PRECIOUS METALS RECOVERED BY CYANIDE 



PROCESSES. 



BY CHARLES E. MUNROE. 



[Charlos Edward Munroo, head professor of chemistry George Washington university; 

 born Cambridge, Mass., May 24, 1849; educated in the public schools of that city 

 and at the Lawrence scientific school of Harvard university; assistant in chemistry 

 Harvard, 1871-74; professor of chemistry United States naval academy, 1874-86; 

 chemist United States naval torpedo station and war college, 1886-92; expert spe- 

 cial agent in charge of chemical industries in the United States census bureau since 

 1899 ; has been president of the American Association for the Advancement of Science 

 and of the American Chemical society. Author of over 100 monographs on chem- 

 istry and explosives.] 



The latest returns show that there are 109 estabhshments, 

 in 12 different states, using a cyanide process for the extraction 

 of the precious metals from tailings or ores. Of these estab- 

 hshments, 29 cyanide the ore or taihngs without other treat- 

 ment; 27 crush the ore previous to cyaniding; 5 concentrate 

 the ore; 20 combine amalgamation for coarse gold with, cyanid- 

 ing for the finely divided gold; 18 combine concentration 

 and amalgamation with cj^aniding; 6 combine smelting, and 

 in some instances amalgamation with cyaniding; and 4 com- 

 bine chlorination, with and mthout amalgamation, with 

 cyaniding. In one year these establishments treated 3,089,- 

 673 tons of ore and 199,689 tons of old tailings, or 3,289,362 

 tons in all, and produced 776,050 fine ounces of gold, valued 

 at $15,972,268, and 1,741,546 fine ounces of silver, valued at 

 $871,878; the products included also 15,000 pounds of copper, 

 valued at $1,670; 741,000 pounds of lead, valued at $12,494; 

 and 8,726 pounds of mercury (recovered from tailings), valued 

 at $5,620, so that the total value of all the products was 

 $16,863,930. 



The returns showed directly that of the total output 

 of precious metals 289,305 ounces of gold, valued at $5,947,- 

 888, and 560,872 ounces of silver, valued at $287,614, were 

 extracted from 1,156,643 tons of ore and tailings by means 

 of some cyanide process of recovery. It is estimated that 

 in those operations in which amalgamation, chlorination, 

 smelting, or several of these processes were combined with 



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