The extraction by leaching of ni from laterite ore containing 6-7 pct mgo is improved if the high-mg ore is pelletized, dried, and heated 10-60 min at 350 deg-450 deg c in a CO atmosphere, no longer than necessary for reduction of iron oxide, and transferred to another hearth or furnace having a neutral atmosphere at 650 deg-750 deg c for a similar short time before leaching. The pyrophoric ore must be cooled in the nonoxidizing atmosphere below 200 deg c before extracting the ni and CO with ammoniacal (nh4)2so4 solution. Thus, 92-94 pct extraction of ni from ore containing >7 pct mgo was obtained by this process when the reduction temperature was 350 deg- 450 deg c, followed by the second heating in argon at 705 deg c, whereas the extraction after reduction at 500 deg-700 deg c could be as low as 60-65 pct.
U.S. Pat. 3,985,556; Oct. 12, 1976; Chem. Abstr. 86:20,036V