The process of U.S. 3,825,651 For extracting au from crushed ore as a vapor having the composition auxcl6, where x is fe, al, or ga, and condensing the vapor to recover au, is improved with respect to more complete evolution of the vapor, by mixing activated carbon with the cl2, the source of fe, al, or ga, and the ore, to adsorb the vapor complex after heating to 200 deg.-500 Deg. C. The ore can be >200 mesh, and the cl2 can be diluted with air or inert gas, and should be provided in about the same weight as ore, at 5-60 ml/min for approximately 5-60 min. Usually 0.5-5 pct promoter by weight of ore is sufficient. After chlorinating the ore, the calcine is quenched, ground to <28 mesh, slurried to 5-50 pct solids, and mixed with 0.01- 5.0 Lb frother/ton for flotation to collect the au-laden carbon. The frother concentrate is cleaned conventionally and the au can be recovered from it by cyanidation, electrolysis, or fusion. The best au recovery was 93-94 pct at 400 deg.-500 Deg. C for 30-60 min; shorter periods or lower temperatures gave less recovery. An oxide ore containing no sulfide or fe gave 84 pct au recovery when pyrite was used as the promoter in this process, 66 pct when powdered fe was the promoter, and chlorine with no promoter gave 20 pct recovery.
U.S. Pat. 3,834,896; Sept. 10, 1974; Chem. Abstr. 82:P19,845u