Processes for Producing Synthetic Pyrite

Abstract

Process of making high purity, synthetic FeS 2 , and an electrochemical battery employing such synthetic FeS 2 in the positive electrode. Synthetic FeS 2 may be prepared by a sulfidation process comprising reacting ferric oxide, hydrogen sulfide, and elemental sulfur at a temperature above the melting point of element sulfur. Synthetic FeS 2 may also be produced by a milling process that comprises (i) milling iron powder and sulfur powder in the presence of a milling media and a processing agent to provide a homogenous powder mixture, and (ii) treating the powder mixture to form FeS 2 . In the milling process, the powder mixture may be treated to form FeS 2 by heating the powder mixture or subjecting the powder mixture to a subsequent milling operation.

1 . A method for forming FeS 2  comprising:
 intimately mixing iron powder and sulfur powder in the presence of a process control agent and a milling media to form a substantially homogeneous powder mixture, and   annealing the powder mixture for a sufficient period of time to form FeS 2 .   
     
     
         2 . The method according to  claim 1 , wherein annealing the powder mixture comprises heating the powder mixture at a temperature of at least about 400° C. to a temperature below about 740° C. 
     
     
         3 . The method according to  claim 1 , wherein annealing the powder mixture comprises heating the powder mixture at a temperature of at least about 450° C. to a temperature below about 500° C. 
     
     
         4 . The method according to  claim 1 , wherein annealing the powder mixture comprises raising the temperature at a rate of about 1 to about 3 degrees per minute until the desired annealing temperature is reached and holding the temperature at the desired annealing temperature. 
     
     
         5 . The method according to  claim 1 , wherein the annealing temperature is achieved by raising the temperature at a rate of about 1 to about 3 degrees per minute through the melting point of sulfur, and subsequently raising the temperature to about 450° C. at a rate greater than about 3 degrees per minute. 
     
     
         6 . The method according to  claim 1 , wherein the process control agent comprises a hydrocarbon and is substantially free of an oxygen moiety. 
     
     
         7 . The method according to  claim 6 , wherein the process control agent comprises pentane, heptane, hexane, octane, nonane, decane, or a combination of two or more thereof. 
     
     
         8 . The method according to  claim 1 , wherein the amount of process control agent initially charged to the system is from about 5 to about 12 percent by weight of the total weight of iron powder, sulfur powder, and milling media. 
     
     
         9 . The method according to  claim 1 , wherein the iron powder and sulfur powder are provided in a 1:2 molar ratio of iron to sulfur. 
     
     
         10 . The method according to  claim 1 , wherein the milling media is chosen from a steel media, ceramic media, a glass media, a zirconia media, a tungsten/cobalt media, or mixtures of two or more thereof. 
     
     
         11 . The method according to  claim 1 , wherein the milling media comprises a steel media. 
     
     
         12 . The method according to  claim 11 , wherein the sulfur powder is provided in an amount in excess of the stoichiometric amount required for forming FeS 2 . 
     
     
         13 . The method according to  claim 1 , wherein the weight ratio of iron powder and sulfur powder to milling media is in the range of from about 1:4 to about 1:10. 
     
     
         14 . The method according to  claim 1 , further comprising milling a dopant with the iron powder and the sulfur powder. 
     
     
         15 . The method according to  claim 14 , wherein the dopant comprises a conductive material chosen from at least one metal, graphite, carbon black, or a combination of two or more thereof. 
     
     
         16 . The method according to  claim 1 , wherein the FeS 2  comprises carbon entrained from the process control agent. 
     
     
         17 . The method according to  claim 16 , wherein the FeS 2  comprises about 1% by weight or less of carbon. 
     
     
         18 . The method according to  claim 16 , wherein the FeS 2  comprises about 0.15% by weight or less of carbon. 
     
     
         19 . Synthetic FeS 2  formed by the method according to  claim 1 . 
     
     
         20 . A method for forming FeS 2  comprising:
 performing a first milling operation comprising intimately mixing iron powder and sulfur powder in the presence of a process control agent and a milling media t form a substantially homogeneous powder mixture;   removing the process control agent; and   performing a second milling operation comprising milling the homogeneous powder mixture for a sufficient period of time to form FeS 2 .   
     
     
         21 . Synthetic FeS 2  formed by the method according to  claim 20 .