US1494674A - Chemicomechanical process for making an unalterable white pigment - Google Patents

Description

May 20 1924- DWORZAK CHEMICOMEGHANIGAL Pnocss Fon MAKING AN UNALTERABLE WHITE PIGMENT Filed May 26, 1919 E957* f2 aol? SfcoA/D FZ 001? i pigment.

Fatcnted May 20, 1924. i

UNITED lSTAT-as ADOLPH DWORZAK, 0F ST. LOUIS, MISSOURI.

CHEMICOMECHANICAL PROCESS FOR MAKING AN UNALTERABLE -WHITE PIG-KENT.

Application led Hay l26, 1919. Serial No. 299,873.

To all whom it may concern:

Be it known that I, ADoLrH Dwoaziui, a citizen of Russia, residing at the city of St. Louis and State of Missouri, have in-v vented a new and useful Chemicomechanica-l Process for Making an Unalterable White Pigment, of which the following is a speciiication.

My invention relates to improvements in chemico-mechanical processes for making au unalterable white pigment and 'my object is to provide simple, economical and uniform chemical treatment therefor and to provide apparatus for uniformly andy continuously and uniliterruptedly performing the several chemical steps, in a manner to continuously receive and convey raw materials through' the treatment steps to a continuous delivery of the finished product without manual assistance.

For my process I take common zinc blende which I convert into a purified solution of zinc sulphate and I take common baryta rock which I convert into a purified solution of barium sulphide and I then mix these two solutions at a proper temperature and in equimolecular proportion thereby producing the double precipitate which forms my I then grind, Wash and otherwise physically refine my precipitate thereby making it suitable for its intended use.

In my drawing I illustrate, in plan, three groups of mechanisms, which groups are by preference arranged one above another. as on' thefirst, lsecond and third floors. of a building, so that I may economize in thc `conveyance of substances from certain machines to subsequent machines. by gravity, and in my specification I employ numerals for designating the several mechanical treating means.

The zinc blende most suitablelfor my purpose is that containing about a sixty per cent metalliccontent. This I grind on an ordinary differential roll indicatedy by the numeral 5, on the drawing, and which is fed with the zinc blendeby an ordinary conveyor designated A, the differential roll being adjusted to deliver the mashed orc of such ineness as to let it pass a 40 to 60 mesh screen. The pulverized ore is next conveyed by a chute B to a rotary roast-ing furnace 6 located by preference on the second floor, it being fed to the furnace 6'by a continuous feeder 7 located at one end of the furnace. The rotary furnace 6 is heated by fuel, which is fed from the opposite end through a fuel feeder 8.

As the ore enters the furnace 6 it is ex posed to a graded'system of temperatures which at the entry end of the furnace' is not to exceedl570 F. As it progresses through the furnace by means of a screw conveyor, up to about three fourths of the furnace length it meets increasing temperature until at the three fourths point it is exposed to a temperature of about 1170o F. the temperature within the furnace decreases toward the discharge end where the temperature is not to exceed 660 F. The time during which the ore is treated is approximately six hours.` The purpose of this roasting step in the process is to drive ofl' the sulphur, bismuth, antimony and any other volatile impurities. l

The thus roasted. andoxidized ore is gravity delivered from the furnace 6, and at the delivery temperature, to an `enameled trough' 9.

At this point dilute sulphuric acid is added for the next step in my process. In order to make an acid solution of the proper strength I provide a lead linedtank 10 with an agitator 11 which tank has a delivery pipe 12 controlled by a valve 13. In this tank I prepare a mixture of sulphuric acid and water, the condensate from certain or various of the heating coils employed in my process, to a specific density of 1.160. The trough 9 is equipped with a screw conveyor so arranged as to move the roasted ore, .for its delivery from the vtrough 9 and at the same time thoroughly mix it with the acid solution. The trough 9 is provided with exteriorheating coils which maintain the mixture of roasted ore and sulphuric acid at a temperature of about 300 F.

The screw conveyor also is heavily enameled. to protect it from the corrosive action of the sulphuric acid.

Thereafter From trough 9 by means of its screw conveyor the mixture of ore and acid is delivered to a series of oblong, closed topped treatment tanks designated by numerals 14, 16 and 18, Each tank 14, 16 and 18 is provided with a screw conveyor designated 15,

17 and 19 and both the interoir ofthe tanks as Well as all exposed parts of the screw conveyors are protected from corrosive action of the acid either by lead covering or by `heavy enameling.

When the mixture of roasted ore and sulphuric acid is delivered to the tank 14 there is a. certain amount of sedimentation and in order to conveniently handle both the sediment land supernatant liquor I make these tanks of a novel shape lnamely that of a truncated substantially square, pyramidv which I place with its major axis at an an le of approximately ten and three fourths egrees to the horizontal.

The action of the screw conveyor is that of moving the sediment upwards on the given degree toward the end of the truncated pyramidal tank from which it is ejected into the larger end of an exactly similar tank 16 with its conveyor 17. At this point I add fresh dilute sulphuric acid from tank 10. The delivery from tank 16 is to tank 18 in which an exactly similar step is conducted, but in which tank the last metallic zinc out of the treated (roasted) zinc ore, is separated by its treating solution, namely the dilute sulphuric acid.

The conveyor I19 of tank 18 delivers the treated ore to a sump pit 20 where it is washed to recover any zinc left, with water, the condensate previously referred to, and the wash water removed by a pump 21 to tank 14. f'

During the step of treatment in the tanks 14.-, 16 and l18 the dilute sulphuric acid converts .the lzinc content of the roasted ore into soluble zinc sulphate which is carried along in solution. may obtain it is necessary that theconte'nt of these treatment tanks shall be heated to boiling point and to this end the tanks are provided with lead coils fed with steam.

The liquor containing the zinc as sulphate is pumped froml the third ofthe serieso tanks 18 by a pump 22 to tank 23. In tank 23 the zinc liquor is diluted with Water (oi condensation) and agita-ted until it is ofv a speciic density of 1.380,. The sulphuric acid treatment as above recited yields a solution of the zinc blende and accordin `to the proportion of ore and acid this solution may or may not contain free acid. Free acid is i objectionable to my process and if it be found here it is at this point to be neutralized by the addition of more zinc blende until a neutral solution is produced which neutral solution I call my zinc liquor.

By' the above recited series of steps I have extracted from the zinc blende all lof the available zinc and have adjusted the specific density of its solution to a point best adapted to my process of making unalterable white pigment and the sludge is drawn `oi at the ttom of said tank to pit 20 from which it In order that this effectmaybe discarded orreturned to be retreated if its zinc content justifies.

The zinc liquor as thus prepared contains extraneous and objectionable compounds, which as is well known to thosel versed in the art, cause by their chemical changes, reactions, 'or deteriorations, a degradation from pure white and itis therefore essential to the process of making an'` unalterable White that these be elminated.' The zinc liquor in tank 23 is therefore conducted from the top of the tank ytoan enameled or lead lined tank 24.

An intermediate step at this point is an electrolytic one, which takes place in the electrolytic cells 23. The -purpose of the electrolysis is that of the elimination of copper, and other bases of corresponding electrolytic potential. Bases of the cop er po# tential class are first electrolytica ly deposited at relatively low volta eS, while such bases as cadmium may simi arly be electrolyticall deposited but, with increased voltage, t 1e applicationrof lheat and as an adjunct agitation by heated air, all inthe presence of powdered zinc which is then added in the tank 24 inv which there occurs a second electrolytic treatment.

The zinc liquor now freed from the above mentioned bases and held in tank 24 is boiled by lead coils fed with steam and a itated 'by an 'air agitator which may be fe with hot air, or, should it be desirable to lower the temperature quickly, with cold air.

Much of the im urities thatV have been thrown down by e ectrolysis and the zinc dust are held in suspension in the zinc liquor wherefore it becomes necessary to remove them. The zinc liquor is therefore pum ed from the tank 24 by a pump 27 to a fi ter 28, where the several impurities mentioned abeve are removed from the zinc liquor.

The step of boiling in the tank 24 by heated coils 25 and agitation by air agitator 26 and pumping by pump 27 and filtering by filters 28 is twice repeated by duplicate apparatus, including tank 30, withl its heatin coil and agitator, pump 31. filter 32, an tank 33 with its heating coil and agitator, pump 34 and filter 35..

In` tank 30 barium carbonate' is added in suiiicient quantity to react with, and precipitate any iron that may be present and electrolysis is applied to precipitate any other lmpurities which may settle out 120,

ooI

'other in their rimpressed voltages, each voltage being appropriate to its particular electrolytic step and which actions are performed in the presencefof an additional appropriate reagent.

The resulting liquor is then cooled with air and tested for neutrality and if found acid the acid condition is neutralized by the addition of zinc oxide and .the foregoing neutralizing step is adjusted to give a neu,

tral solution at this step.

The liquor is now diluted with Water (the condensate) to adjust'its specicdensity to 1.283.

The liquor thus prepared consists primarily of zinc sulphate solution after passing through the filtration step 35 and is now suitable for the preparation of my unalterable White pigment and is stored in tank 36 for use later in the process.

i Concurrent with the preparation of the above described zinc sulphate solution I prepare a barium sulphide solution. This solution is prepared by taking crude baryta rock, pulverizing it in an ordinary pulverizer 37, to a neness corresponding to 100 mesh screen. Coal is likewise pulverized, the grade of coal being such as to contain not less than 14000 B. t u.' per pound.

The baryta rock and the powdered coal are thoroughly mixed in a mixer 38. The

proportion of ground baryta rock andground coal is approximately per cent of thel former and 30 per cent of the latter which proportionality depends upon the barium content of the baryta and the sulphur content of the coal. This mixed powder is wetted with just suliicient water to form a paste and this paste is gravity fed to a long rotary furnace 39 through which it travels continuously, this furnace-is in all respects similar to. furnace 6, used in the treatment of the zinc blende, but. in the treatment of the baryta and coal mixture the maximum temperature is approximately 1600o F. and exposed for a much shorter period, namely two and one halfl hours.

By this step, the baryta rock is converted into barium sulphide which is soluble. The material thus treated is delivered from the furnace 39 to a heated trough 40. The Whole step herein recited being identical with the parallel step in the described zinc treatment.'

From the trough the baryta product is delivered to a series of three truncated, square, pyramidal lixiviators similar in all respects to tanks'14, 16 and 18 and their screw conveyors 15, 17 and 19, where the barium sulphide is extracted, the nienstruum i being Water.

filter separates the barium sulphide held in solution from any sludge Generated by the ash content of the coal, wlliich sludge may have'been carried along with the barium sulphide solution. barium sulphide from vmost of the sludge it is passed through a tank, in lall respects similar to the tank 20, from which tank the pump 41 is fed. v

The barium sulphide liquor thusfreed from foreign insoluble matter t is finally stored in tank 43 and this solution forms the companion solution for the zinc sulphate solution stored in tank 36. In order that this solution ymay chemically fit the adjusted zinc sulphate solution it is diluted with water (the condensate) to a specific density of 1.151. This barium sulphide liquor being near the point of saturation and consequent crystallization must be maintained at a temperature of at least 125 F. l

As has been previously stated this process consists in an equimolecular precipitation between zinc sulphate solution of a specific density, by preference 1.283 and a barium sulphide solution of specific density of, by preference, 1.151 andit may be determined by simple chemical considerations that equimolecular balance is established when such solutions are mixed in the proportion of 1109' parts of the one to 1891 parts of the other, respectively. y

In order to insure complete solubility of -these vreagents and to insure most favorable chemical action between them I eli'ect this reaction at the boiling point of the solutions and in order to further simplify my process I use thetanks 36 and 43 as. measuring tanks and they are therefore of sizes corres onding to the proportionality above recite In effec-ting the mixture of these two solutions I first admit the proper amount of zinc sulphate into -the mixing tank 45 and immediately thereafter I admit the barium sulphide solutionto the same tank. It. being desirable to admit the barium sulphide solution quickly the tank 43 is therefore provided with an adequately large delivery pipe., I provide tank 45 with an agitator 46 to insure very active agitation and in order to insure a complete double precipitation I continue to agitato the mixture for no less than 15 minutes. The zinc sulfate and the barium sullid react upon eachother in the well-known manner to form a precipitate of zinc sulid and barium sulfate.

In order to free the At the completion 0f this reaction I pump the mother liquid and its precipitate` by pumps 49 and 50, to a battery of filters 5l, 52, and A."i-l. The filtrate being conserved 1in an appropriate tank and the precipitate being conveyed to rotary dryer 57. My product is now in its highest state of purity for which reason the interior of dryer 57 is enameled. This dryer is heated, either by waste gases from earlier steps in the process, or by steam, and maintained at a temperature of approximately 300'F.

Connected with dryer 57 is a suction fan 58 whose purpose. is to remove the Water vapor generatedI in the drying. In order that the drying process may be continuons the interior of the dryer is provided with a helical flight whereby the material in Athe act of drying is moved longitudinally of the dryer and toward its discharge end. By this specific arrangement I avoid a continuous mixing of the thoroughly driedprecipitate with moist precipitate. Theprecipitate, when thoroughly dried dumps out of the discharge end of the dryer directly into the bin 59 and the communication between the dryer 57 and bin 59 is so constructed that this last operation 'is out of contact with the atmosphere. Communicating with the bin 59 at the -bottom there isa drum provided with only one opening which opening shall not exceed in dimension one fifth of the drum circumference. This drum fits accurately, as may be: the. bottom of the bin and is air sealed to it against atmosphere. lVhen the drum'has been filled `with precipitate it is revolved so that the opening descends to a lowermost position discharging the precipitate into a second bin whereupon it is returned to its former position to receive anew charge. l Contained within the last mentioned bin is a pair of ribbed rolls through which the precipitate in-its course of travel must pass. The purpose o't'these rolls is to crush the precipitate so that no particles ot' it shall be larger than of an inch,

After'the crushing,v the precipitate is delivered by gravity and out of Contact. with air to kiln 60 which is revoluble where the crushed precipitate is reheated for calcination to a temperature of 1000o F. for a period of thirty minutes and any residual moisture -is driven oit, extracted and removedv by exhaust fan 58 (which keeps a certain vacuum in the furnace). all out of contact with the atmosphere. The exhaust fan produces a partial vacuum in t'he'kiln 60, so that calcination proceeds under a partial vacuum.'v lAfter the precipitate has4 been finally ldried and highly heated it is dumped from exit end -61 of kiln 60 into cold` water tank 62. The cold water quenching tank is so disposed that any steam generated bv quenching the highly heated precipitate'may not enter the kiln 60 and4 also prevents contact with air'. y

In this last kiln (60) roasting any possible sulphur content in' the precipitate is driven off and should therebe any other substances aside from the highly refractory y double precipitate this process of calcina-y tion volatilizes them.

When the pigment falls into the cold Water of the tank 62, should thereremain any refractory soluble matter it will vbe dissolved, and to secure the thorough elimination of any such soluble' matter as well as to insure rapid' cooling this water is constantly renewed. The tank 62 and the remaining tanks 63 and 64 of this series are in all respects similar to the truncated, square pyramidaltanks 14, 16 and 18, and the pigment served to these tanks is handled in a corresponding manner and finally delivered to a sump'pit 65.

From the sump pit it is pumped by pum 66 to a battery of wet grinding mills 6 where it is ground to a tineness correspond-f ing to 200 mesh. From the delivery of the battery of the mills -67the pigment passes on to a rotary screen 68 Where a constant stream of Water is played on the groundY pigment. returning the coarse material to pit whence it is again pumped to mill 67 to be reground.

The material of requisite tineness-which passes through the screen 68 falls into a tank 69 and thence to a `series of tanks 70, similar to the tanks 14, 16 and 18. From this system of tanks 70 the liquid containing the pigment runs into concrete pits 71 where the pigment is Washed 'permitting the elimination of any alkaline salts or other foreign matter.- The Washing in tanks 71 is by means of Water which is constantly fed in from the bottom and this washing is assisted by air agitation.

This water bearing any soluble impuritiesflows away over the tops of the tanks.

The washing is continued till the Water shows no chemical reaction. 4The igment is then collected in pit 72 from which it is removed by pump 73 through pipe 74 to tank 75, which tank is oflarge diameter and provided with a ho per bottom, this hopper bottom 'is provide with pi e 76 and a valve connected to pump 77 which delivers the pigment to the filter 78. The purpose ofthe tank 75 is to permit the sedimentation of the pigment so that the pump 77 kand the filter 7 8V may handle a minimum of liquid. The pigment 'which is caught in filter 78 is conveyed by a pipe80 from which the pigment is pressed into a dryer 81, similar to the dr er 57. i

From the ryer 81. the pigment is gravity fed to pulverizing mills 82 which again pulverize the mate-rial to a fineness of a 200 mesh screen.

The reground pigment is delivered to a bin 83 either by a conveyor 'or blower fan 84, and the now finished for packing.

I claimy 1. The process which consists in causing to react upon each other at substantially their. boiling temperature, a pure aqueoussolution of zlnc sulfate and a pure aqueous 1 lll pigment is ready solution of barium sulfid, separating the resulting precipitate from the liquid, and drying the separated precipitate.

2. -The process which consists in causing a pure aqueous solution of zinc sulfate to react upon a pure aqueous solution of barium suliid, separating the resulting precipitate from ythe liquid, drying such separated precipitate, crushing it, and then subjecting it to calcination at a temperature higher than that used during the above-mentioned drying operation.

3. The process which consists in causing solutions' of zinc sulfate 'and of barium sulfid to react upon each other, separating the resulting precipitate from the liquid, drying such separated precipitate, crushing the dried product and then subjecting it to a temperature higher than that used during the above-mentioned drying o eration, quenching the hot product, grin ing and Washing the quenched product, separating the liquid from the solids, and iinally drying Aand grinding such solids.

4. The process which conslsts in causing to react upon each other, a ure aqueous solution of zinc sulfate of a ensity of 1.283,

and a pure aqueous solution of barium sul- 5j The process which consists in causing i to react upon each other at substantially their boiling temperature, a pure aqueous solution of zinc sulfate of a densit of 1.283 and a pure aqueous solution of barium suld ot a density of 1.151, separating the resulting precipitate from the liquid, drying the precipitate at about 300 iF., crushing the dried precipitate and then heating it for calcination, to about 1000 F. under exclusion of air, quenching the hot calcined product in cold liquid,.gr1nding and washing the quenched product, separating the liquid from the solids, and finally drying and grinding suchsolids.

6. The process which consists in causing to react upon each other, solutions of zinc sulfate and of barium sulfid, separating the resulting precipitate from lthe liquid, drying the precipitate, crushing the dried precipitate, and then calcining it under a partial vacuum.

l' ADOLPH DWORZAK.

Images