Misschien: scheidingssmeltmiddel
Liquation. The rich crust is transferred to a cast-iron kettle installed in a refractory-lined furnace. The kettle is first filled with lead, which is melted by burners firing at both the top and bottom of the furnace. Firing is then continued only in the top zone to maintain a temperature of 720�C. The bath is covered with an eutectic sodium chloride–calcium chloride flux to minimize oxidation of zinc. Borax-based fluxes may also be used as cover.
Blocks of rich crust are added periodically and allowed to melt. As melting takes place, the lead-rich phase sinks to the bottom and is withdrawn from the kettle by a syphon. The lighter silver–zinc phase rises and floats on the surface of the lead. After sufficient silver–zinc alloy has accumulated, it is tapped from the top section of the kettle. In this manner it is possible to achieve a 120:1 concentration of the silver in the crust which is passed on for retorting. The lead removed from the bottom of the kettle typically contains 0.5% silverand 2% zinc.
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