FI71916C - Method for treating anorthosis and using the by-product obtained by the procedure. - Google Patents

Description

71 91 6

Method for treating anorthosite and use of the by-product obtained from the method

The present invention relates to a process for dissolving anorthosite with sulfuric acid to produce aluminum sulphate and to the use of a dissolution residue obtained as a by-product in the process.

Aluminum-containing silicate minerals, such as anorthosite, have been known to be treated with mineral acids, e.g., sulfuric acid, to transfer the aluminum content of the mineral to an acid solution and recover it as an aluminum salt, such as aluminum sulfate.

One difficulty with this type of treatment process has been the simultaneous dissolution of the silicon contained in the mineral as silicic acid, which has a strong tendency to precipitate as a gel. This gel makes it difficult to filter the undissolved product, making it even impossible. In addition to the extraction solution containing aluminum and further processed into aluminum sulphate, the process generates a large amount of insoluble dissolution residue as a by-product, which contains mainly silica and, in the case of an orthosite-sulfuric acid treatment, also calcium sulphate precipitated in the process. From the point of view of the economics of the process, it would therefore be highly desirable to find process conditions in which the main product, i.e. the aluminum salt, is obtained in good yield, while the leach residue acquires properties through the process which allow it to be successfully utilized.

FI patent application 77 1014 relates to a continuous process for recovering alumina from aluminum-containing silicates, such as anorthosite, by treating the anorthosite mineral in a dissolution step with warm sulfuric acid and possibly hydrochloric acid. According to the application, an acid with 50 to 271916 750 g / l of free sulfuric acid and 0 to 300 g / l of free hydrochloric acid is used for the extraction of the raw material. About 90% of the aluminum content dissolves when the acid treatment is performed for about 1-2 hours at about 100 ° C. However, according to the only example in the application, the filtrate obtained has an alumina content of only about 6% and a water content of 73%, so that the filtrate is disadvantageously lean in view of its further processing.

The insoluble silica residue and precipitated calcium sulfate are filtered and can be calcined to form calcium sulfate and produce cement or "wollastonite."

FI patent application 80 0329 also relates to a process for extracting silicate minerals, such as anorthosite, with mineral acid. In this method, it has been found possible to carry out the extraction of silicates without the formation of a harmful silica gel by carrying out the extraction using the largest possible particle size of the individual mineral granules so that the outer surface is as small as possible, which improves the filterability of the residual solution.

According to Example 1 of the application, in which the dissolution of the anorthosite was carried out at about 100 ° C using relatively dilute 6N HCl, the aluminum content of the filtrate obtained was 36 g Al / l.

It is proposed to mix the filtered and washed leach residue obtained after the hydrochloric acid treatment, e.g. with cement, resulting in a light, porous material with good thermal insulation properties. In contrast, strength-enhancing or binding properties are not mentioned.

It is also known to use silica powder as a concrete admixture, which has a high specific surface area (about 20 m 2 / g) and which is separated from the flue gases during the production of iron. This silica is a so-called a pozzolanic substance, it is alkaline and has self-curing properties.

3 7191 6

The present invention relates to an improved process for treating anorthosite with sulfuric acid by dissolving so that, in addition to aluminum sulphate formed in good yield as the main product, a solid, easily separable dissolution residue is obtained which has been shown to have very advantageous strengthening and whitening properties when used in curable compositions.

According to the invention, this object is achieved by treating the finely divided anorthosite with concentrated, about 40 to 60% by weight, preferably 50 to 60% by weight, aqueous sulfuric acid at elevated temperature, separating the insoluble residue obtained from the filtrate to be reprocessed, and that the leach residue is washed to minimize its water-soluble alumina content.

The process of the invention is preferably carried out using finely ground anorthosite having a particle size d50 of less than about 125 and more preferably less than about 60, as a raw material, in order to obtain rapid dissolution of the anorthosite. The weight ratio of the anorthosite to the solution of the selected concentration depends on the delay time of the solution. That is, an excess of anorthosite degrades the solvent yield and a lower amount, in turn, leaves free acid in the product, which may interfere with the further process. The acid used is preferably 93% by weight of concentrated sulfuric acid, which is diluted, for example, with the washing residue of the dissolution residue to a dissolution concentration. Dilution raises the temperature of the acid so that the anorthosite dissolves rapidly. The exothermic reaction heat raises the temperature of the reaction mixture to a boiling point, about 120-130 ° C, which ensures a good dissolution yield in a short time, usually about one hour. Of course, lower temperatures, but preferably above 100 ° C, can also be used, whereby the reaction time is correspondingly longer. If a sufficiently finely ground anorthosite with a particle size d ^ Q ~ 40 - 60 μιη is used as starting material 4 71916, the residence time in the reactor can be shortened and the equipment reduced, and it is usually not necessary to add additional heat to the process in addition to the exothermic reaction heat. Under these conditions, most of the aluminum contained in the anorthosite dissolves in the filtrate, while obtaining a leaching residue which is excellent in properties for use in reinforcing materials.

According to the invention, the concentration of sulfuric acid used must remain in the range of about 40 to 60% by weight of H2SO4. A stronger acid gives an overly concentrated Al 2 SO 4 solution, which may crystallize as the temperature of the entire reaction mixture decreases. The accompanying dissolution residue promotes crystallization. The leaner acid, on the other hand, causes gelling difficulties due to the higher water content, whereby the separation of the residue, for example by filtration, becomes difficult and even impossible.

When the dissolution reaction is complete, the desired amount of water can be added, if desired, to facilitate separation of the solid. Water can be added earlier during the treatment, but in this case gelation may occur and considerable amounts of water will have to be used. In this case, the solution is easily diluted too much and the necessary subsequent concentration is no longer economically viable.

In order to illustrate the gelling tendencies of different reaction systems, the following are exemplary analyzes of two different grades of Lapland anorthosite, namely grade A (more reactive grade) and grade B (less reactive grade) and their behavior in sulfuric acid solutions of different concentrations.

Il 71 91 6 5

Anorthocyte analyzes

Quality A Quality B

A1203 30 29

SiO 2 43.5 43.0

Fe 1.3 1.6

Na 1.0 1.0

Ca 13 13 <350, ym 80 (rough) 42

Experimented reaction systems Grade A (more reactive)

Koe no. anort. H2SO ^ System behavior fineness concentrated.

____ weight -% ________ 1 · 50% <80 ym 36.8 strong gelation 2. - "- 46.7 solid 3. -" - 49 thick 4. - "- 54.4 leached well 5. 100% <125 ym 54 symptoms of porridge, somehow seeped

Grade B (less reactive) 6. 50% <42 μm 39.2 strong gelation 7. - "- 44.5 symptoms of porridge 8. -" - 49 infiltrated fairly well 9. - "- 58.8 infiltrated well

From the above values, it can be seen that the more readily soluble more reactive anorthosite A (finely divided anorthosite, 100% <125 μm) had a lower limit of sulfuric acid concentration of about 55% and about 50%, respectively (coarse anorthosite 6,71916 50% <80 μπι). The less reactive anorthosite B had a lower limit of sulfuric acid concentration lower than grade A, about 45%, so the less soluble anorthosite also gels harder, and more water can be used in the system. Thus, the lower limit of the acid concentration to be used also depends to some extent on the quality of the anorthosite. For practical purposes, however, an acid concentration of less than 40% is hardly possible due to the excessive tendency of the system to gel. As already mentioned above, too high a concentration of sulfuric acid causes the filtrate to crystallize as the reaction temperature decreases, which in turn determines the upper limit of the acid, about 60%.

The salt melt obtained after the sulfuric acid leaching can be diluted, preferably to a solution containing about 8 to 13% Al 2 O 3, with an optimum concentration for filtration of 10 to 11% Al 2 O 3. The insoluble silica body and the precipitated calcium sulfate are preferably separated by filtration, and the residual solvent is washed thoroughly, for example, with water to minimize the water-soluble alumina content. The aluminum sulfate solution can be concentrated by adding concentrated (93%) sulfuric acid and aluminum hydrate such that about 50 to 60% by weight of the total aluminum is derived from aluminum hydrate, and the resulting melt is crystallized. This gives a solid aluminum sulphate with an Al 2 Cl 2 content of about 17% (Al ~ 9%).

As already mentioned above, the residue obtained in the dissolution after treatment is treated by washing to reduce the amount of water-soluble alumina contained in the residue, preferably to a concentration of less than 1.0% by weight, and in particular to a concentration of less than 0.2% by weight. When prepared according to the invention, the dissolution residue acquires properties which make it an excellent hardening, in particular initial strength, additive in curable masses.

Namely, it has been found that the solidification properties are influenced by the degree of washing of the mother liquor, i.e. the residual aluminum oxy-11 71916 7 di. The less water-soluble alumina in the dissolution residue, the better the binder properties of the dissolution residue. This is probably due to the fact that the water-soluble aluminum salt penetrates the pores and reduces the specific surface area of the dissolution residue. It is assumed that it is precisely the large specific surface area, which is preferably more than 50 and in particular more than 70 m 2 / g as measured by the nitrogen absorption method, that is one of the main factors influencing the hardening of the curable masses.

The dissolution residue according to the invention is characterized by a silica body with a specific surface area of about 50 to 100 m 2 / g and CaSO 4 in the anhydrite form. By its nature, this dissolution residue is not pozzolanic to microsilica, its aqueous solution is slightly acidic and has no tendency to self-cure. It is apparently made reactive and suitable as an admixture or binder for concrete by its high specific surface area and the silicon bonds formed during dissolution, which are substantially supplemented by the anhydrite gypsum which forms the hydrate gypsum. The interaction of these forms calcium silicate compounds activated by sulphate ions, e.g. with cement or blast furnace slag.

Due to their advantageous binder properties, the leach residue according to the invention can be used as part of a binder in conventional curable compounds, such as concrete. It can be used as a cost-reducing binder component to replace, for example, cement or blast furnace slag in mine backfilling and shotcreting. It can also be used as a filler to partially replace the finer part of the aggregate in concrete, where good results have been obtained, for example, when the material of the natural filler less than 0.125 mm has been replaced by a dissolution residue (approx. 5% of the total aggregate). In curable masses, the ratio of binder to aggregate is not critical, and for the purposes of the invention, the bond: frame-to-matrix ratios commonly used for such masses can be used. In such pulps, the dissolution residue obtained according to the invention can be used as a partial substitute for binder and / or filler, provided, however, that the amount of dissolution residue thus used is not more than 75% by weight and preferably not more than 50% by weight of the total binder.

In addition to good binder properties, the leach residue prepared according to the invention has a very high whiteness due to both the whiteness of the silica and the whiteness of the precipitated calcium sulphate, which is able to mask the color of any colored impurity particles present. Due to this whiteness, the leach residue can be used, for example, as a partial substitute for white cement, for example in washed concrete tiles, or as a substitute for satin white to increase the degree of reflection of building materials.

The following examples illustrate the invention.

Example 1

Gulf of Lapland anorthosite, grade B, was ground in a ball mill to a particle size of d5Q ~ 40 μΐη. 405 kg of magnetically enriched finely divided anorthosite were mixed with 350 kg of water to which 395 kg of concentrated (93% by weight) sulfuric acid had been added to an acid concentration of 49.3% by weight. The heat of exothermic reaction raised the temperature to 130 ° C. The reaction was allowed to proceed for about 2 hours with constant stirring, at which time about 90% of the aluminum content was dissolved in the acid. Prior to that, 1 hour and U hours later, analyzes were performed to give the following values: insoluble acid. vesiliuk. free residue A12 ° 3 Al203 a12 ° 3 1 h 24% 9.5% 9.4% 0.45%

Uh 25% 9.5% 9.2% 0.47% 9,71916

After dissolution, it was diluted with water and the slurry was filtered warm (80 ° C) to separate the insoluble silica body and precipitated calcium sulfate. The Al 2 O 3 content of the aluminum sulfate solution was 11%. The filter cake was washed twice with water (120 l each). 215 kg of a dissolution residue with a water-soluble alumina content of 0.8% by weight and a specific surface area of 80 m 2 / g were obtained.

The filtrate was further used to prepare solid aluminum sulfate.

Example 2

Replacement of Portland cement with a leach residue prepared according to the invention.

In this example, the binder properties of the dissolution residue formed in the dissolution of anorthosite are investigated. For this purpose, test prisms 7cm x 7cm x 7cm were cast. Medium coarse sand was used as the aggregate with a mixture ratio of 1 part binder, 9 parts sand and 1.75 parts water. The binder used was a) pure Portland cement, b) Portland cement, 50% of which had been replaced by a leach residue from grade B anorthosite, which had been washed to an aqueous alumina content of 2.0% by weight, and c) Portland cement, of which 50% was replaced by a leaching residue made from grade B anorthosite, which had been washed to a water-soluble alumina content of 0.18% by weight.

The specimens were stored at 100% relative humidity and + 18 ° C. The strength results are the averages of the three pieces at a time.

The results obtained are shown in the following Table I: 10 71916

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11 71 91 6

It can be seen from the values in the table that the leach residue b) mixed with cement does not act as a binder, while the leach residue c) has strong binder properties. Namely, the corresponding prisms had a strength of 14 days even higher than the corresponding strength of pure cement.

Example 3

Replacement of white cement with a leach residue prepared according to the invention.

In this example, the strength of white cement was compared with the strength of binders in which part of the white cement (50% and 75%, respectively) had been replaced by a leach residue prepared according to the invention (grade A or B). The ratio of binder to aggregate was 1: 3, and a mixture of fly ash, fine and coarse sand with 18% fly ash as a filler was used as the aggregate to correct the sand size distribution according to the ideal curve. Strength tests were performed in the same manner as in Example 2.

12 71916

Table II

LJ = Dissolution residue VS = White cement VL = Water soluble Sample LJ specific surface- VL- Compressive strength lower m ^ / g (MPa) 2 days 7 days 14 days

White cement 100% 1.6 5.6 9.4 LJ 50% 50 - 60 0.8 1.0 3.6 6.0 VS 50% LJ 75% 50 - 60 0.8 0.3 0.8 1, 4 VS 25% LJ 50% 70 0.2 1.9 5.6 6.2 VS 50% LJ 75% 70 0.2 3.3 5.4 5.1 VS 25%

It can be seen from the table that a leach residue with a high VL alumina content gives poor strength values, and especially when more than half of the cement is replaced by a leach residue. On the other hand, if the same leach residue is washed to reduce the VL alumina content and correspondingly to increase the specific surface area, significantly higher strength values are obtained, and in particular better initial strength values when replacing 75% of the white cement with the leach residue.

Il 13 71916

Example 4

Use of leach residue as filler.

This example compared the use of the leach residue as a concrete filler to a similar silica-filler concrete.

Casting and compressive strength testing of test specimens (150 mm cubes) was performed according to standard SFS 4474. The water-cement ratio of the vertai-lubetone was 0.675, and the target slope was 4 sVB. The anorthosite leaching residue in the filler-concrete was replaced by a natural anchorosite leaching residue of less than 0.125 mm in the natural filler (approx. 5% of the total aggregate).

The flexural tensile strength was determined from 500 x 100 x 100 mm beams.

The following results were obtained for compressive and flexural strengths.

Table III

Compressive strength (MPa) Bending tensile strength (MPa) _____________7 days____28 days___90 days___________28 days____________

Ordinary 21.5 26.5 29.5 5.4 concrete 21.5 27.0 28.5

Anortos. residual solution 18.0 28.0 41.5 5.8 filler concrete 17.0 28.5 41.5

Silica fill 29.0 39.5 44.0 6.1 reinforced concrete 28.5 39.0 44.5

It can be seen from the results in the table that replacing part of the aggregate with the anorthosite leach residue gave silica h 71916 filler-concrete correspondingly improved compressive and flexural strength values compared to ordinary concrete. However, the leach residue used according to the invention has a clear advantage over silica-filler concrete due to its whiteness.

Example 5

The whiteness and reflection enhancing effect of the leach residue prepared according to the invention was measured by preparing a series of concrete specimens using a binder and aggregate in a ratio of 1: 2. The degree of whiteness was measured using a standard

The following results were obtained:

Binder Whiteness (%)

White cement 100% 79.3

White cement 50%

Dissolution residue A or B, 50% 82.4

Dissolution residue A or B, 100% 81.0

Whiteness values of 86.5% and 86.6% were obtained for the two slurries of pure leach residue.

Experiments were also performed to measure the degree of reflection on specimens with a ratio of binder to aggregate (lime-vi) of 1: 1. Reflection values were measured using a standard

The following results were obtained: 11 »71916

Binder H e_ij_a s t u_s a § t e_ _ £%]

White cement 100% 80.1

White cement 90%

Satin white 10% 83.1

White cement 90%

Dissolution residue A or B, 10% 82.0

It can be seen from the results that, for example, replacing half of the white cement with a leach residue gives a significantly better whiteness of the cast concrete compared to the white cement binder alone. A similar improvement can also be seen in the reflection values of white cement-concrete products, where the leach residue (10%) achieves an improvement comparable to satin white. Thus, the dissolution residue obtained according to the invention can also be used as a satin white substitute as a reflection enhancer.

Claims (10)

16 71916 A process for treating an anorthosite to prepare alurium sulphate and a solid dissolution residue by dissolving in sulfuric acid at elevated temperature, characterized in that the finely divided anorthosite is treated with 40 to 60% by weight, preferably 50 to 60% by weight, of aqueous sulfuric acid, insoluble. the residue is separated from the filtrate containing most of the aluminium content of the anorthosite and further processed into aluminum sulfate, and the leach residue is washed to minimize its water-soluble alumina content. Process according to Claim 1, characterized in that the dissolution residue is washed to a water-soluble alumina content of less than 1.0% by weight, preferably less than 0.2% by weight. Process according to Claim 1 or 2, characterized in that the specific surface area of the dissolution residue obtained after washing is more than 50 m 2 / g, preferably more than 70 m 2 / g. Method according to one of the preceding claims, characterized in that the washing is carried out with water. Process according to Claim 4, characterized in that concentrated (93%) sulfuric acid is used as the acid, which is diluted to the dissolution concentration with the washing water of the dissolution residue. Process according to Claim 5, characterized in that the particle size of the finely divided anorthosite is less than 125 μιη, preferably about 40 to 60 μm and the temperature of the reaction mixture is about 120 to 130 ° C. Use of the leach residue obtained by the process according to claim 1 as a strength and / or whiteness-improving additive or filler in curable masses, such as concrete, characterized in that up to 75% by weight, preferably up to 50% by weight, of the leach residue is used , calculated on the total amount of binder. Use according to Claim 7, characterized in that the leach residue is used to replace a part, in particular up to about 50% by weight, of the amount of cement and / or blast furnace slag in concreting, such as mine filling and shotcreting. Use according to Claim 7, characterized in that the leach residue is used as a substitute for white cement or satin white. Use according to Claim 7, characterized in that the dissolution residue is used as a filler to replace the finer part of the aggregate in the curable masses. 71 91 6 Patent krav;