US1415526A - Process for recovering selenium and noble metals from electrolytic slimes and the like - Google Patents

Description

RTE D. STATES PAET MASUIMI GmASHIG-E AND DENZO UN'O, OF KYOTO, JAPAN.

PROCESS FOR REGOVEAING SELENIUM AN'D NOBLE METALS FROM ELECTROLYTIC SLIMES AND THE LIKE.

No Drawing.

Kamikyo-ku', Kyoto, Japan, both J apanese' subjects, have invented certain new and useful'Improvements in and Relating to a Process for Recovering Selenium and Noble Metals from Electrolytic Slimes and the like; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process for extracting non-metallic elements of the sulphur grou and the noble metals, such as silver, gol platinum and the like, from refuses, for example, electrolytic slimes, mattes and fluedust, produced in refining copper, silver, gold platinum and similar metals.

This invention consists in completely separating-selenium and other elements of the sulphur group and the noble metals from each other, and in bringing elements in both groups by the same operation into such forms as render them readily recoverable. Separating the two groups and at the same time bringing thehelements in both groups into easily recoverable form has, so far as we know, been impossible in any known process heretofore used.

The process consists in fusing a mixture containing the non-metallic elements of the sulphur group and the noble metals with reagents capable of effecting a separation of these constituents from each other, in fusion products of different specific gravities insoluble in each other, andrecovering from the fusion-products the valuable contents. This may 'beattained by fusionwith a collector of the noble metals, preferably lead, and an alkali metal compound: Suitablealkali metal compounds are the caustic alka-- lies and the alkali carbonates and nitratesa Alkali metal compounds of this character are generically designated by the expression an alkali metal flux. When the fusion is completed the mass naturally divides itself into three layers or zones according to the difference of specific gravities of its constituents. All the noble metals contained in Specification of Letters Patent.

recover both at the same time. to this invention it is possible to recover the Patented May 9, 1922.

Application filed October 1, 1919. Serial No. 327,736.

the material, will constitute-the bottomlayer in the form of a lead alloy or alloys while selenium and the like, forming compounds with the alkali-metals, will float and form the uppermost layer. The remaining metals together with other metallic salts will constitute the middle layer.

The object of this invention is to provide a very simple, efficient and-inexpensive process whereb all the selenium and other elements of t e sulphur group and the noble metals contained in the materials treated,

may be extracted and completely recovered in elemental form.

If selenium or other elements of the sulphur group are contained'even in a tracein any noble metal, the good 'quality of such metal is damaged' The removal of such impurity during refining is, therefore, a matter of great importance.

Since selenium and like elements have strong chemical ailinity for the noble metals, and as they appearin the same group with the latter in course'of analysis, it has hitherto been practically impossible to separate the non-metallic elements and the noble metals one from the other, in such a manner as to According non-metallic elements of the sulphur group and the noble metals from a mixture containing the same without substantial loss of any of the constituents. This is realized by utilizing the following properties in combination, namely, (1) prominent chemical af- .finitybetween non-metallic elements of sulphur group and alkali-metals, (2) easy formation of alloys of lead with noble metals, I

and natural separation of non-metallic elements of sulphur group combined with alkali-metals, on the one hand, and alloys of lead with noble metals, on the other, accord ing to thedifi'erence of specific gravities of the products in the fused state.

. In order that the invention may be ea sily v understood, an application of the process for extracting and recovering the element selenium and the noble metals from an electrolytic slime produced in copper refining, will now be described and illustrated, by way of example.

In carrying out the process for example, with electrolytic slime which usuall contains selenium, silver and gold as wel as a small proportion of copper, one or more of the caustic alkalies, alkali carbonates or nitrates, is added to the slime in such quantity as is sufficient, or more than sufiicient to convert the whole of the selenium contained in the slime into alkali compounds of selenium. .At the same time, lead is also added to the slime in such av proportion as to form an alloy with the noble metal contained therein. If lead is present in the slime used, the addition of the same may be entirely omitted or the amount decreased in proportion to the lead-contents of the slime, The ingredients are carefully mixed and subjected for two or three hours to a suitable temperature, preferably 800-900 0., which will vary according to the amount of selenium and alkalies present. It is understood that the temperature and time factors will vary somewhat with the character of the material under treatment. lVhen the chemical reaction is completed, the fused substances naturally separate into three layers according to the difference of specific gravities of the respective fusion-products.

The noble metals converted into lead al-" loys will form the undermost or bottom layer together with a portion of copper if the same is present in the original material treated.

The alkali selenides, selenites or selenates will form the uppermost or surface layer, while the middle layer will be composed of residual copper and other metallic salts in case copper or other metals are contained in the material originally treated.

Chemical reactions occuring during the fusion, may be represented by the following equation where, for brevity, it is assumed that the noble metal present is silver only 1. When caustic soda is used:

2. Then sodium carbonate is used 3. When sodium nitrate is used:

It is understood that similar reactions will occur if gold, platinum or other metals of this group are present in the material undergoing treatment.

The function of the lead is simply to form alloys with the noble metals which are present in the free state during fusion.

The separation of gold and other noble metals may be accomplished by any well known process for example, cupellation.

In order to recover the selenium from the surface layer-mass the latter is dissolved in water and an acid, for example, sulphuric or hydrochloric, added thereto to neutralize the excess alkali, after which air is passed through the solution to precipitate the selenium present. This-reaction may be represented by the following equation Selenium may still remain as selenite or selenate in the solution. It may be reduced to elementary form by passing sulphur-dioxide .through the acidified solution, and this reaction may be represented by the following equation Na,SeO,+2SO +H O:Se-l-2NaHSO,

Tellurium may often occur associated withselenium in the slime and if present passes into the surface layer together with selenium and other non-metallic elements.

When the surface layer is treated in the manner stated above, tellurium is precipitated at the same time as selenium. Separation of tellurium and selenium may be effected by any of the known processes.

The process of this invention may be applied to mattes and flue dust in exactly the same manner as in the case of eletrolytic slimes except that the mattes must be finely pulverized before alkalies are added to the same.

We claim 1. A process for treating material containing non-metallic elements of the sulphur group and the noble metals, compris-.

ing fusing the same in the presence of a collector of the noble metals and an alkali metal flux, and recovering the non-metallic elements of the sulphur group and the noble metals from the fusion-products.

2. A process for treating material containing non-metallic elements of the sulphur group and the noble metals, comprising fusing the same in the presence of lead and an alkali metal flux and recovering the nonmetallic elements of the sulphur group and the noble metals from the fusion-products.

3. A process for treating material containing non-metallic elements of the sulphur group and the noble metals, comprising fusing the same in the presence of lead anda sodium flux, and recovering the nonmetallic elements of the sulphur group and the noblemetals from the fusionsproducts.

Lamaze 4. A process 'for treating material containing selenium and the noble metals, com prising fusing the same in the presence of a collector of the noble metals and an alkali 5 metal flux and recovering the selenium and the noble metals from the fusion-products.

5. A process for treating material containing selenium and the noble metals, comprising fusing the same in the presence of lead and an alkali metal flux, and recover- 10 ing the selenium and the noble metals from the fusion-products.

In testimony whereof, we afiix our signatures.

MASUMI GHIKASHIGE.

DENZO UNO.