US2713555A - Electrolytic refining of antimony - Google Patents

Description

July 19, 1955 J. F. NEELY ELECTROLYTIC REFINING OF ANTIMONY Filed May 22, 1951 LAU/VDEI? United States Patent '0 This invention relates to in electrolytic refining of new and useful improvements antimony. More particularly, the invention relates to the use of a plating tank having a plurality of spaced plates, one end plate being an anode and the opposite end plate being a cathode, each of said plates being apertured to permit a gradual, re-

stricted flow of electrolyte from one end of the tank to the other, all of said plates being supported within the plating tank. With such an arrangement, each plate, other than the end plates, becomes cathodic on one surface and anodic on the opposite surface and metal will be deposited on the cathode side of each plate, assuming that suflicient electromotive force, current and concentration of electrolyte are employed.

One feature of the invention is a means whereby the individual plates may be mounted in the plating tank. For each plate an inflatable rubber tube is fixed along the sides and bottom of the tank, in the general form of a U, the plate fitting against the tube. When the tube is inflated, the plate is forced against the side of the tube and the tube is forced against the sides and bottom of the tank, thus preventing circulation of liquid past the edges of the plate. The inflatable tube, therefore, provides a convenient means facilitating installation and withdrawal of plates. It will be understood that other means for supporting the plates in the tank may be employed.

The apparatus employed is singularly compact and inexpensive to construct and operate. Particularly, the plating tank occupies a very small space compared with other plating tanks of comparable capacity, is quite i11- expensive to construct, and the cost of operation is low.

One adaptation of the invention is in the electrolytic reduction of antimony from stibnite, a process which has not heretofore been successfully accomplished on a commercial scale. The instant process makes possible the use of low-grade stibnite, which abounds domestically, whereas smelting processes in common use require a high-grade ore which is not domestically produced in suflicient quantities.

The process involves the dissolving of ground ore in a caustic solvent such as sodium hydroxide, the filtering of the pregnant solution to remove undissolved ore and dross, the plating of the pregnant solution to deposit out the metal in a tank such as has been described, the recovery and make-up of the solvent, and the scraping of the deposited metal from the plates.

The apparatus and method are useful in plating of metals and in the electrolytic reduction of various ores. In the reduction of ores directly to metal by electrolytic deposition, in addition to the chemical problems involved in determining the solutions best suited to extracting the metallic content from the ground ore, there is an electrical problem involved which has not heretofore been solved by existing and known methods. The deposition of metal from pregnant solutions on the cathode plates of electrolytic cells is accomplished at low voltages and the voltage must be accurately regulated. In the usual construction of an electrolytic cell, it is customary to employ a number of metallic plates, spaced, and alternately anode and cathode, there usually being one more anode plate than cathode. The anode plates, being the positive electrical connection required,

each to the other. The results in a great multiplicity of electrical connections which must be so arranged that they may be quickly and easily disconnected from the cathode plates in order that the cathode plates may be removed wherever it is desired to scrape off the metal which has been deposited thereon from the pregnant solution.

In the very nature of an electrolytic action gases are released and excessive corrosion takes place at all of this multiplicity of electrical connections. Using a direct current at very low voltages (usually of the order of two a very short wire or other metal connection besultant metallic deposit.

The electrolytic cell hereinafter described overcomes these obstacles in that, in effect, i

be required.

By the hereinafter described means and method is assured limited by the specific For convenience of description of the invention, it will be assumed that the process and apparatus are employed in the deposition of antimony from its ore, it being understood that the invention is capable of other uses within the scope of the appended claim.

The solvent used to dissolve the ore is a caustic, preferably NaOH.

The ore may be stibnite, ground to 20 mesh or finer. One of the features of the invention, as has been stated, is that the ore may be low grade. Further, the invention may be used to work over ore dumps of smelting and flotation plants wherein the dumps contain an appreciable quantity of antimony.

The ore is deposited in inner tank 11 having a filter 12 along its bottom, larger tank 13. Solvent is continuously allowed to flow into inner tank 11 from storage tank 14, thus contacting the ore and dissolving out the antimony. In order to improve the action, the inner tank 12 may be vibrated by any convenient means. After all the charge of ore in inner tank 11 has been exhausted, the inner tank is removed and dumped and a fresh supply of ore deposited in inner tank 11. The pregnant solution or electrolyte produced is preferably at about 2% saturation. Such a solution results, for example, from use of 100 pounds of 3% ore in 300 to 350 pounds of solvent. The resulting pH ranges between 5 and 8, preferably 7.

The solution resulting from the action, together with a certain amount of undissolved material and impurities, passes through filter 12 in the bottom of inner tank 11 and is discharged adjacent the top of outer tank 13, thereupon flowing into the bottom of first launder tank 16. Said first launder tank is divided into two substantially equal compartments by horizontally disposed ceramic filter 17, which separates out most of the impurities in the electrolyte, the impurities sinking to the bottom and being periodically removed. Adjacent first launder tank 16 is second launder tank 18 receiving the purified electrolyte from the top of first launder tank; additional impurities sink to the bottom of this tank. It will be understood that filter material may be employed in second launder tank 18, if required.

From the top of second launder tank the purified pregnant solution may flow into plating tank 19, or, optionally, into a pregnant solution storage tank (not shown) from which it may later be drawn off into plating tank 19.

Plating tank 19 involves certain structural features. It is preferably generally rectangular in cross-section and fashioned of wood or other material not readily affected by the solutions employed. Supported within tank 19 is a plurality of transverse plates 21, such as iron plates inch thick, spaced apart 2 inches. An even number of plates 21 is employed. Plates 21 are vertically mounted in tank 19, one convenient means being by use of an inflatable rubber tube 22, shown in crosssection in Fig. 4, each said tube 22 being permanently affixed to the sides and bottom of tank 19. The inner edges of tube 22 are provided with wings 23 extending out from the tube body and adapted to engage and secure opposite surfaces of plate 21 along the edges thereof. Said tubes 22 are U-shaped and molded to fit in the manner shown in said Fig. 4. The space between wings 23 forms a slot within which plates 21 may slide. A valve 24 is fitted to each tube so that the tubes may be inflated and deflated, and upon inflation form a watertight seal between plates 21 and the sides and bottom of tank 19. By this or other means, plating tank 19 is separated into a plurality of compartments by plates 21. When it is desired to remove a plate, tube 22 surrounding the edges thereof is deflated, permitting plate 21 to be withdrawn.

It will be understood that other means may be employed to divide tank 19 into a plurality of cells. For example, resilient tubes which are not inflatable may be employed. It is important, however, that the plates be held in the tank in such manner that leakage of solution around the edges is minimized, yet the plates may readily be withdrawn.

The invention is useful in plating metals from solutions of various metals. Thus it is not necessary that said tank being suspended within the metal in the pregnant solution be derived directly from ore, as has been described, for electrolytes derived from other sources may be employed. From whatever source, pregnant solution flows into one end of tank 19 through port 26 from second launder tank 18 or any other source, and first plate 21a acts as a baflle preventing direct flow longitudinally through the tank. However, the first and alternate plates are provided with a row of small holes 27 of, for example, A in. diameter, spaced upwardly a short distance from the bottom edge of said plates. Intermediate plates are provided with similar small holes 27 spaced downward from the upper edges. Thus a circuitous flow of electrolyte is provided down between one pair of plates and up between the next, said flow being maintained out through discharge port 28 in the end of tank 19 opposite port 26. Valve 29 is provided in the discharge line, said valve being regulated to maintain the liquid level such that tank 19 does not overflow.

First plate 21a is made an anode by connection in conventional manner with the positive side of a source of direct current. The last plate, there being preferably an even number of plates, is made a cathode. The voltage impressed is the number of plates multiplied by two volts-i. e. if twenty plates are used, the desirable voltage is 40 volts. If more than six volts per plate are used, there is a tendency for holes to form in the plates, and if substantially less than two volts are used, there is insufiicient electromotive force to accomplish plating. The current density is between 7 and 9 amps per square foot of surface area per plate. It will be understood that optimum voltages and amperages vary dependent upon the metal being plated. Since there is no direct electrical connection between the source of current and the intermediate plates, each plate sets up its own cell action, giving each plate a positive effect on one side and a negative effect on the other side and this causes the metal to be deposited on the negative side of each intermediate plate. When the coating has built up to an extent that it bridges the gap between plates or tends to scale off and fall to the bottom of the tank, the plates are removed by deflating tubes 22 (if such means is employed to hold the plates) and pulling the plates out by lifting holes 31 along the top edges. Since there are no electrical connections on intermediate plates, the multiplicity of connections and disconnections employed in conventional plating apparatus is avoided. After removal, plates 21 are scraped to remove the metal deposited.

Solution flowing from plating tank 19 passes through 3-way valve 32 and thence to one or the other of foot tanks 33. Said foot tanks 33 are alternately filled from plating tank 19, and after each tank 33 is filled sufficient caustic or other solvent used is added to build up the required strength of solution, and the contents are then pumped by pump 34 back up to storage tank 14 for recirculation.

It will be understood that whereas a preferred embodiment of the invention has been described and illustrated, changes may be made therein without departing from the spirit of the invention and the scope of the appended claim.

What is claimed is:

A method of refining antimony for stibnite comprising, dissolving out the metal in said stibnite with sodium hydroxide solvent; filtering out undissolved ore and dross; laundering the filtered pregnant solution; and depositing out said antimony by continuously flowing said pregnant solution as an electrolyte in a continuous, circuitous path through a plurality of adjacent cells continuously communicating one with the other through restricted apertures, said cells being defined by removable, parallel iron plates, and passing an electric current through each of said cells, by making the end plate through which said solution enters an anode and the opposite end plate House Feb. 5, 1895 Elmore Aug. 21, 1897 6 2,212,588 Csanyi Aug. 27, 1940 2,331,395 Holmes Oct. 12, 1943 2,542,989 Carter et a1 Feb. 27, 1951 OTHER REFERENCES Report of Investigations No. 3491, Feb. 1940, Bureau of Mines, by J. Koster and M. B. Royer pages 4 and 5.

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