REFINING OF PRECIOUS METALS
We carry out refining process to recycle scrap gold bars, used gold jewellery as well as gold waste created from our manufacturing process. Our refining process is for gold and silver only. The refining process is depicted in the diagram below:
• Melting and granulation
Firstly, the refinable materials such as scrap gold bars or used gold jewellery are melted and granulated to provide a large surface area of the materials to react with solutions as part of the refining process.
The granulated materials will then go through a dissolution process which involves dissolving the granulated materials in a heated aqua regia solution (a mixture of nitric acid and hydrochloric acids). Gold and most other metals will dissolve in aqua regia.
• Refined gold
After the dissolution process, a solution is produced. The solution is then treated with a reducing agent to precipitate pure gold. The reducing agent that we use to precipitate the gold is iron sulfate. The precipitated gold is then filtered, washed and dried to produce high purity gold powder. The refined gold is then ready to be used.
• Refined silver
The resultant sludge from the precipitation of gold, and filtration, washing and drying process contains many materials as well as silver in the form of silver chloride. The sludge is then treated with nitric acid which reacts with the silver chloride to produce a solution containing silver. This solution is then filtered and the solution is collected in another container. Subsequently, by adding silver precipitant crystals to the solution, the silver-bearing solution will precipitate into silver. The refined silver is then washed with water, dried and ready to be used.