AU2014280962B2

AU2014280962B2 - Process For The Cold Hydrochemical Decomposition Of Sodium Hydrogen Aluminosilicate

Info

Publication number: AU2014280962B2
Application number: AU2014280962A
Authority: AU
Inventors: Alexander Welter
Original assignee: Pleason Ventures Ltd
Current assignee: Pleason Ventures Ltd
Priority date: 2014-12-24
Filing date: 2014-12-24
Publication date: 2020-10-22
Anticipated expiration: 2034-12-24
Also published as: AU2014280962A1

Abstract

5 The process for the cold hydrochemical decomposition of sodium hydrogen aluminosilicate relates to the metallurgy of non-ferrous metals and especially to the field of the production of alumina by the alkaline hydrochemical process. In the production of alumina by the alkaline hydrochemical process, the silicon dioxide comprised in the ore being treated is united to the sodium hydrogen aluminosilicate 0 (Na2Al 2Si 2 O8-2H20) that is insoluble in alkaline media. When treating red mud the invention enables the hydrochemical decomposition of crystallised sodium hydrogen aluminosilicate to produce sodium aluminate, silicic acid gel and an iron ore product. The sodium aluminate is fed back to the alumina production process, whereas the silicic acid gel and the iron ore products represent commercial products. 1/3 bauxite aluminate soln. for circulating liquor aluminate decomposition in the from the Bayer- leaching soln. dissolution Bayer-Process Process a- a 53= 1.5 + 1.7 1 ~A1 20 3= 120 +150 g/dm 3 concentration, washingAlO=12+15g/m decomposition of red mud solid phase!sprto chelate soln. heating, coagulation of silicic acid solid phase separation slccai e sicon-free chelate soln. NaHCO3 soln. * Decomposition of chelate separation of the sodium hydrogen carboaluminate precipitate sodum hydrogen carboaluminate Y mother liquor NaAl[CO3](OH2) evaporation, cooling CO2 calcination regeneration of mother lquor sodium aluminate sodium hydrogen circulting chelate Na20 Al2O3 carbonateD precipitated 1Fg1

Description

1/3

bauxite

aluminate soln. for circulating liquor aluminate decomposition in the from the Bayer- leaching soln. dissolution Bayer-Process Process a- a53= 1.5 + 1.7 3 1 ~A1 20 3 =120 +150 g/dm concentration, washingAlO=12+15g/m

decomposition of red mud

solid phase!sprto

chelate soln.

heating, coagulation of silicic acid

solid phase separation slccai e

sicon-free chelate soln.

NaHCO3 soln. *

Decomposition of chelate

separation of the sodium hydrogen carboaluminate precipitate

sodum hydrogen carboaluminate

NaAl[CO3](OH2)

Y mother liquor

evaporation, cooling

calcination CO2 regeneration of mother lquor

sodium aluminate circulting chelate Na20 Al2O3 sodium hydrogen carbonateD precipitated 1Fg1

Process for the cold hydrochemical decomposition of sodium hydrogen aluminosilicate

The invention relates to the metallurgy of non-ferrous metals, especially to the field of production of alumina by the alkaline hydrochemical process.

The alkaline hydrochemical process for processing aluminosilicate ores into alumina is particularly applicable for silicon-poor bauxite, whereas it is of only limited interest for other aluminosilicate ores (silicon-rich bauxite) or not applicable (for clays, bauxite similar rocks or sillimanites), basically due to the high losses of useful components such as sodium and aluminium oxide with sodium hydrogen aluminosilicate (viz. Spravo6nik metallurga po cvetnym metallam. Proizvodstvo glinozema, M., Metallurgija, 1970, p 141).

In the production of alumina by the alkaline hydrochemical process, the silicon dioxide comprised in the ore being treated is united to the sodium hydrogen aluminosilicate (Na 2Al 2Si 2 O-2H 8 20) that is insoluble in alkaline media. The formation

of the sodium hydrogen aluminosilicate causes losses in the reusable components, i.e. the sodium and aluminium oxide in the stockpiled red mud during the processing of high-grade bauxite. When processing low-grade bauxites with a high silicon dioxide content the losses of reusable components are so high that they have to be further processed by sintering.

The known consecutive variant for processing silicon-rich bauxites is the sinter process from Bayer (see A.I. Lajner, Proizvodstvo glinozema, M., Metallurgija, 1961, S. 575). In this process, red mud with a high A1 2 03 and Na20 content is sintered in a mixture of limestone and soda. The aluminate liquor resulting from the leaching of the sinter cake and separated from silicon is mixed with the aluminate liquor from the Bayer process for joint decomposition. The disadvantages of this process are the high capital investment costs, the high fuel consumption and the considerable environmentally harmful emissions, wherein the composition of the red mud hinders the sintering of the prepared charge.

An alkaline process for the production of alumina from clay by sintering is known (ibid pp. 142-143). The essence of the process consists in sintering the charge consisting of clay, limestone and calcined soda, wherein solid sodium aluminate is formed at high temperature from the aluminium oxide contained in the charge, is converted into solution and is subsequently precipitated out of this solution as aluminium hydroxide, wherein the silicon dioxide on sintering is bound to the dicalcium silicate that is insoluble in alkaline solution. This process, due to its high costs in materials, energy and fuel, as well as the high capital costs and the considerable environmentally harmful emissions, has lost its industrial significance.

An alkaline-acidic process for the production of alumina from silicon-rich aluminium ores is also known (see RF-PS no. 2440296, cl. CO F7/20, published 2012). In this process the starting material is leached out to form alkali metal hydrogen aluminosilicates that are decomposed at low temperature by treating the mud with the weak solution of a strong acid, wherein the aluminium and the alkali metals go into solution. Aluminium hydroxide is then separated from this solution. The principal disadvantage of the alkaline-acidic process consists in the complicated recovery of the strong acids.

Disclosed herein is a process for the hydrochemical decomposition of sodium hydrogen aluminosilicate which may reduce the losses of valuable components when processing bauxites to alumina and/or the production of alumina from other aluminosilicate rocks.

In one aspect there is provided a process for the cold hydrochemical decomposition of a sodium hydrogen aluminosilicate containing material, comprising the following steps: (a) decomposing the sodium hydrogen aluminosilicate containing material at low temperature with a chelate solution in the presence of a weak acid to form a mixture comprising: soluble compounds of: an aluminium chelate, silicic acid and a sodium salt of the weak acid, and insoluble contaminants; (b) separating the insoluble contaminants from the mixture to form a contaminant-depleted solution; (c) adding a coagulator to the contaminant-depleted solution to form a

2a

coagulator-containing solution; (d) heating the coagulator-containing solution to a temperature of 100 - 120 0C to coagulate the silicic acid thereby forming a coagulated silicic acid-comprising mixture; (e) separating coagulated silicic acid gel from the coagulated silicic acid comprising mixture to form a silicic acid-free solution; (f) decomposing the silicic acid-free solution by treating it with an excess of sodium hydrogen carbonate to form a precipitate of sodium hydrogen carboaluminate and a mother liquor; (g) separating the sodium hydrogen carboaluminate precipitate from the mother liquor; (h) concentrating the mother liquor by evaporation to form a concentrated mixture; (i) cooling the concentrated mixture to form a cooled concentrated mixture; (j) carbonising the cooled concentrated mixture with gaseous carbon dioxide under a pressure of at least 16 bar to form a sodium hydrogen carbonate precipitate and a chelate-containing solution; (k) separating the sodium hydrogen carbonate precipitate from the chelate containing solution; (1) calcining the sodium hydrogen carboaluminate at a temperature of 700 - 900 °C to form sodium aluminate; and (m) using the sodium aluminate to produce alumina.

Crystalline sodium hydrogen aluminosilicate is decomposed at low temperature with the help of a circulating chelate, namely with the aqueous solution of a mixture of the sodium salt of ethylenediaminetetraacetic acid and a weak acid. The decomposition of the sodium hydrogen aluminosilicate affords the soluble compounds of the aluminium chelate, of the silicic acid and of the sodium salt of the weak acid: Na2Al 2ASi 2 O2H 20 + 2NaHg4..edta+ 2x/y HyA -- 2Na[Aledta] + 2H 4 SIO 4 + 2x/y NaA + 2H 2 0 [1]

in which A is the anion of a weak acid, x is the degree of substitution of the hydrogen atoms of the carboxyl group of the ethylenediaminetetraacetic acid by the sodium atoms, and means 1, 2, 3 or 4, y is the basicity of the weak acid and means 1 or 2.

A coagulant is then added to the resulting solution that is then heated so as to coagulate the silicic acid, the obtained silicic acid gel is separated from the solution and the aluminium chelate is decomposed by treating the solution with excess sodium hydrogen carbonate:

Na[Aldta] + 4NaHCO 3 = NaAI[CO 3 ](OH)21 + Na 4edta + 3CO2 + H 2 0 [2]

Decomposition of the aluminium chelate affords a precipitate of sodium hydrogen carboaluminate and the mother liquor of the chelate. The sodium hydrogen carboaluminate precipitate is then separated from the mother liquor. The latter is subsequently evaporated, cooled and regenerated by carbonisation under pressure with gaseous carbon dioxide; the sodium hydrogen carbonate crystallises out and is separated from the solution.

Na 4edta+ (4-x)CO2 + (4-x)H 20 -- NaxH( 4xedta + (4-x)NaHCO3 [3]

NayA + yC02 + yH 20 = HyA + yNaHC0 3 1 [4]

The regeneration products, i.e. the solution of the chelate and the weak acid as well as the sodium hydrogen carbonate are circulating products.

The sodium hydrogen carboaluminate is then calcined to form sodium aluminate:

t NaAI[XO 3 ](OH) 2 -- *NaAIO2 + H 20 + C021 [5]

The sodium aluminate is dissolved in the aluminate solution and then fed back for the production of alumina by the Bayer process.

The following schemes illustrate examples for carrying out the invention:

Fig. 1 Red mud processing;

Fig. 2 Alkaline hydrochemical processing of clay to alumina, the weak acid is carbonic acid;

Fig. 3 hydrochemical alkaline processing of clay to alumina, the weak acid is acetic acid.

Example 1 - red mud processing (see Fig. 1).

Composition of the solid phase of the red mud: Na20 - 12.8 %, A12 0 3 - 18.6 %, SiO2 - 19.2 %, Fe 2 03 - 33.9 %, TiO 2 - 4.3 %.

The solid phase of the red mud was decomposed under the following conditions:

- circulating chelate solution: - concentration of the disodium salt of ethylenediaminetetraacetic acid: 120 g/dm 3 and concentration of the acetic acid: 7%, - temperature: 25 °C, - decomposition time: 3 hours, - ratio liquid phase: solid phase: 10 : 1.

The liquid phase of the reaction products is filtered off from the insoluble precipitate. Composition of the precipitate (iron ore product): Na20 - 0.31 %, A1 20 3 - 4.70 %, SiO2 - 3.40 %, Fe 2 03 - 75.3 %, TiO 2 - 7.3 %.

The extraction of the solid phase of the red mud into the liquid phase amounted to Na 20 - 98.8 % and A1 2 0 3 - 89.0 % respectively.

The liquid phase was then held at a temperature of 120 °C for 2 hours in order to coagulate the silicic acid. The resulting silicic acid gel with the composition: Na 20 - 1.5 %, A1 20 3 - 1.4 % and SiO2 - 77.9 % was filtered off and the silicon-free solution was then decomposed at 90 0C by treatment with a 30 % stoichiometric excess of a sodium hydrogen carbonate solution. The decomposition afforded a precipitate of sodium hydrogen carboaluminate of the following composition: Na 20 - 20.4 %, A120 3 - 34.4 %, SiO2 - 0.4 % und Fe 203 - 0.03 %. This precipitate was then filtered off and calcined at a temperature of 700 °C for 30 minutes. The resulting sodium aluminate had the following composition: Na 20 - 36.3 %, A12 0 3- 62.2 %, SiO2 - 0.8 % and Fe 20 3- 0.1 %.

Example 2: Alkaline hydrochemical processing of clay to alumina (see Fig. 2).

A batch of clay with the composition Na 20 - 0.25 %, A12 0 3 - 37.50 %, SiO2 - 44.80 %, Fe 2 03 - 1.59 % and TiO2 - 2.51 % was leached out with a solution of caustic liquor under the following conditions: - concentration of Na20ky: 120 g/dm 3

, - ratio liquid phase: solid phase: 7 : 1, - leaching time: 5 hours, - leaching temperature: 102 °C.

The solid phase formed during the leaching process was filtered off and washed. The chemical composition of the solid phase of the leaching product from the clay was as follows: Na 20 - 19.0 %, A12 0 3 - 29.70 %, SiO2 - 36.30 %, Fe 2 03 - 1.50 % and TiO 2 - 2.50 %. Composition of the material constituent: principally sodium hydrogen aluminosilicate (NA 2AI2-Si 2O 8-2H 20).

The sodium hydrogen aluminosilicate was decomposed under the following conditions: - circulating chelate solution: - concentration of the disodium salt of ethylenediaminetetraacetic acid: 100 g/dm3 - ratio liquid phase: solid phase: 10 : 1, - temperature: 25 °C, - C02 pressure 40 bar, - decomposition time: 4 hours.

The liquid phase of the reaction products was separated from the insoluble contaminated precipitate and held under a C02 pressure of 16 bar at a temperature of 120 °C for 2 hours in order to coagulate the silicic acid. The resulting silicic acid gel with the composition: SiO2 - 84.60 %, A12 0 3 - 0.63 %, Na20 - 1.15 % was filtered off and the silicon-free solution was then decomposed at 25 °C by treatment with a 30 % stoichiometric excess of a sodium hydrogen carbonate solution.

The sodium hydrogen carboaluminate precipitate was filtered off from the solution. The composition of the precipitate: Na 20 - 21.40 %, A1 2 0 3 - 36.80 %, SiO2 - 0.81 %.

The sodium hydrogen carboaluminate was calcined at a temperature of 700 °C for 0.5 hours. The resulting sodium aluminate had the following composition: Na 20 - 35.80 %, A12 0 3 - 61.50 %, SiO2 - 1.40 %.

Example 3: Hydrochemical processing of clay to alumina (see Fig. 3).

The batch of clay was leached out as in Example 2. The sodium hydrogen alumonate was decomposed under the following conditions: - circulating chelate solution: - concentration of the disodium salt of ethylenediaminetetraacetic acid 100 g/dm 3 and concentration of acetic acid 7%, - temperature: 25 °C, - decomposition time: 1.5 hours.

The liquid phase of the reaction products was filtered off from the insoluble contaminated precipitate and held at a temperature of 120 °C within 2 hours in order to coagulate the silicic acid. The resulting silicic acid gel with the composition: SiO2 - 83.50 %, A12 0 3 -0.50 %, Na 20 - 0.60 %, Fe 203 - 0.05 % was filtered off and the silicon-free solution was decomposed at 90 0C by treatment with a 30

% stoichiometric excess of a sodium hydrogen carbonate solution.

The sodium hydrogen carboaluminate precipitate was separated from the solution by filtration. Composition of the precipitate: Na 20 - 21.30 %, A12 0 3 - 36.70 %, SiO2 - 0.51%.

The sodium hydrogen carboaluminate was calcined at a temperature of 700 °C for 0.5 hours. The resulting sodium aluminate had the following composition: Na 20 - 35.9 %, A12 0 3 - 62.0 %, SiO2 - 0.83 %.

Claims

1. A process for the cold hydrochemical decomposition of a sodium hydrogen aluminosilicate containing material, comprising the following steps: (a) decomposing the sodium hydrogen aluminosilicate containing material at low temperature with a chelate solution in the presence of a weak acid to form a mixture comprising: soluble compounds of: an aluminium chelate, silicic acid and a sodium salt of the weak acid, and insoluble contaminants; (b) separating the insoluble contaminants from the mixture to form a contaminant-depleted solution; (c) adding a coagulator to the contaminant-depleted solution to form a coagulator-containing solution; (d) heating the coagulator-containing solution to a temperature of 100 - 120 °C to coagulate the silicic acid thereby forming a coagulated silicic acid-comprising mixture; (e) separating coagulated silicic acid gel from the coagulated silicic acid comprising mixture to form a silicic acid-free solution; (f) decomposing the silicic acid-free solution by treating it with an excess of sodium hydrogen carbonate to form a precipitate of sodium hydrogen carboaluminate and a mother liquor; (g) separating the sodium hydrogen carboaluminate precipitate from the mother liquor; (h) concentrating the mother liquor by evaporation to form a concentrated mixture; (i) cooling the concentrated mixture to form a cooled concentrated mixture; (j) carbonising the cooled concentrated mixture with gaseous carbon dioxide under a pressure of at least 16 bar to form a sodium hydrogen carbonate precipitate and a chelate-containing solution; (k) separating the sodium hydrogen carbonate precipitate from the chelate containing solution; (I) calcining the sodium hydrogen carboaluminate at a temperature of 700 - 900 °C to form sodium aluminate; and

(m) using the sodium aluminate to produce alumina.

2. The process according to claim 1, where the chelate solution comprises sodium salts of ethylenediaminetetraacetic acid as well as ethylenediaminetetraacetic acid itself.

3. The process according to claim 1 or 2, wherein the sodium hydrogen aluminosilicate is decomposed at a temperature of 20 - 45 °C.

4. The process according to any one of claims 1 to 3, wherein the silicic acid-free solution is decomposed by treatment with a 30-100% stoichiometric excess of sodium hydrogen carbonate relative to the total amount of aluminium chelate in the silicic acid free solution.

5. The process according to any one of claims 1 to 4, wherein separation of the coagulated silicic acid gel from the coagulated silicic acid-comprising mixture is performed using a circulating solution comprising seed crystals of silicic acid.

6. The process according to any one of claims 1 to 5, wherein separation of the hydrogen carboaluminate precipitate from the mother liquor is performed using a circulating solution comprising seed crystals of hydrogen carboaluminate.

7. The process according to any one of claims 1 to 6, wherein the sodium hydrogen carbonate precipitate separated in step (k) is used in step (f).

8. The process according to any one of claims 1 to 7, wherein the chelate-containing solution separated in step (k) is used in step (a).

9. The process according to any one of claims 1 to 8, wherein the sodium hydrogen aluminosilicate containing material is a red mud, and the insoluble contaminants comprise iron ore.

Pleason Ventures Ltd Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON