Find out about the process for recovering gold and precious metals from waste materials
Recovering and refining gold and precious metals from waste materials
Orovilla, among its many activities, also specialises in the recovery, analysis and refining of gold, silver, platinum, palladium and other precious metals from goldsmithing (discards and disused jewellery) and industry.
This type of activity, carried out in-house, stands out for its great attention to the entire production process and the meticulousness with which each stage is carried out.
We are able to guarantee our customers absolute process transparency and the possibility of carrying out any type of direct verification during the material analysis stages.
The purity of the precious metal recovered and refined is almost absolute and guaranteed thanks to appropriate important certifications
Gold and precious metal analysis
The specific technical standards taken as a reference for analysing and determining the fineness of gold and silver are those laid down in the Regulation implementing Legislative Decree No. 251 of 1999 (ISO UNI EN 11426/2000).
Sampling. A sample weighing approximately 0.25 grams is taken from the recovered material. The sample is carefully analysed and weighed, then wrapped in a thin lead sheet together with the inquarctation silver, in a ratio of 1 to 3. This process will subsequently allow the two metals to be perfectly divided.
Melting. This material is then placed in a cupel (called a crucible) and transferred to a furnace at a temperature of 1150°, until all the metal is completely melted. Lamination. At this point, a bead is obtained, which, when pushed through a rolling mill, turns into a thin strip. This activity is essential so that the separating acid (i.e. nitric acid) can act more effectively.
Boiling. The strip is then placed inside a flask, together with some chemicals that prevent the acid from overflowing, and everything is brought to a boil. The boiling phase must be repeated two or three times.
Annealing. At the end of the analysis phase, a gold cornet is obtained, which is transferred to a crucible, where it is annealed at a temperature of 800°/1000°.
Definition of the degree of purity. At the end of the annealing process, the pure gold cornet obtained from this stage of the process will be reweighed: a simple calculation of the ratio between the initial weight and the final weight, multiplied by one thousand, will give the degree of purity of the examined sample
Gold and Precious Metal Refining
There are many different ways to carry out the refining process, depending on the title of the alloy; for titles above 700°/°, the process is carried out by attack with aqua regia.
Melting and solidification. The rods are melted in a crucible and the metal obtained from the melting is poured into a pool of water, where the solidification process takes place in flakes,
Melting. The flakes are transferred in turn to a large tank and then dissolved with aqua regia (i.e. a mixture of hydrochloric acid and nitric acid in a 3:1 ratio). In a first phase, the melting takes place cold and then by heating; this phase lasts a total of about three hours.
Precipitation. Once the melting is complete, the liquid is allowed to cool, which is then filtered under vacuum and transferred to a tank, where the precipitation of the gold is carried out by adding bisulphite. At this stage, forced aspiration under a hood is carried out to facilitate the evacuation of sulphur dioxide, which develops during the gold chloride reduction operation.
Washing. The part of the liquid that settles at the bottom of the vessel, together with the precipitated gold, is vacuum filtered. The gold remaining on the filter undergoes several washes with hot water and then with cold water,
Melting and creation of the Bar. With a fineness of 999.9°/° it is melted down to produce an Bar. The pure gold recovered from this process can now be placed on the market and the cycle starts again.
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Via Pitagora, 11 - 20016, Pero (MI) ITALY MM1 - Molino Dorino underground station Tel: +39 02-8853 We receive by appointment only, from Monday to Friday from 09.00 to 16.00. We are closed on Saturdays and Sundays. Click HERE to book
Via Mazzini, 16 - 20123, Milan ITALY MM1 - MM3 undergound station Duomo Tel: +39 02-8853 We receive customers in the historic office and in the new shop, by appointment only, from Monday to Friday and from 09.00 to 16.00. We are closed on Saturdays and Sundays. Click HERE to book