What are the impacts of different precious metal refining processes on the environment?

What are the impacts of different precious metal refining processes on the environment?
There are many types of precious metal refining processes, and different processes have different degrees of impact on the environment. The following will elaborate on the impact of different precious metal refining processes on the environment.

1. Impact of silver refining process on the environment
   The impact of aqua regia dissolution-reduction method to purify silver in gold on the environment:
   When the precious metal smelting plant refines and purifies gold by aqua regia dissolution-reduction, the high content of impurity silver in the gold powder obtained will affect the quality of subsequent gold ingots. In this process, the main environmental impact may come from the use of aqua regia. Aqua regia is highly corrosive and toxic. If it is not handled properly, it may cause pollution to the soil and water.
   In order to improve the precipitation efficiency and degree of silver chloride, it is necessary to examine the influencing factors such as hydrochloric acid concentration and temperature. In this process, silver-containing wastewater may be generated. If it is not effectively treated and discharged, it will cause harm to the environment. At the same time, in the process of determining the process conditions, multiple tests may be required, which consumes energy and resources and will also put a certain amount of pressure on the environment.
   Environmental impact of silver refining by methanesulfonic acid leaching – electrowinning:
   Based on methanesulfonic acid (MSA) as the base chemical, the refining method based on electrowinning after leaching silver is designed, which has the characteristics of less ecotoxicity compared with the traditional silver nitrate-based electrorefining process (Moebius electrolysis).
   In this process, hydrogen peroxide is used as an oxidant to carry out stirring leaching experiments on silver particles containing about 94% silver. The experiment showed that the leaching rate of silver can exceed 90% under the conditions of elevated temperature (65°C or 80°C), solid concentration of 500g/L and stoichiometric ratio of H₂O₂:Ag = 3:1. At the same time, increasing the solid concentration and temperature can also improve the selectivity of leaching the impurity palladium (Pd), reducing the potential impact of impurities on the environment.
2. Impact of gold and silver co-production process on the environment
   Life cycle assessment of gold and silver co-production process:
   Gold and silver are extracted through the gold-silver co-production process or the gold-silver-lead-zinc-copper co-production process. A study conducted a life cycle assessment (LCA) on these two gold and silver refining processes, using SimaPro software version 8.5, the International Life Cycle Reference Data (ILCD) method and the cumulative energy demand method (CED).
   The assessment results show that among the gold-silver co-production process and the gold-silver-lead-zinc-copper co-production process, refining through the gold-silver co-production process has a greater impact on the environment. In addition, the refining of gold has a greater impact on the environment than the refining of silver. Among the main impact categories, the most critical is human toxicity (cancer and non-cancer effects). The results of the cumulative energy demand method show that the consumption of fossil fuels in the precious metal refining process is greater than all other sources of energy demand.
3. Impact of the process of recovering precious metals from copper anode mud on the environment
   The impact of NaOH roasting-water leaching-cooperative acid leaching process on the environment:
   The process of NaOH roasting-water leaching-cooperative acid leaching is proposed to remove base metals from waste copper refining anode mud and enrich precious metals at the same time. Under the optimal process conditions, the process can effectively remove base metals such as copper, nickel, antimony, lead, tin, arsenic and sulfur, while the retention rate of rare precious metals silver, gold and palladium is high.
   The environmental advantage of this process is that by optimizing the process parameters, the use of chemical reagents is reduced and the pollution to the environment is reduced. At the same time, the valuable metals in the leachate are effectively recovered, the utilization rate of resources is improved, and the discharge of waste is reduced.
   The impact of nitric acid-citric acid co-leaching process on the environment:
   In the process of recovering silver, palladium and gold from the precious metal enriched slag of waste copper refining anode mud, nitric acid-citric acid is used to co-leach silver and palladium, sodium chloride is used to precipitate silver, and glucose is used to reduce it to obtain high-purity silver powder.
   In this process, the H⁺ released by the continuous ionization of citric acid greatly enhances the leaching power of the system, and the complexation of citric acid radicals promotes the leaching of silver and palladium. This process is relatively green and environmentally friendly, reducing the negative impact on the environment. In addition, the nickel in the gold leaching slag is fully enriched and can be used as an ideal raw material for smelting nickel, realizing the comprehensive utilization of resources.

IV. Impact of vacuum gasification separation technology on the environment
Impact of vacuum gasification separation technology of rare and precious metal multi-alloys on the environment:
The vacuum gasification separation technology and equipment of rare and precious metal multi-alloys have been invented, and a new green, efficient and short-process production technology of rare and precious metals with “high-temperature smelting capture-solution electrolytic enrichment-vacuum gasification separation-cascade refining” as the core has been constructed.
This technology has broken through the problem of efficient separation of “heavy metals and precious metals”, “dispersed metals and precious metals”, and “precious metals and precious metals”, and extracted precious metals such as gold, silver, platinum, palladium, and selenium with a purity of 99.99% from raw materials with a content of only one millionth. Compared with the traditional cyanidation method for extracting precious metals, this technology avoids the production of highly toxic substances such as cyanide-containing waste residues and waste liquids, and is more environmentally friendly.
In summary, different precious metal refining processes have different impacts on the environment. When choosing a precious metal refining process, its impact on the environment should be fully considered, and a greener, more environmentally friendly and efficient process should be selected to achieve sustainable development of the precious metal refining industry.