| 摘要 |
<p>The process utilises the precipitation of silver sulphide as a heavy-metal salt which has low solubility in the alkaline medium. It is advantageous that a solution equilibrium is not established, enabling full precipitation. The slightly alkaline medium also means that no sulphur dioxide is formed and the thiosulphate is not decomposed, so that unnecessary contamination of the silver sulphide does not occur. By subsequent drying of the silver sulphide, the latter is prepared for reduction by means of air in an incineration furnace. At the temperature of about 650@C prevailing therein, conversion into elemental silver and sulphur dioxide then takes place. The silver isolated in this way is very pure and can be purified further by subsequent treatment with a reducing flame.</p> |
