US2006853A - Iron-free alum - Google Patents

Description

July 2, 1935. W s, wlLsQN 2,006,853

IRON FREE ALUM Filed May 11, 1932 FIG.

TANK l-SI DAY Z'i" DAY 3@ DAY 4T! DAY 5U DAY 6m DAY s 1 1 Mr Hl lPIRE A Li Ml X Hl FIRE. MRE

B Ml- Hl ISIREE` EMRE Ll Ml ,f `l c Hl lPIRE a 2M-RE x Ml l,/ Hl

FIG. 2F

E 'bric/m Curve beh/een PbQe and 305e'LuM .Solu'on LEsEN )mev Fi. 1:

lbs. @20, www on @aan looms. Pb o,2 Arron/vw Patented July 2, 1935 UNITED STATE-s PATENT oFFIcE,fgf

This invention relates to the removal of' iron salts fromsolutions of alum (aluminum sulfate) whereby an iron free alum is obtained, and* it has application to the process of Semper and Fahlberg, described in British Patent 5,579 of 1881 which involvesV the usev of lead peroxide.

l Ordinary commercial alum is manufactured from bauxite (aluminum hydrate) and sulfuric acid. The product contains a small .amount of iron which is reduced to the ferrous state during the process of manufacture; and is practically free from ferrie iron.k It consists approxirnately of 17.3% A1203; about .7% A1203 being inexcess .of the S03 equivalent.V This grade 'of alum is used extensively in the manufacture of paper sizing, water filtration, dyeing, tanning, purication of glycerine, etc. The product seldom contains-'more than .45% of iron as FezOa. The term iron free alum as now employed in the art designates an `alum which contains substantially less iron Vthan the ordinary cominercial` grade, the amount thereof not exceeding .002% as-Fe203 This grade of alum nds use in the sizing of fine book or ledger papers, in the manufacture of paper coat, dry colors, in tanning White leather, and in various dyeing operations. inasmuch as bauxite of a grade which will give an iron .free'alum doesnot exist it is necessary to employ pure aluminum hydrate the cost of which is approximately three times that oi the costper unit of A1203. Accordingly, a process for removing the iron from ordinary alum is needed.

vAlthough many such processes have beensug'- gested,none have found commercial application. In thisconnection, note should be made of the fact that many processes will reduce the amount ofl iron in alum. However, if a process is incapable of producing an alum having .002% FezOs or less, it is worthless since commercial alums having relativelyhigh or lowV iron contents command the same market pricefk The principal object of this invention is to provide a method oi removing iron and analo- 'f gous impurities, effectively, from alum solutions whereby a product having any desired maximum iron content can be obtained. A further object of the invention isfto aord a method which 'enablesy one to remove the iron from alum without loss of any of the alum. An additional object of the invention is to provide an effective lead peroxide reagent as well as `a method of` regenerating the same.

A further object of the invention is to provide a counter-current process for the lremoval of iron whereby good yieldsflotiron free alum'are obtainable with but'small quantities of the deferruginating agent. 'The invention likewise contemplates a method of treating alumsolutions whereby the iron therein is rendered read.- ilyf susceptible to the peroxide treatment.

According to the Semper-Fahlberg process, a

Vconcentrzatted alum solution, which is neutral 'or at least should not contain a Vlarge excess. Vof acid, is mixed With 570-20170 (based on the Weight ofthealum) of lead peroxide. Ferrie plumbate is said .to form, which isr .separated fromthe alum solution by permitting the same to settle, andthereafter decanting the Vclear liquid, or by filtering the suspension. g Lhave observed Ath'attlie reaction appears to involve` an adsorption` phenomenon rather than the formation of a ferricplumbate, Thus, for example, an iroricontainingalum solution which hasv beenbrought into equilibrium with a Vquan-l tityfofV lead peroxide will 'contain some iron notwithstanding the fact that there is a very large' stoichiometric excess of lead peroxide, assuming that ferrie plumbateis formed. However, by adding an additional quantityfof lead peroxide; and agitating .the .suspension in orderl to bringV abouta state ofs.equilibriurn,the resulting alum solution will be found` to containy less iron than before, thus indicating that the extenty of the deferruginationkis a function` of the quantity of the lead peroxide added. If, on the other hand, a solution of iron free, alum be added to ther suspended peroxide which isin equilibrium with the iron containing alum solution, some of the iron which has been adsorbed by the peroxide will-be returned to .th e solution.

Briefly stated, the present invention contemplates the preparationof a lead peroxide from redleadand nitridacid. After repeatedwashing, the-peroxideso formed isadded toan iron 4o containing alum solution which has vpreviously been treated with a. partially'spent peroxide. The concentration of fthe, solution is not important, although -solutionsinexcess,of 30 B.` impedelsettling materially.- .After the peroxide has been kagitated in the alum solution thoroughly and is allowed to settle, the; solution is decanted and yav subsequent chargeoi alum solution is introduced into the tank Vwhich contains a higher percentage.l ofV iron than' the previous charge. 50 After the removal of the. iron has advanced to rthe desiredextent, the Asolution `of .alum is evaporated to the desired concentration in the rusual manner. The spent-,peroxide is Washed substantiallyrree from alum bsolution and thereafter revivied by repeated treatment with acid, preferably sulfuric, containing progressively less iron. The removal of the iron from the spent lead peroxide appears likewise to involve an adsorption phenomenon, and it is, therefore, advantageous to remove the iron by a series of counter-'current acid treatments, each successive acid wash having less iron than the next preceding until inthe final treatment fresh acid is ernployed. The number of treatments may, of course, be varied, in general the greater the number of treatments, the less acid is required. Inasmuch as the peroxide settles rapidly from the acid solution, a large number of treatments are possible during a relatively short period of time as compared to the settling operations in the alum treatment. After the reviviiication is completed, the lead peroxide is used again, the alum solution first treated therewith being one which has reached its'last stage of deferrugination.

' The accompanying drawing illustrates diagrammatically one method of procedure wherein.

" YPreparation of alum solution vThe crude alum solution which is employed should be as concentrated as possible in order to obtain a maximum output of product per unit volume of capacity. On the other hand, aV

solution which is so concentrated that its viscosity is appreciable impedes sedimentation of the lead peroxide to suchan extent as to prolong the cycle of operation thereby likewise reducing the capacity. In general, I found that a solution of basic alum of 30 B. concentration is about as strong as can be settled expeditiously.

L"Ordinary crudealum contains approximately .5% FezOa. In'order to assure that the ironv isA completely oxidized, a small quantity of sodium chlorate or sodium hypochlorite, or similar oxidizing agents are added to theelum in the course of its preparation, preferably just aftercthe reaction between the bauxite and sulfuric acid. l Y

' Iron containing alum, particularly when' dissolved in water, ages, that is, undergoes a change which is usually accompanied by a brown co1- eration. This change appears to be due to a change in the condition or form of the iron salt. In its changed condition, the iron salt is absorbed by the peroxide ineiciently.l The change'takes place rather slowly ,and itis possible under ordinary conditions'to complete the removal of the iron before the non-absorbable form'i's produced. However, from time to time delays are incurred which have,v an adverse effect so far asthe alum solution is concerned because of the formation of the relatively nonabsorbable iron salt. This form can again be converted to the absorbable form by heating the solution (to a temperature which need not attain its boiling point), and thereafter cooling thefsolution. This simple procedure seems to reveisethe aging process so far as the iron s alt'sware concerned, and renders them readily susceptible ag'ain to the" action of lead peroxide. AAdsorption of the iron may be effected-at ordinary-room temperature. However. I have 0b- Lead peroxide may be made by various methods. In general, I have found that lead peroxides made in an alkaline medium are distinctly inferior to those made in an acid medium. By far the best results have been obtained with lead peroxide which has been prepared by reacting red lead at room temperature with nitric acid of a concentration which will give a lead nitrate solution which is nearly saturated. Various factors affect the quality of the peroxide product. For example, the peroxide deteriorates rapidly in dilute nitrate solution and in water. I have found, however, that the deterioration may be prevented if the lead peroxide is stored in a spent condition, that is, one that is charged or has adsorbed on its surface a ferrie salt. Before using the peroxide it must be revivified in the manner described more fully in a subsequent portion of this specification.

Other sources of lead peroxide than that from red lead and nitric acid may be employed. Similarly, the lead peroxide may be charged with an iron salt and reviviiied regardless of the method by which the peroxide has been made. It is to be noted that because the process as a whole is one involving an adsorption phenomenon, the physical characteristics of the peroxide are irnportant. Moreover, I have found that some grades of red lead result in a lead peroxide which is of a better quality than others. The most practical method of determining the quality of red lead which I have found is to make a small sample of peroxide and check its action on an alum solution containing a standard amount of iron.

Rem'm'ftcatz'on of peroxide The spent peroxide is revivied by first washing the peroxide free of alum solution. This may be done conveniently by washing the same repeatedly with water. The dilute alum solution which results may be used to dissolve crude alum or may be concentrated and returned to an appropriate stage of the deferruginating cycle. Thereafter the peroxide is treated successively with dilute aqueous sulfuric acid solutions. For this purpose a i%-l0% solution will be found to be satisfactory.

Inasmuch as the removal of the iron appears to involve an adsorption phenomenon, it is convement and advantageous to treat the peroxide progressively with acid solutions containing successively less dissolved iron salts. The acid solutionfwhich is decanted from the peroxide after the rst treatment may be discarded or preferably returned to the crude alum process Where it is reacted with bauxite to produce the ordinary commercial grade of alum.

In general, the revivirication involves agitating the peroxide with the solution of acid, permitting the peroxide to settle and decanting or otherwise separating the solution from the solid peroxide. y Inasmuch as the settling operation is r rapid, it:is convenient and economical pto yem-` ploy relatively small amounts of acid and subject the peroxide to a number v,of such successive treatments. Obviously, if desired, one `,may-.employ relatively large amounts of acidj and thereby .reducerthe numberof treatments.; However, this increases the consumption of acid employed in the revivication. Y

The number of Vsuccessive acid treatments depend upon the quantity of acid employed. Iihave found that, from;5 to, 1.0 treatments are practical. Following the last treatment-the peroxide is washedV with water to remove the 'remaining midafternwhich it is-ready forV use in the treatment of alum solutions. -Inasmuchas the revivifiedA peroxide deterioratesv with age; 7insofar as its adsorption property is concerned,l it is.,a`d`. visable to employ it promptly after reyivication.

pefeugivrating cycle `The removal of the iron from the alum solution involves, preferably, successive treatments of alumV solutions with peroxide containing successively less iron.V In other words, the crude aluml` solution moves counter-currently 'with' respect to therevivied peroxide, The peroxide which is employedin the rst treatment of the alum solution'i's most highly charged with iron, whereas the peroxide employed in the final treatment ofthe alum solution is the freshly revivied material. j c i' V'A better understanding/of the` procedure involved may be had by reference'to the accom- Panyng diagram 'The diagram illustrates the cycle of operation which has been'found `suitable in treating'alum containing `aplnroximately .5%,1iez0aY A solution of 25-'BO Be. concentration is prepared in the manner previously described, suitable precautionsl have been taken to assure the presence of all offthe iron'in aferriorst'ate. c

A solution of this type respond to a three stage' deferruginating cycle, each stage requiring approximately V24 hours. It is convenient under these conditions to employ five tanks (A, B, C, D, and E) of approximately equal capacity. At the beginning of the' first day, tank'A Vbe assumed'to contain an alum solution which is ,inl its last stage of deferrugination. Tank B Vcon,- tains an alum solution which is starting its intermediate or'second day ofdeferrugination. Tank l C contains fresh or' crude alum solution. Tanks D'and E are idle although they may be used for revivificaton purposes, if desired. For this purpose, tank D would containV peroxide whichV is to be washed free of alum and thereafter subjected to the early stages of revivication, Whereas tank E contains peroxide undergoing the later stage of revivi'fication and washing operation preparatory for deferrugination. Y

The alumis'olutions vcontained in tanks A,fB, and C are agitatedthoroughly in order toobtain a uniform suspension of the peroxideand thereby establishan adsorption equilibrium between the iron in the solution and the ironv adsorbed on the peroxide. ThisY period-of agitation,

varies although Vone to two'hours will, in general, be found to beadequate. Equilibrium itself is' practically instantaneous once the suspension is completed. y'Il'iereafter the agitation is discontinued and the peroxide is permitted to settle atfthe bottom of the tank; v Y n V*At the end of the first day, `the supernatant liquid contained in tank B is siphoned orpumped into'tank E where it isfadm'ixed withthe freshly pumpedV to tank C.

revivified peroxide in persuance of the nalstage of deferrugination.l The supernatant liquid in tank'A- is completely Vdeferruginated,r and is siphoned or `pumped into a suitable storage tank or evaporating kettle, wherein the water isremoved and the iron free alum product produced,

andthe supernatant liquid in tank CV istrans` mitted to tank A. Followingthese transfers,

ployed as Well Vas Vthe extent4 of sedimentation,

tank C will contain a certain amount of .partially deferruginated alum after-'the decantation op-` eration. Thisalum solution is recovered .by repeated ,addition of water and decantation. or

and revivication of tank D is subjected tocontinued reviviflcation preparatory for its use ,during the third day in the deferruginating cycle. Following the secondday, alum solution contained in tank E is decanted or pumped to the iron free solution storage. The supernatant liquid in tank'cB is pumped into tankE'and the supernatant liquid in tank A is pumped intoVV tank D, which contains freshly revivied peroxide; Thereafter the solution of crude alum is introduced into tank A. j

Following the third day of operation, the ,iron free alumsolution in tank D is pumped to the iron'free alum storage. `The supernatant liquid in tank A isA pumped into tank D, and the super- In the meantime, the peroxide' natant liquid in tank Eris pumped-.to tank C,

thereafterj'a crude alum solution is introduced into tank E. The spent peroxide Acontained inr tank A is washed free of alumfduring the fourth day of operation and subjected to the early stages of revivification. VThe partially revivied peroxidexof tank B is subjected to continued rr,evivii-loation and thereafter to the kwashing operation to remove the'revivincationliquors r preparatory-for the deferruginating cycle of fthe fifth day. At the end of the fourth day the iron freealum'in tank C is pumped to the iron freealumy storage. The supernatant liquid in tank D ispumped to tank B which contains fresh peroxide'v andthe supernatant The cycle of operation set forth above is ex-v emplary ofone method of procedure whichv involves a; three stage cycle of .deferrugination Obviously, two, four or more stages may be employed. I found, however, that for the ordinary gradeof crude alum', a three one-day-stage cycle is adequate and avoids aging of the alum. The above method'fof procedure, contemplates anY intermittent counter-current treatment of alum solution.- Obviously, a continuous counter-cur-` rent cycle in which the ilow of alum solution iscounter-current to the movement of the peroxide particles `and in -which the clearrv alum solution rwhich is dischargedimmediately after liquid in tank E is l having been in contact with freshly revivified roxide may be employed in lieu of the intermittent counter-current flow of the materials. An important feature in each instance is the same, namely, that the progressive stages of equilibria between the peroxide and the alum solution are such that the partially deferrugi'- nated alum reacts with the freshly revivified peroxide Aand the crude alum reacts with the partially spentl peroxide. a To illustrate the results attainable by the present process, five tanks each of approximately 2000 cubic feet capacity and each charged with approximately 5700 pounds of peroxide are capable of deferruginating a crude basic alum (17.3% A1203) containing .36% Fe203 at the rate of 28.6 tons per day to produce a product containing .0001%-.0002% FezOa. Even when the crude valum contains as much as .5% FezOs, the product will be found to contain well below the maximum limit of iron permissible in iron free alum;

An analysis of the alum solution at the end of the several stages of deferrugination indicates that the iron content varies substantially as follows: i

\ Percent FezOa Crude alum .360

lst stage '.152 A 2nd stage .0095 3rd stage .0002

To illustrate the advantages of a counter-current'treatment, if one were to produce an alum solution containing .0002% FezOs from a crude alum containing approximately .36% Fe2O3 in a single stage, it would require approximately 206,000 pounds of peroxide of a quality similar to that provided by the present invention and used in the foregoing example.

When it is remembered that a substantial amount of alum is not separable from the peroxide by decantation (in the afore-described three-stage procedure the peroxide contains approximately .45 pounds of alum per pound of peroxide at 20 C. after decantation) it will be apparent that it would be impractical to employ a singlestage process since substantially all of the alum solution would be retained by the peroxide.

Even if one desired to produce an alum containing .002% FezOs by a single-stage process one would require 25,800 pounds of PbOz to reduce the iron content from .5% FegOa to` .002% FezOa. Inaddition to the difficulties involved in handling such large amounts of peroxide one is also confronted with the problem of washing the peroxide with water to recover the entrained alum solution. Moreover, the dilute alum solution so, obtained must be evaporated which is in itself a serious objection to the process and results in a substantial additional expense. From the foregoing it is obvious that the Semper-Fahlberg processwhich involves the use f .Li-20% of peroxide would be ineffective insofar as fulfillingthe requirements of present day iron free alum specifications is concerned. Figure 2 is representative of the equilibrium condition which exists between lead peroxide and an iron containing alum solution. From this chart it will be apparent that an alum solution containing approximately .1% Fe2O3'is in equilibrium with lead peroxide which contains approximately 3% of its weight of FezOs adsorbed thereon. It will likewise be apparent that ,a

solution containing .00O1% FezOa is in equilibrium with a lead peroxide which contains approximately .3% FezOa. Stated otherwise, in order to produce an alum which contains .O001% FezOa theilead peroxide with which it is ultimately in equilibrium can contain no more than .3% FEzOa adsorbed'on its surface.

In connection with the chart it is to be borne in mind that the amount of iron oxide adsorbed on the lead peroxide refers to the iron which is recoverable -by a revivication treatment and not to'the iron which would be indicated by an ultimate analysis. In other words, lead peroxide may contain'some iron as an impurity which does not enter into the equilibrium reaction. It is also to be borne in mind that since the condition and history of the peroxide have an importanteifect onits capacity to adsorb iron the curve Will vary, particularly with respect to its axis of abs'cissas, although its general contour will remain approximately the same. The present process is adaptable to the removal of materials other than iron from alum. Thus, for. example, an alum which contains arsenic, chromium, manganese, nickel or cobalt or v'mixtures of compounds of these metals may betreated in an analogous manner whereby their removal is effected as in the case of iron. In some instances the removal of these impurities appears not to involve an adsorption phenomenon. Moreover, some of the peroxide is lost or destroyed. The loss of peroxide suffered maybe offset by the addition of an equivalent quantity of fresh peroxide.

Inasmuch as more iron can be tolerated in commercial alum than would normally be present when one reacts sulphuric acid with the commercial grade of bauxite, it is convenient to omit'the washing operation whereby the alum solution is separated from the spent peroxide before revivifying with acid and to revivify the alum containing peroxide counter-currently with sulphuric acid. The acid together with the dissolved iron and alum solution associated with the spent peroxide may be utilized in the manufacture of ordinary commercial grade of alum.

Tne mechanical features of the operation are similar to those employed in deferruginating cyclel- Thus, the partially spent sulphuric acid, which contains some iron is agitated with the peroxide whereby an equilibrium is established. The suspension is then permitted to settle and the supernatant liquid is pumped to the crude alum department. Thereafter the peroxide is agitated withv a sulphuric acid solution which contains less iron than that employed in the next preceding revivication stage and which has been .obtained as a supernatant liquid from the next preceding charge of peroxide undergoing revivification. The supernatant liquid which isobtained during this treatment is used inthe first stage of revivirlcation of a subsequent charge of spent peroxide. In all, seven such stages of revivication are employed, the final stage involving the use of a 6% aqueous solution of pure sulphuric acid. The resulting peroxide is finally washed, substantially free from sulphuric acid with water, after which it is ready for use in the deferruginating cycle corresponding to tank A at the beginning of the rst day, as illustrated in the diagram.

The fresh acid solution gains in iron content with each successive treatment as indicated by the following results which have been obtained in the .treatmentof .the spent peroxide resulting Y which can be utilized economically rthe crude alum department. Y y

A convenient procedure for effecting a seven stage reviviiication involves the use of seven tanks each of approximately 600 cubicfootcapacity. Six may be assumed to be'lled" with acid. solutions having differing percentages of iron diss'olvedtherein'. The seventh tank contains a freshly prepared 6% solution of sulphuric acid. For effecting the first stage Vof revivication of the spent peroxide,` acid containing a maximum amount of iron is introduced and thoroughly mixed with the peroxide solution which by reason of imperfect decantaton contains some entrained alum solution. Such peroxide corresponds, for example, to that contained in tank D on the first day as represented in Figure 1. After sedimentation the supernatant liquid is decanted and transferred to the crude alum department where it may be admixed with fresh sulphuric acid andthereafter reacted with bauxite in the usual manner to form alum.

The next stage of revivification involves introducing and thoroughly mixing with the peroxide the-acid contained in onev of the seven storage tanks, the iron content thereof being less than Vthat which was employed in the first stage but is greater than that in any of the other revivifivcation liquor tanks. After sedimentation the supernatant liquid is pumped into one of the vempty tanks where it is held preparatory for use in the rst stage of Wrevivification of the next succeeding charge of spent peroxide. For the next stage the peroxide is thoroughly mixed with an acid solution containingA successively v `less iron than the nextpreceding. After sedimentation thesupernatant liquid is pumped into one of the empty storage tanks and held in readiness for use in the treatment ofthe'next succeeding batch of lead peroxide. This cycle f is continued through the seventh stage in which fresh acid is employed.

It is to be noted that one may employ, in lieu spent peroxide, iii the saine manner ofv intermittent -cintfr-current process a ivjiviiiearisii is ciiiiijiiiius anqwiii his characteized'- by {the fact that the `.I re'sl'i acid contacts lifpartially r'eviv'ed peroxide w ere as the" iron containing acid contacts witri the de'scrpti; it will Y parent that the present invention ,affords a con-1 venie'nt," o'no'mi'caland practical processforremoving i is 'characterized no noni-recoverable mate"- alli'i'sf Xpsiv evtllipIIi-enl?V (Jr cult operating co dtions and enables onelto rit les of pdict Of any de reci-iron con exit* wi comparatively small investment osts'a 'lie invention contemplates a novel lead peroxide reagetand `method lof preparing the' salire, which is pje'c'iiliailyv adapted i for' effecting the objectsA of ifiieiiiveniioii. vThe invention likewise aimais"l a' method of removing iroiri fromY Basic aifincontra-sited to ille iieiie i trai 'or slightly acid alum r'igi this resp ci:

iiriio byiarihe gie tjis that-ora basic naitiiie. f addition,- tiie invention include afepri veien'tadcd iicz'tl iiietfrod of rgenerat g aVV peroxide wh e Vvno lo'ssv material'sl'isjinf- 'ci'iii'edi iid sbviaifes vile liilziiiiA or loss-golf, valiiii'i by ressort of'agiig tnefiiii 'presentin aiifalijiin solution; nFinali by 'reasfo'ri-v of the4 discovery of the' principles Y fvai;v the" invention airiids-{ai metillod` of 'procedure whereby a commercial Althoug'lt has ,beeiidescribedi detail and k(eti-miie4 iioiiica'tio'ns have beenrindicat'ed, it will be apparent to those skilled in the art that the invention is not so limited, but is susceptible to numerable modifications withoutA departing from vthe spirit thereof or the scope of the appended claims.

What I'claim is: y

1. The method of removing water soluble inorganic ferric salts from an alum solution, which consists in'treating a crude aqueous alum solution containing the iron, with lead-peroxide whereby the iron is removed from the alum solution by the peroxide, said method being characterized in that the alum solution moves countercurrently with respect to the peroxide in the course of the treatment.

2. The method of removing water soluble inorganic ferrc salts from `an aqueous alum solution by means of lead peroxide characterized in an intimate suspension of the peroxide in the alum solution and subsequent separation of the alum solution from the peroxide.

3.1The method as defined in claim 2 and further characterized in that the separation of the .peroxide is effected by sedimentation and decantation of the clear supernatant alum solution.

4. The method as defined in claim 2 and further-characterized in that three`V stages of treatment are employed.

5. The method as denedvin claim 2 and further characterized in that the alum treated is a basic aluminum sulphate.

6. In themanufacture of iron free alum the steps of treating an aqueous solution of alum with lead peroxide wherebythe iron is removed from the solution bylsai'd peroxide, subsequently separating the spent peroxide `from vthe alum solution, treating the peroxide vmixture successively with dilute sulphuric acid,v the acid of each successive treatment-,containing less iron, washing the resulting peroxide vfree from acid and nally returning the washed peroxide to the alum solution treating process. e v

'1. The method as dened in claim 6 and iurther characterized in that the peroxide is subjected to a counter-current revivication treatment wherein fresh acid moves counter-currently with respect to the peroxide undergoing revivication, whereby the fresh acid contacts the peroxide which issubstantially free of iron and the spent acid contacts the peroxide containing a maximum of iron.

8. In the manufacture of iron free alum the steps of ktreating anaqueous` solution of alum with lead peroxide whereby the iron is removed from the solution by said peroxide, subsequently separating the spent peroxide from the alum solution, treating the peroxide mixture with dilute sulphuric acid, whereby the iron contained in the peroxide is removed and the peroxide thus revivified, separating the acid solution from the peroxide, returning the revivied peroxide for reuse, and reactingthe acid solution containing the iron and the sulphuric` acid with bauxite.

9. In the removal of iron salts from an alum solution by means of lead peroxide, the step of rendering the iron susceptible to peroxide treatment, which consists Ain heating the alum solution toan elevated temperature not substantially above the normal boiling temperature thereof and subsequently cooling said solution.

10. The Vmethod` of removing iron salts from an alum solution by means of lead peroxide as dened'in claim 12, and further characterized in that the suspension of the peroxide in the alum solution is maintained at a temperature of approximately 20-50 C.

*1 1. The method as defined in claim 12, and further characterized in that the concentration of the alum solution is not substantially in excess of 30 B.

l2. A multistage counter-current process for the removal of water soluble iron salts from an alum solution, which involves agitating an alum solution with a lead peroxide reagent whereby a uniform suspension is obtained, and effecting sedimentation of the suspension, said process beingk characterized in that the fresh peroxide is treated with alum which is in its final stage of deferrugination and the crude alum solution is treated with a partially spent peroxide.

13. The method as dened in claim 12 and further characterized in that the alum solution is caused to undergo three successive stages of deferrugination counter-currently with respect to the peroxide reagent.

14. The method of removing water soluble inorganic ferric salts from an alum solution, which consists in treating a crude aqueous alum solution containing the iron, with lead peroxide whereby the iron is removed from the alum solution by the peroxide, said method being characterized in that the alum solution is contacted with the peroxide in successive stages and further characterized in that during the nal stages of the treatment a peroxide is employed containing less iron than the peroxide employed in the initial stages of the treatment.

WIILIAM s. WILSON.

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