RU2620679C1 - Method for utilizing alumochromic catalyst waste - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: charge components are mixed by means of joint wet grinding in a ball mill, plastic moulding of the moistened mixture is carried out, followed by drying to the residual humidity of 4% and firing at the temperature rise of 1-2°C/min up to 1160°C and holding at the maximum temperature within 2-3 hours. The alumochrome catalyst waste has the bulk density of 1.3-1.5 g/cm³ and the composition, wt %: chromium in terms of Cr₂O₃ 0-25, Al₂O₃ (Gamma modification) 73-89, K₂O 1-2, SiO₂ 0-6, impurities of iron to 0.5-0.7, impurities of nickel, copper, zinc, titanium up to 0.2. In the charge, low-melting clay of the following chemical composition is used, wt %: SiO₂ 60-70, TiO₂ 0.5-1, Al₂O₃ 10-15, Fe₂O₃ 2-7, MnO 0.1-1, CaO 2-4, MgO 1-5, Na₂O 1-4, K₂O 2-5, P₂O₅ 0.1-0.5, SO₃ 0.09, LOI 6, 10.

EFFECT: increasing the strength and water resistance of construction ceramics due to the introduction of charge based on low-melting clay into the composition.

4 ex, 2 tbl, 1 dwg

Description

The invention relates to a method for the disposal of aluminum-chromium catalyst wastes, including their introduction into the composition of low-melting clay mixtures and subsequent encapsulation during heat treatment in the body of a fired ceramic shard.

The technical result is an increase in the strength, water tightness of building ceramics due to the introduction of aluminum-chromium catalyst (hereinafter AChO) into the composition of the waste mixture and regulation of the firing temperature.

A known method of neutralizing chromium-containing wastes of galvanic production, including passing them through an electrolyzer with anodes of iron or aluminum. Under the influence of direct current, the anode ions pass into the solution and, as a result of hydrolysis, form water-insoluble hydroxides that act as a coagulant. In electrolysis, processes of chromium reduction, coagulation and separation of the formed precipitate occur, followed by clarification of the water from the suspension in the sump.

This technical solution has insufficient safety (the allocation of explosive gas mixtures during electrolysis), the need for bulky equipment, and an insufficiently appropriate process scheme in which some components are bonded to form other, albeit less toxic ones.

A known method of processing radioactive waste (RAW) by their implementation in concrete or bitumen.

The biggest disadvantage of this inexpensive and simple way of introducing radioactive waste into concrete is the high rate of leaching of radionuclides from the cured product. Bituminous products have a lower solubility in groundwater or saline seawater, but the radioactive waste tarning process is more complex and risky due to the risk of ignition. Due to the danger of radiation heating, the method is characterized by a low content of radioactive waste per unit cured volume.

There is also known a method of neutralizing chromium-containing wastes of galvanic production, including their dehydration and subsequent reduction of metal-containing sludge oxides by thermal exposure to carbon.

The disadvantage of this technical solution is the incomplete extraction of chromium from waste (about 85% of the chromium contained in the precipitate is extracted). In addition, in the presence of oxides of toxic metals (for example, cadmium), their recovery is inevitable. Thus, additional operations will be required to purify the resulting product from toxic impurities.

Known ceramic mass for the manufacture of bricks, including, by weight. %: clay 92-98, copper ore dressing waste 2-8. (RF patent No. 2099306, IPC ⁶ C04B 33/00, publ. 12/20/1997).

The disadvantages of the invention include the fact that products of known ceramic mass have low strength characteristics.

The closest technical solution to the present invention is a method of disposing aluminum-chromium catalyst wastes to produce ceramics from low-melting clay (patent No. 1682348, class C04B 33/00, publication date 10/07/1991, authors Zhenzhurist I.A. et al., SU, prototype ) The known method involves mixing fusible clay (loam), bentonite and waste aluminum-chromium catalyst containing hexavalent chromium, preparing the molding mixture, pressing and firing products at 1050 ° C. The strength of the products obtained is up to 20 MPa.

The claimed method differs from the known one in that the charge contains less aluminum-chromium catalyst (0.5-12 wt.%), As well as the fact that the products are made by plastic molding. This increases the strength of the products.

The objective of the invention is the neutralization of dangerous hexavalent chromium (hereinafter Cr (VI)) contained in the large-tonnage waste of an aluminum-chromium catalyst, which in terms of danger belongs to group I, according to GOST 12.1.007-76, by encapsulating Cr (VI) in the body of the fired ceramic based on fusible blends. This ensures complete environmental cleanliness of the finished product, for example, in the form of facing facade ceramic tiles. The technical result obtained by carrying out the invention is expressed in obtaining a high-strength ceramic aggregate of heavy concrete, clinker tiles and bricks, characterized by environmental cleanliness with a very low Cr (VI) content and high physical and mechanical characteristics.

The problem is solved in that the method of neutralizing waste aluminum-chromium catalyst (hereinafter AXO), including their introduction into the clay mixture and subsequent firing, is characterized in that the previously dry low-melting clay is ground in a laboratory ball mill with the ratio of "balls: clay = 1: 1 -5 "for 15-30 minutes to a fraction of less than 16 mm, then 0.5-12 wt. % AXO and the mixture is mixed “clay + AXO” in a ball mill with the ratio “balls: (clay + AXO) = 1: 1” for 5-10 minutes, followed by preparation of a plastic raw mix with the addition of water in an amount of 19-23 %, exposure of the obtained raw material mixture in sealed plastic bags for 24 hours at a temperature of 25-35 ° C, the manufacture of a ceramic plastic molding with a pressing pressure of 1.5-2.0 MPa, drying the molded ceramic product for 24 hours at room temperature and then over 12-24 hours at a temperature of 30-100 ° C to a residual moisture content of less than 4%, firing when the temperature rises at a speed of 1-5 ° C / min to 960-1160 ° C, holding at maximum temperature for 2-3 hours, followed by cooling for 24 hours at a rate of 1 ° C / min.

The difference between the invention and the prototype is the following:

- a two-component mixture is used, in which the waste of aluminum-chromium catalyst in an amount of 0.5-12 wt. %, which allows to reduce the cost of the finished product;

- raw materials are dried for 12-14 hours at a temperature of 30-100 ° C to a residual moisture content of 4%;

- while the composition of the mixture is formed in the following ratio, wt. %:

clay 88-99.5

waste alumina catalyst 0.5-12.

In contrast to the claimed invention in the prototype, the charge is a two-component mixture consisting of low-melting clay of the following chemical composition: SiO ₂ - 60-70, TiO ₂ - 0.5-1, Al ₂ O ₃ - 10-15, Fe ₂ O ₃ - 2-7, MnO - 0.1-1, CaO - 2-4, MgO - 1-5, Na ₂ O - 1-4, K ₂ O - 2-5, P ₂ O ₅ - 0.1 -0.5, SO ₃ - 0.09, pp - 6.10 and 0.5-12 wt.% And waste aluminum-chromium catalyst of the following chemical composition, wt.%: Cr ₂ O ₃ - 10-25, γ-Al ₂ O ₃ - 73-89, K ₂ O - 1 -2, SiO ₂ - 0-6, impurities of iron - up to 0.5-0.7, impurities of nickel, copper, zinc, titanium - up to 0.2, bulk density 1.3-1.5 g / cm ³ , humidity 0.9-5.0%. The multicomponent composition of the charge in the prototype determines the complex reproducibility of physical and mechanical properties. As a result of the use of natural raw materials in the prototype, the delivery of which requires additional transport costs, the cost of the finished product increases.

In order to assess the physicomechanical characteristics, control cylinders 16 × 16 mm in size were made, formed on the basis of burdens consisting of low-melting clay of the Saray-Chekurchinsky deposit (hereinafter referred to as S-Ch clay) and additives in the form of AXO waste, which were introduced in an amount of 0 ,5; 1.5; 6 and 12 wt.% Of clay consumption. The molding moisture content of the charge was 19-23%. The studied compositions are shown in table 1.

An analysis of the results of studies of the effect of AXO additive on the water absorption of a ceramic crock showed that at 960 ° C a small dosage of AXO equal to 0.5 wt. %, helps to reduce water absorption of the crock from 15.4 to 11.5% (by 25.32%). With a further increase in the dosage of AXO to 1.5; 6 and 12% water absorption increases slightly, but remains less than for the composition without AXO, respectively, by 16.23; 12.34 and 5.84%. An increase in temperature to 1060 ° C and the amount of AXO from 0.5 to 12% leads to an almost linear increase in water absorption from 9.8 to 13.3%. It can be stated that at low temperatures (960 and 1060 ° С), the AXO practically does not enter solid-phase transformations with clay minerals and their destruction products.

With an increase in temperature to 1160 ° C, the nature of the results changes dramatically. With an increase in the dosage of AXO to 12%, water absorption increases to 3.3%. Therefore, one of the effective methods of regulating water absorption is the firing temperature, because its increase from 960 to 1060 ° C on average leads to a decrease in water absorption by about 1.15-1.2 times, and at 1160 ° C by 8 times. An increase in firing from 1060 to 1160 ° C leads to a decrease in water absorption by 4-8.7 times.

The water absorption data of the samples are interrelated with the indices of density and tensile strength during compression of the crock.

At 960 ° C with an increase in dosage from 0 to 12%, a decrease in density is observed from 1.91 to 1.81 g / cm ³ . At 1060 ° C with an increase in dosage to 12%, a decrease in density is observed from 1.93 to 1.73 g / cm ³ . The highest density of the crock (2.13 g / cm ³ ) is achieved with 6% AXO at 1160 ° C. This is apparently due to the fact that the refractory additive in the form of catalyst waste begins to sinter at higher temperatures than 960 and 1060 ° C.

An analysis of the results showed that the introduction of an AChO additive helps to increase strength in the entire dosage range from 0 to 12%. At the same time, at 0.5%, an abrupt increase in strength is observed: from 47.7 MPa to 87.4 MPa (by 83.22%). In the range (1.5–12%) of AChO, the strength of the samples remains higher than the control by 28.72–56.81% and is equal to 61.4–74.8 MPa.

Thus, it can be argued that due to the introduction of an AXO additive in the range from 0.5 to 12 wt. % of clay consumption, changes in water absorption, average density and strength of calcined samples can be purposefully controlled. It was found that the best properties of the samples are ensured at a firing temperature of 1160 ° C. The optimal dosage of AXO is 0.5 wt.%, Providing the highest strength of the shard (87.41 MPa).

Such high strength of the shard made it possible to produce, on the basis of the developed optimal compositions of the blends with the addition of AXO, samples of facade clinker tiles and bricks of grades of strength “500”, “600”, “700”.

To assess the environmental cleanliness of the developed materials in the control samples, the Cr (VI) content was determined, are given in table 2.

If we take into account that the concentration of Cr (VI) in the waste of AXO itself is 25 mg / g, i.e. exceeding the MPC by a hundred times, due to their introduction into the composition of the low-melting mixture on clay S-Ch in the amount of (0.5-12) wt. % of the clay consumption and subsequent encapsulation in the body of the ceramics fired at 960-1160 ° C, the Cr (VI) content decreases by 102-424 times.

From the data shown in table 2, it is seen that the presence of Cr (VI) was found in all samples, even in those in the composition of the batches of which the addition of AXO was not introduced. Apparently, Cr (VI) inclusions, which in the temperature range of 960–1160 ° С are not completely encapsulated in the calcined shard even at 1160 ° С, are also present in the feedstock - low-melting S-H clay. In addition, for samples based on mixtures of pure fusible clays, the Cr (VI) content almost halves with an increase in the calcining temperature from 960 ° C to 1160 ° C. In all samples calcined at 960–1160 ° С, the Cr (VI) content is 2–4 times higher than the standard MPC.

A somewhat different picture is observed when AXO is added to the composition of a mixture on fusible clay. In this case, an increase in the dosage of AXO from 1.5% to 12 wt. % promotes an increase in Cr (VI) in samples from 0.142 to 0.244 mg / g, or 1.72 times.

The specific embodiment of the invention is illustrated by the following examples.

Example 1. Clay in the amount of 88 wt. % mixed with AXO in the amount of 12 wt. % in a ball mill for 5-10 minutes, followed by preparation of a plastic raw mix with the addition of water in an amount of 19-23%, exposure of the resulting raw mix in sealed plastic bags for 24-36 hours at a temperature of 25-35 °, the manufacture of ceramic products plastic molding at a pressing pressure of 1.5-2.0 MPa, drying the molded ceramic product for 18-24 hours at room temperature, and then for 12-24 hours at a temperature of 30-100 ° C to a residual moisture content of less than 4%, firing at rising temperatures s with a speed of 1-2 ° C / min to 960 ° C, exposure at maximum temperature for 2-3 hours, followed by cooling for 18-24 hours at a speed of 1-5 ° C / min. Obtained by this method, a ceramic product has a strength of 15-20 MPa.

Example 2. A technology similar to the technology described in example 1, except that clay in an amount of 94 wt.% Is mixed with AXO in an amount of 6 wt.%, And the molded product is fired at temperatures up to 1060 ° C. The ceramic product obtained in this way has a strength of 25-30 MPa, which is 55-60% higher than the figure in Example 1. Also, samples obtained by this method have an average density of 1.83-1.88 g / cm.

Example 3. A technology similar to the technology described in example 1, except that clay in the amount of 98.5 wt. % is mixed with AXO in an amount of 1.5 wt.%, and the molded product is fired at temperatures up to 1160 ° C. Thus obtained ceramic product has a strength of 70-75 MPa, which is 4-4.5 times higher than the result obtained in example 1. The rate of water absorption of the samples by weight is 13%.

Example 4. A technology similar to the technology described in example 1, except that clay in the amount of 88 wt. % mixed with AXO in the amount of 12 wt. %, and the molded product is fired at temperatures up to 1160 ° C. Thus obtained ceramic product has a strength of 60-65 MPa, which is 3.5-4 times higher than the result obtained in example 1. Samples obtained by the specified method have an average density of 2.04-2.08 g / cm ³ that 11% higher than the density of the samples specified in example 2. The rate of water absorption of the samples by weight is 14-15%, which is 15% higher than the figure obtained in example 3.

As can be seen from the above examples, the strength and water resistance of the samples obtained by the proposed composition and preparation technology exceed the corresponding parameters of the prototype samples.

Higher physico-mechanical characteristics of ceramic samples compared to prototype samples are due to the fact that during the firing process, the decomposition products of the clay component of the charge interact with aluminum, calcium, iron and magnesium oxides that are present in additional materials and waste. This contributes to the partial appearance of the pyroplastic phase, which accelerates the occurrence of solid-phase reactions with the predominant formation of mullite, hematite, anorthite, augite, etc. Comparing X-ray diffraction patterns for samples of pure S-H clay calcined at three different temperatures, we can conclude that with an increase the firing temperature, a more complete filling of the structure of the crock and glass phase with mullite, hematite crystals and a decrease in the fraction of silica and feldspars due to their partial melting along the miner contour are observed Ala and transition to the glass phase (Figure 1).

The higher water resistance of the ceramic samples of this invention compared to the prototype samples is due to the fact that with an increase in the dosage of AXO from 1.5 to 12%, the total number of pores decreases, therefore, the structure becomes denser. So, in the absence of an AXO additive, the average density of a crock burnt at 1160 ° C is 2.05 g / cm ³ , at 0.5% AXO - 2.07 g / cm ³ , at 1.5% AXO - 2.09 g / cm, with 6% ACh reaches 2.17 g / cm ³ . This is due, firstly, to the large volume of crystalline neoplasms formed during high-temperature firing of the fusible mixture in the presence of an AXO additive, secondly, to a more complete filling of the intergranular space by the neoplasms, and thirdly, to an increase in the density of the glass phase due to its reinforcement with crystals. It should be noted that a further increase in AXO to 12% reduces the density to 2.06 g / cm ³ .

Claims (8)

A method of disposing aluminum-chromium catalyst waste, which consists in obtaining high-strength ceramics based on fusible clays and aluminum-chromium catalyst waste, characterized in that the ceramics are made from a mixture in the form of a mixture of 88-99.5 wt. % fusible clay and 0.5-12 wt. % waste aluminum-chromium catalyst by plastic molding, comprising the following steps: - at the first stage, dry fusible clay is ground in a ball mill for 15-30 minutes to a fraction of less than 16 mm; - at the second stage, clay is mixed with 0.5-12 wt. % waste aluminum-chromium catalyst by co-grinding in a ball mill for 5-10 minutes; - at the third stage, a plastic raw mix is prepared with the addition of water in an amount of 19-23%; - at the fourth stage, molding is carried out from the obtained raw material mixture of the semi-finished product by plastic molding at a pressing pressure of 1.5-2.0 MPa; - at the fifth stage, the resulting semi-finished products are dried at a temperature of 30-100 ° C to a residual moisture content of less than 4%; - at the sixth stage, firing is performed when the temperature rises at a speed of 1-2 ° C / min to 1160 ° C, exposure at maximum temperature for 2-3 hours, followed by cooling for 24 hours at a speed of 1 ° C / min, while fusible clay has the following chemical composition, wt. %: SiO ₂ - 60-70, TiO ₂ - 0.5-1, Al ₂ O ₃ - 10-15, Fe ₂ O ₃ - 2-7, MnO - 0.1-1, CaO - 2-4, MgO - 1-5, Na ₂ O - 1-4, K ₂ O - 2-5, P ₂ O ₅ - 0.1-0.5, SO ₃ - 0.09, pp - 6.10; waste alumina catalyst have the following chemical composition, wt. %: Cr ₂ O ₃ - 10-25, γ - Al ₂ O ₃ - 73-89, K ₂ O - 1-2, SiO ₂ - 0-6, iron impurities - up to 0.5-0.7, impurities nickel, copper, zinc, titanium - up to 0.2, bulk density of 1.3-1.5 g / cm ³ and humidity of 0.9-5.0%.

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