The aqua regia refining process is used to refine gold alloys using a combination of acids and chemical products. The aqua regia solution consists of a mixture of hydrochloric acid HCL and nitric acid HNO3. The refining process can be broken down into several steps:
- Analysis of the gold to be refined
- Production of Au grains or thin strips needed for the refining process
- Refining process
- Separation and recovery of the AgCl produced in the refining process.
- Precipitation of the gold in solution using chemical products
- Filter and rinsing of the gold powder
- Analysis of the refined gold
- Melting of the Au into final required shape (ingots, grains etc)
There are certain limits to the aqua regia refining process:
Best suited for refining gold with an initial purity of at least 600/1000. Initial purities below this value will reduce the production capacity as well as increase process times.
Recommended maximum silver percentage: 10-12 %. Percentages above these values can reduce production capacity as well as increase process times.
The gold refining plants produced by Italimpianti Orafi can refine all gold alloys that are within the above stated parameters or thereabouts.
For the aqua regia refining method, the gold must be either melted into fine grains – this is normally done using a melting furnace (our FIM model) and a grain tank (our RPG model) – or very thin strips. Strips are best because they have a large surface area and dissolve completely when emerged in the aqua regia solution. Grains, due to their irregular shape and size, are more difficult to dissolve and some are often leftover in the reactor at the end of the process. On the other hand, they are very quick to produce compared to strips.
Waste products of the Aqua Regia refining method
Non-precious, heavy metals left over in the waste solutions can be treated and recovered using water treatment plants. These units recover metals by producing hydroxides that then have to be sent to specialised companies for treatment and disposal.
Chemical products needed for the Aqua Regia refining method
The reagents are:
- Nitric acid HNO3 at 36 Bè
- Hydrochloric HCl at 21 Bè
- Various chemical precipitation products
Results of the Aqua Regia refining method
The IAO aqua regia refining units can guarantee a minimum purity of 999.5. Experienced workers can achieve 999.8.
Description
- Refining capacity : 80 kg of grains per day per unit
- Purity obtainable with aqua regia tumbler: 999,5/1000
- The plant is made up of :
- Steel structure platform coated in anti-acid paint
- N.1 850 lt PPL cylindrical tumbler chamber (reactor). The chamber is fitted with a double-lock loading door and discharge valve. The rotation of the chamber is controlled by an inverter.
- Two containers 100 lts/tumbler in which the acids (nitric and hydrochloric) are stored prior to be sent to the tumbler chamber. These containers are positioned to the side of the tumblers.
- Glass condensors to condense the acid fumes during the refining cycle.
- N.1 filter trolley fitted with a diaphragm pump to filter and transfer the king water solutions. The diameter of the filter area is 800 mm.
- N.1 800 lts cementation tank fitted with stirrer and fume condensor
- Various PPL storage and decantation tanks 4000 lts
- Two acid storage containers each with a 2000 lt capacity (one for nitric acid, the other for hydrochloric acid) . Each container is placed inside a 3000 lt safety tank to be positioned outside the factory.
- Acid transfer process :
- Two diaphragm pumps will transfer the acids from the external storage tanks to the 100 lt PPL containers inside the refining dept.
- The workable volume of the tumbler is 300-400 lt
- Fixed speed tumbler rotation
Ex-Factory, Italy
Price: € 105,300.00
Packing: TBD
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