US2076909A - Electrolytic iron manufacture - Google Patents

Description

rlllllllllL CELL ahpwto'cs I Ml Her C1 27 6. Erik anJ B yw i B. MILLER ET AL ELECTROLYTIC IRON MANUFACTURE Filed Sept. 21, 1931 April 13', 1937.

w v fi L Lrllii 23F llllll Ill" w g 2 ,Lu: 2 ".5 f K .1. UHHHI U Patented ear. it, rest ELECTROLYTIC IR'ON MANWA f Delaware Application September 21, 1931', Serial No. stress iscleims.

This invention relates to the manufacture of electrolytic iron, particularly in the form of pipes or tubes.

The production of electrolytic iron has been'a subject or investigation for many years,,but up to the present time no commercial process has been sumciently successful to establish and maintain itself as an industry. In the few processes which have been tried on any substantial scale,

the high consumption oii electrical energy, the low I the use of highly concentrated or dilutesolutions.

by changes in temperature of the electrolyte, by the use of oxidizing agents and by variously modifying other steps and factors involved in the process. Such changes while apparently improving theprocess in some respects have not materially aided in reducing. the cost of production.

The primary object of the present invention is therefore to overcome the difficulties previously encountered and produce electrolytic iron tubes or other forms by a profitable commercial operation.

A further object of the present invention is to provide a commercial process for the manufacture of electrolytic iron tubes or sheets, by which a consistent smooth deposit of iron may be obtained in an economical manner.

A further object of the invention is the production of electrolytic iron sheets or tubes having a thickness suitable for present and future commerlcal uses. tubes or sheets made by previously triedprocesses is only about 0.2 inch, while usually they were only 0.1 inch in thickness. Tubes of such thickness would not fulfill the requirements of modern boiler or oil still practice, or be suitable for high pressure gas and oil pipe lines. By the process of the present invention heavy walled tubes of any desired thickness may be made.

A further object of the invention is to provide a process'whereby ores may be exploited where their content of phosphorus or of sulfur or both makes it impractical to use them in present ferrous metal production processes. Experiments have shown that an anode having a relatively high content of phosphorus orsulfur, or both, has no efiect on the cell voltage, and that such an anode gives a cathode deposit well within the commercial limits for these substances.

The greatest known thickness for A still further object oi! the invention is to provide a process for making electrolytic iron in which various important factors are so controlled that iron tubes may be produced on a commercial scale at a cost comparable with that for producing steel tubes.

Another object of the invention is'the provision of a cell for the electro-deposition of iron which includes a specially controlled acid electrolyte and an anode having special properties.

With these and other objects in view the process of the present invention for the manufacture of electrolytic iron tubes or sheets comprises one in'which the anode composition, the electrolyte composition, temperature and acidity, the circulation of the electrolyte, the spacing of the electrodes and other factors are accurately controlled.

Further objects and advantages of the process will be apparent to those skilled in the art from the follewing detailed description taken in con.- nection with the accompanying drawing, in

which:---

Fig. l is a not showing of apmratus suitable for carrying out the process of the inventiom' Fig. 2 is alongitudinal view partly in vertical section of one of the cells shown in Fig. 1;

Fig. 3 is a cross-section taken on the line 3-3 of Fig. 2, and.

Fig. 4 is a cross-section of the cell shown in Fig. 2 taken on the line t-t.

Referring to Fig. 1 of the drawing, the general features of the process will be described in connection with the elements of the apparatus shown. In accordance with the present invention the iron to be deposited electrolytically as tubes or sheets, is deposited from an acid solution of ferrous chloride also containing sodium chloride solution, hydrochloric acid and sodium fluoride are introduced into a sump 2, from which the solution mixture is withdrawn through a pipe 6 and passedby a pump 8, pipe l0 and valved pipes it into a plurality of heating and storage tanks it, it and it. (Any suitable numbermay be used.) In these tanks the solution is heated to a suitable temperature by means ofdirect steam introduced from a steam main 20 through submerged tubes 22 mounted in each tank. The solution in tanks it, it and it may also beheated electrically .or by steam coils 2t which may be connected through valved pipes with the steam main 20. They storage tanks are also used as settling chambers for the removal of any suspended solid matter which may be presfluoride. In starting the process the ferrous eat in the electrolyte. Such deposits as maysettie out in the tanks are withdrawn through valved drain pipes 26.

In carryingout the process electrolyte is usu- 5 ally supplied to only two (or less than all) of the tanks at any one time, and the heated electrolyte is continuously withdrawn from these tanks through valved discharge lines 28 and conducted by means of conduit 30 to a series of cells 32, 34, etc. The electrolyte is introduced into each cell from the line 30 through a valved connection 36. While electrolyte is continuously introduced into each cell it is also continuously withdrawn therefrom through drain pipes 38 into a pipe 40 which leads to the sump 2. During the operation of the process the electrolyte is circulated at'a very rapid rate through the cells and back to the heating tanks in order to prevent any sediment settling out in the cells and to maintain the temperature and composition of the electrolyte in the cells substantially constant.

Any convenient number of cells may be used in connection with the lines and 40, only two being shown in Fig. 1 for purpose of illustration.

A more detailed showing of the cells 32, 34, etc.,.is given in Fig. 2 to Fig. 4, from which it will be seen that the electrolyte is introduced at the bottom and near the middle of each cell and withdrawn from both ends thereof. comprises an anode composed of a pair of preferably semicylindrical cast iron pieces 42 suitably supported and insulated from the remainder of r the cell as shown in the drawing. Within these semicylindrical anode elements is mounted a rotatable cathode 44, supported by blocks 45 outside the cell casing proper. The cathode may be rotated at any suitable speed by means of a motor 48.

The cell casing is divided into at least three compartments by means of partitions 50, through which the cathode extends. The cathode may be provided with deflector rings 52 adapted to prevent electrolyte which flows along the cathode through the partitions 50, from flowing outside the cell casing. The end compartments outside partitions serve as collecting basis for the electrolyte, which is discharged through pipes 38. As shown in Fig. 3 the partitions 50 may be provided with overflow notches 54 to accommodate electrolyte in excess of that which flows through the relatively small space between the cathode 44 and the partitions 50. (Due to the relatively large amount of electrolyte circulated through the cells there may be a greater amount introduced than would flow through the space around the cathode.)

Electricity may beconducted to the anodes in any suitable manner, for example, by connections made to the anode supports as indicated in the drawing and from any suitable source not shown. Likewise current may be conducted to the cathode through, brushes 56 or by any other suitable means.

In order to improve the iron deposit on the cathode the deposit is-wiped during the rotation Each cell ously tried processes was largely due to the necessary use of high cell voltage and relatively low current density. One process for example used a voltage of 5 in order to obtain a current density of 60 amps. per square foot. In this connection it has been discovered that an ironanode substantially free from carbon, silicon and manganese gives a much lower cell voltage than other iron. Furthermore, the presence of sulfur'and phosphorus in the iron has no adverse eflect'on the cell. The iron for the process therefore may contain such quantities of sulfur and phosphorus as to be entirely unsuited for the manufacture of steel.

In preparing the anode pieces for the cells, a blast furnace iron which may be high in phosphorus, is subjected to a modified Bessemer treatment in that the iron is thoroughly blown with air to remove any carbon, silicon and manganese present. Then instead of recarburizing the iron as in the usual Bessemer process the iron is drawn at the end of the air blow and cast into anode pieces in substantially the form shown in Fig. 4. The cathode may comprise an ordinary steel tube having suitable mounting flanges substantially as shown in Fig. 2.

In starting up the apparatus a substantially clean solution of the desired composition is made up preferably in the sump 2 and then pumped into tanks l4, l6 and I8. The preferred solution I grams per liter of sodium fluoride which prob- The solution is made ably acts as a butler. acid by the addition of hydrochloric, hydrofluoric or other acid until the solution has a pH value of from about 4 to 6, for example 5. The pH value of the electrolyte may be readily determined as follows: Take a 10 c. 0. sample, dilute it with 40 c. c. of water and filter. To 10 c. c. of the filtrate add three drops of methyl orange; to a second 10 c. 0. add 3 drops of methyl red. The methyl orange-tinted solution should be yellow, and the methyl red-tinted solution should be red to show a pH of about 5. This simple test is based on the fact that the neutral point of methyl orange is 4.2, while that for methyl red is 5.8. The dilution of the sample has substantially no effect on its pH because the solution is well buffered.

The use of a ferrous iron electrolyte of the particular concentration range referred to is preferred because the experimental work on this process has demonstrated that such a. concentration range gives alower cell resistance than either a more dilute or a more concentrated solution. M

After the electrolyte has been made up and all tanks (l4, l6 and I8) filled, the electrolyte in tanks l4 and I6 is heated to a temperature of from 65 to 106 C. (preferably to 0.). Circulation of the electrolyte is then started from tanks l4 and I6 through lines 28 and 30 to cells 32, 34 etc., as previously referred to; the cells being cut into the circuit one at a time. During this operation (and before if desired to check its properties) a portion of the electrolyte is bypassed through a valved pipe 62 into a control box (or room) 64 then into sump 2 through a pipe 68. The temperature acidity and concentration of the electrolyte passing. through the control box 64 may be determined by well-known instruments or tests, the results of which may be used as a basis for any necessary additions of acid or of the salts referred to, or. for the correction of any other property of thesolution. Changes in temperature, concentration, gravity and acidity "may be adjusted automatically from the control box by the use of well-known devices for this purpose. While satisfactory iron deposits may be obtained by maintaining the temperature of the electrolyte in the range of from 65 to 106 C. it has been found that at temperatures of from 90 to 95 C. the voltage is lower for a given current density than that required for the same currentdensity at lower temperature. Atthe preferred temperature range (90 to 95 C.) the loss from evaporation of the solution is much less than at higher temperatures.

The electrolyte is circulated at a relatively high rate from thetanks through the cells for the purpose of maintaining the temperature and to keep the electrolyte in a high state of agitation in the cells. The rotation of the cathode is maintained at a'peripheral speed of about 100 meters per minute. This rotation also serves to agitate the electrolyte and to assure a substantially con- I stant supply of fresh hot electrolyte in the space between the cathode nd anode. The anode pieces 42 are spaced sot at all parts of the-cathode are equally distant therefrom, and so that the space between the cathode and anode pieces is as short as possible. With the method of control used in accordance with the present invention it is possible to use a. spacing between the electrodes as small as one half inch or less. The smaller the spacing the lower the resistance in the electrolyte and the lower the cell voltage becomes. As the anode material is removed by electrolysis the thickness of the iron deposited on the cathode increases, but if desired any necessary adjustment in the spacing between the electrodes may be made during a run by moving the i0 anode pieces closer to or away from the cathode.

Under the conditions given above it has been found possible to maintain a current density of 100 amps. 'or higher per square foot and at the same time not have a. cell voltage greater than one. The importance of this relationship is apparent when it is realized. that the higher the current density the-more rapid therate of iron deposition, and the lower the voltage the more economical the process. In one specific run under substantially the conditions-herein described the cell voltage-was 0.84.

. As the operation of the process proceeds the cells 32, it, etc., may be alternately cut out of the system, the cathode removed and the deposited iron stripped therefrom in any suitable manner. For example the deposited iron maybe removed by. heating and rolling, a method com monly referred to in the art. It will be seen therefore with a number of cells connected to so the lines 30' and Ml that cells will be constantly cut in and out of the circuit.

After about eight hours operation with tanks it and it, tank is which is filled with electrolyte will be heated and cut intothe system, while tank it will be out out of system and the electrolyte therein allowed to settle. After the electrolyte in tank it has been allowed to stand and settle for a suitable period of time any sludge settled out therein may be withdrawn through the valved pipefifi to any suitable storage. The relatively clear stratifled solution may be drawn ofi and conducted into the circuit or other storage if the tank needs cleaning. After the tank It has been cleaned, it is then ready to he refilled, 75 heated and used in place oitank it. Instead of using the settling it, it and i8 other suitable means may be employed for heating the electrolyte and a filter may be used for removing any suspended material.

The salt (sodium fluoride) used in connection with the process of the present invention is very eifective for maintaining the proper pH range.

even though relatively large amounts oi acid are added at a time. If sodium fluoride is not available other fluorides soluble in the electrolyte may be used, for example potassium fluoride or hydrofluoric acid. g I It is the object of the present invention to operate the process under such conditions that the electrolyte will be protected as far as possible from oxidation, and to avoid the presence of organic impurities (or organic addition agents) in presence of carbon, phosphorus or sulfur.

Having described the invention in its preferred 1 form what is claimed as new is:

1. In the process of depositing iron electrolytically on a rotary cathode substantially surrounded by an iron anode submerged in a ferrous chloride electrolyte containing sodium fluoride,

the improvement which comprises mechanically rubbing the cathode as it rotates, supplying elecor about 10b amperes per square ioot'oi" cathode surface at a voltage of about one, maintain 'ing the concentration of ferrous chloride in the electrolyte at from 350 to too grams per liter oi ferrous chloride tetdrate and that of sodium fluoride at from 10 to 20 grams per liter,

eating the electrolyte to a temperature or from 65 to 166 (2., and mainng the pHvalue of the electrolyte between about 4 and 6.

2. The process'deflned in claim 1 in which the cathode is rotated at a, peripheral speed of about 100 meters per minute.

3. In the process of manufacturing electrolytic iron tubes in which iron is deposited on -a. rotating cathode substantially surrounded by a cast iron anode substantially free of carbon submerged in a ferrous chloride electrolyte contained in a cell chamber, the improvement which comprises continuously circulating the electrolyte from said chamber through a heating zone in which the electrolyte is heated to a temperature of from to C. and then back to the said chamber, maintaining all parts of the cathode substantially equidistant from the anode,

said electrolyte containing-from ill to 20 grams per liter of a soluble fluoride, and controlling the concentration of the electrolyte to maintain it slightly acid and'the content bi ferrous chloride tetrahydrate between 350 and sec liter. I

i. The process defined in claim 3 in which said cathode is rotated at a peripheral speed or about wiimeters per minute, and mechanically wiping said cathode during said rotation. I

5. The process defined in claim 3 in which the acidity. of the electrolyte is maintained at a pH value between 4 and 6 by the periodic addition of hydrochloric acid thereto.

grams per 'tricity to the electrodes at a current density electrolytic iron/comprising from 350 to 450 grams per liter of ferrous chloride tetrahydrate, 10 to 20 grams per liter of sodium fluoride, said electrolyte having a pH value of from 4 to 6 and being substantially free of organic constituents. "I. The process of electrolyticallyconverting a high sulfur, high phosphoruscast iron into a low sulfur, low phosphorus, iron. which com- 10 prises using an iron of such high sulfur and phosphorus content but substantially free of carbon silicon and manganese as anode material in an electrolytic cell in which the electrolyte is slightly acid, contains from 350 to 450 grams per liter of ferrous chloride tetrahydrate and from 10 to grams per liter of a soluble fluoride, and maintaining the temperature of said electrolyte between 65 and 106 C.

8. The process of electrochemically converting 20 impure ferrous metals containing phosphorus or sulphur into the substantially pure metal, which comprises subjecting such an impure metal substantially free of carbon, silicon and manganese as an anode in an electrolytic cell to the action of an electric current and-an acid electrolyte maintained at a temperature between 65 and 106 C., depositing the substantially pure metal on a cathode in said cell, and maintainingthe hydrogen ion concentration insaid electrolyte such that the electrolyte has a pH value of from 4 to 6 inclusive.

9. In the process of depositing iron electrolytically on a rotary cathode mounted between iron anode elements submerged in an electrolyte contained in a cell chamber, the improvement which comprises supplying electricity to the electrodes at a current density of approximately 100 amperes per square foot and at a voltage of about one, maintaining in the electrolyte a concentration of ferrous chloride tetrahydrate of, from 350 to 450 grams per liter and maintaining the electrolyte at a temperature of from 65 to 106 0., and sufllciently acid to give a pH reading of .from 4 to 6.

10. In the process of refining iron in which cast iron is used as anode material in an electrolytic cell for making electrolytic iron, the improvement which comprises electroplating the cast iron anode material on to a cathode 50 mounted in an electrolyte in said electrolytic cell, said anode material comprising cast iron which has been air-blown while in a molten state until it is substantially free of carbon and thereafter cast into the desired anode shape, and said electrolyte comprising an acid ferrous iron solution containing a small proportion of a soluble fluoride buffer agent, and maintaining the can pH value of the electrolyte between about 4 and 6.

' 11. The process of electrolytically depositing a firm smooth coat of iron on a cathode mounted in a body of an acidic ferrous electrolyte, which comprises passing an electric current having a voltage of about one at a current density of approximately.100 amperes per square foot of cathode surface between said cathode and a cast iron anode mounted in said body of electrolyte closely adjacent said cathode, said anode comprising cast iron substantially free of carbon silicon and manganese, and maintaining a small proportion of a soluble fluoride bufler agent in said electrolyte to control the pH value thereof.

12. A process for producing electrolytic iron, which comprises depositing iron on a cathode mounted in an acid ferrous chloride electrolyte maintained at a temperature of from 65 to 106 C. and containing a soluble fluoride in sufflcient proportion to act as an inorganic bufler agent for maintaining the acidity-of said electrolyte at from 4 to 6 pH value.

13. In the process of manufacturing electrolytic iron tubes in which the iron is deposited on a rotating cathode substantially'surrounded by a cast iron anode substantially free of carbon and submerged in a slightly acid ferrous chloride electrolyte contained in a cell chamber, the improvement which comprises continuously circulating the electrolyte from said chamber through a heating zone in which the electrolyte is heated to a temperature of from 65 to 106 C.

and then back to said chamber, maintaining all parts of the cathode substantially equidistant from the anode, controlling the concentration of theelectrolyte'to maintain the ferrous chloride content thereof equivalent to from 350 to 450 grams per liter of ferrous chloride tetrahydrate, said electrolyte also containing from 10 to 20 grams per liter of a soluble fluoride.

14. An electrolyte for use in the manufacture of electrolytic iron, comprising an acid ferrous chloride solution containing a relatively small proportion of a soluble fluoride compound but in suflicient proportion to act as a builer for the electrolyte for maintaining it at a pH value of from 4 to 6.

15. A process for producing electrolytic iron, which comprises depositing iron on a cathode mounted in an acid ferrous electrolyte maintained at a suitable temperature for electrolysis, said electrolyte containing suificient fluoride in solution to act as a buffer agent to aid in controlling the pH value of the electrolyte, adding acid to the electrolyte during the electrolysis, and maintaining the pH value of the electrolyte at from 4 to 6 during the electrolysis.

COLIN G. BENJAMIN MILLER.

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