In today's world, jewelry is very popular. High demand creates demanding quality products. The development of the jewelry industry does not stand still, new ways of processing appear. One of such methods of working with precious metals is refining.
Refining concept
Refining is a complex process consisting of several stages, as a result of which a precious metal is obtained, maximally purified from impurities. Thanks to cleaning, a higher test is achieved, which significantly affects the quality of products and cost.
Refining raw materials
The most common raw materials for refining are gold and silver, less commonly platinum.
Also suitable for the procedure:
- jewelry scrap;
- household and technical scrap;
- coins;
- schlichovy and draft gold.
Refining is a procedure that is carried out in special plants. The incoming raw material contains many impurities; upon receipt, it will undergo melting in powerful furnaces. After that, the optimal refining method is selected, and the process starts.
Despite the complexity, refining is a treatment available for implementation at home with certain skills and tools.
Refining tools
To carry out refining at home, it is important to have special equipment:
- Crucible. This is the container in which the metal melts, it is able to withstand very high temperatures. Buying a crucible is not difficult, it can be found in specialized stores. So that the melting process does not take much time and at this stage there are no difficulties, it is recommended to purchase a crucible furnace. Modern installations are implemented with an already integrated crucible of various volumes. Important! The crucible must be clean and used only for processing one type of metal. For convenience, you can mark with the type of metal used.
- Tweezers. It must be large and durable. Tweezers are used to transfer zinc to prepared gold.
- Strong knitting needle with a thickness of at least 2 mm. It can be steel or titanium. The knitting needle is needed for stirring molten metal, it is sold in any store for jewelers.
- A flask with a volume of at least 0.5 liters. It is intended for boiling, the glass of which it is made must be refractory.
- Electric hob and hood. It is important that the spiral in the tile is closed. The cap is needed to cover the crucible. The design is easy to make on your own: soak asbestos and mix it with gypsum in a 1: 1 ratio.
Gold refining. Expendable materials
To carry out the procedure at home, the following materials will be required:
- borax - clean and designed for single use, because its reuse will not clean, but will greatly pollute the precious metal;
- nitric acid 65-70%;
- hydrochloric acid 36-38%;
- zinc for loosening gold.
The initial stage of gold refining - melting
Where to begin? Refining is a procedure that requires compliance with the rules at all stages. Even a slight deviation from the sequence will not lead to the desired result.
Gold refining begins with the melting of metal. It is important to properly prepare the crucible - it must be dry and heated. Annealing a wet crucible is not allowed to prevent cracking.
Borax is poured into the crucible and leveled along its bottom. Above is a raw material containing gold. The heating process begins, with an increase in temperature, the metal acquires a red tint. At this point, you need to fill up the borax on top and continue heating.
Loosening zinc
There are two popular ways of refining gold at home: using zinc or copper. The simplest method is the purification of a precious metal with zinc, it serves as a baking powder of gold molecules for easy extraction of impurities.
After the appearance of a dense coma of gold floating in the storm at the bottom of the crucible, you can proceed with the addition of zinc. It is placed in a crucible in small portions. Failure to comply with this rule will result in the release of the alloy, as gold and zinc have different melting points (they differ by more than 500 degrees). The temperature of heating with the addition of zinc must be constantly increased.
After the zinc is completely dissolved , the alloy must be stirred with a spoke and the temperature lowered.
Extraction of the alloy from the crucible and its grinding
To continue refining gold, the alloy must be removed from the crucible. Extraction occurs with tweezers, lump immersed in water. At this stage, the alloy should have a silver color.
Then, the ingot obtained is ground in a regular mortar. The process is not difficult - it is very fragile. For the best result, the degree of grinding should be maximum.
Gold washing
A flask is installed above the stove, and the resulting powder is poured into it. There is added nitric acid in an amount of not more than 50 ml.
The reaction should be immediate - the release of multi-colored steam begins. This procedure is preferably performed in the open air - the vapor is very corrosive. After some time (when the reaction weakens), another 50-100 ml of acid is added.
After completion of the reaction, the flask should be slowly heated until a clear vapor appears. Heating stops and cold water is poured into the flask. The resulting solution must be shaken - the gold particles will settle to the bottom, and the water must be carefully drained, avoiding the loss of gold. The procedure is repeated several times, with each subsequent washing, the water becomes cleaner, its full transparency indicates the completion of the washing phase.
With a clear implementation of the technology, pure gold will remain at the bottom of the flask without any impurities or zinc.
The final stage - getting a gold bar
In order for a precipitate of gold particles to form into a more familiar gold ingot, it must be melted and bleached.
To do this, golden flakes are filtered with gauze, in it they are strewed with brown. Then the gauze is dried and placed in a crucible, covered with a cap. The crucible is placed on the tile - the heating process begins. As a result, a lump of gold forms, and gauze smolders. For deeper purification of gold, you can again sprinkle it with brown.
After complete solidification of the gold, the lump is removed from the crucible and subjected to boiling in the bleach (solution from hydrochloric, nitric acids and water) for no more than 5 minutes. Then it is washed in running water.
The result is a gold bar of the highest standard.
Gold refining with copper is identical to zinc refining. The difference is that copper is initially melted, and gold is added to it in small portions. In the refining process, additional equipment is required - rollers. They are designed for rolling the finished alloy of copper and gold into thin strips, which should be cut as finely as possible. Then these small particles are placed in the flask and go through the same steps: heating, washing, re-melting and the formation of the finished ingot.
Platinum refining at home
All platinum metals are rare elements. Most often, their refining occurs in special backwaters. Rare amateur jewelers clean platinum at home.
But if such a need arose - the method of refining is chosen exclusively chemical. The technology is the same as when refining gold.
Refining Safety Rules
Refining of precious metals, carried out at home, must be carried out in compliance with safety rules:
- The room in which the refining takes place should be spacious, not cluttered with foreign objects. This is especially true for flammable things.
- It is recommended to use an exhaust design, because chemical fumes are very toxic, and open windows will provoke a draft that interferes with work.
- Refining is necessary in refractory gloves and an apron. The body must be completely covered by clothing that is not resistant to burning.
- Special glasses are put on the eyes, and the mouth and nose are closed with a respirator.
- Hair has the ability to absorb toxic substances, so it is also advisable to close them.
The jewelry industry does not stand still, and today it is possible to obtain precious metals of the highest standard, without the content of impurities. It is important to understand that gold obtained by refining at home is prohibited for sale. In most cases, amateurs simply conduct experiments with raw materials, or refine gold and platinum, as well as other metals illegally. The manufacture of jewelry from home-made gold is prosecuted by law, refining is carried out only at special refineries or at jewelry enterprises.