US1337058A - Purification of zinc solutions - Google Patents

Description

UNITED STATES PATENT OFFICE.

SAMUEL FIELD, OF LONDON, ENGLAND, ASSIGNOR TO THE METALS EXTRACTION CORPORATION LIMITED, OF LONDON, ENGLAN'D.

PURIFICATION OF ZINC SOLUTIONS.

No Drawing.

To all whom it may concern:

Be it known that I, SAMUEL FIELD, a subject of the King of England, residing at London, England, have invented certain new and useful Improvements in the Purification of Zinc Solutions, of which the following is a specification.

This invention is for improvements in or relating to the preparation of zinc solutions for electrolysis, and itrefers more particularly to' the purification of zinc sulfate solutions obtained'by the treatment of zinc ores or zinc-containing materials with sulfuric acid from which solutions the zinc is subsequently deposited electrolytically.

As is well-known, to obtain a successful deposition of zinc by electrolysis, the .zinc sulfate liquors must be of a high order of purity; impurities such as copper, cadmium, iron antimony, arsenic, nickel and cobalt must be completely eliminated or substantially so, as they affect adversely and very seriously the deposition both qualitatively and quantitatively.

In some cases, as with cadmium, the metal is deposited with the zinc and renders it brittle and valueless. In the treatment of zinc sulfate solutions by electrolysis I have found that one of the most serious impurities is the metal nickel, which even in minute quantities, prevents the satisfactory formation of a zinc deposit on the cathode; indeed, after a good deposit of zinc has been obtained, if nickel enters into the solution, the deposit of zinc may become pitted and rapidly disappear, and to get a satisfactory electrolysis of zinc sulfate solutions I have found it necessary that the nickel be reduced to a quantity of the order of one-half to one part per million of liquor or less.

It has hitherto been common practice to remove these impurities in a series of steps by precipitating each with a suitable preclpitant. It is an object of the present invention to provide a process whereby a number of metals other than zinc may be completely precipitated in a single operation.

Copper, cadmium and similar very elec- Specification of Letters Patent.

Patented Apr. 13, 1920.

Application filed September 26, 1919. Serial No. 326,577.

tro-negative metallic impurities have hitherto been removed from zinc solutions by tube milling with zinc balls or agitating the solutions with zinc dust, and the methods employed for removing iron also result in the simultaneous removal of arsenic and antimony when present.

solutions with zinc fume or blue powder in the presence of a small proportion of'acid, for example 0.1% or less at a temperature of 80 to 100 C. whereby the nickel content of the solution is reduced to substantially 0.5 part per million or less.

In carrying the present invention into effect to obtain a pure solution of zinc sulfate from ores or zinc in containing materials for the subsequent electro-deposition of the zinc, the zinc ore or zinc-containing material, roasted if necessary, is treated with the acid, for example, acid liquors from the electrolytic cells in which zinc has been deposited, and from the solution'thus obtained any iron, arsenic and antimony are first removed by known methods. The solutions are run into a tank fitted with suitable arrangements for heating, and provided with a paddle or agitator to effecif gentle stirring. Sulfuric acid is added in a quantity of 7 to 14 lbs. of 70% acid to 5 to 0 tons of liquor, and the solution is raised to a temperature of from 80 C. to 100 C. The zinc fume or blue powder is then added. A much larger proportion of zinc is employed than is theoretically necessary to replace chemically or electrochemically the impurities.

The solution is stirred gently in order to bring about a maximum contact between the zinc and the liquors, and any copper. cadmium and nickel present are readily precipitated. Thus the three metals, copper, cadmium and nickel are readily removed in a single operation with concomitant saving of time, labor and other charges, reducing the cost of purification.

It has, however, been found that the re moval of nickel and cadmium from zinc solutions by this method is greatly facilitated by the presence of copper. Normally copper is present in many of the ores and products which are amenable to the electrolytic recovery of zinc. In the absence of copper and to take advantage of this discovery I add copper to the solution by one or other of several methods. Thus a $0111- ble copper salt, for example copper sulfate, may be added to the solution. Alternatively a small quantity of suitable copper ore, for example, one of the carbonates may be added in the process of extracting the zinc from the ore or other zinc-containing material. When copper is present the immediate precipitation of this more electronegative impurity establishes electro-chem- -ical conditions which effect the precipitation of cadmium and nickel.

It has further been observed that when zinc is used at an elevated temperature for the removal of nickel in the absence of acid, there is a tendency to the formation of basic zinc sulfate. This substance produced on the zinc slows down the rate of precipitation of the nickel. With the use of acid as herein described this formation of basic zinc sulfate is much less marked. If formed, however, its retarding effect on the process of purification can be counteracted by the addition of a furthersmall quantity of acid, or alternatively, the basic sulfated zinc may be washed with weak sulfuric acid which can be subsequently added to the acid liquor used for the solution of the zinc from the ore or other material. The

acid Washed zinc is thus rendered effective for further purification.

What I claim as my invention and desire to secure by Letters Patent is 1. The hereindescribed process for the preparation of zinc sulfate solutions (free from copper) for electrolysis by purifying the solutions from nickel and cadmium, which consists in adding a small proportion of acid, heating the solution to a temperature of 80 to 100 0., adding a small proportion of copper in soluble form, adding zinc powder, and agitating the mixture whereby the nickel content of the solution is reduced to substantially 0.5 part per million or less.

2. The hereindescribed process for the preparation of zinc sulfate solutions for electrolysis by purifying the solutions from nickel, copper and cadmium, which consists in adding a small proportion of acid, heating the solution to a temperature of 80 to 100 C., adding zinc powder, agitating the mixture and adding free acid to the zinc solution during the process of purification, whereby the nickel content of the solution is reduced to substantially 0.5 part per mil-. lion or less.

8. The hereindescribed process for *the preparation of zinc sulfate solutions for electrolysis by purifying the solutions from nicke copper and cadmium, which consists in adding a small proportion of acid, heating the solution to a temperature of 80 to 100 C., adding zinc powder, agitating the mixture whereby the nickel content of the solution is reduced to substantially 0.5 part per million or less, and treating the precipitate with dilute acid to revivify the zinc for re-use.

In testimony whereof I aflix my signature.

SAMUEL FIELD.