Abstract: The invention concerns a means for supporting the material being treated in continuous-action heat treatment furnaces. The support means consists of a cooled roller (5), on the periphery of which at least two cooled rollers (7) with substantially smaller diameter have been placed. The roller (5) is placed outside the furnaces (13, 16) and/or between two consecutive furnaces. Supporting of the material (18) is carried out by the aid of one roller (7) at a time, the roller (7) rotating at the speed of moving of the material. By the aid of the drive (3) provided for the roller (5), the mutual positioning of the rollers (7) can be changed.

Abstract: The residual acid mixture containing metals which has been produced in the steel pickling process is regenerated to become new HF/HNO.sub.3 pickling acid by applying H.sub.2 SO.sub.4 addition and evaporation. The metal sulphate salt produced in evaporation is converted into scarcely soluble iron jarosite Na[Fe.sub.3 (SO.sub.4).sub.2 (OH).sub.6 ] and chrome and nickel hydroxide, the last mentioned metal hydroxide being obtained as a separately utilizable precipitate.The metal sulphate salt is separated from 60% H.sub.2 SO.sub.4 solution, wherein the main part of the salt is also crystallized. For promoting the crystallization, part of the salt is crystallized in a side line where 80% H.sub.2 SO.sub.4 concentration is used. The acid slurry produced is carried back to the crystallizing stage in the main line.