Abstract
Very often, the production of silver causes devastating environmental issues, because of the use of toxic reagents like cyanide and mercury. Due to severe environmental damage caused by humans in the last decades, the social awareness regarding the sustainable production processes is on the rise. Terms like “sustainable” and “green” in product descriptions are becoming more and more popular and producers are forced to satisfy the rising environmental awareness of their customers. Within this work, an alternative environmental sound silver recovery process was developed for a vein type silver ore from Mina Porka, Bolivia. A foregoing characterization of the input material reveals its mineral composition. In the following mineral processing, around 92.9% silver was concentrated by separating 59.5 wt. % of non-silver minerals. Nitric acid leaching of the generated concentrate enabled a silver recovery of up to 98%. The dissolved silver was then separated via copper cementation to generate a metallic silver product of >99% purity. Summarizing all process steps, a silver yield of 87% was achieved in lab scale. A final upscaling trial was conducted to prove the process’ robustness. Within this trial, almost 4 kg of metallic silver with a purity of higher than 99.5 wt. % was produced.
Highlights
Silver usually occurs in lead, zinc and copper ores due to its chalcophile properties, and it is the most common by-element in primary gold ores
The third point represents the cumulative results of the non-magnetic product of the first cleaning step, the loss increased to 27% and in the seventh step the loss increased to 53% in total
Represents the feed, the second data point shows the cumulative results for conductor and semiconductor combined to product and the third point represents the conductor as product
Summary
Silver usually occurs in lead, zinc and copper ores due to its chalcophile properties, and it is the most common by-element in primary gold ores. Because of these characteristics, the bulk of produced silver (i.e., 70%) originates from the production of above mentioned matrix metals. Zinc and copper ores are processed in pyrometallurgical routes and generate high amounts of sulphur dioxide. Arising process residues often contain arsenic and lead. The most important gold recovery processes are based on leaching with cyanide or thiosulfate, and using amalgamation. The cyanide process consists of a leaching step and separation via precipitation. The amalgamation process consists of the dissolution in mercury. The generated mixture is characterized by low melting and boiling temperatures, so it is heated to separate the mercury via evaporization [1,2,3]
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