CA1176430A - Process for producing alumina and ferric oxide from aluminium carriers with high iron and silicon content - Google Patents

Abstract

The invention concerns a process for the preparation of alumine and ferric oxide from low-grade aluminium and iron carriers. The processes, in addition to conventional technological steps, comprises the steps of dissolving the iron content of a ground, mineral material in an aqueous hydrochloric acid solution containing 200 to 420 g./lit. of hydrochloride acid at 90 to 130°C, eliminating the iron from the slurry of from a solution obtained by filtration of the slurry, with an anion exchange resin or semipermeable membrane or cloth, continuously or discontinuously, eluting the iron from the ion exchange resin and recycling hydrochloric acid and sulfuric acid in a closed system.

Description

3~
PROC~SS FOR PRODUCI~G A~UMI~A AND ~ERRIC OLIDE
~ROM ALU~IU~ CARRIERS WI~ HIGH IRON A~D SILICO~
CONTE~T

q~he invention ~elate~ to a new proce~ for producing alumina a~d ~erric o~ide from aluminium carrier~ with high iron and si`1icon content~ More p~rticularly~ the invention concerns a method ~or producing alumi~a and ~erric oxide from aluminium .
carrler~ pre~erably ~rom low-grade bau~ite~ claye~
red mud, etc. in a purity~ which make~ ~urthsr ~anu~acturing w~thout addltional puri~icatio~ po~sibleO
- It is well known that high-quality bau~ite~
lO. raquired for the Bayer process are only restrictedl~
a~ailablo and their ~upply i~ decreasing year bg year, On the other hand, alu~ini~m- and iron-contain-ing waste ~atter~, e~g~ red mud9 colliary rock~9 coal a~h, etc~ are produced in an increasin.g amountD
~here l~ there~ore, a high demand ~or economlc method~ by which aluminium and/or iron can be racorered ~rom the~e and other low-grade carrier~9 e,g, low-~rad0 baux~te~, clay mineral~ and ~latee,D
~he:re are numerou~ methodZ3 known in the art 20 to rcco~er alumir~ium or iron ~rom low-grade carrîer~8 ~ener~ aluminlum ie reoovered ~rom carrier~ having ~mall or reduced iro~ co~cen tratiorl, while for .re~
covering iron, carrier~ enriched iIl iron are gerlerally employedO The phy~ic~1 method~ u~e~ r 25 the eeparation of di~ `e~ent type~ o:~ row m~teri.al~
A 2123~-75 ~L76~301

- 2 -e.g. washin~, flotation, separation by ~pecific gravity9 etcO ~enerally cannot produce the re-quired ~elective separatio~. Thi~ i9 a difficult problem, ~ince for in~tance the additional puri~i-cation o~ aluminium alloy~ produced from aluminiumcarrier~ with a hi~h iron and ~ilicon concentra-tion i~ rather complicated and cannot be p.er~ormed economically. Similarly~ the treatment of aluminium carriers with a high ~ilicon content with sul~urou~
or sulfuric acid i~ not economic eitherO
~ he pyrolytic methods also provide rather poor re~ults, when carried ou.t on low-grade aluminium carriers. It has beeri a-ttempted -to subject aluminium~
containing raw materials to chemical deironization by sulfuric acid, hydrochloric acid, ammonium salts thereof or chlorine ga~. In this way, however, a ~ubstantial amoun~ o~ alumina i~ also dissolved, the separation is difficul-t, and hence high los~es in aluminium are re~ulted.
Since the energy demand of the electroly~i~
of` aluminium chloride i~ con~iderably less than that of' the electroly~i~ of alumi~a, oe~eral method~
have been developed f`or the conver~i.on of` alumina into aluminium chloride by chlorinat:ion and for the production o~ aluminium f'rom aluminium chloride~
Such proce~es are for example di~closed in the Hungaria~ Patent Specifications ~o~ 160 229 and f ~i ~6~3 162 348. ~hese methods~ however~ involve serious problem~ in the operation5 require special equipment~ and the purity o~ the aluminium obtained ie also not ~atisfactory~
~ccording to another method di~clo~ed in the Hungarian Patent Specification 150 459 low~
grade aluminium carrier~ are calcined at 650 C~
ground and treated with a 20 % aqueous hydrochlorid acid solution. In this way aluminium, calcium, iron, etc. are dissolvedO ~he solution i~ then ~iltered, deironized with a ~trongly basic ion ~xchange resin~
the aluminium chloride solution is evaporated and iron i3 eluted ~rom the resin with a slightly acidic aqueous ~olution. By this method iron and silicon can be ~eparated from aluminium~ The method can, however9 not be employed f~or manufac-turing bauxites, since under the given conditions aluminium oxide~
are very poorly ~oluble, the purity of the obtained alumina io not ~atisfactory and -the problem o~ the recovery of' the mother liquor~ has not been ~olved.
~hi~ proces~ is, therefore, very expen~:Lve and the filtration of the ~olution with concentrated hydro-chlorlc acid require~ extreme precaution~ and i~
very ~low.
It can be e~tabli~hed that there i~ no method known in the art for an economic recovery of alumina and ferric o~ide ~rom low-grade aluminiu~

~ 9.76~3~
carriers in an appropriate purity.
The present invention provides a process for obtaining alumina and ferric oxide from a material which contains aluminium~ iron and silicon, which process comprises:
~ a) treati.ng the material at 90 to 130 QC with from one to two volumes of aqueous hydrochloric acid containing from 200 to ~20 g./li-t. of hydrochloric acid, thereby obtaining a solution of ferric chloride and a deironized product ~ b) contacting the solution o:E ferric chloride with an anion exchange resin which obsorbs ferric chloride and hydrochloric acid~ sub-sequently eluting ferric chloride and hydrochloric from the resin, returning hydrochloric acid to the process for treatment of further material and sub-jecting the ferric chloride to pyrolytic decomposition at about 850 C to obtain ferric oxide, (c) adding concentrated sulfuric acid to the deironized product in an aboutstoichiometric amount, calculated for the soluble oxides and heating the mixture to about 140 to 160 C to obtain an aluminium sulfate solution ~d) separating the sulfuric acid and aluminium sulfate solution, returning separated sulfuric acid to the process for treatment of further cleironized product and subjectlng the aluminium sulfate to pyrolytic de-composition to o~tain '6-~1203.
In tlle process according to the invcntion bauxites havi.ng a low module and/or contal.ning laterite, siderite and red mud, colliary rocks, coal ash and clays can for example be used as starting materials. Mineral row materials and ~ ~ 7 -- 5 ~

hydrochloric acid ~olution are contacted in a mu-tual proportion of 1:1 to 1:2. Iron di~solved in the form o~ ~erric chloride is eliminated by strongly ba~i~ anion excha~ge resin~, pre~erabl~
containing trime-thyl amine (dimethylethanol amine) or pyridine active group~. The anion exchange resin can be employed also as a membrane or cloth in a batch-type or continuou~ proces~ Iron can be ab30rbed from a ~iltered ~olution but ~ati~-Eactory re~ult~ are obtained al~o by leading the~lurry containing ferric chloride in counter-flow with the elutin~ aqueou~ solution, alon~ the ion exchange cloth or membraneO( To -the deironized residue concentrated ~ulfuric acid ie added in an about ~tochiometric amount calculated for the soluble ogide~, the mixture i~ heated up to 140 to 160 C with stirring, and hydrochloric acid ~et free during ~ul~atization is recycled into the deironization procee~ as an azeotropic mixture.
The exces~ of sulPuric acid, which i~ di3tilled of~ at 300 to 400 C during the auto-thermic reaction i~ aloo recycled into the eul.Eati.eation ~tep.
The nearly acid-free, heat-treated ~ulfate mixture, which ha~ loet its cry~tal water and ha~ been di~ir~tegrated into a .~inely divided, powder~
product i~ di~olved in water and the undi~solved, deh~drated oilicate~ and titanate~ are ~iltered o~f, ~76~3 optionally in the pre3ence o~ f'locculating agents. I~ de3ired, the ~iltrate can be ~ubjected to a ~urther deironization, which can be carried out by extraction or ion exchange~
'~he ~erric chloride and aluminium sul~ate ~olutions obtained durin~ the procedure are evaporated, whereupon they are subjected to thermal decomposition at about 850 C. ~he hydro-chloric acid and sulfuric trioxide formed are re-cycled into the corre~ponding, earlier stages of ~he proces~ and~ apart f'rom minor lo~Ye~, hydro-chloric acid and 3ul~uric acid are kept in a closed cyclic proce~. Pyrolysi~ resul-t~ in the formation of ferric o~ide and a major amount o~ ~-alumina in a ~ati.sfactory purity, with a good ef~iciency, ~ hough the proce~s according to the inven-tion includes some technological step~ known in the art 9 these are combined with each other and with furthsr, entirely new reac-tion steps in a speci~ic way, which make~ the u-tilization o~
low~grade, aluminium contain:ing miner~l raw material~ ~or producing alumina and ~erric oxide pos~ible. By the in~tant proce~s alumina and ferric o~ide are directly obtained in a quality, which is suitable ~or f'urther man~c~uring. It ~hould ~urther be empha~ized tha-t by the proces~
according to ~he invention aluminium and iron, i , .., . I

~76~3 which mutuàlly contaminate each other, can aimultaneously be i~olated in a ~ati~actory purity by an economic technology~ This i~ a highly une~pected re~ult 3 since none of the prior art processe~ could garantee the ~ame or similar results.
Further detail~ o.f the invention are illu~trated by the following, no~-li~iti~g ~amples.
E~ le 1 Deironizatio~ o~ bauxite and pr~e~tion o~
~erric oxide ___ ____ 26 ton~ o~ bau2ite having a grain size o~
about 30 mm~ are ground to a grain si~e of about 300 microna in a wet ball millO ~auxite contain~
50 % A1203, 22 ~o ~e203 a~d 6 % SiO2. 17 ~. of water are added to the bauxite and the granulate is heated up to 65 ~C in a heat exchangerO To the bau~ite ~lurry 32.4 ~. o~ a 34 % (420 go/lit~) hydrochloric acid solution are added ? and the bauxite i~ digested i.n ~even ~tage~, for 1.5 houra~
Duri~g thi~ treatment about 90 ~0 o~ the iron content o~ the starting ma-terial ia di~olved~
which corre~pond~ to 5 ton~ of ~erric o~ide, i~e.
about 10 tons of Feal3. To hal~ of the volume of the digeated slurry 500 g./tons o~ Sedosan flocculating agent are added in an amount o~
500 g~/tons 9 and the ~lurry i~ ae-ttled down i~
i~ a ~our-stage "Dorr" sedimentator~ It is then ~IL7~3~

~iltered through ~ive acid-resistant cylindric filter, having an area of 20 m . eachg and i~
washedq The ~eC13 ~olution i9 evapora-ted to a conce~tration of 200 g./lit. Fe3~ and -the concentrate i~ decompo~ed at 520 C in a pyrolysator to give 4.5 torlY of ~e203 i~ a purity o~ about 90 % and azeotropic hydrochloric acid.
Hydrochloric acid i9 ~upplemented with fre~h acid and i9 then recycled into the manufacturing proce~s~
The deironi~ed bauxite can advantageousl~ be processed by the ~ayer method, ~ince during it~
further -treatment red mud i9 not formed.
a~
D~i70r~z- tlDn o~ the bBU~itg ~3~E~
~ ohlorio aci.d b.Y anion e~c~
Half o-~ the ~olume o~ dige~ted bauxite slurry obtained in E~ample 1~ which con-tains 28 g./lit. of Fe3+ and 220 g./lit. of hydrochloric acid in -the aqueou~ pha~e, i~ introduced into a dialy~ator~
r~he dialysator is 0quipped with an anion selective cloth containing dimetharlolamine groups, and the bauxite ~lurry contairling hydrochloric acid and water are led in counter flow along the two opposite side~ of the cloth~ r~he slurry and the aqueous phaae are u~ed in a volume ratio o~
1:1. Iron i~ dialysed from th0 slurry into the ~i L3~
g aqueou~ pha~e a~ FeC13~ The pores o~ the cloth are clogged by the slurry, therefore, it i~
practically unpermeable for the aqueou~ phase~
Hence, -the Fe3~ concentration o~ the bauxite 31urry i9 decra~ed below 1 g~/lito~ while it~
aluminium content remain~ practically unchanged~
~he ~eC13 ~olution obtained i9 converted into ferric oxide a~ de~cribed in Example 1.
Exam~e 3 The~ ration of alumina ~uitable ~or in~ a~drou~ AlCl and ~erric o~ide ~rom

3 ~-- _ low-eE~ e ...
As a starting material 28 ton~ o~ low-grade bauxite containing 46 % A1203, 15 % ~e203 and 18.6 %
SiO2 are used~ The row material i5 broken and wet milled up to a grain ~ize of about 300 micron~
The bauxite i~ digested with 65 ~. of a 200 g./lit. aqueous hydrochloric acid solution (azeotropic mixture). Dige~tion i9 carried out in containers (duplicator~) in ~even ~tage~, for two hour~. The input temperature i~ about 60 to 85 C and the output temperature i9 about 105 to 130 C.
'~he bauxite slurr~ i~ settled in a Dorr ~edimentator whereupo~ it i~ ~iltered through ~ilter cylinder~ and i~ sub~equently wa~hed. The solution contain~ abou-t 20 g./lit D 0~ iron and ,~

~7~3~

about 200 g~/lit~ of hydrochloric acid. l'he solu-tion is deironized on a.n ion exchange column ~illed with a resin Yarion AT 660~ containing trimethylamine active moietie~. ~he ~peci~ic load of the column i9 10 ~ o hourO When the solution leaving the colum~ corltain3 2 g./lit. o~ ~e3~, the ion exchange procedure i~ stopped a~d the re~in i9 wa~hed to iron-free with water corresponding to twice of its volume~ ~fter this regeneration the column can be u~ed again for deironization.
~he eluted ferric chloride solution is evaporated to a concentration o~ about 1000 g.~lit. of ~eC13 and therea~ter it ig thermally decomposed ~o Fe203.
The hydrochloric acid obtai~ed during e~aporation and pyroly~is is coriverted into concentrated hydro-chloric acid in ab~orbers used also in the prepara tion o~ h~drochloric acid.
The filter cake contai~s about 13.3 t.
hl203, 0~58 t. ~e2Q39 -34 t. CaO and 0016 t~ MgOo q'o dissolve the ~oluble oxides a calculated amount (42 t~) of conce~trated sul~uri~ acid i~ ndded to the cake, in acid re~istant autocla~e~, where the ~ubsta.nce i9 heated ~or about 30 minute~ in two stages. ~rom t,he ~lurry water is evaporated and the autothermic procedure of the alumi~ium sulfate formation is ~tarted, as a result o~ which the ~lurry is heated approximately up -to 160 C J Before ,. ~

7~3~

~olidification the slurry i~ introduced into an oil-heated pipe mill, where the o~ides are digested at about 400 C and the ~lurry ~o~idifie~. The sul~uric acid, which i~ released duri~g the heating, i9 distilled of~ and, a~ter conden~ation, can be used up again.
The powdery product obtained i9 dissolved i~ 52.2 ~. of water, keeping the solid to liquid ratio at about 1:2. The mi~ture i3 concentrated in Dorr evaporators a~d the in~oluble residue, which contains siliGates and tita~ium oxides a~ major compone~t~ filtered off and wa~hed at 70 C.
~he filter cake, after dryingy can be u~ed for ceme~t production or a~ a titanium oxide 30urce.
If alumina i~ to be prepared in a high purity, the 3ulfate-containing solution can be ~urther puri~ied by an anio~ exchange re~in. In thi~ ca~e the aluminium sulfate ~olution, contain-ing about 400 g./lit. of aluminium sulfate and about 12 g./lit~ of ferric sulfate a~ impuri-ty, i~ adju~ted to pH 1.5 to 4 and i~ pas~ed through a colum~ ~illed with ~arion AP (an anion exchange re~:in containing pyridine active group~ Under these condi-tion~ the impuritie~, including iron are efficiently ad~orbed on the ~tronely ba~ic anion exchange resinO The solution leaving the column contain~ at most 0.5 g./lit. of iron~ 'rhe ; 12 - ~76~3~

ion e~change resin can be regenerated with an aqueou~ sulf~ric acid ~olution containing 100 go/lit~
o~ sul~uric acid.
The purified, aluminium sul~ate-containing ~olution i~ evaporated, dehydrated and i3 treated at 340 C~ At thi~ temperature the a:Luminium ~ul~ate disintegrates in-to a white powder, which is subjected to thermal decompo~ition at 800 to 1000 C 9 12~5 ton~ o~ a product ~ubs-tantiallg consisting of ~-alumina and about 35 ton~ of S03 ga~ are obtainedO ~he ga~ i~ introduced i~-to a sul~uric acid absorber and i~ recycled to the ~ul~ating step.
The alwmina obtained can be u~ed for the preparation of AlC13 very well3 ~i~ce at a temperature of 450 to 500 C it can be chlori~atecl with a practically theoretical (lOO ~) yield.

Pr~e~tion of ferric oxide and alumina ~0 fr~ m red mud ~he red mud u~ed a~ a raw ma-terial contain~
17 9 % A1203~ 34.6 ~0 Fe203, 5.1 % TiO2~ l~. 2 3.8 % ~aO and 6.2 Na2Q. For l ton of a dry red mud having the above compo~ition 985 kg. o~ HCl (100 %) can be calculated, and there~ore~ the red mud i~ treated with 2~35 ~. of an aqueou~ hydro~
chloric acid ~olution, having a concentration o~
~, . .

~t7~30 420 g./lit. in an autoclaYe 7 at 130 C for 2 hours. During this treatment 166 kg. of A1203 and 337 kg. o~ ~e203 are dis~olved. The slurry i~ admixed wi-th Varion AT re~in in a ratlo o~
3-1, and the re~in, on which iron i~ ad~orbed, i~ separated from the ~lurry by filtration with vibration~ Iron i~ eluted from the re~i~ with water, the ~eC13 solution i9 evapora-ted and i~
converted into ferric o~ide by thermal decompo~i-tion~ The released hydrochloric acid and the hydro-chloric acid~containing ~olution filtered off ~rom the deironiæed ~lurry in the presence of Sedo~an ~locculati~g agent~ are subjected to fractionated evaporation~ In thi~ way an azeotropic hydrochloric acid solution i~ obtained~ which i~ recycled into the deironization ~tep. '~he evaporation residue, ~ub~tantially con~isting of AlC13 0 6~20 i9 purified and can be marketed as AlC13 of "technical purity"
or can be 3ubjected to thermal decompo~ition in a pyroly~ator, to yield A1203. In the whole procedure an about 8 ~ lo~ ~n hydrochloric acid can be ob~erved, due -to the Na20 and CaO content of -the red mud.
'rhe major advantages of the proce~ according to the invention can be ~ummarized a~ ~ollow~:
- '~he inven-tion provides a procea~ for the utilization of low~grade aluminium and iron ~L~76~3~

carriers, ~uch ag laterite and siderite-contain-ing bauxite~ 9 or bauxite~ having a high silicon concentration~ red mud~ clay~, etc. Up to -the pre~ent there ha~ been known no economic proce~s to recover the aluminium and/or iron con-tent of ~uch low-grade carrier~.
- Startin~ ~rom the above raw ma-terials a practically silicon- and iron-~ree alumina can be prepared in a 80 % purity~ Since the product e~sentially con~ists o~ ~-alumina~ it is very active and can be u~ed a~ a ~tarting material in chlorometallurgical proce~ses, ~uch a~ chlorina-tion at 450 to 500 C with a mixture o~ C0 gas and chlorinating ga~, under atmospheric pre~ure.
- In addition to alumina, the proce~
according to the invention yield~ a further product containing 90 to 99 % of ~e203. Thi~
product i~ ~ubstantially free of pho~phorus and sulphur, and is therefore equally ~uitable for metallurgioal and other indu~trial purpo~es, e.g~
~or the production of ~erromagnet~, pigments, etc.
- ~y the proces~ of the present invention the de~ired product~ are obtained with an e~cellent yield (over 90 %) and highly ~electively~
~ The proce3~, not like the Bayer proce~, can be accompli3hed without the formation o~ large amount~ of unde~lrable ~olid and liquid wa~te ,, J.~

~6~3 mat t er3 0 - Hydrochloric acid and ~ulfuric acid are used in a clo~ed cyclic proce~s 9 only the ~mall 1093e~3 should be ~upplemented 9 and the 5 proce~ there:Eore very economic,, ,~

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for obtaining alumina and ferric oxide from a material which contains aluminium, iron and silicon, which process comprises:
a) treating the material at 90 to 130 °C with from one to two volumes of aqueous hydrochloric acid containing from 200 to 420 g./lit. of hydrochloric acid, thereby obtaining a solution of ferric chloride and a deironized product b) contacting the solution of ferric chloride with an anion ex-change resin which absorbs ferric chloride and hydrochloric acid, subsequently eluting ferric chloride and hydrochloric from the resin, returning hydro-chloric acid to the process for treatment of further material and subjecting the ferric chloride to pyrolytic decomposition at about 850 °C to obtain ferric oxide c) adding concentrated sulfuric acid to the deironized product in an about stoichiometric amount, calculated for the soluble oxides and heating the mixture to about 140 to 160 °C to obtain an aluminium sulfate solution d) separating the sulfuric acid and aluminium sulfate solution, returning separated sulfuric acid to the process for treatment of further deironized product and subjecting the aluminium sulfate to pyrolytic de-composition to obtain ?-A12O3.

2. A process as claimed in claim 1 wherein the material which contains aluminium iron and silicon is bauxite having a small module or containing laterite or siderite, red mud, colliery rock, coal ash or clay mineral.

3. A process as claimed in claim 1, wherein the anion exchange resin contains trimethyl amine, dimethylethanol amine or pyridine active groups.

4. A process as claimed in claim 1, wherein the anion exchange resin is in the form of a membrane or cloth and the absorption and elution of ferric chloride are carried out continuously or discontinuously in counter-current flow.

5. A process as claimed in claim 1 wherein hydrochloric acid released when sulfuric acid is added is returned to the deironization step, in the form of an azeotropic mixture.

6. A process as claimed in claim 1 wherein excess sulfuric acid distils off from the sulfuric acid treatment step at 300 to 400 °C is re-turned to the sulfuric acid treatment step, wherein a substantially acid-free sulfate mixture is obtained.

7. A process as claimed in claim 1, wherein the residue after the treatment with sulfuric acid is dissolved in water, filtered and subjected to a further deironization step by extraction or ion exchange.

8. A process as claimed in claim 5 wherein the filtration is carried out in the presence of a flocculating agent.

_ I ~