RU2440940C2 - Method of recycling fluoro-anhydrite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to technology of recycling fluoro-anhydrite, a by-product of hydrofluoric acid production. The method involves adding a lime-containing component to fluoro-anhydrite in order to neutralise the sulphuric acid component, granulating the obtained mixture and then using the granules in production of construction materials. The lime-containing component used is dispersed electric steel melting slag in amount of 5-85% of the weight of the fluoro-anhydrite.

EFFECT: improved strength properties of the recycling product, simple and cheap technology of recycling fluoro-anhydrite.

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Description

The invention relates to technologies for the disposal of caustic products of processing mineral concentrates and is recommended for use in processes involving sulfuric acid processing.

A known method of disposal, including the dilution of fluorohydrite leaving the furnace, 20-30% addition of slag, followed by use of the obtained binder in the roadway or as part of small wall blocks / RU 2046097 C1 /. The disadvantage of this method is the use in a mixture of a component with an increased, 4-9%, chromium content. In addition, this type of slag does not apply to common types of waste and therefore its use is associated with significant costs for its long-distance transportation.

A known method of utilization of fluorohydrite, including the neutralization of acid residues in the product with lime, which is introduced in a 28-73% excess of the stoichiometric amount, further dilution of the mixture with 10-30% of the addition of dump fluorogypsum and subsequent granulation of the obtained ternary mixture / RU 2171791 C1 / . The disadvantage of this method should be considered the use of large quantities of lime and wet gypsum taken from the sludge storage facility, which complicates and increases the cost of the neutralization process, and also complicates the disposal of its product due to the low strength and water resistance of the granules.

The technical objectives of the invention are:

- simplification and cheapening of the technology of utilization of fluorohydrite, increasing the strength properties of the product of utilization and expanding the scope of its application.

This problem is solved by introducing into the composition of the fluorohydrite dispersed electric steelmaking slag in an amount of 5-85% by weight of the starting fluorohydrite and granulating the resulting mixture.

Experimental verification of the proposed method was carried out on fluorohydrite of the Polevsky cryolite plant, containing a different amount of sulfuric acid, using auxiliary materials, the name and chemical composition of which are given in table 1.

The chemical composition of the materials used

Table 1 Component Name The content of oxides, wt.% SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ Cao MgO SO ₃ Steelmaking slag 15.14 27.16 0.86 43.27 5.93 4.70 Furnace Fluorohydrite 2.06 - - 40.15 - 56.93 Dump fluorips 3.47 4.45 2.00 37.53 0.53 45.82

To assess the level of acid neutralization in the composition of fluorohydrite, an indirect indicator was used in the form of compressive strength of a slag gypsum binder, since its value is inversely proportional to the acid content in fluorohydrite. The strength index was evaluated on tablet samples with a diameter of 28 and a height of 20 mm, molded on a semi-rigid consistency test. The resulting samples were stored in air-wet conditions. Immediately prior to testing, they were dried and then tested for compressive strength.

table 2 Neutralization method Conditions and result of neutralization Granular product T, ° С H ₂ SO ₄ , wt.% τ _neutral day r,% W% ρ _n , g / dm ³ R _compress MPa According to the prototype 350 0.70 > 6 5 8 900 5 The claimed 95-100 0.40 one - 5 1460 10

τ _neutr , days - the duration of the neutralization process in days; r (retur) is the amount of fraction up to 1.25 mm in size required to obtain granules of a given size; W,% - humidity of the obtained granules; ρ _n , g / cm ³ - bulk density of the granules; R _SJ, MPa - limit compressive strength of the granules of the cylinder.

Table 2 compares the results of the proposed method of neutralization and prototype. The amount of slag used to neutralize was 1 part to 9 parts of anhydrite. When neutralizing the prototype, in addition to lime, an additional 30% of dump gypsum taken from the dump was additionally introduced into the mixture.

It follows from the presented that, in comparison with the prototype, the process of neutralizing the initial mixture is possible at a low temperature. At the same time, the duration of the neutralization process is reduced by a factor of 6, and the acid residue in the product is much lower.

Table 3 contains data on the composition and strength properties of the samples of tablets obtained on the product according to the claimed method of neutralization, depending on the amount of slag used to neutralize fluorohydrite.

Table 3 The content of slag, wt.% 10 25 fifty 70 85 The water demand of the mixture,% 10.5 twenty fifteen 45 35.5 The compressive strength, MPa, 7 days 2.20 9.40 10.90 23.30 18.10

From the table it follows that the strength of the briquettes is largely determined by the content of slag. With an increase in the slag content from 10 to 50%, the strength of the samples increases by about 5 times, and for 70-85% it increases by 10 times. Based on the above, it is advisable to use mixtures with 10-20% slag content as an additive that regulates the setting time of Portland cement. At a higher slag content, it is advisable to use the granular mixture as a porous aggregate for lightweight concrete, and also as a complex gypsum slag additive in Portland cement, which simultaneously replaces gypsum stone and blast furnace granulated slag. A slag content of less than 5 and more than 85% is impractical, since the strength of the briquettes in the indicated interval is maximum and sufficient both when using granules as a substitute for gypsum in cement (5-30% of slag), and to replace crushed stone in concrete (30- 85% slag).

Table 4 compares the results of testing fluorohydrite granules as an additive that regulates the setting time of cement with gypsum stone, a traditional additive, and granules obtained by the prototype. In all formulations, the SO ₃ content was 2.5%. The grinding of cement, including 20% of blast furnace granulated slag, was carried out under the same conditions. The resulting cements were tested according to GOST 310.1-3-76 and GOST 310.4-81.

Table 4 Type of gypsum component % in cement S _beats , m ² / kg W / C,% Setting time R _izg / R _szh , MPa Start the ending steaming 28 days Gypsum stone 5.7 304 25,2 3 hours 45 minutes 4 hours 50 minutes 4.9 / 29.8 6.9 / 49.4 Prototype granules 5,0 311 25.7 5 hours 25 minutes 6 hours 15 minutes 4.7 / 28.7 6.8 / 51.7 Granules according to the claimed method 4.2 485 28.8 5 hours 20 minutes 8 hours 30 minutes 4.2 / 26.5 6.8 / 50.5

S _beats , m ² / kg is the specific surface area of cement; * - according to the prototype. The value of W / C corresponds to the test of normal density. The amount of steelmaking slag in the granules is 30%. From table 4 it follows that fluorohydrite granules with the addition of steelmaking slag as part of Portland cement are a complete substitute for gypsum stone. Moreover, the proportion of clinker in the composition according to the claimed method is lower by the amount of slag contained in the granules, that is, in this case, a certain reduction in the cost of cement is provided.

Pellets based on fluorohydrite and 70% slag with a size of 8-10 mm hardened in air-wet conditions for 7 days, and then were used as aggregate in concrete in combination with quartz sand and cement M400D20 with a water-cement ratio of 0.5. The bulk density of the granules was 1100 g / l, the average density was 1.57 g / cm ³ and the turned strength was 30-70 kg / granule. The concrete mixture was molded into cube samples with a rib of 70 mm, hardening under normal conditions for 7 days. In the control composition, the granules were replaced with crushed granite fractions of 5-10 mm. As a fine aggregate used sand with a particle size of 2.5. Samples with a rib of 70 mm solidified in wet sawdust were molded from a mixture of this composition. Table 5 contains the results on the compositions and strength properties of concrete on slag gypsum granules.

Table 5 No. The composition of concrete, kg / m ³ I / O Concrete properties cement crushed stone granules sand ρ, g / l R _cr ^7s , MPa R _compress ^28s , MPa one 300 1200 - 600 0.5 2250 5,6 11.9 2 * 300 - 900 600 0.5 1650 2.2 4.9 3 300 - 900 600 0.5 1950 5.1 10.8 four 400 - 900 500 0.5 1950 20.7 35,2 * - according to the prototype

From the presented it follows that the fluorohydrite granules obtained by the present method are suitable as aggregate for lightweight concrete with a density below 2000 kg / m ³ , which significantly expands the scope of their possible effective use. Compared with the prototype, the strength of concrete on these granules with equal cement consumption is twice as high.

Thus, the use of the proposed method allows for more effective neutralization of the acid component of fluorohydrite, and the obtained granular product has improved consumer properties - accelerated hardening and increased strength. In the case when the granules are used to regulate the setting time of cement, it is possible to reduce the proportion of clinker in the cement by the amount of slag contained in the granules. When granules are used as artificial aggregate, then on their basis it is possible to obtain high-strength concrete of the M300 grade - composition 4, Table 5. The high hardening rate and strength index of fluorohydrite with the addition of the composition are probably due to the presence of calcium aluminates in the composition of electrosmelting slag, which, as is known, provide similar indicators for alumina cement. Thanks to the addition of slag, fluorohydrite granules can be used in material-intensive areas as a substitute for natural gypsum - as a regulator of setting time in Portland cement and as a substitute for crushed stone in building concrete.

Using the invention will not only simplify and reduce the cost of neutralization of fluorohydrite, but also significantly increase the amount of utilization of fluorohydrite, which currently does not exceed several percent. This will significantly reduce the loss of space for their dumping.

Claims (1)

A method of utilizing fluorohydrite, including introducing into its composition a component containing lime in order to neutralize the sulfuric acid component, granulating the resulting mixture with subsequent use of granules in the production of building materials, characterized in that dispersed electric steel melting slag in an amount of 5 or more is used as a component containing lime up to 85% by weight of fluorohydrite.