US2039331A - Method of treating a zinc bearing ore material - Google Patents

Description

y 1936- T. A. MITCHELL I Q 2,039,331

METHOD OF TREATING A ZINC BEARING ORE MATERIAL Filed NOV. 5, 1954 FILTER oezczzsoucl AL ZnCl CQCI:

J'F'Eoucrmnl FUE'NHCE w --|E- ZnS +cao+c Zn+CqS+CO CO v HIR Z C Fumes 31 2 :33.1

ICONDENSERI ZINc.

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grime/WM THo/vms H. MITCHELL Patented May 5, 1936 UNITED STATES IMETHOD OF TREATING A ZINC BEARING ORE MATERIAL Thomas A. Mitchell, Denver, Colo., assignor to Hughes-Mitchell Processes, Incorporated, Denver, 0010., a corporation of Wyoming Application November 5, 1934, Serial No. 151,475

6 Claims.

This invention relates to a method of treating a zinc bearing ore material and deriving zinc metal and zinc compounds therefrom.

An oxidized zinc ore may contain a considerable quantity of zinc oxide intermingled with various other ore materials and the gangue, and many problems have been faced heretofore in deriving zinc metal from such an ore, and particularly if it is complex in its nature. For example, a high content of lead in a roasted zinc sulfide ore makes it difficult to smelt the ore by standard procedure and to recover zinc metal therefrom.

A primary object of this invention is to provide an economical and eflicient method of treating an ore material containing zinc oxide together With other compounds for the production of zinc metal or zinc oxide.

A further object is to provide a cyclic process of treating an ore material containing zinc oxide, which involves a preliminary hydrometallurgical procedure combined with a reduction furnace step that cooperate with one another and result in the economical production of zinc metal. Various other objects will be apparent in' the following disclosure.

Referring to the drawing, I have there shown as a flow diagram the various steps required for deriving zinc metal from a zinc sulfide or'e or other material containing zinc oxide; but it is to be understood that the primary features of this invention may be employed for the treatment of various other types of zinc bearing material,

and that the various steps of the process may be suitably modified in accordance with the nature of the substance being treated.

Assuming that the ore is a complex ore containing zinc sulfide associated with other materials, such as iron and lead sulfides together with the usual gangue, this ore may be roasted in accordance with standard procedure to develop a considerable amount of zinc oxide therein and, if desired, the process of the prior patent to Mitchell No. 1,943,331 of January 16, 1934 may be adopted in so far as it applies to the present process, and particularly where the ore tends to sinter easily during the roasting operation or where it is desired to convert the major portion of the-zinc sulfide to zinc oxide and to obtain a pulverulent material which may be readily treated by fluid reagents. It, however, is to be understood that various other types of roasting operations may be employed within the scope of t is invention, and that if zinc sulfate is formed,

it will be readily converted to zinc chloride by ZnO+CaClz+COz=ZnClz+CaCO3 In accordance therewith, I propose to treat the oxidized ore material, and preferably while still hot as it comes from the roaster, with a solution of an alkaline earth metal chloride, such as barium, strontium or calcium chloride, and in the presence of carbon dioxide gas. This step results in the conversion of zinc oxide to zinc chloride with the precipitation of alkaline earth metal carbonate, although an excess of alkaline earth metal chloride may remain, if desired, in the solution. This particular procedure is preferably carried out in an absorption tower, in which the roasted ore material or other zinc oxide bearing material employed in the process is in a finely divided condition, and preferably one which will pass through a screen of meshes to the linear inch. Ordinarily, I use'cal- .cium chloride as the chlorine bearing reagent and in a strong aqueous solution. The ore material together with the calcium chloride solution is preferably passed downwardly over a series of baflles in a high absorption tower, while carbon dioxide gas is maintained in the absorption tower under a sufiiciently high pressure to insure an efficient reaction. If desired, the absorption tower may be jacketed and heated to any suitable temperature by an externally heated gas, such as may be derived from the roaster. Also, various provisions will be employed to insure that the resultant zinc chloride solution is of a sufiiciently high concentration for the purpose. This may be obtained by passing the sludge of ore particles and solution repeatedly over the bailies of the tower by means of a recirculating pump, and the operation will be kept up until the zinc chloride solution is-of a sufficiently high concentration. Also, the temperature and pressure on the gas will be so regulated as to render'the process efficient. It is preferred to have the temperature of the solution near the boiling point and to apply sufficient pressure on the gas, such as one atmosphere or more, to insure that a considerable volume thereof is in intimate contact with the ore sludge. If zinc sulfate is formed during the roasting operation, or is present for other reasons, the alkaline earth metal chloride will react directly therewith and form zinc chloride together with a precipitate of alkaline earth metal sulfate. Hence, it is not necessary to roast a sulfide ore wholly to the oxide condition. In this way, it is easy to obtain a zinc chloride solution which has a strength as high as 50 B.

When the zinc chloride solution has been made sufiiciently strong, then the ore residue and solution are passed through a suitable filter or other separating apparatus which serves to withdraw the solution from the ore residue, and the latter may then be treated as desired. The zinc chloride solution, which may contain calcium chloride, may now be treated in any suitable manner to purify it from undesired elements, as is determined by chemical analysis and in accordance with the nature of the material being treated. Any suitable and standard procedure may be adopted for this purpose.

The next primary feature of the invention involves the chemical reaction of:

In accordance with this equation, calcium sulfide or other alkaline earth metal sulfide, such as barium or strontium sulfide, has the capacity of precipitating zinc sulfide from its chloride solution. It will be understood that if calcium chloride is used in the first stage, then calcium will preferably be used at this point. It is likewise desirable to employ barium or strontium sulfides at this stage if their chlorides were used in the preliminary chloridizing operation, although one may use two different metal ions, if desired. The process is described herein as involving the use of calcium compounds only.

In order to carry out this second stage step, it is preferred that the calcium sulfide be present in a finely divided condition, and that it be suspended initially in a solution of calcium chloride of high strength so as not to dilute the reacting solutions unnecessarily. Then, this suspension of calcium sulfide is introduced into the solution of zinc chloride of high strength, and the mixture is thoroughly agitated, with the result that zinc sulfide is formed as a precipitate and calcium goes into solution as calcium chloride. If the initial zinc chloride solution were of 50 Beaum, the resulting calcium chloride solution may be' of approximately 40 B. This means that the calcium chloride solution is, therefore, in condition for re-use in-the process without evaporation of its water content, or it is available for other purposes. It, of course, is feasible to regulate the concentration of the solutions as desired.

It will now be appreciated that I have provided a very simple procedure for forming zinc sulfide from a zinc sulfide ore or any zinc oxide material, and this zinc sulfide may be recovered and utilized as an article of commerce or otherwise treated. I

In case it is desired to produce zinc metal or zinc oxide, this may be accomplished by heating the zinc sulfide with lime and carbon. To this end, the zinc sulfide is separated from its calcium chloride solution on a suitable filter, and the zinc sulfide may be washed or otherwise treated to remove the undesired solution therefrom. The zinc'sulfide may now be mixed with lime and coke which are proportioned to react in accordance with the following equation:

ZnS+CaO+C:Zn+CaS+CO The lime, carbon and zinc sulfide may be mixed in the proportions of 59% ZnS, 34% CaO and 7% carbon, as measured by weight. Various procedures may be adopted for mixing the material, which may be accomplished with the zinc sulfide either wet or dry. One simple method is to take the wet zinc sulfide as it comes from the filter and washing steps and mix it intimately with lime and coke in the proper molecular proportions, or with the reagents in excess if desired, and then to form small briquettes of theingredients. These are then introduced into a suitable reduction furnace, and heat as is required is applied to cause the conversion of the zinc compound to the metal.

It will be appreciated that this reduction proc-- ess involves a self-contained reaction in which the oxygen content of the lime and the carbon are present in amount sufiicient to free the calcium and permit it to react with the zinc sulfide to form calcium sulfide and leave metallic zinc. This reaction does not require an excessive amount of carbon, as would be necessary if one were reducing zinc sulfate instead of zinc sulfide. Also, if alkaline earth metal sulfide remains in excess with the zinc sulfide, this will not matter and particularly if one uses the oxide of the same metal as was used in making the zinc sul- The carbon monoxide gas given off from this furnace may be now oxidized to carbon dioxide by burning the same in air, and this carbon dioxide is then available for returning to .the first absorber stage, as is indicated on the drawing. Thus, the process is cyclic with regard to the carbon dioxide evolved from the reduction furnace. It is also to be understood that the ore residue containing the calcium carbonate, as derived from the first absorber stage, may be treated with dilute hydrochloric acid to decompose the calcium carbonate and re-form carbon dioxide for further use in the process, as well as calcium chloride in solution, which may be likewise returned to process.

The reduction furnace may be of any suitable construction, and this particular phase of the process may be carried on in accordance with the requirements; butit is preferable that the furnace temperature be sumciently high so that the zinc will be evolved in a vapor condition and condensed in a suitably cooled zone outside of the reduction zone. This serves to separate the zinc from the residue of calcium sulfide and leaves the latter free for return to process, as indicated on the drawing. The zinc fumes, after being caught in a condenser, may be molded into slab formor otherwise recovered. If desired, the zinc fumes may be oxidized by the admission of air to the hot fumes which serves to burn the same to zinc oxide. The zinc oxide may be recovered by means of a baghouse of suitable design.

It will now be appreciated that these various steps cooperate towards a useful result. In this way, I have provided a process whereby a considerable proportion of the zinc content of an ore may be first converted to zinc oxide and then to zinc sulfide, and finally to zinc metal by a series of steps in which compounds of an alkaline metal are utilized in all of the stages, and in which various compounds employed as reagents are used and recovered cyclically in the process. The economical advantages of this procedure will be readily apparent. I

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent is:

1. The method of recovering zinc from an ore material containing zinc oxide comprising the steps of treating the material in finely divided condition with a solution of alkaline earth metal chloride and carbon dioxide and forming zinc chloride, separating the resultant solution from the ore residue and treating it with sufficient alkaline earth metal sulfide to precipitate the zinc as a sulfide, and thereafter heatingthe zinc sulfide with alkaline earth metal oxide and carbon to reduce the zinc sulfide to zinc metal and form alkaline earth metal sulfide, and separating the zinc from the furnace residue.

2. The method of claim 1 in which compounds of the same alkaline earth metal are employed as reagents at the various stages, whereby the alkaline earth metal chloride and sulfide may be returned for cyclic use in the process.

3. The method of making zinc sulfide from a raw ore containing the same comprising the steps of roasting the ore and producing a finely divided ore material containing zinc oxide, treating the product with a solution of an alkaline earth metal chloride and carbon dioxide and producing a solution of zinc chloride of high concentration, treating the zinc chloride solution with alkaline earth metal sulfide in amount suflicient to precipitate all of the zinc as a sulfide, and thereafter separating the zinc sulfide from the solution, said alkaline earth metal sulfide being initially suspended in a strong solution of the chloride of the same alkaline earth metal as was used in the chloridizing step, whereby the resultant solution will be 01 high strength and capable of reuse in the process. 7 v

4, The method of making zinc from a raw ore containing the same comprising the steps of roasting the ore and producing a finely divided ore may terial containing zinc oxide, treating the product with a solution of an alkaline earth metal chloride 5. The method of claim 1 in which the zinc -metal is volatilized by heat and thus separated from the furnace residue, after which the fumes are treated with air to form zinc oxide.

6. The method of treating an oxidized ore material containing zinc oxide comprising the steps of converting the zinc oxide to a chloride by treating the ore in finely divided condition with calcium chloride in a strong aqueous solution and carbon dioxide gas, and continuing the treatment until a strong solution of zinc chloride is obtained, separating this solution from the ore residue, treating the solution with calcium sulfide suspended therein and proportioned to precipitate the zinc as zinc sulfide, separating the precipitate from the solution, mixing it in stoichiometric proportions with lime and carbon for producing zinc, and heating the mixture to produce zinc as a vapor which is thus distilled from the residue and recovered.

THOMAS A. MITCHELL.

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