WO1999008959A1

WO1999008959A1 - A process for producing silica acid

Info

Publication number: WO1999008959A1
Application number: PCT/GB1997/002189
Authority: WO
Inventors: Solomon Flax
Original assignee: GOODANEW MARTIN ERIC; Promeks ASA
Current assignee: GOODANEW MARTIN ERIC; Promeks ASA
Priority date: 1997-08-14
Filing date: 1997-08-14
Publication date: 1999-02-25
Anticipated expiration: 2000-02-14
Also published as: AU3948997A

Abstract

The invention provides a process for the production of silica acid, comprising combining a silica-containing material with a calcium chloride solution, baking the mixture in an oven at a temperature of at least 800 °C to produce a cake, processing the cake into particles, leaching the same with a strong inorganic acid selected from the group consisting of hydrochloric acid, nitric acid and mixtures thereof at a temperature of up to 110 °C to produce a pulp, filtering the pulp to produce a silica acid sediment; and channeling the filtrate into a reactor for heating to evaporate HCI for reuse in the above leaching.

Description

A PROCESS FOR PRODUCING SILICA ACID

BACKGROUND OF THE INVENTION The present invention relates to a process for producing silica acid.

More particularly, the present invention relates to a process for processing silicates and aluminum silicates by hydrometallurgical techniques to produce silica acid and aluminum oxyhydrate, as well as to recover the metal impurities contained therein in oxyhydrate and hydrate form.

A hydrometallurgical method is known for extraction of aluminum (alumina) from bauxites with high silica content, as well as from nefelins by baking them with soda and limestone with subsequent leaching in caustic soda solution according to the reaction:

AI₂0₃'Siθ₂+Na₂Cθ₃+2CaCθ3→2NaAI0₂+2CaO'Si0₂+3C0₂ (1 )

Another method known for production of active silica acid - silicagel - involves the treatment of sand (Si0₂) with caustic soda at a temperature of 800 - 900°C and subsequent leaching of sodium silicate and precipitation of silica acid with H₂S0₄, HCI or carbonic acid. A similar process has been described for the manufacture of amorphous silica from rocks (US Pat. no. 5,445,804) involving initial dissolution of the rock with an alkaline solution.

A method is also known for production of silica acid, or white soot, by treating silicon tetrachloride (SiCI₄) or silicon tetrafluoride (SiF₄) silica with water vapor at temperatures of 1000°C - 1100°C. The existing methods for silica acid production have a number of drawbacks.

In the method for extraction of alumina from bauxites, in the course of baking aluminum-silicate raw materials with soda and limestone, part of Al₂0₃ interacts with CaO and Fe₂0₃ to form triple compounds insoluble in water or alkali solutions, such as XCa0'YFe₂0₃ ^»ZAI₂0₃ which leads to major aluminum losses (wherein X < 2, Y < 2, and Z = 1 ).

In the classical route to silicates, the caustic soda used for melting with Si0₂ is a relatively expensive material. The sodium silicate, produced after melting, is treated with steam, after which solutions are obtained that are difficult to filter.

Moreover, in the course of precipitation of silica acid from sodium silicate solution with HCI according to the reaction:

Na₂Si0₃+2HCI→2NaCI+H₂Siθ3 (2)

the sodium and hydrochloric acid present combine to form NaCI from which regeneration of NaOH and HCI is not economically viable.

In production of silica by gas-phase methods, expensive materials are used, such as silicon tetrachloride and silicon tetrafluoride. These materials are obtained by processes of chlorination and fluorination which are environmentally unfriendly. Another disadvantage of the gas phase method is the necessity to perform hydrolysis of SiCI₄ at temperatures of 1000°C - 1100°C to achieve the reaction:

t° SiCI₄+2H₂0→Si0₂+4HCI (3)

SUMMARY OF THE INVENTION

The object of the present invention is to provide a process for extraction of active silica acid from silica containing materials and both alumina and silica from aluminum silicate raw materials using reagents that are inexpensive and that may be completely regenerated.

Thus, with the above state of the art in mind, the present invention provides a process for producing silica acid, by means of combining silica- containing materials with a calcium chloride solution, baking said mixture in an oven at a temperature of at least 800°C to produce a cake, processing said cake into particles, leaching the same with a strong inorganic acid selected from the group consisting of hydrochloric acid, nitric acid and mixtures thereof at a temperature of up to 110°C to produce a pulp, filtering said pulp to produce a silica acid sediment; and channeling said filtrate into a reactor for heating to evaporate HCI, for reuse in the above leaching step.

The present invention further provides a process wherein the silica containing material further contains alumina. In the case of alumina-siiicates, a metal chloride sediment is formed and said sediment is thermohydrolysed at a temperature of about 150°C - 350°C to hydrolyse metal chlorides contained therein.

In a further embodiment of the present invention a combustible carbon- containing material is added to the silica-containing material to improve the handling properties during calcination, wherein the combustible material is selected from the group consisting of wood, sawdust, charcoal, oil-shale and black oil, as will be exemplified hereinafter.

In preferred embodiments of the present invention said silica containing component is microsilica, quartz, a spent SiO₂-AI₂O3 catalyst, ashes from coal, flint, clay and other silica or alumina-silicate containing materials.

In the present invention, the amount of calcium chloride added is preferably between stochiometric and 10% excess above the stochiometric amount for said reaction, and said baking is performed at a temperature of about 800°C - 1200°C.

In preferred embodiments of the present invention said acid is at a concentration of at least 5% and said leaching is carried out at a temperature of at least 70^βC and preferably at least 100°C. Especially preferred is the use of hydrochloric acid of at least 5% concentration, and most preferred at least 15% concentration.

Furthermore, after leaching, free hydrochloric acid in the form of an HCI-H₂0 aseothrop of ~20% concentration is isolated from the solution and reused in the leaching process. In the case of alumina-silicates, the sediment formed after isolation of the aseothrop undergoes thermohydrolysis at temperatures of about 280°C - 400°C.

In the case of mainly silica containing materials, metal admixtures are precipitated by addition of calcium oxide, removed by filtration and the calcium chloride filtrate is reused in the initial mixing procedure.

As indicated, the pulp obtained is filtered and the filtrate is channeled for production of aluminum, iron, calcium and other metals, while the silica acid is washed, dried and classified.

The silica product obtained form the process of the present invention contains > 99.5% of Si0₂; and has a well-developed surface up to 800 m²/l gr and high oil absorption capacity (D.B.P. test > 400 ml/100 gr).

Hydrochloric acid solution of metal chlorides (Al, Fe, Ca and others) are concentrated by evaporation and the precipitate undergoes thermohydrolysis. This enables almost complete regeneration of hydrochloric acid and calcium chloride. Metal admixtures are extracted in the form of concentrates containing hydroxides and oxihydrates of the corresponding metals.

It is another object of the present invention to recover not only aluminum, but also the other metal impurities such as iron, titanium, vanadium, nickel, rare earth metals, lead, etc., which are normally intermixed with and found in silicates and aluminum silicates, with the exception of calcium, magnesium, sodium and potassium, as explained hereinafter. While the invention will now be described in connection with certain preferred embodiments in the following examples, and with reference to the appended figures so that aspects thereof may be more fully understood and appreciated, it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims. Thus, the following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of formulation procedures as well as of the principles and conceptual aspects of the invention.

DESCRIPTION OF THE FIGURES Fig. 1 : Process flow diagram for production of silica acid, metal hydrates and oxyhydrates.

Fig. 2 : Flow sheet of a plant for silica production.

Fig. 3: Process flow diagram for production of materials containing low metal content (e.g microsilica, quartz).

EXAMPLES Example 1

Process realization is presented in Figures 1 and 2 for a spent refinery cracking catalyst (R.C.C.), based on Si0₂ - Al₂0₃. The R.C.C. catalyst containing the following composition:

Si0₂-62%; AI₂0₃-26.3%; CaO-O.35%; MgO-1.91%;

Fe₂O₃-0.79%; Ln₂O₃-1.28%; CuO-0.026%; NiO-0.36%;

PbO-0.0037%; ZnO-0.035%; Ti0₂-1.45% is channeled along Line 1 into Mixer 4; into the same mixer calcium chloride solution is channeled along Line 2 and wood sawdust or another carbon- containing product - along Line 3.

The charge is composed of: catalyst :CaCI₂ (recalculated at 100%): carbon-containing raw materials = 1: >1.0 : >0.05

The amount of CaCI₂ and carbon-containing raw materials may vary both ways depending on the composition of the initial silica-containing raw materials.

After thorough stirring the charge is channeled into Baking Furnace 6 along Line 5. The baking is performed at a temperature of 900°C for a period of about 3 hours (depending on the composition of the initial raw materials, the temperature may vary from 800°C to 1200°C, and baking time from 1 to 3 hours). In the course of baking, reactions take place between the catalyst components and calcium chloride, e.g.:

2SiO₂+CaCI₂+H₂0→CaO»2Si0₂+2HCI (4) AI₂θ3+CaCl2+H₂O-»Ca0.Al2θ3+2HCI (5) TiO₂+CaCI₂+H₂O→CaTiθ3+2HCI (6) etc.

The cake is transferred from furnace 6 along line 7 into reactor 8, where quenching of the cake takes place. Water is transferred into the same reactor along line 9. In the reactor a rapid cooling of the cake down to 40^β- 60°C occurs. The cake is transformed by quenching into fine powder, which makes it usable without additional milling. Gas from baking furnace 6 is channeled along line 12 into scrubber 13. Water is also channeled to scrubber 13 along line 9¹. In the scrubber, saturation of water with hydrochloride takes place until an azeothropic mixture is formed that contains ~20% of HCI used for the leaching process.

The finely divided cake is channeled from the quenching reactor along line 10 into leaching reactor 11 where 20% hydrochloric acid is channeled into the same reactor along line 14 from scrubber 13.

The leaching process is performed at a temperature of 90°-100°C with constant stirring for a period of about 2-3 hours.

The processes taking place during leaching are described by reactions 7 and 8:

CaO^«2Si0₂+2HCI->CaCI₂+2H₂SiO₃ (7)

CaOΑI₂0₃+8HCI→2AIC!₃+CaCI₂+4H₂O (8) etc.

The pulp after leaching is transferred to vacuum filter 16 along line 15; water is channeled into the same filter along line 9¹¹ to wash the silica. The washed silica is transferred along line 18 for drying to dryer 19. Silica drying is performed at a temperature of 120°-150°C. The dried product is channeled for packing along line 26. The product obtained contains > 99.5% of Si0₂; specific surface area (B.E.T.) ≤800 m²/g; test for dibutyl phthalate (D.B.P.) = < 400 ml/100 gr; bulk density d > 0.23 g/cm³.

The filtrate from vacuum filter 16 is sent along line 17 into reactor 20, where evaporation of the solution and hydrolytic decomposition of metal chlorides takes place at the temperature > 150°C. Under these conditions chlorides of Fe, Al, Ti and other metals are hydrolyzed, while chlorides of calcium, magnesium, sodium and potassium are not and they are recycled to the calcium chloride solution of step a.

The hydrolysis proceeds in the following way: AICI₃+2H₂O→AIO(OH)+3HCI (9)

FeCI₃+3H₂O→Fe(OH)₃+3HCI (10) etc.

Gas from hydrolysis reactor 20 is transferred along line 12¹ into scrubber 13, where the gas is scrubbed and 20% hydrochloric acid is produced.

The hydrolyzed product is transferred along line 21 into reactor 22 where it is leached with water at room temperature, the water being transferred along line 9¹¹¹.

In the course of leaching CaCI₂ and MgCI₂ are transferred into solutions. CaCI₂ concentration in the solution is <1000 g/l. The pulp from leaching reactor 22 is transferred by line 23 to a filter- press, where CaCI₂ solution is isolated from metal hydrates.

CaCI₂ solution is channeled along line 2 to the head of the process to be mixed with the initial silica-containing product and afterwards to baking; metal hydrates in the form of concentrates are channeled along line 27 for further processing.

The concentrates have the following composition: AI₂0₃-85.52%; Fe₂0₃-2.56%; Ln₂0₃-4.17% CuO-0.08%; NiO-1.16%; PbO-0.01 %; ZnO-0.11 %; Ti0₂-4.72%; CaO-1.13%; MgO-0.51 %

Extraction of aluminum and other metals into the concentrate reached > 95%.

Example 2

Ashes from burning power stations and other industrial applications were used as initial raw material. The ashes were of the following composition:

AI₂0₃-29%; Si0₂-51.7%; Ti0₂-3.74%; Fe₂0₃-3.7%;

MgO-2.2%; CaO-9.4%;Na₂0-0.13%; MnO-0.05%;

ZnO-0.01 %; PbO-0.01 %; CuO-0.01%; V₂0₅-0.05%

Processing of this material was performed under the conditions of Example 1. The HCI regeneration degree reached > 90%. Efficiency of production of - silica, CaCI₂ solution and metal concentrates was > 95%. The products obtained were of the following composition:

1 ) Silica: Si0₂-99.6%; D.B.P.<275mi/1 OOg; B.E.T.<630m²/g; d bulk<0.20g/cm³

2) calcium chloride solution:

CaCI₂-900g/l; MgCI₂-5g/l; Al, Ti, V, Fe, etc. - trace

3) metal concentrate:

AI₂0₃-77.6%; Fe₂0₃-10.4%; Ti0₂-10.0%; CaO-1.5%; MgO-0.3%; V₂0₅-0.2%

Example 3

As raw material flint clay with the following composition was used:

Al₂0₃-31.2%; Si0₂-62.7%; Ti0₂-4.43%; Fe₂0₃-1.16%; MgO-0.20%; CaO-0.19%; Na₂0-0.06%; V₂0₅-0.036%

Processing of this raw material was performed under the conditions of Example 1. The process parameters were similar to those used in Examples 1 and 2. A slight difference was observed in the composition of metal concentrates due to the differences in the chemical composition of the initial raw materials. Silica obtained from flint clay contained:

Si0₂-99.65%; D.B.P.≤350^m'/100g; B.E.T.≤ 800^m2/100g; d bulk<0.18⁹/cm³

EXAMPLE 4

As a raw material, microsilica with the following composition was used: Si0₂ - 95.1 %; AI₂O₃ - 0.026%; Na₂0- 0.23%; Fe₂0₃ - 0.83%; CaO - 0.15%; MgO - 0.13%; K₂O - 0.3%; C - 2.5%; SO₄ ^'2 - 0.6%. Processing of this material was performed under the conditions of example 1.

Since microsilica contains a small amount of admixtures, its processing was simplified, the operations of hydrolysis and leaching were excluded.

Admixtures (Fe, Al, Mg etc.) were separated by means of neutralization with

CaO up to pH=11-12. This procedure yields solutions which are pure relative to Mg. The flow sheet for microsilica is given in Fig.3.

The products obtained were of the following composition:

Silica: Si0₂ 99.8%, DBP > 275ml/100g; B.E.T.≤ 700m²/g; dbulk < 0.459 g/cm³.

Calcium chloride solution: CaCI₂ - 700g/l; Mg, Al, Fe etc. - trace

Metal concentrate: Fe₂O₃ - 54.8%; K₂O - 15.8%; Na₂0- 14.1 %; CaO - 5.0%;

MgO - 8.6%; AI₂0₃ - 1.7%. EXAMPLE 5

Quartzite with the following composition was used as a raw material: SiO2 - 99.5%; AI₂O₃ - 0.02%; Na₂O- 0.01%; Fe₂O₃ - 0.25%; CaO - 0.11%; MgO - 0.10%; K₂O - 0.01%.

Processing of this material, after initial grinding down to ~1mm particle size was performed under the conditions of examples 1 and 4.

Quartz contains a lower amount of admixtures than microsilica, therefore this product was processed according to the shortened scheme (see Fig.3): after evaporation the CaCI₂ solution was directed to the beginning ("head") of the process without purification for five cycles. Products analogous to those described in example 4 were obtained.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meanings and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

WHAT IS CLAIMED IS:

1. A process for the production of silica acid, comprising: a) combining a silica-containing material with a calcium chloride solution; b) baking said mixture in an oven at a temperature of at least 800°C to produce a cake; c) processing said cake into particles; d) leaching the same with a strong inorganic acid selected from the group consisting of hydrochloric acid, nitric acid and mixtures thereof at a temperature of up to 110°C to produce a pulp; e) filtering said pulp to produce a silica acid sediment; and f) channeling said filtrate into a reactor for heating to evaporate HCI for reuse in step d.

2. A process according to claim 1, wherein a combustible carbon containing material is added to step a, selected from the group consisting of wood, sawdust, charcoal, oil-shale and black oil.

3. A process according to claim 1, wherein said silica-containing material is an alumina silicate and the sediment formed in step e contains a metal chloride.

4. A process according to claim 3 wherein, said sediment is further processed by thermohydrolysis at a temperature of about 150° - 350° to hydrolyse metal chlorides contained therein.

5. A process according to claim 1 wherein said silica containing material is microsilica.

6. A process according to claim 1 , wherein said silica containing material is quartz.

7. A process according to claim 3, wherein said silica containing material is a coal ash.

8. A process according to claim 3, wherein said silica containing material is a flint clay.

9. A process according to claim 3, wherein said silica containing material is an F.C.C., R.C.C. spent catalyst.

10. A process according to claim 1, wherein said baking is performed at a temperature of about 800°C-1200°C.

11. A process according to claim 1 wherein the amount of calcium chloride added is between stochiometric and 10% excess above the stochiometric amount for said reaction.

12. A process according to claim 1 , wherein said leaching is carried out at a temperature of at least 70°C and preferably at least 100°C .

13. A process according to claim 1, wherein said cake is leached in > 5% hydrochloric acid solution.

14. A process according to claim 1, wherein after leaching, the free hydrochloric acid in the form of an HCI-H₂0 aseothrop of ~ 20% is isolated from solution and reused in the leaching process.

16. A process according to claim 4, wherein said sediment, after isolation of the aseothrop, undergoes thermohydrolysis at temperatures of about 280°C - 400°C.

AMENDED CLAIMS

[received by the International Bureau on 02 June 1998 (02.06.98); original claims 1 and 2 replaced by amended claim 1; remaining claims unchanged (1 page)]

1. A process for the production of silica acid, comprising:

a) combining a silica-containing material with calcium chloride solution and

adding a combustible carbon containing material selected from the group consisting of

wood, sawdust, charcoal, oil-shale and black oil;

b) baking the mixture produced in step (a) in an oven at a temperature of at

least 800°C to produce a cake;

c) processing said cake into particles;

d) leaching the same with a strong inorganic acid selected from the group

consisting of hydrochloric acid, nitric acid and mixtures thereof at a temperature of up

to 110^βC to produce a pulp;

e) filtering said pulp to produce a silica acid sediment; and

f) channeling said filtrate into a reactor for heating to evaporate HCI for reuse

in step (d).

3. A process according to claim 1 , wherein said silica-containing material is an

alumina silicate and the sediment formed in step (e) contains a metal chloride.

4. A process according to claim 3 wherein, said sediment is further processed by

thermohydrolysis at a temperature of about 150°C - 350°C to hydrolyse metal chlorides

contained therein.