Patent ID: 8114186

Claim:
A method for manufacturing of iron powders or micro-alloyed steel powders for powder metallurgical applications, comprising the following process steps: spray roasted iron oxides, originating from waste hydrochloric acid pickle liquors, exhibiting a specific area in excess of 2.0 m 2 /g and total residual chlorides over 400 ppm Cl − , are used as a raw material source, and are in a first process step, mixed with water yielding a slurry and at least one neutralization agent is added into the slurry, exhibiting pH-data in the order of 7.0±1.0 and yielding upon filtering the slurry, a filter cake, and in a second process step, the water soluble chloride contents of the iron oxides are reduced by washing the filter cake with water, resulting in the total residual chlorides being reduced to less than 350 ppm Cl − , and in a third process step, the washed filter cake is transformed by wet milling and the addition of surfactants and binders into a suspension and then is spray dried into green iron oxide micro-granules, exhibiting diameters in the order of over 95% in the range of 5 μm to 300 μm, and in a fourth process step, the iron oxide micro-granules are transformed into pre-sintered iron oxide micro-granules by a short thermal treatment for a few seconds under oxidizing conditions at temperatures between 900° C. and 1350° C., such that the pre-sintered iron oxide micro-granules exhibit lower specific surface area and at the same time the non-water soluble residual chloride content is further reduced, and in a fifth process step, the pre-sintered iron oxide micro-granules are reduced by gaseous reduction media, yielding reduced iron powders or micro-alloyed steel powders exhibiting a bulk density in excess of 2450 g/dm 3 , and the reduction product is cooled to room temperature employing a reducing or inert atmosphere.