Precious Metal Refining Process
The precious metal refining process is a critical step that forms the basis of modern industry and is becoming more efficient and environmentally friendly with continuously improving technologies. High-purity precious metals are particularly significant in various sectors, ranging from the jewelry industry to electronics. The most well-known precious metals are gold, silver, and platinum, but others such as palladium and rhodium also fall into this category.
Commercial Processes
Commercial processes for refining precious metals involve specialized techniques and technologies designed to purify raw or recycled materials containing precious metals. The refining of precious metals is a meticulous and complex process as precious metals are typically found in nature combined with other minerals and not in their pure form. The objective is to obtain metals with the highest possible purity by removing undesired components through a series of chemical and physical processes. Large-scale smelter-refinery plants form complex flowsheets based on copper, lead, and nickel metallurgy. Pyrometallurgy (smelting) is generally used for the initial steps, while hydrometallurgy (wet chemical processes) is used for the final separation and refining processes. The first step in ore processing involves conventional multistage crushing and ball milling followed by smelting.
Chlorination Process
Chlorination process is one of gold refining’s oldest and most widely used pyrometallurgical methods, in which chlorine gas is bubbled through molten gold. The base metals and silver are removed as chlorides, which either volatilize or form a molten slag on the surface of the melt.Operating this process requires significant technical skills and involves significant health and safety risks due to the use of chlorine gas. Additionally, expensive fume extraction and treatment facilities are necessary. As a result, this process is not suitable for small-scale refining.
Cyanide leaching
Cyanide is an inexpensive, yet highly toxic reagent that is effective in leaching gold from low-grade minerals. The crushed and ground ore is then mixed with a dilute solution of sodium cyanide (or potassium cyanide). It forms a water-soluble cyanoaurate compound. While cyanide leaching is an effective method for gold extraction, it poses environmental risks due to the toxicity of cyanide.
Aqua Regia Process
Aqua Regia Process is a commonly employed method for extracting and purifying precious metal from various sources, such as ores, electronic waste, and scrap jewelry. This process is commonly used by both jewellers and refineries on a small to medium scale and can produce gold with a purity of up to 99.99%. Gold and most other metals contained in the feed dissolve in aqua regia; however, silver forms an insoluble silver chloride precipitate under typical conditions used. The solubility of silver is greatly affected by temperature and chloride concentration. If the temperature is lowered or the chloride concentration is diluted, some silver will precipitate from the solution as AgCl. Silver is the most frequent source of contamination in refined gold, so dilution and cooling are used to reduce AgCl solubility before filtration. It is important to take additional care to maintain consistency in the process. The gold-free solution obtained can be used to recover platinum, palladium, and other PGMs in a downstream process. However, a two-stage reduction has a major drawback, which is the presence of recirculating gold inventory. The holding costs can be significant, depending on the plant size. Gold refining with aqua regia is an environmentally friendly solution. It combines sustainability and environmental awareness. To ensure a green refining process, the process emphasizes the correct use of chemicals and effective waste management.
As Proses Makina Co.
We are committed to environmental responsibility and therefore use the Aqua Regia Process. This method produces less chemical waste and is more efficient than other conventional refining methods, allowing customers to receive more product in less time. This helps us contribute to a sustainable future by minimizing our environmental impact while maintaining the highest level of customer satisfaction.
