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Feb. 1, 1966 EIU MUNEKATA ETAL 3,232,744 Recovery Reduction

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Feb. 1, 1966 EIU MUNEKATA ETAL 3,232,744 Recovery Reduction Feb. 1, 1966 EIU MUNEKATA ETAL 3,232,744 PROCESS FOR PRODUCING IRON OXIDE WITH A LOW SILICA CQNTENT Filed Nov. 5, 1962 grinding flotation flotafion oxidizing roasting roos fedora riffic acid fraafrne/f recovery reductionducti === - - - - - - iron powder INVENTOR. Eil kat al BY Attorney 3,232,744 United States Patent Office Patented Feb. 1, 1966 2. 3,232,744 as magnetite and hematite etc. is readily improved by PROCESS FOR PRODUCING RON OXE WITH flotation. However this is not so, for iron oxides and A LOW SCA CONTENT their gangue minerals ore originally hydrophilic and have Eiji Munekata and Kensuke Suehiro, Tokyo, Takuya a similar floating property, so that it is impossible to ex Ueda, Zushi-shi, and Taketora Sobayashi, Tokyo, 5 pect such a high degree of separation that satisfies the Japan, assignors to The Noguchi Institute, Tokyo, requirements in the applications of powder metallurgy. Japan, an incorporated body of Japan Pyrites ores are among the iron ores mined in prac Filed Nov. 5, 1962, Ser. No. 235,460 Claims priority, application Japan, Nov. 16, 1961, tically every place of the world and cinders obtained 36/.4572 by roasting said pyrites are also an iron oxide source 0 readily available, but non-ferrous metallic impurities such 5 Claims. (C. 75-2) as Copper, zinc, lead and the like, or impurities such as This invention relates to the production of silica- and Sulfur, phosphorus, arsenic and the like are included in silicate-free iron oxides of high purity from pyrites ores. the cinders. One method has been used to remove said In particular, this invention relates to the production impurities which comprises treating the cinders with dilute of iron oxides suitable for obtaining high-purity iron 5 acidic solution, for example, less than 5% solution of powders used in powder metallurgical application which mineral acid such as hydrochloric acid, sulfuric acid, are low in silica- and silicate-gangue from pyrites ores con nitric acid and the like, but has not been Satisfactory. taining predominantly said silica- and silicate-gangue as With regard to the separation of siliceous gangue, for impurities. example, even if flotation of the cinders is carried out, it More particularly, this invention relates to the produc 20 is difficult to effect a high-degree of Separation like the tion of iron oxides suitable for high-purity iron powders case of iron oxide ores. Even if magnetic separation is as raw materials of powder metallurgy, high grade steels, carried out after these cinders have been reduced, the alloys and the like. The product iron oxides contain a Separation of the gangue is insufficient for the same reason small amount of siliceous-gangue, non-ferrous metals such as in the case of magnetite. As there are no effective and as copper, zinc, lead, etc. and other non-metallic impuri 25 Suitable methods, though some of them are utilized in ties such as sulfur, phosphorus, arsenic, etc. Said pro the production of usual iron and Steel, the production of duction uses as raw ores pyrites containing such impurities pure iron powders suitable for the need of powder metal as above mentioned in addition to the gangue impurities lurgy has not been successful. in which silica and silicate are predominant. It is a principal object of this invention to carry out It is desirable that impurities are contained in as small 30 the fiotation of pyrites ores before roasting. It is already amounts as possible in reduced iron powders used in well known that pyrites more readily float due to its powder metallurgical applications. In particular, gangue hydrophobic property, as compared with hydrophilic minerals containing those siliceous impurities must be siliceous-gangue. A method for enriching pyrites ores removed as thoroughly as possible because such hard in by means of the flotation are now practised in many purities as silica- or silicate-minerals are especially detri mines. As will be mentioned herein, however, attempts mental to the strength of finished product and injure Were never made to produce iron oxides for pure iron moulding equipments. As reduced iron powders have powders applicable to powder metallurgy as raw ma been reduced from iron oxides in the solid state, im terials, which are produced from high-grade pyrites con purities, in particular siliceous impurities therein, cannot taining little siliceous-gangue, for example, less than 0.5% be removed as slag contrary to the case where usual 40 of Said siliceous-gangue as SiO2, most preferably less iron and steel are produced. Therefore high grade ores than 0.2%, said high-grade pyrites being made by the which contain as little silicate impurities as possible must fiotation of the pyrites. When the pyrites ores are be employed as raw iron ores. treated under appropriate conditions, it is possible to Many of commercially available reduced iron powders Separate the high-grade pyrites ores containing, for ex used in powder metallurgical application are of mag 45 ample, less than 0.5% of the gangue as SiO, most pre metite origin and a process is now prevalent which com ferably less than 0.2%, far more easily as compared prises pulverizing said magnetite and magnetically Sep with iron oxide ores. If the process is employed ac arating it from the non-magnetic silicate-gangue. Al cording to this invention which comprises starting with though magnetite is considered readily separable from the pyrites ores and roasting them as they are after the gangue by means of a magnetic separator since magnetism flotation, iron oxides of high purity never seen before of magnetite differs considerably from that of gangue in can be obtained which contain little siliceous impurities, cluded therein, in many cases imperfectly liberated parti for example, less than 0.5% of said impurities as SiO, cles are attracted by the magnet due to the megnetism most preferably less than 0.2%. These iron oxides can of magnetite contained therein. Therefore, it is difficult 55 be obtained more easily than by magnetic separation of to avoid gangue particles being mixed in with pure mag iron oxide ores or reduced iron powders without the netite particles, and also difficult to obtain ores which limitation on raw ores. Contrary to the conventonal meth are low in siliceous impurities, for example, those con od using iron oxide ores such as magnetite and the like taining at least less than 1% of said impurities as SiO2 wherein only limited raw ores may be employed, this by mere magnetic separation when usual ores are em invention makes it possible to utilize, as raw ores, very ployed. Since only those ores from particular places 60 cheap pyrites ores minted throughout the world. It are now used as raw materials for producing reduced iron should be said that the economical value of the present powders in powder metallurgical application, the mini invention is very high and the commercial significance mum cost of such products are restricted. Moreover in Surprisingly great. producing iron powders from magnetite concentrates by It is the second object of this invention to roast the direct reduction, it is impossible to fully remove such above-mentioned pyrites concentrates to produce iron impurities as sulfur, phosphorus and the like. Raw ores oxide and to refine it using nitric acid. In many cases which can be used are also limited in this respect. Be non-ferrous metallic impurities such as copper, zinc, lead cause Sweden is especially rich in good raw ores, iron and the like and other detrimental impurities such as powders for powder metallurgical purposes are produced 70 sulfur, phosphorus, arsenic and the like are included in in great quantities in this country. the pyrites ores in addition to siliceous impurities. In It may be thought that the quality of iron oxides such order to produce purer iron powders, it is necessary to 3,232,744 3. 4. remove these impurities and refine the pyrites. Since In the flotation of the first step of this invention, the many of these impurities show solubilities similar to that pyrites ores float easily as they differ considerably in a of pyrites in nitric acid, it is impossible to refine the foating property from hydrophilic gangue minerals as pyrites concentrates as they are by using nitric acid. illustrated above. Therefore, it is possible to separate Once the pyrites concentrates are converted into iron 5 the high-grade pyrites ores containing, for example, less oxides by roasting, a great difference occurs in Solu than 0.5% of gangue as SiO2, most preferably less than bility between the iron oxides and aforementioned in 0.2%, as compared with the iron oxide ores, provided purities provided that the concentration and the tem that flotation conditions are appropriately selected such perature are appropriately selected in this nitric acid as in the degree of grinding, the concentration of a mineral treatment, as described below. And then, it becomes pos O Solution, the class of concentration reagents, their amount sible to refine the iron oxide ores by nitric acid. That added or the like. is to say, the iron oxides are relatively insoluble in nitric Although finely divided ores are employed in the flota acid but non-ferrous metallic oxides such as copper, Zinc, tion, the degree of grinding is dependent upon the par lead and the like are dissolved in nitric acid with ease. ticular ore. In many cases, however, it is necessary to Sulfides of iron, copper, zinc, lead and the like, remain 5 grind the ores to pass at least a 100-mesh screen. ing in the ores due to incomplete oxidation in the roast It is effective to carry out the flotation in at least two ing, are also decomposed and dissolved in nitric acid Steps of roughing and cleaning.
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