US518732A

US518732A - Art of producing metallic zinc

Info

Publication number: US518732A
Authority: US
Publication date: 1894-04-24
Anticipated expiration: 1911-04-24

Description

(N0 Mdel.)

P. c. GHOATB.

ART OF PRODUCING METALLIC ZINC. No. 518,732. Patented Apr.i,24, 1894,.

fave 71707" V Z f r (SQ-{Locals UNITED STATES PATENT. OFFICE.

PARKER C. GHOATE, OF NEW YORK, N. Y., ASSIGNOR TO THE ELECTRICAL ZINC COMPANY, OF NEW JERSEY.

ART OF PRODUCING METALLIC ZINC.

SPECIFICATION forming part of Letters Patent No. 518,732, dated April 24, 1894. Application filed January 21, 1892. S rial No. 418, 842%. (N specimens.)

To a whom it may concern.-

Be it known that I, PARKER O. CI-IOATE, a citizen of the United States, residing in the city of New York, in the countyand State of New York, have invented certain new and useful Improvements in the Art of Producing Metallic Zinc, (Case N o. 4,) of which the following is a specification.

, My invention relates generally to the production of zinc from its ores and the object of my improvements is to. provide an economical method of producingcommercially pure metallic zinc. While my process may be applied to the 1 production of zinc as a metal from any of its ores, it is more especially valuable when employed in connection with the large class of ores known as blendous or complex which contain besides zinc numerous other metals such as gold, silver, iron, lead, arsenic, antimony, bismuth, cadmium, 850., in varying proportions, and which on account of the difficulty of working them economically have heretofore been discarded at the mines in great quantities as waste products. In working such ores for the extraction of metals other than zinc, as heretofore practiced there has been a total loss of. the zinc, except when utilized as a pigment, and at the same time its presence causes heavy losses of the other metals such as gold, silver, 850. Although in many cases these ores arevery rich in zinc, which is often the most valuable constituent, all attempts to treat them for the extraction of that metal commercially have failed even at the expense of the sacrifice of the other constituents of value. Thus the ordinary method of producing metallic zinc from the ore by distillation is entirely inapplicable to 40 these complex ores, since so many other metals are distilled with the zinc and enter as impurities into the metallic product as to make it undesirable for the commercial uses to which metallic zinc is applied.

Although numerous attempts have been made to that end no method has been heretofore devised by means of which it has been possible to continuously produce pure metallic zincon a profitable commercial scale, by electrolytic deposition. The difficulty in utilizing electrolysis as a means of producing pure metallic zinc is primarily due to the fact that zinc is electro-positive to many of the metals which are present with it in the ore and so much so as to deposit or precipitate upon itself from acid solutions most of these metals, and if any such metals be allowed to be present in the bath in solution with the zinc they will be deposited with it and appear as impurities in the product. In depos- 6o itingzinc from solutions of its salts free acid quickly appears in the bath through the action of the current upon the solution and, un- 7 less neutralized or annulled, soon brings the operation to a stand still by re-dissolving the zinc from the cathode as fast as it is deposited thereon. Hence even though a pure zinc solution be originally formed and the operation of depositing a pure metallic zinc be begun it can only be maintained and carried on by 7c neutralizing or annulling the free acid and in such a way that soluble, depositable impurities shall not enter into the bath, where they will be a source of prohibitory trouble and expense. By my improvement I overcome these difficulties, for it is a result of my process that the condition in which I take the zinc wherewith to maintain the electrolytic solution enables me to neutralize the acid set free in the bath in an efficient and economical manner and at the same time to maintain the solution in its original state, without the continued use of precipitants or other similar means of purification.

The defects of prior electrolytic processes have largely come from the fact that in regenerating the solution the ore itself was used as the neutralizing agent for annulling the free acid so that all soluble matter present with the zinc in the ore went into the solu- 0 tion as often as it was regenerated and had to be continually removed therefrom. In my process on the contrary, I, at the outset take the zinc in a state from which all the soluble impurities can easily be eliminated before 5 the zinc goes into solution, while such insoluble impurities as go into the electrolytic baths will readily separate themselves out during the working of the charges, so that in this way I am able to annul the free acid in the mo bath and maintain a practically pure and nearly neutral solution for the action of the electric current.

tilize any of the zinc or lead contents.

From the point of View of my process, a pure solution is one which is free from those metals which would be electrolytically deposited before or along with the zinc and would thus enter into and contaminate the product.

To the end therefore of maintaining the purity of solution referred to my invention consists broadly in producing a commercially pure metallic zinc by depositing the zinc by electrolysis from an aqueous acid zinc salt electrolyte, maintained and regenerated by dissolving in the acid set free in the bath by the electric current an oxidized zinc fume freed from its impure soluble constituents which are more volatile than zinc, such as the oxides of antimony, arsenic, cadmium, &c.

The accompanying drawing shows a sectional elevation of a form of apparatus which may be used in connection with my process, containing a vessel in which the solution is formed, and the baths for the electrolytic treatment of it, together with feed and overflow tanks, and also a pump and connecting pipes for keeping the solution in circulation.

Any usual or suitable mode may be adopted for obtaining the zinc fume to be used in my process. As an example of one well known method, the ore may be first crushed and then when it contains an excess of sulphur, it may be roasted ata moderate temperature not sufficiently high to volatilize the zinc, in order to drive 01f the excess of sulphur. The partially desulphurized ore may then be mixed with carbonaceous fuel, such as coal screenings in a furnace in which air is admitted beneath its grate, and may be roasted at a temperature high enough to volatilize the zinc until the zinc contained in the ore is driven ofi. The volatilized zinc and other volatilized bodies may then be caught and collected in a bag room in the ordinary manner. The resulting product will be substantially pure oxide of zinc in the shape of a fine powder known as fume, mixed with such lead as was volatilized with the zinc when lead occurs in the ore. There may also frequently occur with the zinc and lead fume, as condensed products, other volatilizable constituents, which may have been present in the ore, such as the oxides of antimony, arsenic, cadmium, 850. These constituents are all volatilizable at a lower temperature than zinc and lead. Hence when they occur in appreciable quantities I dispose of them by subjecting the fume to a moderate heat at a temperature of from 500 to 800 Fahrenheit in any well known form of muffle furnace, thereby revolatilizingsuch more volatile constituents, care being taken not to apply sufficient heat to revolameans of this roast the fume is purified from its more volatile constituents, thereby easily eliminating all those impurities which are soluble in the electrolyte employed and which would otherwise enter into solution with the zinc and contaminate the deposited product.

Other metals which may have been contained in the ore, such as iron, gold, silver, &c., are not driven off with the volatilized product but remain in the furnace in the form of cinder or slag and may afterward be smelted out and recovered in the usual manner.

I do not confine myself to the above described mode of producing or purifying the zinc fume, as this may be done in any suitable way, it being only necessary to my invention that I should have for maintaining the electrolytic bath by regenerating the same and annulling the free acid therein, a zinc product of such a nature chemically that it will not carry to the bath an acid molecule for example a zinc salt and one which is properly purified from the soluble impurities contained in the ore. The zinc solution to be subjected to electrolysis may be primarily prepared by forming a solution of a zinc salt or salts in any usual or suitable manner and with any suitable acid or mixture of acids provided only that the solvent acid used is not a solvent of lead where lead is present in the zinc product used in regenerating the solution; thus the solution may be prepared by dissolving metallic zinc in dilute sulphuric acid, or sulphate of zinc in water. In case the solution as first prepared contains in solution any impurities which would be deposited with the zinc upon the cathode, they must be removed from the solution before the production of pure zinc canbe begun. This may be done by passing a current through the solution until all the impurities are deposited upon the cathode or precipitated out. The impure deposit or precipitate thus obtained should then be removed and if carrying zinc may be returned to the roasting furnace for volatilization and purification. I may however obtain a pure solution in the first instance by the use of the purified zinc fume already described. For this purpose the fume is mixed with dilute sulphuric acid as a solvent, in a treating tank shown in the drawing at A, in such proportions as to form a concentrated solution. The zinc will be dissolved, while the other constituents such as the lead sulphate, &;c., which constitute the only impurities now remaining, being insoluble are not acted upon and consequently sepa rate out and settle to the bottom of the tank, leaving a clear solution which contains of all the elements originally present in the core, only the zinc, from which the others will now have beenseparated by the preceding steps of the process. The clear solution is next drawn off through a pipe seen in the drawing at 1, into a feed tank B, whence it is conveyed to the electrolytic baths 0, c, o, by

pipes

2, 2, 2, opening into the bottoms of the baths. The pure solution is now ready for the depositionof the zinc contained in it by the application of the electric current. For this purpose the baths are supplied with anodes of suitable material such as lead or carbon, insoluble'in the solution and cathodes which may be plates of zinc or copper.

The anodes and cathodes are connected with mains L L, leading from a suitable source of electricity D, such as a dynamo of proper capacity. If desired the solution may be heated to lower the resistance of the baths. Current is now applied and zinc from the solution is deposited upon the cathodes. As the zinc is deposited free acid is liberated in the baths and being lighter than the solution rises to the surface. In order to neutralize the free acid and at the same time maintain the original degree of purity and gravity of the solution, the free acid is drawn from the baths through overflow pipes, 3, 3, 3, and carried to a tank E. The treating and feed tanks and the baths and overflow tanksshould be set upon different levels so as to produce a natural flow from the treating tank and through the baths and thence to the overflow tank. By means of a pump P the acidulated solution in the tank E is raised to the treating tank A, through the pipe 4. It is there neutralized by the addition to it of a fresh supply of purilied zinc fume, the zinc being soluble in the dilute free acid, After any insoluble constituents of the fume have settled out the solution is led to the feed tank B and thence, as required, to thebaths to maintain the solution therein. Since 'the overflow from the baths will contain a considerable proportion of zinc a portion of it may if desired be returned directly to the feed tank B, through the pipe 5 to be passed again through the baths instead of being regenerated in the first instance. In

this mannerl easily and effectually annul the free acid, and maintain the solution in its original state, sinceI always have a sufficient supply of purified zinc fume therefor,and thus enable the process to be carried on indefinitely. At the same time I maintain a continual circulation through the baths and prevent the stratification of the acid which would take place if the solution were not kept in motion.

In case there should be small amounts of zinc salt in the oxidized zinc fume used in annulling the free acid it will not seriously interfere with the operation of the process since any difficulties that might arise from its presence may be easily obviated by removing a small portion of the solution from time to time and substituting water in its place. There will practically be no loss of Water will have to be added to the solution from time to time in small quantities to supply the slight loss that will take place. The deposited zinc may be stripped oi the plates and melted, or where zinc plates are used as cathodes the plates may be melted whenever a sufliciently heavy deposit has been formed upon them.

Any other convenient electrolytic apparatus may be employed, and I wish it to be understood that I do not limit myself in any portion of my process to any particular form of apparatus for putting it into practice. Nor does the manner oforiginally preparing the electrolyte to be used nor the degree of purity attained therein form any part of my present invention which is directed particularly to regenerating the bath by neutralizing thefree acid liberated therein in such a way as to maintain the solution in its origina purity.

The advantages of my invention will be readily apparent to those skilled in the art since it enables the easy and economical production of zinc from its ores, and by its use vast quantities of ore heretofore waste and of no value can be reduced to their component metals and made valuable.

Having thus made known my improvement, what I claim as new, and desire to secure by Letters Patent, is

1. The hereinbefore described process of continuously producing metallic zinc by electrolysis, which consists in depositing the zinc from an acidulated solution of a zinc salt, drawing 06 from the bath the free acid liberated therein, dissolving in such acid oxidized zinc, in the state of fume, freed from its more volatile soluble impurities, and returning the solution thus formed to the bath from time to time, as required, to maintain the electrolyte, substantially as set forth.

2. The hereinbefore described method of maintaining and regenerating an acid zinc electrolyte which consists in dissolving in the acid set free in the bath during electrolysis oxidized zinc in the state of fume, freed from its more volatile soluble impurities, and maintaining the electrolyte with the solution thus PARKER C. CIIOATE.

Witnesses:

BENJAMIN BARKER, .Ir., OLARKsoN A. OoLLINs.