palmer: bornite as silver precipitant 351 



MINERALOGY. — Bornite as silver precipitant. ^ Chase Palmer, 

 Geological Survey. 



In an introductory chapter of their studies in silver enrich- 

 ment Palmer and Bastin- by quantitative experiments have 

 shown that chalcocite (CU2S) is decomposed completely by a 

 dilute solution of silver sulphate. As a result of this reaction 

 all the copper of the chalcocite enters the solution as cupric 

 sulphate, while free silver and silver sulphide in equivalent 

 amounts are deposited. Many years ago R. Schneider^ recorded 

 a similar observation on the conduct of cuprous sulphide (CU2S) 

 with dilute silver nitrate solution, but inasmuch as other obser- 

 vers have issued conflicting statements concerning the products 

 of the reaction, it seemed advisable to study the reaction anew 

 with silver sulphate solution. According to these recent experi- 

 ments the proportions of the substances appearing in the re- 

 action between chalcocite and silver sulphate solution may be 

 expressed by the abbreviated equation: 



CuoS + 2Ag2S04 = 2CUSO4 + 2Ag + AgoS. 



Anthon* had observed that by interaction with silver nitrate 

 solution pure cupric sulphide (CunSn) is changed completely to 

 silver sulphide and soluble cupric nitrate without deposition of 

 free silver and this observation has been repeatedly confirmed 

 by others. As a precipitant of silver ore, therefore, one gram of 

 pure covellite is capable of depositing 2.26 grams of silver in 

 the form of silver sulphide. On the other hand, one gram of 

 pure chalcocite is capable of precipitating 2.7 grams of silver, 

 one-half of which is combined with sulphur as silver sulphide 

 and the other half is free silver. 



Conspicuous among the more complex sulphides commonly 

 associated with native silver is bornite. The mineral contains 

 copper, sulphur and iron, but its chemical composition has 



1 Published by permission of the Director of the United States Geological 

 Survey. ' 



2 Palmer, Chase, and Bastin, Edson S., Metallic minei'als as precipitants of 

 silver and gold. Economic Geology, 8: 140-170. 1913. 



3 Pogg. Annalen der Physik, 152: 471. 1874. 

 ^Journal f. prak. Chemie, 10: 353. 1837. 



