Use of Hydrogen in the Production of Bullion and Metal Powders

It is known that after completion of the chloride process in the refining of silver and gold, the purity of the metals is 998-999 for silver and 995-996 for gold. Metals of such purity do not meet the requirements of modern technology. To raise the purity level, sponge silver or gold is remelted into anodes for subsequent electrolytic refining. The electrolytic silver and gold are then remelted into bullion. Many refining plants obtain bullion of precious metals by using crucible-type induction furnaces in which the metals are melted in air under a layer of flux (sodium borate). The molten metals are poured into special measuring molds and the surface of the cast ingots is machined to a commercial finish. To improve the quality of the ingots, we have devised a method that includes melting the metals in hydrogen. To realize the method, the ingot molds we used were different sizes of specially designed cassettes made of graphite MPG-6.7. The required amount of silver or gold was charged into each cassette and the latter was placed in a quartz reactor and hermetically sealed. The melting operation was begun after hydrogen was injected into the reactor. The surface of the molten metals is rid of oxides in the presence of a strong reducing agent (hydrogen). The liquid metal is cooled to room temperature after melting has been completed, the reactor is emptied, and the cast ingots are extracted from the molds.