US961924A - Process for refining gold. - Google Patents

Description

Empire,

cnuoo UNITED strAT s Li LitimitiJts PATENT OFFICE.

HEINRICH WOHLWILL, 0F HAMBURG, GERMANY, ASSIGNOR TO THE FIRE OF NORDDEUTSCHE AFFINERIE,

'OF HAMBURG, GERMANY.

PROCESS OF REFINING GOLD;

961,924. No Drawing.

To all whom it may concern:

Be it known that I, Hnmmon WOHLWILL, a subject of the Emperor of Germany residing at 31-35 Elbstreet, Hamburg, erman have invented new and useful Improvementsin Processes of Refining Gold, of which the following is a specification. This invention has reference to the purification 0f impuregold, or gold alloys, and has particular reference to an electrolytic method of producing chemically pure gold from impure gold alloys, by employing the Iianrlile as the anode in a suitable electrolytic The present invention constitutes anv improvement on the processes described-and claimed in Letters Patent, Nos. 625,863 and 625,864;, granted to Emil WohlWill, May '30, 1899. a

In treating gold containing a relatively large percentage of silver as the anode in an electrolytic bath, consisting of a gold solution containing free hydrochloric acid or chlorids, according to the method described in the patents above referred to, it has been found 1n practice, that when the proportion of silver in the material to be refined, exceeds six per cent, it is necessary, periodically, to mechanically remove the deposit of chlorid of silver which forms upon, and covers the anode. .Ifthis removal of the chlorid of silver is omitted, gaseous chlorin is evolved at the anode, and interferes with the operation of the process. It has been found that the greater the density of the current used, and. the greater the percentage of silver in the gold anode, the sooner this condition obtains. For this reason, the process cannot be sat'sfactorily employed to purify many varieties of gold coming from the mines, except by the use of a current of considerably lower density than can be employed in the purification of varieties of gold containing a smaller proportion of silver. By reason of the necessity of employing such current of lower current density, in refining. gold containing a considerable ercentage' of silver, the o eration' is roonged, and'the removal of t e chlorid o silver from the anode materially increases the costof the process.

Now, I have found that it is possible to wholly prevent the'development of chlorin' Specification of Letters'Patent. Patented J 11119 Applieation flled March 10,1909. Serial in. 82,476.

' sion of. the bath.

at the surface of the anode, and consequently to refine old containing a very large ercentage, 0 silver by electrolysis in materially less time and at considerably lower expense than has been possible by the method hereinbefore referred to, by using anasymmetrical alternating electric current instead of a direct .current.

Asymmetrical currents are produced either i by commuting a direct current at small and unequal intervals of time, as for example, alternately every 1/50 and 3/50 seconds, or such currents may be produced by the simultaneous use of a direct current and an alternatin' current connected in parallel. I prefer owever, to produce the asymmetrical current ina still difl'erent way, to wit by connecting a source of direct current and a source of alternating current 1n series.

This I commonly do, by connecting a direct current dynamo and an alternating current dynamo in a series. It will be understood that in an asymmetrical alternating current, the curve of the current will be equal to the curve of an ordinary alternating current, but it will oscillate, not on the zero value, but on the value of the direct-current as the zero line.

' The quantitative efllect of asymmetrical currents when applied to the refining of 7 gold in accordance with the hereinbefore referred to process, is practically-the same as that of the. direct current alone; that is to say, the quantity of gold, dissolved the ano is practicall lated from t e strength of the direct current alone, in accordance with- Faradays law. The advantageous effect of the alternating component of the asymmetrical. current is however, exhibited in various ways. For example, as soon as the alternating current is led into the direct current circuit, in

which the electrolytic bath is included, the

electric tension of the bath indicated on a direct current voltameter falls, and the greater the strength of the alternating current, the greater the fall in the electric tenchange in their manner of'action, the ch being especially noteworthy in respect of n e r anode V By reason of the employment of the al- Both poles exhibit a fr P de, and precipltated at the cathode} equal to the quantity .calfcu- .ternating current with the direct current,

the latter can be considerably increased without producing an evolution of chlorin at the'anode, consequentl the necessity of removing deposits of c lorids .from the anode is avoided.

, When currents exceed a certain limit of density, in the present process, there '15 produced a slight evolution of oxygen, at the anode." This evolution is however, so insign'ificant in volume, that the loss of current produced thereby, is without importance, and such evolution has. in fact, a slightly advantageous feature in that it facilitates the falling ofi of the deposit of-chlorid of silver which forms upon the anode. When the current denslty is materlally increased over the limit referred to, the development of oxygen becomes greater, and'thereby the -rent is too great,

loss of c rrent becomes materla It may be here. stated, that the smaller theproportion of silver, and the higher the ratio of the alternating current to the h of the direct current, the higher current. Therefore, in the use of the asymmetrical current, the developmentot any considerable amount. of gas atthe anode, as exhibited by the detachment of more than single small bubbles from the anode, indicates that the strength of the direct ourand the direct current must therefore, either be moderated or the strength of the alternating current increased. For example, impure gold containing about ten per cent. of silver, according to the old process hereinbefore referred to, permits of no higher anodic density of the current than about 750 amperes to the s uare meter, and necessitates the scraping o of deposits of silver chlorid from the anode every three-quarters of an hour. The

same gold, can however, be treated in accordance with the present process with an asymmetrical current, the alternating component of which has a strength of approximately 1 to 1.1 timcs that of the direct current, with a density of the direct current of 1250 amperes to the square meter, without renderingv any scraping off of the chlorid from the anode necessary. The

present process also renders possible, the

treatment of gold alloys contalning a considerably larger proport1on of silver than can be satisfactorily treated by the use of the direct current alone. 'For exam le, gold containing twenty per cent. of silver can be satisfactorily refined by the present process, by using an asymmetrical current, the

strength which is to that of the strength of the direct current component" as 1.7 is to 1, with a density of the direct current component of 1200 amperes to'the square meter. With a of the alternating component of.

somewhat lower density of the direct current component, the process can be used for the refining of gold still richer in silver; in fact, the use of the asymmetrical current in accordance with the present process permits of the purification of .all classes of gold which are encountered in actual practice.

The use of asymmetrical alternating currents, and particularly the fact of being able to use direct currents of high density therein, carries with it a still further advantage. In the electrolytic treatment of gold with a direct current of the density commonly used in gold solutions, containing an excessive quantity of hydrochloric acid or chlorids, it is found that about ten per cent. of the quantity of gold, of the anodes, falls in minute particles into the slimes, from which it must be recovered by a separate chemical process. When, however, the asymmetrical alternating current is used in the same situation, only a. small amountot gold falls into the slimes and this only at the beginning of treatment, when the plate has not yet been covered with silver chlorid. After this, practically no gold whatever, falls into the slimes, so that, in the operation of the present process, the-slimes consist almost exclusively of chlorid of silver.

In as much however as a small quantity of gold falls into the slimes at the beginning of the treatment, and some gold particles arising from the mechanical isintegration of the anodes, fall into the slimes at the end of the treatment, the presence of gold in the slimes cannot be wholly avoided; but this quantity rarely exceeds one per cent. of the quantity 0 if the use of currents of particularly high densities as for example, of a density in excess of 1000 amperes to the square meter, is not of importance, the process ofiers the signal advantage that the quantity of hydrochloric acid or chlorids to be added to the electrolytic bath, may be materially less than the quantity necessary when the direct current is used alone. .By the use of asymmetrical alternating currents in accordance with the present process, gold can be refined with' direct current densities of 1000 amperes or less to the square meter in a solution heated from 60 to 70 C., and containin only fromabout 1% to 2 per cent. hydroch oric acid of 1.19 s ecific gravity, while in the treatment with irect currents, there is required about four times as muchacid, that is to say about 7 per cent. hydrochloric acid. On the other hand, the heating of the bath to a temperature-of about 60 or 70 C.', can be dispensed with in the present process when the proportion of by in the solution amounts to 7 er cent. or

frthe gold treated. Furthermore,

drochlonc acid 7 from, 600 to 1000 amperes to the square visahle; that is to say, a density of the total "meter. I current corresponding to from I In the electrolytic treatment of gold in" U accordance w'th the old process ereinbefore-referred to, the 'heating-ofthe bath is I a J1250*+1315 as5s 7o absolutely essential, as the direct current ,ampemgmo the 'uare meter, 1 :thisbwse; when alone? m coldl f the Volta e of the direct current component though b l reqmslte denslty of is about from 1 to 1.1 volts per bath and the mntffoo i 9 Square meter, \total voltage per'cell as indicatedfon a hot current component is not allowed to exceed \not more than l0 per cent, greater, is ad- P du preclpitatimn fZ' Q gold wire oltam'eter, is about 1.4 volts. From v iol'm'of P gi i m m 1 1mm this, the voltage of the alternati current darklbmwn 6 use 0 3 3 componentcan be'calculated as fol owsz, metrical current notonly renders IMPOSSlblG 15 to increase the cathodic density of the curt..= -,/(1.4 (1.1): .866 volts.

rent-as well as the anodic-density-of the curl a n% the ca acity offlfihe v y 3.0 e

rent, ma warm solut1on, -but also to refine mimosflt Wm aesim 1e to conslder 1.3

the gold my a cold sohmon the use of volts as the maximum voltage of the direct etricalcurrentswhoseirect com o- V as mm P current, and 1 as 'the maxlmum voltage of -20 nenthas a density below 1000 amperes to'thethe alternating current p bath. AS the f fz s f perfect y coherent 'dynamos are connected in series, the armaprecipi a es.

I n thel ractical operation of the process I fi i g g a g ggfiggzg ifig g f ifig fig fi p i g i gi gi g gg gg i? 2; current, i, The frequency of the alternatalternating current dynamo are connecte sg canpbe varied wmhlp the u l in genes a cimmt? mcludmg the 616cm? The streng hs and Voltage of the currents bath and the direct ailment dynamo 1S employed may vary-widely accordin to the excited unt1l a polarized-direct current am characterof the n to b fin d g If th '30 meter inserted mthe circuit, indicates the 01d contains than 8 e t 6 v desired strength of the direct current. P Gen thedensityiof' the direct current component can be advantageously increased, or, if preferred, the strength of the alternating component relative to'the direct current com'ponent can be diminished.

It is found in ractice, that the ratio of the strength of t e alternating. current to I that of the directicurrentcannot be advan tageously diminished below a certain limit. For instance, if the strength of the alternating current becomes less than .707 of that of the direct current combined current will cease to be an alternating current' and wi become a mere undulatory direct current of eriodically varying strength, in which case, the peculiar advantages of-the combined Icurv rent hereinbefore set forth, are lost.

rent mtenslty 9 i i i In the practice of my process,Iordinarily Strength of the direct 3 to bewequa work with a gold chlorid solution heated 50 to the strength of the alternating current, from 60 to 700 and coma-filingv at least as for example, to 200 amperes, the hot wire. 7 per cent free hydnm one MEL In 15 ammeter must mdlcate cases gvhere tog mucfh importance not attac e to ra i ity 0 treatment an one can 80000 283 ampeljesf therefore be satisfied with a density of the Th total Voltage f m Win h h p w r direct current between 500 and 1000 amconsumptionis to be calculated, is indicated peres to the square meter, the treatment can. 12. by a hot wire voltameter.- Ihe degree voltake place either at the tem erature inditage dependsof course, on the strength of cated, the bath containing hy rochloric aci the total current. For example, if gold is in the proportion of from L} to 2 per cent. ,being treated, which contains about 10 per of the solution, or the treatment can take cent. of silver, a density of the direct current place with a cold solution in which case 7 12! component of about 1250 amperes to the per cent. of hydrochloric acid as is emsquare meter,and a density of the alternatployed, Instead of using'hydroc oric acid ing currentcomponent which isequal to, or in the gold chlorid solution, I may substithis desired strength of the direct current is represented by i and if it is desired to work with' a virtual intensity of the alternating 35 current represented by 6,, the Virtual inten- 4 sity of Y the total current obtained y the combined use of the two currents',can be calculated according to the formula i a/i 01,.

This total current can only be measured b a hot wire instrument. In addition to the direct current ammeter,-a hot wire ammeter must therefore also b inserted in the 45 asymmetrical current circuit. The alternat ing current dynamo is then excited until the tute either Wholly or partially therefore trolyzing a solution of a gold salt by pass- 25 chlorids such for example, as sodium 'ing an asymmetrical alternating current chlorid. therethrou h, with such gold or gold alloy i "In the preferred practice of mg process, I as the anode. 4

5 emplo thinly rolled sheets of ne gold as process of electrolytically refining catho es and introduce gold into the elecgold or gold, alloys, which consists in elec- 30 4 trolyte in the form of a gold chlorid solutrolyzing a solution containing'gold chlorid tion in proportion as the gold contentof the and another chlorid with an excess of the 7 bath is diminished, in the o eration or the latter, by passing an asymmetrical alternatx 10 process. In refining gold w ich contains a in current therethrou h with such gold or material percentage of lead, may advango (1 alloy as the ano e. 35 tageously introduce sulfuric ac1d to the bath, 3.. A process of electrolytically refining preferably in a quantity-approximately gold or gold alloys, which consists in elec equivalent to that of the free hydrochloric tro yzing a solution of old chlorid, con-, 15 acid present. taining hydrochloric acig, by passin an While I somewhat prefer to em loy I asymmetrical alternating current t ere- 4 hydro-chlor ic acid in the gold bath it 1s to through with such gold or gold alloy as the be understood that I may advantageousl I anode. 1 use a metal or other chlorid. and that suc In testimony whereof I have afiixed my 20 chlorid is the equivalent of hydro-chloric signature 1n presence of two witnesses.

acid for use 1n my process. HEINRICH WOHLWILL.

I claim: Witnesses:

: 1. A process of electrolytically refining ERNEST H. L. MUMMENHOFF,

gold or gold alloys, which consists in 'elec- IDA OHR. HUFERMANN. 1