Dec 12, 2018· Nickel concentrates may be leached with sulfuric acid or ammonia, or they may be dried and smelted in flash and bath processes, as in the case with copper. Nickel requires higher smelting temperatures (in the range of 1350 °C) in order to produce an artificial nickel-iron sulfide known as matte, which contains 25 to 45 percent nickel.