Abstract
In this paper, research on the effects of agitation rate for desilvering tin silver alloy residue by using pyrometallurgy was carried out. SnAg alloy residue with 92 wt.% tin and 3.56 wt.% silver was used in this study, and 99.999 wt.% zinc was added as metal solvent. Residues were melted to a temperature of 400 °C for enriching tin silver alloy. The obtained tin silver alloy was melted in a temperature range of 450 °C to 500 °C by adding zinc to evaluate zinc dissolution. The obtained tin silver zinc was agitated at different agitation rates for 20 min at a temperature of 480 °C, then cooled down while stirring to an eutectic point of tin zinc alloy (198.9 °C) to remove silver zinc dross. X-ray Fluorescent-1800 (XRF-1800) and Field Emission Scanning Electron Microscopy Energy Dispersive Spectroscopy (FE-SEM-EDS) analyses were performed in this research. Different factors including holding time, zinc dissolution, agitation time and agitation rate were evaluated. The results revealed that an agitation rate of 600 RPM, 25% Zn and 60 min at a temperature of 198.9 °C were efficient. Zinc silver was removed as dross every 20 min to get 92% silver separation efficiency, and the use of supergravity centrifuge is highly recommended to get best separation efficiency.
Highlights
Silver has wide applications in electronics, petroleum engineering, chemical and refining industries, jewelry production and alloying [1,2]
The results revealed that an agitation rate of 600 RPM, 25% Zn and 60 min at a temperature of 198.9 ◦ C were efficient
By measuring the dissolution of zinc at 480 ◦ C, and the results showed that the maximum efficient amount of zinc to be added was 25% of the amount of tin silver alloy used for the efficient amount of zinc to be added was 25% of the amount of tin silver alloy used for the first separation stage
Summary
Silver has wide applications in electronics, petroleum engineering, chemical and refining industries, jewelry production and alloying [1,2]. The major challenge is the increasing demand for precious metals and alloys while the natural metal resources are becoming exhausted [3]. It is mentioned that there has been a deficit in silver supply since 2006, while demand is increasing due to industrial expansion. In 2018, The demand silver in jewelry increased about 39 million ounces, industrial silver demand increased at about 50 million ounces, solar cell silver demand increased about 80 million ounces, and minting coins and bars increased more than 100 million ounces [4]. Tin lead alloys were known to be used as solder materials for packaging and interconnecting electronic components. Due to the proved toxicity of lead and its environmental impacts, different countries have taken measures to reduce the use and release of lead into the environment with strict regulations including waste of electrical and electronic equipment (WEEE) and restriction of the use of certain hazardous substances (RoHS) [5,6]
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