Abstract: A pyro-metallurgical process for producing at least one non-ferrous metal or a compound thereof, wherein said metal is selected from the group consisting of arsenic (As), antimony (Sb), lead (Pb), cadmium (Cd), mercury (Hg), silver (Ag), tin (Sn), nickel (Ni), and zinc (Zn), and wherein at least one raw material is fed into a rotary kiln, wherein said at least one raw material comprises at least said metal, and wherein said raw material is heated to produce a volatized material, in which the non-ferrous metal or compound thereof is produced from the volatized material, in which process a magnesium-based additive, is additionally fed in the rotary kiln in an amount of between 0.5 wt. % and 9.5 wt. % relative to the total weight of said raw materials, which magnesium-based additive is heated together with said raw material to produce at least the volatized material and a solid product, thereby counteracting ring formation in the rotary kiln.