US1863420A - Refining of copper - Google Patents

Description

Patented June 14, 1932 ATENT l/VAL'IER O. SNELLING, OF ALLENT OWN, PENNSYLVANIA.

REEINING OF COPPER No Drawing.

My invention relates to improvements in the refining of copper and more particularly relates to improvements in the refining operation technically known as fining or flapping. One of the objects of my present invention is to provide means for the more ellicient oxidation of the impurities present in copper during the lining or flapping operation, and thereby securing themore complete elimination of such impurities. Another object of my invention is to lessen the cost of the refining of copper, through materially reducing the necessary time of the fining operation and of the subsequent poling operation, thereby not only increasing the refining capacity of the refining furnace but very greatly reducing the fuel cost of the entire refining operation.

The purpose of the refining operation is to eliminate from copper such oxidizable impurities as sulfur, selenium and tellurium, arsenic. antimony, bismuth and sometimes also iron, cobalt, nickel, lead, tin, etc. The chemistry of the operation is relatively simple. The copper is melted in a furnace Which is usually of the reverberatory type, and air is then passed over the surface of the molten copper, and sometimes bubbled through the molten copper by means of air pipes inserted into the bath, until a notable percentage of the copper has been oxidized to cuprous oxide. In commercial practice the oxidation of the copper is continued until approximately 0.5% to 0.8% of oxygen is present in combined condition in the molten copper, corresponding to the presence 0t from 4.5% to 7.0% of cuprous oxide in the copper. The cuprous oxide thus present in the molten copper reacts with the oxidizable impurities which are also present in the copper, and results in the elimination of the impurities, sulfur for example being oxidized to sulfur dioxide and passing off as a gas, and many of the other impurities being first oxidized and then eliminated from the copper as slag. At the close of the fining operation the copper coniains from 6.0% to 7.0% of cuprous oxide, which must of course be eliminated, and this is brought about in present commercial practice by an operation known as poling, and

Application filed December 22, 1930.

Serial No. 504,222.

which consists essentially in covering the surface of the molten copper With a layer of charcoal or coke and then plunging beneath the surface of the molten copper poles of green Wood Which, under the influence of the which results from the uprising bubbles of Water Vapor and carbonaceous decomposition products of the Wood.

It will accordingly be seen that the fire refining of copper consists in its essential elements of passing air over or through the molten copper, to form approximately from 5.0% to 7.0% of cuprous oxide, permitting the cuprous oxide thus formed to react With the oxidizable impurities in the molten copper, and then reducing the cuprous oxide back to copper by means of a reducing agent as coke and the pyrolytic decomposition products of'wood.

Because of the relative simplicity of the chemical operations involved in the fining and poling of copper the possibility of improving these operations has apparently been overlooked, and at the present day both the fining and the poling of copper are carried out in a manner that is exceedingly. primitive as compared with many other metallurgical operations, and Which is exceptionally Wastetul of fuel.

In the commercial refining of copper the reverberatory furnaces which are employed"- may have hearths from 30 feet to feet in length and from 14 feet to 18 feet in Width,-

and the depth of the hearth may vary from 15 inches to 40 inches, such reverberatory furnaces having a capacity under present operating conditions of from tons to 300 tons of copper per 24 hours, the present operating cycle being in general such that one complete fining and poling operation is conducted in approximately 24 hours, the exact time being of course somewhat variable, since the fining operation is continued until the oxidation of the copper has gone on sufficiently to result in the presence of about 0.7% of oxygen in combined condition as cuprous oxide, corresponding to the presence of about 6.5% of cuprous oxide in the molten copper, and the poling operation being continued until this very great excess of oxygen and cuprous oxide has been reduced until not more than five one-hundredths of one percent of oxygen is still present in the copper.

In order to clearly explain the increase in efficiency which results from the practice of my present invention, and the quite remarkable decrease in the use of fuel which is thereby effected, it is desirable to explain the operation of fining or flapping as it is now conducted, in order that the distinctions between the present practice and my improved method of fining may be more clearly understood.

Taking as an example a refining furnace having a capacity of 300 tons of copper at a charge, the charge of copper is first introduced and the heating of the furnace is then continued for a period of several hours, until the charge is completely melted. The fusing point of copper is 1083 C. or 1980 F., and accordingly during the entire refining operation the interior of the furnace must be maintained at a temperature in excess of this very high heat. As soon as the charge of copper in the furnace has been melted the oxidation of the copper is commenced. The side doors of the furnace and the skimming door are fully opened, and the flapping of the charge is commenced. The head of a rabble is repeatedly struck against the surface of the metal to force back the thin layer of slag which may cover it, and to project some of the copper into the air so as to secure increased contact with oxygen. This operation is continued, for a period of from three to six hours, during which time approximately 500 square feet of surface of molten copper at a temperature in excess of 1100 C. or 2012 F. and in excess of 1,000 square feet of incandescent furnace wall and roof area is exposed to the inrush of air from the fully opened side doors and skimming door of the furnace. To maintain the temperature of the furnace during the fining operation there must be burned from 15,000 pounds to 20,000 pounds of coal, which performs no useful function in the refining operation beyond maintaining the temperature of the furnace above the melting point of copper during the violent inrush of air which must be maintained for several hours to secure the oxida tion of the copper. Although this enormous consumption of fuel performs no useful metallurgical function, it is entirely true that it has very undesirable effects beyond the cost of the fuel thus wasted, due to the fact that a large part of the sulfur and ash present in the coal thus wastefully burned tends to contaminate the charge of copper being fined, and the sulfur thus added must be removed and the impurities present in the ash of the coal must be slagged off.

When it is remembered that the total amount of oxygen which it is desired to add to the copper is only from 12 pounds to 15 pounds per ton of copper being lined, the extraordinary Wastefulness of the present operation will be better understood. For a period of more than three hours great volumes of cold air rush into the furnace through the fully opened side doors and through the skimming door, to be heated within the furnace to a temperature in excess of 1000 C. or 1832 F. and then discharged through the stack Without having performed more than an infinitesimal portion of the oxidizing effect of which this air is capable. Meanwhile laborers are operating the rabble near the skimming door in the efiect to expose a small area of the copper each instant to the direct oxidizing effect of the inrushing air, and in addition to this in recent years compressed air has also been introduced through iron pip-es the ends of which have been immersed in the molten copper.

At the end of from two to live hours the oxygen content of the copper in the furnace can be increased, by the methods described to the desired range of from 0.6% to 0.8% but the operation, as will be noted from the above description is extremely wasteful of time, of labor and of fuel. It represents the only method of fining known today, however, and is employed in all refining opera tions of copper in every part of the world.

I have discovered means by which the fining of copper can be completed in half the.

time now required in the most modern copper refining furnaces, and with the expenditure of less than half of the fuel now required. My invention also entirely eliminates the present manual or mechanical flapping of the charge, and affords means by which the entire fining operation. can be conducted in a more rational and efficient manner than has been hitherto known.

In order that my invention may be fully understood 1 will now explain the principles underlying its operation, and the method of applying these principles in the practical fining of copper.

l have discovered that although there is relatively little a'finity between copper and the oxygen of atmospheric air, at the temperature which exists in a copper refining furnace, there is a relatively stronger afiinity between the oxygen of atmospheric air and copper at a temperature somewhat higher than that which is used in copper refining, so that it would be possible to materially 'in crease the rate of oxidation of the copper in present refining furnaces if it were possi- I an ble to maintain the copper at a somewhat higher ten'iperature than is now employed. This is not possible, however, in view of the Vast volumes of cold air which it is found necessary to introduce in the refining furnace, in the operation of refining as now conducted.

I have also discovered the surprising fact that although the introduction of a few tenths of one percent of oxygen into copper is slow and diificult, the introduction of additional oxygen into copper, after tne introduction of the first few tenths of one percent, occurs much more readily and much more rapidly. Although I do not wish to limit myself to any particular theory of operation of my improved process, it is my belief that cuprous oxide acts as a catalyst in the transference of copper to oxygen. After copper has been oxidized until there is present in the molten solution a quantity of cuprous oxide in excess of 3.0%, for example, the addition of further oxygen goes on much more readily, part of the cuprous oxide being apparently overoxidized to form cupric oxide or some intermediate oxide, and this compound then shar ing its oxygen with adjacent copper molecules to form additional cuprous oxide, and being itself thereby reduced to cuprous oxide. This action may of course be repeated over and over, the cuprous oxide taking up oxygen to form a more highly oxygenated oxide of copper and then losing part of its oxygen to produce additional cuprous oxide and itself being thereby brought into condition in which both it and the cuprous oxide thus formed can again pass through the same cycle with the production of still further quantities of cuprous oxide.

In the practice of my present invention I prefer to melt the copper which is to be refined in a. reverberatory furnace of the customary type now used in copper refining, there being no difference in this first melting step between my new process and the process hitherto employed. Upon the completion of the melting step, however, my process differs radically from the fining process as hitherto conducted. Instead of opening up all of the doors of the refining furnace and passing through the furnace for a period of some hours vast volumes of cold air in the effort to oxidize a fraction of one percent of the cop per to cuprous oxide, I follow a different and somewhat contrary policy. The firing of the furnace is temporarily stopped or materially reduced, and there is run into the charge in the furnace the desired amount of cuprous oxide, prepared in a separate furnace, the mixing of the copper with the introduced cuprous oxide being preferably facilitated by the introduction of compressed air to vigorously stir the bath of molten copper and to thoroughly admix and agitate the solution of cop peer and cuprous oxide.

To secure the necessary quantity of cuprous oxide I prefer to employ the reactions and relationships which I have discovered to govern the formation of cuprous oxide from copper as above referred to and I find that cuprous oxide can be cheaply, conveniently and efficiently made in a separate furnace in which there is preferably present at all times a large excess of cuprous oxide in comparsion with the amount of copper present. For example, by bubbling'air through a bath containing morethan 10% of cuprous oxide and less than..90% of copper, maintained at a temperature preferably in excess of 1200 C. or 2192 F., I find that I can produce cuprous oxide by the use of a very small fraction of the air whichis required in present fining practice, the presence of more than 10% of cuprous oxide in the molten mixture serving to catalyze the oxidation of the copper to cuprous oxide in a most efficient manner, and the higher temperature existing in my onprous oxide furnace also materially adding to the efliciency of the oxidizing reaction. Copper is added from time to time to the cuprous oxide furnace, as the copper therein is converted into cuprous oxide, and the cuprous oxide formed is transferred when desired to the fining furnace, for the purpose of therein performing its oxidizing function upon the impurities present in the copper as already described.

Although I prefer to form cuprous oxide by the process and in the manner herein described, it is not my wish to strictly limit my invention to the production of cuprous oxide by the method herein outlined, since it is of course possible to produce cuprous oxide by other methods and by other reactions, and

such cuprous oxide may if desired be employed in the practice of my present invention. Similarly, although I prefer to transfer molten cuprous oxide from an auxiliary cuprous oxide furnace to my refining furnace in molten condition, it will be evident that my invention should not be strictly limited to this procedure,since the cuprous oxide formed may if desired be cast into rods, bars or ingots and these solid masses of cuprous oxide may be employed instead of molten cuprous oxide in the preparation of the bath in the copper refining furnace. Instead of employing solid cast cuprous oxide I may employ a sintered or otherwise consolidated mass of cuprous oxide or of a mixture of cuprous oxide and cupric oxide, suitably agglomerated or consolidated in any convenient or desired way.

My invention rests primarily upon my discovery that the conditions of temperature and of concentration of cuprous oxide which necessarily exists within a copper refining furnace although entirely favorable to the oxidation of the dissolved impurities in the molten copper, are very unfavorable to the formation of cuprous oxide. I have discovi ered that it is only at temperatures in excess of the temperature existing within the refining furnace that copper tends to oxidize most readily to form cuprous oxide, and that it is only in the presence of a greater percentage of cuprous oxide than exists as a maximum in the operation of fining that the catalytic or carrier efficiency of the cuprous oxide becomes most marked. Although it is true that by theory an infinitely'small amount of a catalyst should be capable of catalyzing a large quantity of a reacting mixture, as a practical matter some catalysts are very sluggish in their action, and particularly so within an unfavorable temperature range, and in my work I have found that it is only attemperatures in excess of the highest temperatures normally employed-in copper refining, and only with concentrations iii-excess of the maximum quantity of cuprous oxide which is ever employed in copper refining practice, that the accelerated catalytic reactions which I am here describing become of practical significance and usefulness.

I am fully aware that tarnished and slightly oxidized copper is often charged into copper refining furnaces in the normal course of refining operations, and that the production of cuprous oxide is the object of present practice in copper fining operations, and I wish to expressly disclaim as any part of my present invention the fining of copper in the presence of mere traces or very small percentages of cuprous, cupric or intermediate oxides, and l similarly disclaim the catalytic oxidation of copper in the presence of quantities of cuprous oxide representing less than 1% of oxygen. present in the fusion mixture, I fully recognize that such procedure represents no essential variation from existing knowledge. My invention in its broadest sense involves the independent preparation of cuprous oxide under the conditions of temperature and concentration of cuprous oxide which I have discovered to be capable of readily forming this material, and the addition of such cuprous oxide to a charge of molten copper instead of the present method of attempting to form cuprous oxide within molten copper. in a. refining furnace in which the conditions are very unfavorable to the reactions essential to'the oxidation of the copper. By the application of my invention the time of fining of copper is materially reduced, and the amount of fuel required in the fining operation is correspondingly reduced. In addition, the elimination of impurities in the copper is more complete, al-

though the reason for this increased efiiciency has not yet been discovered. It is probably due in part to the fact that the reduced time of treatment avoids the introduction of a very large amount of sulfur and ash from the many tons of coal that are now burned in the maintaining of the temperature of the copper bath during the fining operation, although it does not seem that this factor alone is sufiicient to explain the improved results obtained, and it is possible that the presence of higher oxides of copper in the cuprous oxide prepared at higher temperatures by the present method, together with the cyclic reactions which exist in a closed furnace as compared with an open furnace as now necessarily used, may also play an important part in the reactions involved.

I am of course familiar with the fact that although invention may be involved in the consolidating of two operations into a single operation with improved results, it is only rare that invention is involved in doing in two operations what may be done in a single operation. In the present case, however, I have discovered that the conditions which necessarilyexist within a copper refining furace are unfavorable to the production of the cuprous oxide which is essential to the oxidation of the impurities present in the copper, and that by forming cuprous oxide separately at a higher temperature than exists within a refining furnace and in the presence of a higher percentage of cuprous oxide than is desirable in the refining operation, and then transferring this cuprous oxide to the refining furnace important and unexpected results in both the saving oftime and fuel and the purification of the copper are obtained.

It will be evident that many modifications may be made in the practice of my invention within the limits of the disclosure as herein made, and that accordingly no limitations should be placed uponmy invention except as indicated in the appended claims.

I claim:

1. In the fining of copper, the process which comprises oxidizing copper in the presence of more than 10% of cuprous oxide and admixing the product so prepared with molten copper to form a mixture containing more than 5% but less than of cuprous oxide.

2. In the fining of copper, the process which comp ises oxidizing copper in the presence of morethan 10% of cuprous oxide at a temperature in exces of 1200 C. and admixing the product so prepared with molten copper to form a mixture containing more than 5% but less than 10% of cuprous oxide.

In testimony whereof, I have hereunto subscr bed my name thIsQOth day of December 1930. v

\VALTER O. SNELLING.