US2160955A - Method of metals separation - Google Patents

Description

.15 manner.

Patented June 6, 1939 l 7 UNITED STATES lWETHOD or METALS SEPARATION Harry H. Burton, Whitman, Mass, assignor to Burton-Allen Gold Reclaiming Corporation,

Wilmington, Del., a corporation of Delaware N Drawing.

Application October 19, 1936 Serial N0.V106,373

2 Claims.

.10 into contact with a metallic alloy which latter,

by reason of its fusing point being below the boiling point of the water or other suspending liquid for the pulp, is kept during the process in a molten condition, by heat applied in any suitable The result is the capture and retention by :said molten metallic alloy of all the free or substantially free metallic content (except the iron content) of the ore, sand, or other material beingtreated -with the molten alloy at the same time completely rejecting and excluding from its encompassment practically all of the other ingredients and gangue of the pulp.

I am aware that various proposals have here- .tofore' been made for the use of low-fusion-point 25 alloys, as improvements upon or as substitutes for 'the mercury amalgamation process, in the separation and recovery of free gold, silver, platinum, and the like, from their ores and sands; see, for example, the United-States patents to Hollick, 30 No. 314,578, -March 31, 1885, and Sweanor, No.

394,225, December 11, 1888,both of which propose the use of certain alloys of the bismuth series for this purpose.

But these and all similar previous proposals,

Y and in fact all previous attempts to use molten metallic A alloys in place of mercury for the recovery of free gold, silver, platinum, and the like, have always proven unsuccessful,-(1), for lack of proper steps taken in the preparation of 'the'alloy, to compound and condition the same for the service to which it is to be put, and (2), for lack of any steps taken or substances used in the process to condition the ores free or substantially free metallic content for seizure, and to promote the'aflinity between the values and the molten .alloy.'

One object "of my invention is to provide a metallic alloy of this character having apowerful affinity, in its molten state, for any free or substantially free metallic contentof ores, sands, and like metal-bearing materialspanother object is to provide a method for the use of such and simi- "lar molten a1loys, by-which to insure the capture and retention of practically all of the free metalli c content of the ores and sands undergoing treatment. My invention resides in the .composition as well as in the method of compounding such metallic alloys, and also in the use With same in-the process of certain conditioning agents thatpromote the affinity between said 5 molten alloy and the metallic content of the pulp. Other and further objects, novelties, and advantagesof my invention will be set forth in detail hereinafter and particularly pointed out in the appended claims.

Tneaforesaid Sweanor Patent No. 394,225 describes analloy .vvhose proportions are 50% bismuth, 25% lead, 12 tin and l2 ,%,cadmium' -(being the'alloy otherwise known as Woods meal), and which may be .takenas typical .of the 15 .various fusible alloys heretofore proposed as substitutes for mercury in the separation and recovery of free gold, silver,-etc., from their ores and sands. The ordinary manufacture of this alloy and of similar .low-fusion-point alloys is to fuse the several'ingredients together at a temperature say of 600 Fahrenheit; the .result of such simple fusion is an alloy which, when subsequently rendered molten in water, by heating the latter. say tol90 Fahrenheit, will oftentimes be of nonhomogeneous character,-the molten body ofthe. same exhibiting certain places where the lead or less fusible ingredient is not thoroughly united and. assimilated with the other ingredients. I 1

In any event, whether homogeneous or not, the i molten body. of such an alloy, and all similar bismuth series alloys which are formed by the above-described .known and usual methods of compounding, is frequently sluggish to-amarked .degree, and breaks up readily into smaller areas which, in some cases, can be recombined only ,withconsiderable difficulty. Furthermore, these and similarly prepared alloys of the bismuth series, when 'kept molten by heating of the vwa- 40 ter thatsurrounds them,.have practically, no

.attractionfor. the free or substantially free me- .tallic. particles of any ore or sand which is carried in. suspension bysuch water; that is to say, any. such bismuth series alloy when compounded by the aforesaid known and usual methods will, inthe fused state, present a molten body that rejects and refuses to encompass not only .thedirt, sand, and other non-metallic ingredients ,ofthe pulp, but also in large measure the free or substantially, free metallic ingredients of said pulp,@,said metallic, particles in considerable quantities being-left free to pass off with the sands, -gangue and. non-metallic particles of .said pulp.

I have discovered that the efficacy of such a molten body of alloy, as a means to attract, capture and retain the free metallic content of the pulps of various ores and metal-bearing sands, can be very greatly increased by certain changes in the composition and method of compounding of the alloy, and furthermore, that the susceptibility of such free or substantially free metallic content to be captured and retained by such alloy can likewise be materially increased by the addition to the pulp water of a special conditioning agent, which very markedly enhances the attraction and union between said metallic content and the molten body of alloy.

As regards conditioning and preparation of various alloys of this character, (for example, an alloy containing bismuth approximately 50% lead approximately 25%, tin approximately 12 and cadmium approximately 12 92,), for the special purposes herein dealt with, I have discovered that the efiicacy, when molten, of such and similar low-fusion-point alloys of the bismuth series, for the capture of the free metallic content of ores, etc., can be materially increased by a certain pre-conditioning treatment, i. e., by boiling the alloy, after it has been compounded, in a liquid purifying and fluxing agent, preferably a relatively strong solution of either potassium cyanide or sodium cyanide, or in some cases in a 25% hydrochloric acid solution. By such boiling for fifteen minutes or so in such solution, preferably cyanide, the alloy is not only freed of all of its ordinary impurities, but is converted from a very indifferent to a very active medium (on subsequent meltings) for the attraction and retention of gold, silver, and like metallic particles.

I make no attempt to explain the exact effect on such alloy of this prescribed preliminary or conditioning treatment by boiling in a cyanide solution, nor to analyze the nature of any change, be it molecular, or crystalline, or otherwise, which occurs in said alloy from its subjection to this treatment. However that may be, the fact remains that by such treatment, or pre-conditioning, the particular alloy whose ingredients are given above, or any similar low-fusion-point alloy of the bismuth series, is given a greatly enhanced capacity to attract and retain, in its molten state, the metallic content of the pulps of ores, sands, and like metal-bearing materials brought in contact therewith in the practice of my improved process,-and I therefore claim broad protection on this pre-conditioning of all such alloys.

I have also discovered as regards the facility with which such a molten alloy (preferably preconditioned as above set forth) is able to attract and retain the free metallic content of ores, sands, and like metal-bearing materials, which are brought into contact with such molten alloy, is materially enhanced by using as or with the pulp liquid for such ores, sands, etc., a relatively weak solution of potassium cyanide or sodium cyanide, or other similar brightening and degreasing agent, in liquid form, such as a weak hydrochloric,

or oxalic acid or cream of tartar solution. That is to say, in carrying out my process for the separation and recovery of free gold, silver, etc., from their ores and sands, the latter are preferably in the form of a free-flowing pulp when contact with the aforesaid molten metallic alloy is made; for this purpose, the liquid conditioning agent for the free metallic content, preferably a dilute cyanide solution, which may with advantage be heated to or above the fusion temperature of the metallic alloy, is either introduced to and mixed with the ore or sand as the latter is fed into the system, or said dilute cyanide solution may be added to the water or other liquid in which the ore or sand is already suspended.

In either case, the action of the dilute cyanide solution is to cut and remove at once any greasy or oily deposit, coating or film which may be and frequently is present on the surfaces of the particles of free or substantially free gold, silver, platinum, and the like,--anol the presence of which is always an outstanding obstacle to the capture and retention of said metallic particles by such molten metallic alloy.

As is well known, a long-protracted immersion of gold or silver in a cyanide solution will result ultimately in the metals being dissolved. But in my process, the attack of the cyanide solution on the free or substantially free metallic content of the pulp is wholly superficial, being of such short duration that it merely serves to expose and to brighten the surfaces of the metallic particles. Once this is done, said brightened particles, from the fact that the pulp, by any suitable mechanical devices, is being constantly and continuously flowed over and passed through the molten alloy, are immediately seized and encompassed by said molten alloy,the latter securely retaining all such particles which make even the slightest momentary contact therewith, and effectually resisting any and all influences tending to free any once-seized particles, or to procure their passage, along with the other ingredients or gangue of the pulp, beyond the range of action of said molten alloy. Moreover, even should there occur some slight dissolution of the free gold or silver in the dilute cyanide pulp liquid, the attraction of my improved molten alloy for metallics is so strong that the metals so dissolved will be precipitated from the cyanide solution in the form of a colloidal deposit on the surface of the molten alloy.

I have further discovered as regards the ingredients and the compounding of my improved low-fusion-point alloy, that it is preferable to include a small quantity of antimony or of barium as one of its ingredients. By so doing, and also preferably by using a suitable flux in connection with the initial fusing of the several ingredients Per cent Bismuth 45 to 55 Lead 28 to 22 Tin l 10 to 12 Cadmium l 12 to 10 Antimony or barium l 5to 1 The above ingredients in the two sets of proportions named, or in any intermediate proportions between'the limits indicated, are fused together in thepresence of a suitable flux (borax,

'sea sand, salt, charcoal and bone, or magnetite) at an appropriate temperature, say in the neighborhood of 600 to 700 Fahrenheit; the resultling alloy, having a fusing point at a temperature somewhat below the boiling point of water, will exhibit, when subsequently made molten by heat,

and particularly if it is subjected to pre-conditioning (by boiling in a cyanide solution as above described), a marked superiority over any ordinary bismuth series alloy as regards homogeneity, cohesiveness and liveliness or fluidity. Moreover, my improved alloy compounded substantially as above described, appears, when subsequently made molten, to exhibit the phenomena of lowered surface tension to a marked degree, a factor which contributes materially to the facility with which it will draw into itself for encompassment and retention any and all metallic particles of the pulp which make even the slightest or most transitory contact with the molten body of said alloy.

I claim:

1. In the separation and recovery of the free precious metal content of ores, sands, etc., the improvement which consists in subjecting said ores, sands, etc., in the presence of a dilute cyanide solution, to contact with a molten bismuth series alloy containing a small percentage of antimony said alloy having previously been boiled in a strong cyanide solution and maintaining by heat the molten, condition of said alloy for the non-amalgamative segregation therein of said metallic content.

2. In the separation and recovery of free or substantially free gold, silver, etc., the improvement which consists in adding to the ores or sands thereof a weak cyanide solution, to form a free-flowing pulp, procuring contact of said pulp with a molten bismuth series? alloy containing a small percentage of antimony said alloy having previously been boiled in a strong cyanide solu tion, and maintaining by heat the molten condition of said alloy to procure the non-amalgamative segregation therein of the free metallic content of said pulp.