IN cooperation with the Netherlands East Indies Government, the Bureau of Mines has developed the Caron process for treating manganese-silver ores, in connection with the Clevenger roasting furnace. Although there are exceptions, oxidized silver ores containing the higher oxides of manganese are generally refractory to hydrometallurgical methods of treatment. When these ores are of high enough grade they can be smelted ; indeed, some rather low-grade ores of this type have been smelted at a profit because of their fluxing value. In the past, when these ores could not be smelted, they either were not treated or were treated at low efficiency, generally by cyanidation.
The need for thorough investigation of the problem was therefore evident for some time before the writers began their research.
The investigation proved that there is a refractory compound of manganese and silver-probably a manganite-insoluble in cyanide solution and other common solvents for silver. Although this compound has not been isolated from natural ores, it has been made synthetically, and shows all the characteristics of the natural product.
Furthermore, the authors have shown definitely that heating in air a relatively small amount of a silver compound with a large excess of silica (in the proportions ordinarily occurring in a commercial silver ore) renders increasing percentages of the silver, depending on the temperature, insoluble in cyanide solution. Whether this is a physical or a chemical effect may be debatable, b'ut the evidence the writers can offer seems to favor the formation of a chemical compound, such as silver silicate.
The behavior of silver with silica has an important bearing on the problem.
The Caron process is based on the discovery that when oxidized ores containing a refractory compound of silver and manganese are heated in a reducing atmosphere-so as to reduce completely the higher oxides of manganese to manganous oxideand are cooled under conditions that will prevent reoxidation, * Communicated by the Director.