According to the US Geological Survey, the world's known silver reserves at the end of 2020 are 500,000 tons, silver production in 2019 was 26,000 tons, and in 2020 - 25,000 tons. If the same growth rate continues in the future, world silver reserves may be depleted within 15 years.
In 2020, silver was used in electrical engineering and electronics - 28%; jewelry and silver items - 26%; coins and medals - 19%; photography - 3%; and others - 24%.
Taking into account the fact that the development of the electronic industry also increases the consumption of silver, as electronic products containing up to 28% of all produced silver fail, it becomes extremely important to return it to the production cycle through processing.
For the extraction of metals from electronic scrap, pyrometallurgical and hydrometallurgical methods are used in parallel with preliminary machining. The main approaches in pyrometallurgical processing consist in the fact that parts of electronic devices containing silver and other valuable components, such as electronic boards, are pre-shredded. Since the boards consist of a non-metallic part and metal components, after grinding, metals from non-metals are separated using physical methods. Most of the metals are copper, tin, lead, zinc and other base metals. Therefore, in order to separate precious metals such as silver from them, in the first stage, the resulting metal concentrate is melted. Noble metals remain in the slags obtained during this process. The slags are then subjected to leaching and electrolysis. Hydrometallurgical methods have advantages over pyrometallurgical ones. The main reason for this is a decrease in the emission of toxic gases and dust, which are formed mainly in pyrometallurgical processes. In addition, hydrometallurgical methods are more accurate, predictable and easy to control. One of the types of electronic scrap, the number of which is growing rapidly, are various gadgets, computers, and smartphones. These types of electronic waste are especially valuable due to the high content of precious metals found on printed circuit boards and electronic components (gold, silver, platinum, etc.). There are hydrometallurgical methods for recycling silver-containing electronic waste using nitric acid as a reagent. Other acids are not used for this, since silver occupies one of the last places in the row of metal activity. In one word, silver can be called an inert metal with respect to its reactive chemical properties.
Silver is found in some circuit boards in the form of silver plated copper contacts. Therefore, the removal of silver from copper contacts is one of the stages in the processing of printed circuit boards. Silver is not affected by hydrochloric acid. Despite this, this noble metal has good solubility in oxygenated nitric acid.
Considering all the above properties of silver, when dissolving the solder (tin-lead alloy), nitric acid is used with an extraction time of 2 hours with heating (temperature 60 ° C). At the same time, a certain amount of copper (0.02-0.07 g / l) can be found in the solution. Then, the separated silver-plated contacts were thoroughly washed with distilled water and sent for further processing to remove silver from them. To extract silver, nitric acid was used, and with its help silver contacts were dissolved, reducing it to silver chloride, that is, as a result of the precipitation of silver with hydrochloric acid, AgCl precipitates, after which the precipitate is filtered from the solution, and silver chloride was dissolved in an aqueous solution of ammonia ... At the end of the experiment, silver was precipitated by carburizing copper (a copper radiator was used to cool the laptop).
Thus, in the course of the analysis, it was established that the processing of electronic waste for the purpose of extracting silver is one of the promising directions in increasing the material base of silver production. At the same time, hydrometallurgical methods using an aqueous solution of nitric acid are most effective from the point of view of the completeness of the extraction of silver and the environmental friendliness of the process.
|Position of speaker||doctoral student|
|Publication||Impact Factor journals|
|Affiliation of speaker||D. Serikbayev East Kazakhstan Technical University|