electrolytic copper.

What it is?

Copper refining or electrolysis uses an anode that contains impure copper. It occurs due to ore concentration. The cathode consists of pure metal (titanium or stainless steel). The electrolyte solution consists of sulfate. Therefore, it can be argued that copper refining and electrolysis are one and the same. An electric current causes copper ions from the anodes to enter the solution and precipitate on the cathode. In this case, impurities either leave, or form a precipitate, or remain in solution. The cathode becomes larger than pure copper, and the anode contracts.

Electrolytic cells use an external DC source to respond to reactions that would not otherwise be spontaneous. Electrolytic reactions are used to clean plate metals on many types of substrates.

The use of an electrolytic process for metal cleaning (copper refining, metal electrolysis):

1. Since impurities can significantly reduce the conductivity of copper wires, it is necessary to clean contaminated copper. One of the cleaning methods is electrolysis.
2. When a strip of unclean metallic copper is used as the anode in the electrolysis of an aqueous preparation of copper sulfate, copper is oxidized. Its oxidation proceeds easier than the oxidation of water. Therefore, metallic copper dissolves in solution in the form of copper ions, leaving behind many impurities (less active metals).
3. Copper ions formed on the anode migrate to the cathode, where they are more easily restored than water and metal “plates” on the cathode.

Sufficient current must be passed between the electrodes, otherwise, a non-spontaneous reaction will occur. By carefully adjusting the electric potential, metallic impurities that are active enough to oxidize copper at the anode, the substances do not decrease at the cathode, and the metal selectively precipitates.

Important! Not all metals are reduced or oxidized more easily than water. If so, an electrochemical reaction will first take place, requiring the least potential. For example, if we used electrodes, both the anode and the cathode, the metal potential would be oxidized at the anode, but then water would decrease at the cathode, and aluminum ions would remain in solution.

To create electrolysis, you need to use the following method of refining copper:

1. Pour a solution of copper sulfate into a glass.
2. Place two graphite rods in a solution of copper sulfate.
3. Connect one electrode to the negative DC terminal and the other to the positive terminal.
4. Fill two small tubes completely with a solution of copper sulfate and place a stopper on each electrode.
5. Turn on the power source and check what happens on each electrode.
6. Try out any gas produced with a flaming tire.
7. Record your observations and the results of your tests.

The results should be as follows:

• Brown or pink solid forms appear in solution.
• There are bubbles.
• Bubbles should be colorless.
• The substance is gaseous.

All results are recorded, after which the gas is extinguished by the tire. There is also another way to clean the metal of impurities and extraneous dirt - this is the fire refining of copper. We will tell how this happens later, and now we will present other options for refining the metal.

Copper refining methods - how else can chemical stripping of the necessary metals occur?

Since electrolysis is the effect of sulfates and current, what is an electrolytic method for producing pure products? Completely different things, although similar in the sound of the names. However, electrical refining of copper involves the use of acids. We can say that this is metal oxidation , but not quite.

Pure production is important for the manufacture of electrical wire, since the electrical conductivity of copper is reduced due to impurities. These impurities include valuable metals such as:

• silver,
• gold;
• platinum.

When they are removed by electrolysis and restored in the same way, as much energy is consumed as would be enough to consume electrical power to supply dozens of houses. The cleaned component saves energy by providing even more residential buildings in less time.

In electrolytic refining, an unclean composition is made from the anode in an electrolytic bath of copper sulfate — CuSO ₄ and sulfuric acid H ₂ SO ₄ . The cathode is a sheet of very pure copper. As the current passes through the solution, positive copper ions, Cu ₂ ⁺ are attracted to the cathode, where they take on the electrons and are deposited as neutral atoms, thereby creating more and more pure metal on the cathode. Meanwhile, the atoms in the anode donate electrons and dissolve in the electrolyte solution in the form of ions. But the impurities in the anode do not go into solution, because the atoms of silver, gold and platinum are not easily oxidized (converted into positive ions), like copper. Thus, silver, gold and platinum simply fall from the anode to the bottom of the tank, where they can be cleaned.

But there is also electrolytic refining of copper when tanks are used:

1. Electrolytic treatment tanks are a separate workshop in industrial production. Anode plates are suspended by “handles” in the tank for cleaning electrolytic copper. Pure copper cathode sheets suspended on solid rods are inserted into the same reservoir, one sheet between each anode. When an electric current is passed from the anodes through the electrolyte to the cathodes, copper from the anodes moves into the solution and is deposited on the starter sheet. Impurities from the anodes settle to the bottom of the tank.
2. Injection molding machine with copper anodes (plates). It will smoothly turn into anode plates into molds. After pretreatment, tin, lead, iron, and aluminum are removed. Then the copper material starts charging in the furnace, followed by the melting process.
3. When impurities are removed, slag removal and a recovery phase with natural gas follow. The reduction is aimed at removing free oxygen. After recovery, the process ends with casting, when the final product is cast in the form of copper anodes. The same machine can be used to cast these anodes during component processing or to process scrap metal anodes in an electrolysis smelter.
4. Pure cathode sheets. Modifying anodes extracted from the refining furnace are converted to electrolytic copper with a purity of 99.99% during electrolysis. During electrolysis, copper ions leave an unclean copper anode and, since they are positive, migrate to the cathode.

From time to time, pure metal is scraped off the cathode. Impurities from a copper anode, such as gold, silver, platinum and tin, are collected at the bottom of the electrolyte solution, deposited as anode mucus. This process is called the electrolytic production and refining of copper.

Getting fossil - what types exist and are all necessary in practice?

A slightly different method of metal cleaning. There is also refining copper fire and electrolytic, when one process immediately follows another. An important “separating” step is concentration or concentration. After the concentration is completed, the next step in creating the finished product is the fire refining of copper.

This usually happens near a mine, in an enrichment plant or a smelter. Thanks to copper cleaning, unwanted material is gradually removed, and copper is concentrated with a purity of up to 99.99% grade A. Details of the processing process depend on the type of minerals to which the metal is associated. Sulfide-rich copper ore is processed by the pyrometallurgical method.

Processing and pyrometallurgy:

1. In pyrometallurgy, the copper concentrate is dried before heating in an oven. Chemical reactions that occur during heating cause the concentrate to separate into two layers of material: a matte layer and a slag layer. The matte layer at the bottom contains copper, and the slag layer at the top contains impurities.
2. Slag is discarded and the matte layer is restored and moved to a cylindrical vessel called a transducer. Various chemicals that react with copper are added to the converter. This leads to the formation of transformed copper, called a “blister”. The precipitated one is recovered and then subjected to another process called refining.
3. In refining, air and natural gas are purged to remove the remaining sulfur and oxygen, resulting in the purified composition being processed into a cathode. Metal is cast into anodes and placed in an electrolytic cell. After charging, pure copper is collected at the cathode and removed as 99% pure product.

Processing and hydrometallurgy:

1. In hydrometallurgy, copper concentrate is processed through one of several processes. The least common method is cementation, where metal is deposited on scrap metal in an oxidation-reduction reaction.
2. A more widely used cleaning method is solvent extraction and electrolysis. This new technology became widespread in the 1980s, and approximately 20% of the world's copper is currently produced like this.
3. Solvent extraction begins with an organic solvent that separates the metal from impurities and undesirable materials. Sulfuric acid is then added to separate copper from the organic solvent to form an electrolytic solution.
4. This solution is then subjected to an electrolysis process, which simply puts copper in solution on the cathode. This cathode can be sold as is, but can also be turned into rods or source sheets for other electrolyzers.

Mining companies may sell copper in concentrate or cathode form. As mentioned above, the concentrate is most often refined elsewhere, not in the mine site. Concentrate manufacturers sell concentrate powder containing 24 to 40% copper to smelters and refineries. The terms of sale are unique for each plant, but in general, the smelter pays the miner approximately 96% of the cost of copper in concentrate, minus processing fees and cleaning costs.

Smelters generally charge tolls, but they can also sell refined metal on behalf of the miners. Thus, all risk (and reward) from fluctuations in copper prices falls on the shoulders of dealers.

Fire refining - how dangerous is it?

The most “running” fire refining cannot be not dangerous, however, at present, the processing method is used in most industrial enterprises. Separately, it is worth describing the technology of refining blister copper.

Blister copper is already almost pure (more than 99% copper). But for today's market, this is not very "clean." The metal is further purified using electrolysis. In industrial production, a method called fire refining of blister copper is used. Ink copper is cast into large plates, which will be used as anodes in the cell. Electrolytic refining produces the high-quality high-purity metal required by industry.

In industry, this is carried out on a massive scale. Even the best chemical method cannot remove all impurities from copper, but using electrolytic refining, 99.99% pure copper can be obtained.

1. Anode blisters are immersed in an electrolyte containing copper sulfate and sulfuric acid.
2. Pure cathodes are located between them, and more than 200 A flows through the solution.

Under these conditions, copper atoms dissolve from the impure anode to form copper ions. They migrate to the cathodes, where they are deposited back like pure copper atoms.

• At the anode: Cu (s) → Cu ₂ + (aq) + 2e ^- .
• At the cathode: Cu ₂ + (aq) + 2e ^- → Cu (s).

When the switch closes, the copper ions on the anode begin to move through the solution to the cathode. Copper atoms have already given up two electrons to become ions, and their electrons can move freely in wires. Closing the switch pushes the electrons clockwise and forces some copper ions to settle in the solution.

The plate repels ions from the anode to the cathode. At the same time, it pushes free electrons around the wires (these electrons are already distributed over the wires). The electrons in the cathode recombine with copper ions from the solution, forming a new layer of copper atoms. Gradually, the anode collapses, and the cathode grows. Insoluble impurities in the anode fall to the bottom of the sediment. This valuable bio-product is removed.

Gold, silver, platinum and tin are insoluble in this electrolyte, and therefore do not deposit on the cathode. They form a valuable "sludge", which accumulates under the anodes.

Soluble impurities of iron and nickel are dissolved in the electrolyte, which must be constantly cleaned to prevent excessive deposition on the cathodes, which will reduce the purity of copper. Recently, stainless steel cathodes have been replaced with copper cathodes. Identical chemical reactions occur. Periodically, the cathodes are removed and pure copper is purified. The electrolytic production and refining of copper under these conditions is quite common in non-ferrous metal processing plants.

Electrochemical variant of metal purification

Fire cleaning can be called chemical, because in this process a chemical reaction occurs with other substances and impurities. An example of an oxidative reaction was given above. All types and methods of producing pure copper are similar, as are the electrochemical refining of copper, where identical tactics are used, but in a different sequence.

A chemical auxiliary element is the by-product itself:

• Sodium hydroxide.
• Chlorine.
• Hydrogen.

This is the cheapest way to get expensive raw materials without spending money on an alternative component extraction system. In addition, valuable metals are mined that are noble in composition and valuable in the industrial invention of electrical appliances.

Copper Furnace - Metal Cooking Industry

The copper fire refining furnace is designed in a special way and is capable of processing copper scrap into liquid metal with a controlled content of impurities. It is intended for pyrometallurgical processing of scrap using an economical and environmentally friendly technology. The basic technology proposed for the production of molten copper is suitable for the production of copper rod, strip, billet or other copper products using scrap as a raw material (Cu> 92%).

The potential of the incineration and treatment systems was calculated for the treatment cycle (from charging to recovery) for 16-24 hours, depending on the type of scrap. Copper refining furnaces have a special design and functions:

1. The furnace body is made of steel segments and rigid cross-sectional structures.
2. The furnace is lined with refractory material from the inside.
3. It is equipped with a hydraulic station operating in the tilting mode of the furnace with two speeds: the creep rate when tilted for casting and high speed during movement, which does not require special accuracy.
4. Operations are performed using two hydraulic cylinders mounted on the bottom of the furnace. A special device returns the furnace to a horizontal position during emergency power outages.
5. The material loading door is located in the side of the furnace. It is closed by a door driven by a hydraulic cylinder.
6. The furnace is equipped with cooled spears for copper oxidation and reduction operations.

There is also one universal burner that consumes both liquid and gaseous fuels.

Oxidative refining in industry

The operation of copper oxidation is carried out after completion of the melting of the feedstock. The process is carried out by injecting compressed air into the melt through the tuyeres. The resulting slag is removed manually from the surface of the melt using a special rake and dumped into a container. Slag contains copper, impurities, lead, tin, etc. The reduction process must be carried out to remove oxygen from the melt and reduce copper oxides. The operation is performed by injecting natural gas into the melt.

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Copper (II) ions oxidize iodide ions to molecular iodine, and in this process they themselves are reduced to copper (I) iodide. The initial mixed brown mixture is separated into an off-white precipitate of copper (I) iodide in an iodine solution. Use this reaction to determine the concentration of copper (II) ions in solution. If you add a set volume of a solution containing copper (II) ions to the flask, and then add an excess of potassium iodide solution, you will get the reaction described above.

2Cu ₂ ⁺ + 4I ^- → 2CuI (s) + I ₂ (aqueous solution)

You can find the amount of iodine released by titration with sodium thiosulfate solution.

2S ₂ O ₂ ^-3 (solution) + I ₂ (solution) → S ₄ O ₂ ^-6 (aqueous solution) + 2I ^- (aqueous solution)

When the sodium thiosulfate solution is started from the burette, the color of the iodine disappears. When almost all of this disappears, add starch. The entire iodide refining reaction of copper will be reversible with iodine to produce a deep blue starch-iodine complex, which is much easier to see.

Add the last few drops of sodium thiosulfate solution until the blue color disappears. If you trace the proportions through two equations, you will find that for every 2 moles of copper (II) ions you should have started with, you need 2 moles of sodium thiosulfate solution. If you know the concentration of sodium thiosulfate solution, it is easy to calculate the concentration of copper (II) ions. The result of this attempt is to obtain a simple copper (I) compound in solution.

Phosphorous treatment

Phosphorous copper refining is a phosphoric deoxidized hard copper, which is a durable general purpose resin. It is deoxidized with copper phosphorus, in which residual phosphorus is kept at a low level (0.005-0.013%) to achieve good electrical conductivity. It has good thermal conductivity and excellent welding and soldering properties. The oxide after copper refining in this way, remaining in the solid copper resin, is removed by phosphorus, which is the most commonly used deoxidant.

The table shows different indicators from annealed (soft) to hard state of copper.

Lead frames connect the wiring to electrical terminals on the surface of the semiconductor and large-scale circuits on electrical devices and printed circuit boards. The material is selected to meet the requirements of the process and to be reliable during installation and operation.

The composition of copper after electrolysis

The composition of copper after fire refining includes 99.2% of the metal. In the anodes it remains much less. When impurities are completely removed, 130 g / l of cathode bases remain in the composition. The aqueous solution of vitriol becomes weak, and the acid component of copper cathodes reaches 140-180 g / l. Blister copper contains 99.5% of metal, iron is 0.10%, zinc is up to 0.05%, and gold and silver are only 1-200 g / t.