US2074210A - Method of preparing metallic sulphates from sulphide ores and the like - Google Patents

Description

March 16, 1937. J. H. CALBECK METHOD OF PREPAR ING METALLIC SULPHATES FROM SULPHIDE ORES` AND THE LIKE Filed April l5, 1955 Patented Mar. 16, 1937 METHOD 0F PREPARING METALLIC STIL- PHATES FROM SULPHIDE ORES AND THE LIKE John Henry Calbeck, Columbus, Ohio, assignor to American Zinc, Lead & Smelting Company', St. Louis, Mo., a corporation of Maine Application April 15, 1935, Serial No. 16,521

14 Claims.

This invention relates to the preparation of metallic sulphates from metallic sulphides and has as its principal object the conversion of such sulphide ores as sphalerite, galeria, pyrite, etc., into corresponding sulphatesk. This invention is based on my discovery that if a metallic sulphide` ore, such as ZnS, is heated with ammonium bisulphate, the sulphide is converted into the sulphate of the metal and the ammonium salt is 'l0 reduced to the sulphite, sulphur andv water according to the following equation: l

ZnS+2NH4HSO4=ZnSO4+ (NH4) zSOs-l-Sq-Hzo I have discovered that .this reaction begins at temperatures between 150 C. and 200 C., but the reaction is most rapid and the most satisfactory results are obtained at between 350 C. and 440 C.,\ at which temperature the ammonium sulphite and sulphur are easily volatilized andmay be condensed and collected by appropriate means.

It is not necessary to use temperatures as high as 440 C., which is the boiling point of sulphur, for l the reason that the sulphur is somewhat volatile in the ammonium sulphite and at 350 C.,'al1

V the sulphur will pass over with the ammonium sulphate. I am aware of the fact that ammonium sulphite isprobably dissociated in the vapor phase and is in reality only a mixture of NH3 gas and SO2 gas and water vapor, but

throughout the description I shall refer to the ammonium sulphite as if it were completely volatile as such in order to obtain clarity and brevity.

The invention has for its further object the control of the above described reaction so las 'not only to obtain complete sulphation of the metallic sulphide but also to obtain economy in the use of ammonium sulphate, and further, to obtain the volatile products driven off during' the reaction in a condition in which they 'may be readily marketed or used. vThe method of the inventionv is particular/1y adapted to the production of thel water soluble sulphates, such as copper and zinc,

, which are used extensively in hydrometallurgical and electrometallurgical processes as well as having an extensive market in the forium.Ssulphates.-Y

` sulphate which may be-used as an anticolor in industry or which may be used inthe manufacture of zinc sulphide pigment, according to the (Cl. Z3-125) method outlined in my copending application, Serial No. 688,413.

In order to describe the'invention in detail, the treatment of zinc sulphide ore will be given as an illustration, but it will be understood that the invention is equally efficient for the treatment of other metallic sulphides for the purpose of preparing the corresponding sulphates. Zinc sulphide concentrates are nely ground and mixed with nely ground ammonium bisulphate. The required amount of ammonium bisulphate is determined from the analysis of the zinc concentrates and should equal or slightly exceed two chemical equivalents of ammonium bisulphate for each chemical equivalent of zinc lead, iron and lime contained in the ore. This mixture is now charged into 'a mechanical muflle furnace, prefsalt cake from sodium'bisulphate and common salt. The charge may be passed through the iurnace continuously or it may be treated as a batch. In the former case, the temperature should be maintained at `between 350 C. and 440 C., and in the latter case, the temperature should be gradually increased until a maximum tempera'- ture oi 440 C. is obtained and held there until the reaction is complete.

At the beginning of the reaction, the ammonium bisulphate fuses,'forming a pasty mass, and rapid heating should be avoidedat this stage to prevent rapid evolution of the volatile products from causing excessive frothing or boiling over.

Toward the end of the reaction, the charge becomes slid and, under' the action of the rabbles of the furnace, is broken up so that at the end of y n 4 the reaction it may be discharged from the fur- "nace as small white grains, consisting largely. of

` formed may be purified of the various impurities by methods well known in ythe electrolytic zinc orlithopone industries., t During the heating in the mulile furnace there Vis v'a steady evolution offthe volatile products,

which may be Acollected in various 'well known ways, depending upon the nature of the product s desired and the use to which it is to bel put. It

is common to collect such fume`r` or-volatile products in water and by passing these products` 10 of ammonium thiosulphate. As far as I am aware, a sublimed or fumed ammonium thiosuiphate has never before been prepared. It is well known that ammoniumsulphite and sulphur react' in aqueous solution to form ammo- 15 nium thiosulphate, but to prepare thesalt from solution, evaporation under a vacuum must be resorted to and great care taken to prevent the decomposition of the salt. But I prefer to collect the volatile products in the form of a sub- -20 limate which consists of pure white, crystals of ammonium thiosulphate, and which need no further treatment in order to condition them for market.

'I'he sublimate is best collected in a jacketed 25 steel tower. Before the sublimation is begun,

hot air is passed through the jacket of the towerA to bring the temperature within the tower up slightly above 100 C. in order to prevent moisture condensing with the sublimate. As the sublimate begins to condense in the tower, the temperature rises and cold airis passed through the jacket as required to keep the temperature within the desired limits, 100 C.-150 C. I have discovered that the ammonium thiosulphate is not completely formed just as the sublimate condenses, but that some time is lrequired for the reaction between the sublimed sulphur and the sublimed ammonium sulphite to be completed. 40 In order that this conversion may .be complete `and that the iinal product contain a high percentage of thiosulphate and avery small per: centage of uncombined sulphite, it is highly important that the fume passing'intothe sublimate condenser shallhave yexactly .chemically equivalent proportions of ammonium sulphite and elemental sulphur at all times. In ordery that this may be accomplished, a numberof very important precautions should be taken:

1. The system should bekept free of" air .or other oxidizing gases.

A slight positive pressure on the system cony sisting of the muille and\sublimate condenser will be of considerable help in this regard. For this 55 'purpose I prefer to addga little ammonium sulphate to the charge. This ammonium sulphate breaks downin the ammonia gas and ammonium bisulphate according to the following equation:

The ammonia gas so generated prevents the in filtration of air andyany excessof ammonia may be collected in water in tower or in an absorber connected with the sublimate condenser.

2. The rate of volatilization and the temperature must be adjusted so that the sulphur gen# erated by Reaction (1) will passover with the ammonium sulphite as rapidly as itis formed.

,' Of course, if the temperature is kept at 440 C.

70 or above,' the sulphur will pass into the vapor phase as rapidly as formed and be carried over into the sublimation tower with the other gases.

But if the charge is well agitated the sulphur' will be taken over with the evolved gases at lower temperatures than its boiling point and this is desirable in order to prevent the sublimation of some ammonium sulphate which is somewhat volatile at the temperature of boiling sulphur.

3. The sublimate in the tower should be mainto add a certain amount of free sulphur and to substitute ammonium sulphate to produce NH3 (Equation (2)) for part or all of the ammonium bisulphate called for in Equation (1). The sulphur reacts with the oxygen to form SO2 and this SO2. reacts with free ammonia and excess elemental sulphur to form ammonium thiosulphate.

Ii' these precautions are taken the sublimate collecting on the walls and in the hopper of the tower will consist of between 90% and 99% ammonium thiosulphate inthe form of a dry snow white cake which is easily removed and packed in containers. A

The preparation of the ammonium bisulphate employed may be by the well known method of boiling ammonium sulphate in a pot or kettle until the free ammonia is boiled oi, according to Reaction (2). The molten mass of NH4I-ISO4 may be cooled in pans or flaked and the solid bisulphate pulverized and is ready for charging with the sulphide ore. However, I have found it more convenient to charge the ammonium sulphate into the mechanical furnace with the sulphide ore and allow both Reactions (1) and (2) to take place together. Combining the two equations, we obtain the following, which represents the reaction between a metallic sulphide and ammonium sulphate.

This reaction goes forward rapidly at a temperature of between 350 C. and'400 C. The

zinc sulphate remains in the furnace, the ami K consisting of a muiile section 2 surrounded by ues 3 through which hot gases from theiire box 4 circulate. The muille section 2 is provided with a feed hopper 5. by means of which. the material to be treated is supplied to the muiile section 2, and a discharge pipe 6 and a suitable raking device 1. A sublimate condenser 8v is connected to the muflie section 2 by a pipe 9, and said tower is provided with a jacket I0 through which hot or cold air, as may be required, is circulated by, means of a fan Il to regulate the temperature within the tower. An ammonia absorption tower l2 is connected to the sublimate condenser 8by a pipe Il. The tower l2 is 'partially iiiled 4 n 2,074,210 Y with water through the valved inlet I2. This make the dense ammonium thiosulphate liquor tower I2 is open to the air through a pipe I4 and fan I5 which discharges to the open air. Provision is made to circulate the water through the tower I2 by means of a pump I6 which takes -water from the bottom of the tower through pipe I1 and passes it through the cooling coil I8 and pipe I9 and delivers it into `the top of the" tower at 20. The coil I8 is located ina tank2I 10 through which cold water or other cooling media may Ire circulated, entering through pipe 2| and passing out through pipe 2l". Flow of gas through the system is regulated by a damper 22 Il. in the pipe An example of a typical continuous operation is as follows:

A charge is prepared by mixing 350 poundsflne flotation zinc concentrates, 800 pounds commercial ammonium sulphate and pounds pul- 20 verized sulphur. The furnace is maintained at .a

by turning on the pump begin to pass of! at once into the towers 8 and I2.

45 th'e bottom of the tower.

The sulphur and ammonium sulphitel condense together in the sublimate condenser 8, and the /ammonia gas passes on into the absorption tower I2 where it is dissolved in the cold water. In a short time, the temperature in the sublimate condenser begins to risc and a current of cold air is circulated in the jacket I Il of the sublimate condenser at the proper rate to keep the temperature below 150 C. but above 100 C. Theammonia gas dissolves in the water of the absorption tower I2 with the evolution of heat, and this heat is dissipated by passing the water from the tower I2 through the :,:oolirlg coils I8. As the deposit of sublimate grows in the tower 8, 'it falls from the walls and collects in a suitable hopper 8' at Occasional rapping on 8 may be necessary to the walls' of thetower l the walls from becoming prevent the deposit' on "-so-.thick as to prevent the dissipation of the heat through the walls. The sublimate may be re- 50 moved from the hopper at the lower part of the tower from time to time as required, care being taken to admit as little air as possible in the operation.` As the concentration of ammonia in solution in the absorption tower I2 builds up to a comercial concentration, the solution is removed through any suitable discharge opening, as for example, a spigot 28, and the solution thus removed'frcm the tower is replaced with water. The movement of the rakes in the muiile section 2 center outward to the periphery whence the nonvolatilizedi part is discharged through the pipe 6. The rate of feed of the charge to the furnace should beso adjusted that this discharge consists only of zinc sulphate and the gangue constituents of the ore, such as silica, calcium, sulphate. etc. The zinc sulphate thus `discharged is anhydrous and porous and -dissolves readily in water with the evolution of heat, and this water solution may be purified by well known methods, such as are commonly used in purifying zinc sulphate liquors. The dry ammonium thiosulphate sublimate discharged from the sublimate condenser 8 maybe marketed in the form in which it leaves 7seidtowenoritmeybedissolvedinwaterto of the furnace slowly works the charge from the required for the manufacture of zinc sulphide. The ammonia water solution withdrawn from the tower I2 may be used as a base in the zinc s ulphide process of my application Serial No. 688,413,

- or it may be marketed as aqua-ammonia.

In case it is desired to separate the sulphur fume from the ammonium sulphite fume, this can be done by using two sublimate condensers, similar to the tower 8, the two towers being connected in tandem. In this case the rst tower should be maintained at a temperature between 200 C. and 350 C. and the second chamber below 200 C. In this case a sublimate collects in the first chamber consisting almost entirely of elemental sulphur and in the second tower a sublimate collects consisting `almost entirely of ammonium sulphite.

It is not essential to collect the ammonium thiosulphate as a dry sublimate but it 'may be collected in water to form an aqueous solution. To

do this it is only necessary to replace the sub- Q limate condenser with anL absorption tower similar to the tower I2. In this case the temperature of the solutionshould be maintained near` 100 C. so that the free ammonia may be driven over into the ammonia absorption apparatus.

It will be apparent to those skilled in the art that certain modifications and variations of the process, as illustrated in the foregoing example, may be practiced without departing from the spirit of the invention as defined in the appended claims, and such modifications and departures as fall within the terms o f said claims are intended to be covered thereby.

What is claimed is:

1. In a method of preparing-a metallic sulphate from the corresponding metallic sulphide, the step which consists in calcining the sulphide with an ammonium sulphate at a temperature sufficiently high to volatilize allwreaction products except the sulphates.

2. In a method of preparing a metallicsulphate V from the corresponding'metallic' sulphide, the step which consists in calcining the sulphide with an ammonium sulphate at a 'temperature sufficiently high to volatilize the ammonium reaction products but not high enough to appreciably volatilize the ammonium bi-sulphate -or decompose metallic sulphate.

- 3. In a method of preparing -anhydrous zinc sulphate from zinc sulphide ore,` the step which consists in calcining the zinc sulphide ore with ammonium sulphate atV a temperature suficiently high to volatilize the ammonium reaction products but .not highenough to appreciably decompose zinc sulphate.

n 4. In a method of preparing anhydrous zinc sulphate and ammonium sulphite the step which consists in calcining zinc sulphideore with two chemical equivalents of ammonium bisulphate in the absence of oxygen and at a temperature high enough to volatilize ammonium sulphite but not high enough to volatilize ammonium bl-sulphate.

quantities, which comprises calcining zinc sulphide with twice the chemical equivalent quantity of ammonium sulphate in the absence of oxygen and at a temperature between 150 C. and 440 C., and passing the volatile products ilrst through a tower heated slightly above 100 C. to collect the ammonium sulphite and sulphur and then passing the remaining volatile products from the tower through cold water to collect the ammonia. v

'It A method of preparing ammonium sulphite which comprises calcining a metallic sulphide 'with an ammonium sulphate at a temperature high enough to volatilize ammonium sulphite, but not high enough to volatilize ammonium bi-sulphate nor decompose the metallic sulphate i formed,fand' collecting the ammonium sulphite.

8. A method of preparing ammonium sulphiteV and sulphurin chemically equivalent proportions l for the purpose of preparing ammonium thiosultemperature high enough to volatilize ammonium sulphite and sulphur but not high enough to volatilize ammonium bisulphate, and condensing the resulting ammonium sulphite and sulphur fumes together in a dry chamber at a temperature slightly above 100 C.

9. A method of preparing anhydrous ammonium thiosulphate which comprises calcining zinc sulphide with twice the chemical equivalent quantity of ammonium sulphate at a temperature between 150 C. and 440 C. in the absence of oxygen, condensing from the resulting Volatile products al mixture of ammonium sulphite and sulphur in chemically equivalent quantities at a temperature above 100 C. and holding the resulting sublimate at that temperature until substantially all the ammonium sulphite has been converted into ammonium thiosulphate.

monia in substantially chemically equivalent l0. A method 'of preparing ammonium thiosulphate which comprises calcining zincv sulphide with twice the chemically equivalent quantities of ammonium bisulphate at a temperature lbetween l C. and 440 C. in the absence of oxygen, sublimating the ammonium compounds and leaving a calcine of anhydrous zinc sulphate, then collecting the sublimates of-sulphur and ammonium sulphite and converting them to ammonium thiosulphate.

.11. A non-aqueous method -of preparing ammoniumthiosulphate, which includes subliming ammonium sulphite and sulphur inchemically equivalent proportions and condensing at a temperature above C. and maintaining the sublimates at that temperature until substantially all the sulphite has reacted with the sulphur to form 13. The method of recovering elemental sul- JOHN HENRY CAIBECK.

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