US1127163A - Method of treating mill-scale. - Google Patents

Description

UNITED s 'rnrns PATENT our-ionrnnnnmcx M. menu, or unease ram-s. new roan, gssronon 'ro nnncrno METALLURGICAL comrmx, 0!." MAG or WEST VIRGINIA.

Ana mus, new Yong, A, qoaronarron METHOD 0! TREATING MILL-SCALE.

No Drawing.

Niagara and State of New York, have in- I vented certain new and useful Improvements in Methods of Treating Mill-Scale, of which the following is a specification.

In my prior Patents Numbers 1,081,566 and 1,081,570, patented December 16, 1913, I have described certain processes applicable to the treatment of ores, concentrates, or like products, of the iron-tungstate type, to

. obtain therefrom tungsten or its alloys in which the ratio of tungsten to phosphorus,

expressed as g is materially higher than in the unreduced material.

The present invention relates to the application of processes of this kind to the oxidized material known as high-speed millscale. This scale is produced in considerable quantities as a by-product in the manufacture of high-speed steel, and consists, essentially, of oxid compounds of iron and tungsten, usually with smaller proportions of chromium and vanadium and containing also considerable quantities of cobalt when derived from the so-called cobalt steels. The metals are present in the scale in the form of oxid, but are not, in all cases at least, in their highest state of oxidation.

The following is the composition ot a typical high-speed mill-scale Iron 57.66 per cent' Tungsten 12.25 Chromium 3.23 Vanadium 0.43 Manganese 0.47 Silicon, 0.75 Carbon 0.35

Phorphorus 0.015 to 0.030

By smelting this scale with silicon as a reducing agent, in an electric furnace and in accordance .with the methods disclosed in my prior patents, it may be reduced to an alloy having approximately the composition of the steel from which the scale was originally derived. For example, partial analyses of a mill-scale and the alloy obtained there- Spaciflcatto'n 01' Letters intent.

Amman m d, 4 x;; 8.1914. Serial a. $30.41;.

Patented Feb. 2, 1915.

from by known processes of silicon reduction, are as follows MilLacale. Reduced alloy. Tungsten 11.90 15.60 Qhromium 2.90 3.40 Vanadium 0.49, 0.43

The alloy so, obtained is utilizable as such, or, with appropriate additions, it is available for themanufacture of steels of modified composition. I have found, however, that such high-speed mill-scales usually contain a proportion of phosphoruswhich is distinctly objectionable. Moreover, the product of direct reduction of the scale is comparatively low in tungsten: this of course necessitates the use of a relatively large proportion of the allo in compounding a given steel, fromv whic it results that the phosphorus-content of the steel is not much less than that of the alloy. These dificulties are avoided by treating a millscale, before reduction, with an acid reagent which serves the double purpose of removing iron, and thereb concentrating the tungsten-content, an of removing phosphorus, and thereby increasing the ratio I have to nd that these mill-scales yield a large proportion of their iron, together with substantially all of their phosphorus, to acids, such as sulfuric acid, even in the cold. In other words, the very high temperature to which they have been subjected in the course of their production has not resulted, as might be expected, in converting the iron into such an insoluble condition as occurs when iron-tungstate ores are ignited or calcined. The process involving such acidtreatment of the mill-scale is claimed in my copending application Serial No. 830,417, filed concurrently herewith.

According to the present modification of the invention, the mill-scale is subjected to a reducing operation before removing the phosphorus and concentrating its tungstencontents. An illustrative example in accordance with the present invention is as follows :The scale is ground to pass an eight-mesh screen and is mixed with about the theoretical proportion of charcoal or other carbonaceous reducing-agent, calculated upon its contents of wads of iron and tungsten. Theproportion of charcoal used should be so restricted as to avoid substantial contamination of the reduced roduct by carbon, while efi'ecting as near y complete reduction of the iron and tungsten 'as may be practicable without such contaminainto a bath of sulfuric acid of 1.2 to 1.4 specific gravity and digested for some hours, preferably with agitation. Following this digestion, the residue is'washed to remove the soluble sulfate, dried, and smelted with a small proportion of silicon inthe electric furnace. Silicon is added in approximately the theoretical proportions required for the reduction of such oxids as may have remained unreduced as a result of the first treatment, avoiding such excess of silicon as would yield a reduced product undesirably high in silicon. Lime or other flux may be added in proportion to form with .the silica a suitable slag, as is well understood in this art.

According to this method, up to ninety per cent. of the totaliron-content may be extracted without entailing material losses of tungsten. The resulting alloys may contain up to sixty-five per cent. of tungsten or more according to the amount of iron removed-and are, for practical purposes, free from phosphorus.

I claim:--

1. The herein-described method of preparing tungsten or its alloys from highspeed mill-scale containing tungsten, whichconsists in subjecting the scale to a reducing-operation at a temperature below the melting-point of the reduced product, ex-

tracting a portion of the iron and thereby concentrating the tungsten in such reduced product, and fusing the concentrate in an electric furnace.

2. The herein-described method of preparing tungsten or its alloys from highspeed mill-scale containing tungstem-which consists in subjecting the scale to a reducing-operation at a temperature below the product and removing phosphorus therefrom, and fusing the concentrate in an electric'furnace in presence of a non-carbon reducing-agent.

Y 4. The herein-described method of preparing tungsten or its alloys from highspeed mill-scale containing tungsten, which consists in subjecting the scale to a reducing-operation at a temperature below the melting-point of the reduced product, concentrating the tungsten in such reduced product and removing phosphorus therefrom by an acid reagent, and fusing the concentrate in an electric furnace in presence of a non-carbon reducing-agent.

5. The herein-described method of preparing tungsten or its alloys from highspeed mill-scale containing tungsten, which consists in subjecting the scale to a reducing-operation at a temperature below the melting-point of the reduced product, concentrating the tungsten in such reduced product and removing phosphorus therefrom by an acid reagent, and fusing the resulting purified concentrate in an electric furnace in presence of silicon.

6. The method of preparing low-phosphorus tungsten or ferrotungsten from high-speed mill-scale, which consists in partially reducing said mill-scale, treating the reduced product to increase the ratio of tungsten to phosphorus, and thereafter completing the reduction.

In testimony whereof I aflix my signature in presence of two witnesses.

FREDERICK M. BECKET.

Witnesses:

J. A. HOLLADAY, G. C. FURNESS.