US1769605A - Process for making electrolytic iron - Google Patents

Description

R. D. PIKE PROCESS FOR MAKING ELECTROLYTIC IRON July 1, 1930.

Filed March l5, 1926 DNZOQQ M l) IMZMtIL.

INVENTOR. @0240/ nlvcDl KNEE Patented July i, 1930A UNITED STATES" PATENT OFFICE.

ROBERT D. PIKE, F PIEDMONT, CALIFORNIA. PRCESS FOR MAKING ELECTROLYTIC IRON Application led March 13, 1926. Serial No. 94,454.

My present invention relates to a process for making electrolytic iron from leach liquors in non-diaphragm cells, and includes l a leaching process whereby iron and/or cop- 6 per is dissolved by the action of ferrie iron on metallic iron and/or copper ores and the iron dissolved from the metallic ironand/or copper ores and that used for removing copper and-fother metals (if present) `from solu- 10 tion, is deposited electrolytically in a cell without diaphragms, but having insoluble anodes; such deposition of iron resulting in the regeneration of the liquor for further leaching operations.

Under conditions known hitherto, if iron were to be plated out of solutions in electrolytic cells with insoluble anodes, it has been necessary to employ diaphragms to separate the anolyte from the catholyte, if commercial current eiciencies were to be obtained.

This is because of the wellknown fact, based upon the principles of electro-chemistry, that ferric iron in contact with a cathode will be reduced to ferrous iron before metallic iron can be plated out. This is explained electrochemically by the following equations:

These equations show that deposition of iron cannot occur theoretically when Fem is in contact with the cathode.

I have found in practice that if the electrolytic iron cell with insoluble anodes be run at 70 centigrade or above, with ferrous chloride leach solutions containing about 12% Fe, even small percentages of ferrie iron as low as .1% in the cathoyte will seriously lower current eicienc hese are the conditions ysubstantially o taining in my former applications, Serial Numbers 58,012, 58,009?, and 58,010 (all filed September 23, 1925 and Serial Number 87,509, filed February 11, 1926, in all of which inventions I employ diaphragm cells and keep the concentration of Fe'f substantially,7 below .05%.

I have discovered that if I employ as the electrolyte a solution of ferrous chloride containing preferably about 12% iron in a nondiaphragm cell with an insoluble anode of ksulphide Yrelatively cold dilute solutions of ferric the type hereafter described, at abputroom temperature, and use a current density of preferably 7 amperes per square foot, and

operate the cell so that the eiiluent containsl a It is possible to cm loy widevariationin the concentration an composition of the electrolyte,.in the current density and temperature employed, without departing from -the scope of my invention. For example, in practice the electrolyte will tend to'assume a temperature of from 20 to 30 centigrade, or a littleabove actual room temperature, and this is satisfactory, although I have found it to be a general rule that the effect of Fe**+ in lowering current eiiciency becomes the more pronounced the higher the temperature; and on this account, if it is desirable, as is sometimes the case, to heat the leach solutions for promoting extraction of metals, the reduced liquors should be cooled by 'spraying or other suitable device before returning to the electrolytic iron cells.

f sponge iron or iron scrap is the raw material employed it is unnecessary to heat the leach solutions to promote efficient extraction; but ifv the raw material isfa sulphide mineral, such, for example, as'l'chalcocyte, bornite, or even chalcopyrite, thev leach solutions should be heated, and in the case of `the last-mentioned mineral, to boiling. Some other sul bide minerals, notably galena (lead l), are more easily decomposed by chloride. A preferable method for proceeding is to make sponge iron from copper and precious metal be'arlng cinders from pyrite roasters. The leaching of such iron 1s so conducted, as described hereafter, as to effect a complete separation of the iron from the more noble metals, i. e., copper, silver,`and gold; and these last-named are recoverable as valuable by-products. y

In the accompanying drawing,

The figure illustrates a flow sheet for production of electrolytic iron from sponge iron. With slight modifications, as described below, this flow sheet may be applied to the treatment of any of the materials above mentioned. t

Itwill be understood that there may be considerable variation from the described flow sheet; as, for example, in the composition of the leach solutions and the manner of their application, without departing from my invention, and also thaty diaphragm cells may be employed, if desired. y

Referring in detail to the drawing, return leach from the electrolytic tank house, containing about 12% total iron as chloride, of

which about .75% is ferrie iron, and at a temperature of 20 to 30 centi-grade, enters the agitator 1, where it meets the underflow from the thickener 2, as well as the clarified liquor from the filter 3. The discharge from agitator 1 goes tothickener 4, the underflow of which goes to filter 3. The cake from filter 3 is the exhausted tails free from iron, copper, and other metals which the original sponge iron may have contained.

The overflow from thickener 4 is pumped by pump 5 to agitator 6, where it meets the underflow fromthickener 7. Agitator 6 discharges into thickener 2. The overflow from thickener 2 goes to agitator 8, where it meets the fresh sponge iron, and the agitator 8 discharges into thickener 7. The overflow from thickener 7 is completely reduced copper-free electrolyte. The system described of thickeners 2, 4, 7 and agitators 1, 6, 8, is in effect a counter-current leach arrangement in which the fresh sponge iron completes reduction of the leach, and the fresh leach completes solution of the iron.

However, the sponge iron may contain copper and/or other metals whichare electro-negative to iron; and such metals may be completely dissolved in agitator l, and completely precipitated in agitator 8. They will therefore accumulate in the leaching system. To counteract this tendency, a portion of the overflow from thickener 4 is bled to agitator 9, where sufficient sponge iron is added to precipitate all of the copper and' other metals electro-negative to iron. Agitator 9 discharges into thickener 10, the underflow of which passes to filter 11, the cake of which is principally cement copper and may contain other metals. The clear liquor from lter 114 returns to agitator 9. The

overflow from thickener 10 j oins that from thickener 7.

The full flow of electrolyte is next treated in a tank 12 with H2S to precipitate traces of Zn,

and other relative electro-positive metals. The sulphide precipitate is removed in thickp ener 13 and filter 14. A discard may then be .replaced with fresh ferrous chloride.

The electrolyte next goes to supply tank 15, and thence through electrolytic tank cells 16. These are of the ty e hereinafter described. The anodes are pre erably of plate graphite, and the cathodes steel sheets'with oxidized surfaces to facilitate stripping of the electrolytic iron. The current density is preferably 7 amperes per square foot, and the cell voltage about 1.75. The regenerated leach goes `to tank 17 and pump 18 returns it to agitator 1.

In treating chalcocyte, or other sulphide mineral, the same How sheet is employed as in Fig. 1 except that the mineral, instead of sponge iron, is introduced into the agitator 8. With sulphide mineral there will be no appreciable accumulation of copper in the counter-current system, and all of the copper will be in solution in the overflow of thickener 7. This entire overflow will therefore pass through the copper cementation system 9, 10, 11, and this system will receive no liquor from any other point in the counter-current system. After precipitating the copper and/or other relatively noble metals, the

vliquor passes to the tank 12, and thence on spray pond, or other suitable device (not shown), should be employed, so as to deliver the electrolyte in a relatively cool condition to supply tank 15.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The process of making substantially copper-free electrolytic iron from copper-bearing metallic iron which consists in dissolving the later in a counter-current leaching apparatus with a leach liquor containing ferric iron; bleeding a portion of the liquor from a point in the counter-current system, treat- 0ing this bled portion with suiiicient metallic iron to completely lreduce the ferrie iron in solution and completely precipitate copper in solution, then passing the completely reduced and copper-free liquor discharged from this step, together with the reduced copper-free liquor from the counter-current leach, to electrolytic cells for the deposition of iron and the regeneration of the leach.

2. The process of making substantially copper-free electrolytic iron from copper-bearing metallic iron which consists in dissolving the latter in a counter-current'leaching appamus with c leach qumc conuomg erc xom9 bieding a. portion o the liquor from a, point in che counser-cux'rem sysem, treating 'this bled portion with suciem'. meaic oL. to completey reduce the fem'c iron in scutiom and completely precipitate copper in sointion, then passing the completely reuced ami copper-free liquor discharged from this stepi together with the reduced copper-free Equo? om the counter-current leach, to the top o non-diaphragm cells for she deposion o iron and the regeneration of the each am Withdrawing the regenerated souton from the bottom of the cells RBERT D. PIKE

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