US2588450A

US2588450A - Process of regenerating activated carbon loaded with adsorbed gold

Info

Publication number: US2588450A
Application number: US151999A
Authority: US
Inventors: Zadra John Benjamin
Original assignee: US Department of the Interior
Current assignee: US Department of the Interior
Priority date: 1950-03-25
Filing date: 1950-03-25
Publication date: 1952-03-11
Anticipated expiration: 1969-03-11

Description

J. B. ZADRA PROCESS OF REGENERATING ACTIVATED March ll, T952 CARBON LOADED WITH ADSORBED GOLD Filed March 25, 1950 Il UIQ- JOHN @.ZARA

'v INVENTOR BY `ATTORNEY Patented Mar. 11, 1952 ,PROCESS F REGENERATING ACTIVATED CARBON ,LOADED WITH ADSQRBED YG QLD John-Benjamin Zadra, Reno, Nev.,.assignor-to the United-States, of America-as representedby the Secretary of ,the Interior `ApplicatiorrMarch 25,51950, "Serial'Nm 151,999

1 Claim.

(Granted .under y,the act,of March 3, .1883, as

Vamended l April .30, 1928; 370 0. G. A,'757) The inventiondescribed herein may be manufactured and used -by -orfor the Government-of the VUnited States `for vgovernmental purposes withoutfthe paymentto me of any royalty thereon in accordance -With -theprevisions of the act-of April 30, 1928 (ch. 460, 4j5fStat. VIii-167).

This invention relates to the production of gold and more particularly to the regeneration of activated carbon employed for adsorbing or absorbing gold from dilute.` cyanide solutions thereof.

In my co-ypending application Serial No.jl27',7.61 filed Novemberv 16, 1949, now PatentNo, 2,579,531, entitled Process forlExtracting Gold and Silver, there has been described a process vfor regenerating activated carbon loaded with adsorbed gold involving treating such carbon .with caustic sodium sulfidesolution to extract the gold therefrom, separating .the thus-regenerated activated carbon, stripping the gold Afrom the pregnant caustic Ysodium sulfide solution lby electrolysis between an insoluble anode and a precoated charred excelsior cathode, and recovering the .deposited gold. In this process it ,is necessary to precoat the. charred excelsior cathodeby employing itV as the cathode ina gold cyanideelectrolyte so as to deposit an amount of gold thereon suiii- .cientto reduce its internal resistance to an operative point. This precoating. constitutesan additional phase of the process which it would be desirable to obviate. Additionally, charred excelsior is a particularly fragile substance which can be handled or manipulated-onlywith extreme care. It has A nowbeen found that by mea-ns of the'instant improvement one neednot precoat the cathodematerialbut instead may use -a cathode material of great durability and which is readily available.

In accordance with this invention, there is employed as a cathode material in my abovedescribed processstainless ,steel wool, `preferably alstainless `steel Wool made from Astainless steel containing 4about Y17% chromium and known to the trade as Type-130, Medium Grade. Other stainless steels may, of course, be employed, the only .requisitebeing .that they be not substantially corroded by caustic sodium sulfide solution. For example, stainlesssteelscomposed of iron containing 18% chromium and V8% nickel and those in which a portion -of the iron is replaced by cobalt can be employed; although, as above stated, itehasibeen found Atfha-ifa'l7% chromium stainless steel is not corroded by the electrolyte but is readily disintegrated as will beeXplned hereinafter.

As explained in my above-mentioned co-pending application, the -gold-bearingactivated carbon isl leached with caustic alkalisulde solution, suitably one containing from 1 -to 5% `Stadium suliide and from 2 to 8% sodium hydroxide. .The thus-regenerated activated carbon is washed and returned to the mill circuit for further adsorp- .vided iwith a'negative contact 2.

tion/.of `precious-metal values. The gold-bearing `causticsodium sulfide solution is then employed Vas-anelectrolyte between an insoluble anode and `the stainless steel -wool cathode of this invention.

It is unnecessary to precoat the cathode. Ingen- .,eral, a voltage between twov and six volts, preferablyqabout'three volts, has been found satisfactory in the operationof the electrolysis.

Any suitable electrolytic cell may be employed, such as, for example, the cell described in`-my above-mentionedapplication Serial No. 127,761 co-pending herewith, led November 16, 1949. A very satisfactory electrolytic cell is the circular one described in my co-pending application Serial No. 131,654 led December '7, 1949, now Patent No.2,563,-903 dated August 14, 1951, entitled Electrolytic Cell for the Deposition of Gold and-Silver from Solutions.

`As shown-in the aforesaid application Serial No. 131,654, which was allowed May l5, 1951, a suitable -electrolytic lcell, in which there can be employed the stainless steel Vwool 'cathode of jthis invention,

is illustrated i-n the accompanying drawing. Referring to the drawing, the cathode assembly of the cell comprises, in part, a vertically mounted, 'electrically conductive inlet pipe :I for lintroducing gold sulfide or other metalbearing `solution-into the cell. The pipe I also serves as a negativebusbar or conductor of electricity -in-to the cell and Kfor this purpose is pro- The pipe I is fastened at its lower end toa radially extended disc 3 in such fashion 'as-to make an electrically conductive joint, as Vby welding. Near the lower end of the pipe Iis an aperture 4 for permitting the Asolution Ventering .through the ypipe rI to emerge therefrom into contact with a surround- In order that better electrical contact vmay be made between pipe I and the` stainless steel wool 5, the disc 3 is provided with a plurality of vertically extending Wire rods 'E `spaced about-and parallel to the pipe I. 'The rodsIi, the plate 3 and the pipe I are Vconstructed:Ofian electrically conductive material which is Ynot substantially corroded rby the solutionpbeing electrolyzed. In the case of a caustic alkaline solution of gold, -these members can suitably be .constructed of "stainless-steel, preferably the stainless steel known as "18-8 which containsabout 18% chromium and about 8% 'nickel` the balance being substantiallyall iron.

Inprder to restrain the stainless steelwool 5 in position, a retaining member is provided which isof vsuch form-as to -permitthe egress of solutiongfrom contact with the cathode material into contact with a circumierentially Adisposed anode. As shown, the retainingimember may take the .form of aperforated basket 'I made of hard rub- -ber or other non-conductive material, into which `nests the plate 3 and which'restrainsthe*stainless steel wool-5. As shown, theperioratedfbasket I engages the plate 3 so as to space the rods 6 and the pipe I in their correct locations. A suitable anode 8 peripherally encircles the basket 1 and, as shown, such anode may take the form of stainless steel wire mesh rolled to define an open cylinder. The mesh anode 8 is provided with a positive terminal 9 and is spaced closely adjacent to and encircling the retaining basket 1. The anode 8 and the cathode assembly above described are placed in a, concentrically surrounding weir cup I which serves the purpose of controlling the fluid level in the electrolytic cell while, at the same time, restraining the anode 8 into an equally spaced relationship to the stainless steel wool in the cathode assembly. The weir cup I 0 is provided with cylindrical side walls and preferably a closed bottom, the whole being constructed of hard rubber or other suitable non-conductive, non-corrosive material. A launder II, provided with an outlet I2, embraces the Weir cup I0 and the whole assembly to provide a supporting base therefor. The launder II collects the overow from the Weir cup I0 and directs the stripped solution away from the cell through the outlet I2.

In operation, the retaining basket 'I and the cooperating cathode conducting assembly defined by the pipe I, plate 3 and the rod 6 are filled with stainless steel wool 5. Thereupon, a caustic sodium sulfide solution of gold or other metal-bearing solution is introduced through the pipe I and proceeds through the aperture 4 into contact with the stainless steel wool 5 and the anode 8. After a sufficient quantity of solution lls the Weir cup I0, it overflows into the launder I I and passes out through the outlet I2. The contact '2 is connected with a source of negative current not shown, and the anode connection 9 is similarly connected to the positive current source. Electrolysis then proceeds and gold or other metal to be deposited is deposited largely on the stainless steel wool 5. The electric current passes by way of the solution through the perforations in the basket 'I to the anode 8 and thence out of the cell through the positive terminal 9. As soon as the gold or other metal content of the initial solution has been stripped therefrom, additional gold-bearing solution may continuously be introduced through the pipe I and continuously stripped of its metal content.

Stripped solution is withdrawn from the cell through the outlet I2 and may be used for the solution of additional quantities of gold or the like. After the stainless steel wool 5 has taken up a sufficient quantity of gold or other metal, passage of current and solutionthrough the cell is discontinued and the retaining basket 'I, together with the stainless steel wool 5 and the pipe I, are withdrawn from the cell. The plate 3 is withdrawn from the basket 'I by means of the attached pipe I and the loaded stainless steel wool 5 discharged for working up of its gold content. Thereupon, the plate 3 and attached rods 6 and pipe I are reinserted in position into the basket and recharged with additional stainless steel wool 5. The basket and enclosed cathode assembly are then reinserted into the weir cup I0 inside the anode 8. The cycle can then be repeated.

The following illustrative example shows how this invention may be carried out but it is not limited thereto:

Example 38 grams of stainless steel wool containing 17% chromium and the balance being substantially all iron (Type 430) was placed in the cathode compartment of an electrolytic cell provided with means for introducing electrolyte into the mid-portion of the stainless steel wool cathode, and contact means for connecting the negative bus bar to the stainless steel wool. A stainless steel screen anode was disposed about the periphery of the stainless steel wool cathode but was prevented from contacting the same by means of a hard rubber separator of circular cross-section. Four liters of the gold impregnated stock sodium sulde solution was circulated through the cell at the rate of 4 liters per minute while a current of 9 amperes was used. The electrolyte was employed at a temperature between room temperature and about 35 C. and a voltage of between 2 and 5 volts was required to secure the desired current. The test was repeated four times over a period of 7 days reusing the same stainless steel wool in order to determine the effect of rust or local corrosive action if any. The results of the tests are tabulated as follows:

Milllgrams of gold per liter From the tabulated data'l it is apparent that the extraction efficiency improved with each succeeding test. At the completion of the tests the gold-laden steel wool was dissolved in hot 25% sulfuric acid to dissolve out as much iron as possible from the stainless steel wool. The remaining residue was washed with water, dried and then melted in a graphite crucible while fluxing it with soda ash, borax, silica and nitre. A high purity gold bullion assaying 996 fine and a clean slag were obtained.

Since many apparently differing embodiments of this invention will occur to one skilled in the art, various changes may be made in the embodiments herein described without departing from the spirit and scope of the invention.

What is claimed is:

In a process for regenerating activated carbon loaded with adsorbed gold involving dissolving the gold content with caustic sodium sulfide, separating the regenerated active carbon, and electrolytically stripping the dissolved gold between an insoluble anode and a cathode, the improvement which comprises employing stainless steel wool as the cathode and recovering the gold therefrom, after deposition thereon, by dissolving said stainless steel wool in hot sulfuric acid and separating the solution from the precipitated gold.

JOHN BENJAMIN ZADRA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 591,571 Richards oct. 12, 1897 2,325,660 Chamberlain Aug. 3, 1943 OTHER REFERENCES Transactions of the American Electrochemical Society, vol. 35, published 1920, pages 251, 253, 25'7.