US1324352A - Electrolytic cyanibiwg pjocess - Google Patents

Description

W. A. HUSSEY.

ELECTROLYTIC CYANIDING PROCESS.

APPLICATION FILED AFR-15, 1913. RENEWED APR-1711919. 1,324,352.

Patented Dec. 9,1919.

2 SHEETS -SHEET1 1 INVENTOR,

m My, BY

WITNESSES:

A TTORNEY W. A. HUSSEY.

mcm ownc CYANIDING PROCESS.

I APPLICATION HLED APR. 15, 1913- RENEWED APR. I7, 1 919. 1 3,; ,352, Patented Dec. 9,1919. I I 2 SHEETSSHEET 2- v L Ma INVENTOR,

I BY

A TTORNE Y UNIU STATES PATENT @FFIGE AND ONE-FOURTH TO FRANCIS M.

WRIGHT, BOTH OF SAN FRANCISCO, CALIFORNIA.

ELECTROLYTIC CYANIDIN G PROCESS.

Specification of Letters Patent.

Patented D c; 9, 11919.

Original application filed June 26, 1912, Serial No. 705,947. Divided and this application filed April 15, 1913, Serial No. 761,246, Renewed April 1'7, 1919.- Serial No. 291,964.

To all whom it may concern:

Be it known that I, WILLIAM A. HUssEY, a citizen of the United States, residing at Oakland, in the county of Alameda and State of California, have invented new and useful Improvements in Electrolytic Cyaniding Processes, of which the following is a specification.

The present invention relates to an im proved method of recovering precious met als from pulverized ores containing the same, and is a division of an application filed June 26, 1912, Serial Number 705,947, the object of the invention being to pro yidesuch a method by which said recovery may be more complete than heretofore, effected in much less time, and at a low cost, and with which the operation can be carried on continuously without interruptions except only for the removal of the recovered metals and then at only long intervals of time.

In the accompanying drawings, Figure 1 is a broken vertical longitudinal section of an apparatus for carryingout my improved process; Fig. 2 is a similar view of another form thereof; and Fig. 3 is a diagrammatic view of two electrolytic machines by which my improved process is carried out.

Referring to the drawing, 1 indicates the main body of an apparatus for practising my improved process, composed of insulat- I of the mg material, such as vulcanized rubber, the upper surface of which is formed with a longitudinal series of recesses or depressions 2 forming electrolytic cells, and which is arranged at any suitable inclination. Said apparatus is more fully described in the parent application hereinbefore referred to.

The height of the upper end of the appa ratus is considerably greater than that of the lower end, so that each cell is'at a corresponding depth below the preceding cell and at a corresponding height above the next succeeding cell.

In the bottom of each cell 2, at the upper end thereof, is secured, by a suitable conducting bolt 9, a transverse cathode barll of any suitable. metallic material. 12 indicates a cover which fits closely upon the upper raised edges of the sides 13 of the body apparatus and entirely excludes the light from the interior thereof and prevents the escape of gases directly upward, their longitudinal escape being prevented when the apparatus is in operation by the water flowing into and out of the apparatus, and secured to said cover 12 between said sides 13 are holders -14: of any suitable insulating material arranged in longitudinal series, one above each of the said cells 2.

In the form of the apparatus shown in Fig. 1, there is secured in a recess in the lower end of each holder, an, anode 15, preferabl y of graphite or other suitable material, and in a recess in the upper portion of each holder a pole 16, also'of graphite or other suitable material. Each cell. is, as shown at 17, filled with mercury to a suitable depth. All the anodes 15 are electrically connected by wires 18, and a wire 10, to the positive pole of an electric generator, and all the cathode plates or bars llare also electrically connected by means of their bolts 9, and a wire 19, to the negative pole of said machine. A Wire 20 electrically connects each pole 16 outside the apparatus'with the corresponding bar-ll.

I shall first ex lain the nature of the process employed in t 1e form of apparatus. shown in Fig. 1, before describing the second form thereof.

In this process the pulp to be treated, mixed with a certain proportionof sodium cyanid solution is fed into the apparatus, the electric generator being supposed in operation. On arriving at the first cell and being subjected to electrolysis, sodium cyanid is decomposed, nascent cyanogen being liberated at the anode, deposited on the mercury cathode, and probably forming therewith sodium amalgam. It is found that the mercury and sodium at the surface are, by the force of the electric current, on account of the anode being located at the discharge end of the cell and the cathode, in the intake end thereof, driven in a direction against the flow of the pulp into the intake part of the cell, out of the region of electrolysis. The sodium decomposes the water to form caustic soda, and nascent hydrogen is given off, the nascent cyanogen in the presence of alkali dissolves the fine particles of gold, and the caustic and sodium being soda immediately decomposes any organic or greasy particles upon the gold and renders it bright and readily amalgamable by the sodium amalgam.

It is found that the intake portion of the recess, where this chemical reaction takes place, forms in effect a voltaic cell, generating electricity, which, unless the circuit be completed through said cell, would render the pole 16 polarized, and thus generate a counter electro-motive force, and which would thus prevent any further above-described action of said voltaic cell. It is for this reason that I connect each electrode 16 with the corresponding bar 9 by a conductor 20 outside of the cell, so that the current generated may be conducted away and the counter electro-motive force be no longer developed. It is found that said current thus generated has a difference of potential of about two volts. Each cell is thus composed of an electrolytic region, in which electrolysis takes place, and a voltaic region, in which chemical reactions occur tending to restore to its former condition the electrolyte flowing through the apparatus, and thus completing the cycle of chemical action, at the same time generating low voltage electric current.

It is to be noted that in the apparatus shown in Fig. 1 this chemical action can only take place when the mercury and sodium flow out of the-electrolytic region. In my second form of apparatus, shown in Fig. 2, I do not depend entirely upon the flow of the mercury in the cell to cause its removal out of the electrolytic region, but I also move the electrolytic region itself. In this form of the apparatus, instead of there being-a single anode 15' and a single pole 16, as shown in the first form of the invention, there are, for each cell, a large number of electrodes or poles, each of which is used in succession as an anode of an electrolytic cell, the remainder being then used as poles of voltaic cells. These electrodes orpoles are shown at 21, and corresponding ones, or those in like order, in all the cells are connected by wires 22 to a common contact 23 in a terminal block 24. These contacts 23 are individually connected by wires 26 to spring contacts 27 which normally rest in contact with conductors 28 connected to a wire 29 which is connected by a wire 31 to the nega tive pole of an electric generator 33 and also by wires 32 to the several cathode bars 11. From the positive pole of said generator 2.

wire 34 leads by a wire 35 and individual wires 36 to contacts 37. Said spring contacts 27 carry rollers 38 which are arranged adjacent to the circumference of a cam roller or timer 89, having a raised portion 41.

Said timer is rotated at any suitable speed, so that said ralsed portion 11 contacts with each roller in succession and then ralses the roller so that the spring contact 27 moves out of contact with the conductor 28 and into contact with the contact 37. The slope of this raised portion is such that, just before each spring contact 27 moves out of contact with its corresponding contact 37, the next spring contact 27 of the series moves into contact with its contact 37, so that there is no interruption of the current flowing from the electric generator.

It will be seen that, with this construction, each electrode 21 in succession is included in the circuit through the generator, so that the electric current generated thereby can pass through said electrode and through the pulp to the mercury cathode and then to the cathode bar and back to the generator, and the other electrodes are connected directly with the cathode bars 11 outside the apparatus and thus serve as poles of voltaic cells. In other words, the mode of operation of this form of apparatus is electrically similar to that of the first form, except that the position of that electrode which is in actual operation is constantly shifting, The parts are so arranged, that, first, the current from the generator passes. through the lowermost electrode. 21 the others being short-circuited through the cathode, then through the next higher electrode, and so on up to the uppermost electrode. While the current from the generator is passing through any one electrode sodium cyanid is decomposed by electrolysis beneath said electrode, sodium is deposited upon the mercury cathode immediately beneath said electrode, and, upon the place, that is, the sodium decomposes the water to form caustiosoda, and nascent hydrogen is given 015:. The process applied to each portion of the pulp is that, first, that electrolytic .current is passed through the pulp, with the result before explained, and then this electrolytic current is arrested fora period of time longer than the passage of the current and the chemical and voltaic action before described then takes place. All of the pulp is undergoing this process, although the different portions of the pulp are not similarly acted upon at the same time. One small portion, say one-fifth, of the cell is electrolytic, and the remaining portion is voltaic.

It will thus be seen that in this apparatus not only is the entire mass of pulp moved over the whole of the cathode, but also the effect produced is the same as if the anode were moved over the whole of the cathode.

It is well known that, in the treatment of gold and silver bearing tellurid, arsenical, antimonial, as'well as pyritic ores generally, ordinary cyanid solutions, that is, solutions to which other reagents have not been added, have up to the present time only yielded a aeaaaa partial gold and silver extraction, this result mid) or other halogen cyanid according to being due to the insolubility, and also to the the salt applied.

reducing action, of the minerals incasmg the 2. On being free from electrolysis, the gold or elements, as tellurium, combined sodium forms with water, sodium hydrate with it. The additlon of cyanogen bromid (N aHO), and nascent hydrogen.

or iodid to the cyanid solution is found to 3. hese reagents reduce the cyanogen greatlly aicll izitindlimprci ve the gold exgraction; bromid according to the following equation: but tie (i cut 0 preparing tiese reagents, together i vith their instability, and CnBr+2NaHO+2HN O B B OH O the excessive cost involved, has, in most a n+ 2 cases, made their application useless or pro- The original reagents applied are thus rehibitive. It has also been found that these generated.

alogen cyanids are entirely consumed at By this method there is substantially no each application, and no means up to the loss of the cyanogen compounds, as, after present time have bee-11 known for the re having served their purpose in the electropeated and economical regeneration of these lytic apparatus, they can be pumped back special reagents, so as to permit of the and used over again therein. 1 economical cyaniding of ores of the charac- In the practical application of my imter referred to. proved process it is desirable for economy Now in the employment'of my improved and other reasons to use two electrolytic maprocess for such rebellious ores, the ore, havchines or apparatus. In the first, A, of such ing been first crushed to a pulp, is dismachines there are used graphitized or other charged into the top of the apparatus with insoluble anodes l5, and'in the second ma- 7 a certain percentage of sodium cyanid soluchlne, B, there are used soluble anodes 15", tion containing a haloid alkaline salt, such as zinc. In the firstor upper machine, A, as sodium bromid. W en passing between the main electro-chemical action takes place, the anodes l5 and the cathodes 11, by the while the lower machine B is used fo' the action of the electric current, electrolysis purpose of obtaming a further or more takes place of a certain portion both of the complete electro-deposition-or precipitation sodium cyanid and sodium bromid, which of the gold contained in the electrolyte. thereupon give up their sodium to the The lower machine has soluble zinc anodes mercury and incidentally produce cyanogen instead of insoluble graphitized carbon bromid, which has the valuable effect before anodes for the following reason: The soreferred to in improving the gold extracdium cyanid electrolyte is employed, as has U011, as the cyanogen bromid powerfully atalready been explained, for two purposes. '100 tacks a part ofthe gold, formlng a gold First, to render the larger particles of gold cyanid or bromid, which readily dissolves readily amalgamable by mercury, and, secin the remaining sodium cyanid solution 0nd, to dissolve the finer particles of gold, present in the electrolyte. T and form asoluble cyanid of gold and soow upon passing out. ofthe influence of dium. For the electrolytic recovery of gold the electrolytic current, the sodium decomfrom such. solution of cyanid of gold and poses water and caustic soda and nascent sodium, anodes might be used, as previously hydrogen are pro ucted. Thejcaustic soda stated, which are;'insoluble, as graphitized and nascent hydrogen produce the'very valucarbon, but it is preferable to use solu'ble able result that hey then reducethe free anodes as zinc, the chemical affinity of which cyanogen bromid again to sodium cyanid With cyanogen is very strong. 'and'sodium bromid, while the gold is con- One advantage: gained by using graphtamed 1n an aurous cyanid solution. Any itized or other insoluble anodes in the prigold that is not precipitated from the cyanid mary electrolytic machine, instead of soluble solution by electrolysis in the apparatus can or zinc anodes,'is that the amalgam obtained be recovered by ordinary methods such as in the mercury cathode cells where insoluble the use of zinc dust, or preferably by the or graphitized carbon anodes areemployed use of zinc anodes, as hereinafter more fully is a pure gold amalgam explained.

Thevalue of the invention consists in that, rating the gold from the zinc entering the whereas the powerful cyanogen bromid is mercury of the mercury cathode through very unstable, by this method any excess of the soluble zinc anodes. Also the insoluble unused cyanogen bromid is, until again or graphitizedfcarbon anodes are necessary needed, immediately converted into the 1n the first or primary machine,because in stable compounds sodium cyanid and sodium this machine the nascent cyanogen is of disbromid. tinct value for dissolving this fine, or non- The following chemical reactions occur: amalgamable, gold. In the second or lower 1. NaCn+ aBr, employing a mercury machine, in which the larger portion of the cathode, gives, with the irect electrolytic dissolved gold is deposited, the acid radicurrent, sodium, and CnBr (cyanogen brocals formed at the anodes are no longer needed, and are highly detrimental to the thorough electro-deposition and saving of the gold.

In the second or lower machine, for the purpose of breaking up the double salts of the gold and sodium cyanid (AuNa(Cn) 2 or AuNa(Cn),), I use at stated intervals a salt, as the sulfate of zinc, the addition being made in minute quantity in solution. This, by destroying the sodium 'cyanid in the electrolyte, allows ot' the instant electrode deposition or all gold still present in minute size in the solution.

The following statement will better eX- plain the reaction involved.

The solution of zinc sulfate added to the gold-sodium cyanid solution in the secondary, or soluble Zinc-anode machine slowly forms zinc cyanid, aurous cyanid, plus sodium sulfate. The aurous cyanld and zinc cyanid, held in solution momentarily as colloids, are decomposed by electrolysis with the zinc anode, finally forming metallic gold, which is electro-deposited or precipitated in the mercury, and metallic zin c which also is electro-deposited. There prob' ably also form the zinc-sodium cyanids which are washed away in the machine by the current of water continually flowing. The gold in the secondary or soluble (zinc) anode machine is present in solution as already noted, as gold-sodium cyanid. The solution of zinc sulfate, being slowly added to the cyanid electrolyte, breaks up this compound. The zinc, displacing the sodium, unites to form zinc'gold cyanid, AuZn(Gn) while the SO, ions liberated from the zinc sulfate go over to the sodium to form sodium sulfate. This, while chemically inert in this instance, nevertheless greatly aids in the conductivity of the electrolyte. Goldzinc cyanid, being colloidal in minute amount in solution, nevertheless.remains dis solved sutliciently long to instantaneously effect a complete electro-deposition or precipitation on to the mercury of the gold held in the electrolyte, this being accomplished by means of the soluble Zinc anodes employed, and during the continuous flow of the current.

In order to obtain complete extraction and precipitation of the gold from the ore with: out using a very large number of such machines or apparatus, the pulp is taken from the tail oi the first machine and is passed through an agitator 43 by means of a centrifugal pump 44: and is then delivered to the head of said n'iachine to be again treated "therein. This operation is repeated as many times as is necessary to obtain a thorough extraction oi? the precious values. After this extraction has been accon'iplished, the pulp is then passed on to the second machine. through which in like manner it is passed through an agitator 43 a number of times in succession by means of a centrifugal pump 4:4 being agitated between each passage in the manner above referred to, until a thorough precipitation has been effected.

In the claims, for the purpose of brevity, wherever the word sodium is used, it is understood that potassium or other suitable alkaline metal or radical is to be regarded as an equivalent. Y

I claim 1. The method of recovering metal from metalliferous pulp which consists in mixing it with a compound solution of sodium cyanid with a halogen sodium compound, electrolyzing the solution in the presence. of a mercury cathode, with a current of suflicient intensity, to form a halogen-cyanogen compound and sodium, and then removing the sodium from the action of the current.

The method of recovering metal from metalliferous pulp which consists in mixing it with a compound solution of sodium cyanid with a halogen sodium compound, elec trolyzing the solution in the presence of a mercury cathode, to form sodium and a halogen cyanogen compound and dissolving the metal by a portion of the compound, forming, by means of the sodium, caustic soda and hydrogen, and transforming the unused compound, by means of the caustic soda and hydrogen, into the original sodium compounds.

3. The method of recovering metal from metalliferous pulp which consists in mixing it with a solution of a cyanid with a halo gen salt, converting the solution into a halogen-cyanogen compound and a base, employing said compound to dissolve the metal in the pulp, employing said base to restore the unused compound to the original solution, and repeating the above steps in the same order.

4. The process of regenerating a spent cyanid which consists in electrolyzing a sodium compound solution in the presence of a mercury cathode, to produce sodium, employing the sodium to decompose the water of the solution, thus forming nascent hydrogen, and employing the hydrogen to reduce the cyanid compound to a cyanid.

5. In the electro-cyanidation of refractory gold and silver ores, the process which consists in first forming a solution of sodium cyanid and a haloid salt, decompos ing the solution by electrolysis with a mercury cathode to form a cyanogen haloid compound around the anode and sodium amalgain at the cathode, then interrupting the passage of the current therethrough to permit sodium of the sodium amalgam to decompose water and produce caustic soda and nascent hydrogen, and then intermingling anodic with cathodic products of decomposition to regenerate the original cyanidbroinid solution.

6. In the electro-cyanidation of gold and silver ores, the process Which consists in subjecting a compound solution of a cyanid and a haloid salt to electrolysis, thereby forming a cyanogen haloid salt around the anode and sodium amalgam at the mercury cathode of the cell, subjecting the finely pulverized gold and silver ore to the products of electrolysis, for more thorough dissolution of the gold and silver, then interrupting the passage of the current therethrough to decompose the sodium amalgam formed at the cathode, then intermingling anodic and cathodic products of decomposition to regenerate the original solution applied, then adding a zinc salt to break up alkaline cyanid present in the electrolyte, and finally zinc salt to decompose the alkali cyanids present in the electrolyte.

In testimony whereof I have hereunto set my hand in the presence of two subscnbmg Witnesses.

WILLIAM A. HUSSEY. Witnesses FRANCIS M. WRIGHT, D. B. RICHARDS.

precipitating the metal

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