RU2404921C1 - Method of modifying clay - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention can be used to obtain montmorillonite clay having high exchange capacity. The starting material, which is montmorillonite clay, is first treated with a 10% sulphuric acid solution, washed with distilled water and dried at 20-500C. The acid-treated montmorillonite clay then reacts with a modifying agent - lithium hydroxide in molar ratio clay: modifying agent: water equal to 1:(0.09-0.36):3.6, respectively, at 80-100C for 5-7 hours. The modified clay is then dried at 20-200C. ^ EFFECT: invention cuts on treatment time and amount of lithium hydroxide used, considerably increases sorption capacity of clay with respect to Cu2+ and Fe3+ ions. ^ 3 cl, 2 tbl, 3 ex

Description

The invention relates to methods for the chemical modification of montmorillonite clays.

Montmorillonite clays are characterized by a high exchange capacity, which is explained by the fact that in montmorillonite crystals, ion exchange occurs not only on the outer surface of the crystals, but also inside the crystal lattice between the layers. In montmorillonite, isomorphic substitutions are possible within the crystal lattice; therefore, target ion substitution in the crystal lattice leads to an increase in the sorption ability and selectivity of the mineral due to the appearance of uncompensated charges in the structural cell. The development of simple and cost-effective methods of modifying montmorillonites will allow to obtain products that can be used, for example, for the effective removal of toxic metal ions from aqueous media.

A known method of activating clays by preparing an aqueous suspension, adding sulfuric acid to it, heating, stirring the aqueous suspension, followed by washing the activated clay. In order to increase clay activity while increasing the yield of the target product, an additional potassium-containing reagent is introduced into the aqueous suspension [N. G. Sikharulidze, K. R. Nanobashvili, N. Sh. Tskhakaya, T. M. Kiliptari, E. I. Bakhtadze, B .Sh. Murvanidze. The method of activation of bentonite clays. // Description of the invention to copyright certificate No. 899466 of 01/23/82]. However, the resulting activated product is intended only for bleaching cottonseed oil.

The closest in essence is a method for chemically modifying clays, comprising reacting a solid starting material with MOH, where M is an alkali metal or ammonium cation. The reaction temperature is 50-200 ° C, the reaction time is less than 24 hours (Balbir Singh, Ian Donald Richard Mackinnon, David Page. The method of producing aluminosilicate derivatives. // RF patent No. 2161065 from 12/27/2000).

The disadvantages of this method, in addition to a rather long process time, include rather high concentrations of modifying agents. So, in example 8, 20 g of LiOH and 20 ml of water are used to treat 5 g of solid starting material (clay) the clay: LiOH: water = 1: 4: 4 ratio is used (process temperature 80 ° C, duration 16 hours). As a result of this treatment, the starting materials are saturated in significant quantities with Li ⁺ cations, which during sorption can go into aqueous media in an amount significantly higher than the maximum permissible concentration in water, which is 0.03 mg / l (SanPiN 2.1.4.559- 96).

The objective of the developed method is to obtain a modified clay sorbent with an optimized content of Li ⁺ cations.

Technical result:

- reduction in processing time, as well as a 10–40-fold reduction in the amount of modifying agent (LiOH), which allows to reduce the cost of the finished product and minimize the transition of Li ⁺ cations to aqueous media during the treatment of water from heavy metals, such as copper and iron;

- a significant increase in sorption ability with respect to cations Cu ²⁺ and Fe ³⁺ , despite the partial preservation of the crystalline structure of clay minerals.

The proposed invention from the specified method is characterized in that:

- pre-carry out the processing of clay with a 10% solution of sulfuric acid [Batalova Sh.B. Physicochemical basis for the preparation and use of bentonite catalysts. - Alma-Ata: Science, 1986. - 168 s]. In this case, interpacket cations are leached and a partial dealumination of the montmorillonite crystal lattice, i.e. acid exposes the skeleton of the mineral, maintaining the overall structure, albeit in a loose form;

- dried at a temperature of 20-500 ° C, resulting in a loose, easily crushed clay material;

- the process of modification with lithium hydroxide is carried out at a temperature of 80-100 ° C, the processing time is 5-7 hours. The obtained modified product is washed with distilled water until the excess lithium hydroxide (pH ≈ 8) is removed, dried at a temperature of 20-200 ° С;

- mass ratio of solid (clay): modifying agent (LiOH): water is chosen equal to 1: 0.09-0.36: 3.6.

The conformity of the proposed method for modifying clay with the criteria of "novelty" and "inventive step" is confirmed by the following features:

- pre-treatment of the original clay with a 10% sulfuric acid solution can significantly reduce the content of alkali, alkaline-earth metal cations in the initial clay material, which further reduces both the concentration of the modifying agent and the duration of the modification to 5-7 hours compared to the example given in the prototype;

- a decrease in the concentration of the modifying agent (LiOH) by 10–40 times allows optimizing the content of Li ⁺ cations in the resulting product with a simultaneous increase in sorption capacity.

The claimed invention is characterized by the data given in tables 1 and 2.

Table 1 - the chemical composition of the original clay.

Table 2 - comparative absorption capacity with respect to cations Cu ²⁺ and Fe ^{3+ of the} initial clay, clay samples treated with acid, and modified samples of the proposed method.

Examples of using the proposed method for modifying montmorillonite clays.

Example 1

The initial sample was montmorillonite clay containing the following minerals as impurities: low-temperature quartz, kaolinite, clinoptilolite, illite, feldspars — the chemical composition of the initial clay is shown in Table 1, the content of montmorillonite is 80-86 wt.%. The absorption capacity with respect to the cations Cu ²⁺ and Fe ^{3+ of the} initial clay is presented in table 2.

The initial sample was crushed (particle size 50 μm), treated with a solution of 10% sulfuric acid, the resulting material was washed with distilled water until the sulfate ions were completely removed, and dried at a temperature of 480-500 ° C. The absorption capacity of the acid-treated clay sample is presented in Table 2. Then, a LiOH modifying solution was added to the obtained acid-treated sample, while the mass ratio of solid substance (clay): modifying agent (LiOH): water was 1: 0.09: 3.6. The mixture was stirred to a pasty state and heated for 6 hours at a temperature of 95-98 ° C. At the end of the process, the resulting product was washed to remove excess lithium hydroxide (pH≈8), dried at a temperature of 105-110 ° C, and crushed to a particle size of 50 μm. The content of Li ⁺ cations determined by the method of spectral analysis in this product was 0.5 wt.%.

The absorption capacity of this modified product increases: in relation to Cu ²⁺ cations - by 4.7 times, and in relation to Fe ³⁺ cations - by 3 times in comparison with the initial clay form.

Example 2

The initial sample was ground to a particle size of 50 μm, treated with a solution of 10% sulfuric acid, the resulting material was washed with distilled water until the sulfate ions were completely removed, and dried at a temperature of 50-60 ° C. Then, a lithium hydroxide modifying solution was added to the obtained acid-treated sample. The mass ratio of solid (clay): modifying agent (LiOH): water was 1: 0.18: 3.6. The mixture was stirred to a pasty state and heated for 6 hours at a temperature of 80-95 ° C. At the end of the process, the resulting product was washed to remove excess lithium hydroxide (pH≈8), dried at a temperature of 190-200 ° C, and crushed (particle size 50 μm). The content of Li ⁺ cations determined by the method of spectral analysis in the modified sample obtained by the proposed method was 0.8 wt.%. The sorption capacity of the modified sample obtained by the proposed method with respect to Cu ²⁺ cations increased by 25 times, and in relation to Fe ³⁺ cations - 10 times compared with the initial clay form (table 2).

Example 3

The initial sample was crushed to a particle size of 50 μm, treated with a solution of 10% sulfuric acid, the resulting material was washed with distilled water until the sulfate ions were completely removed, and dried at a temperature of 20-25 ° C. Then, a modifying solution with a 2-fold increased concentration of lithium hydroxide was added to the obtained acid-treated sample. The mass ratio of solid (clay): modifying agent (LiOH): water was 1: 0.36: 3.6. The mixture was stirred to a pasty state and heated for 6 hours at a temperature of 95-100 ° C. At the end of the process, the resulting product was washed to remove excess lithium hydroxide (pH≈8), dried at a temperature of 20-25 ° C, and crushed (particle size 50 μm). The content of Li ⁺ cations determined by the method of spectral analysis in this product also amounted to 0.8 wt.%.

By the value of absorption capacity (Table 2), this sample practically does not differ from the sample obtained as a result of the modification described in example 2.

Studies of the effect of drying temperature after clay treatment with acid showed that there is no influence of the choice of the temperature regime of drying in the range of 20-500 ° C on the quality of the obtained acid-treated product.

It was established that the quality of the modified product does not change during the drying process at any temperature in the range of 20-200 ° C.

Thus, the above examples confirm that the modification of montmorillonite clays by the proposed method makes it possible to obtain their derivatives with optimized safe content of Li ⁺ cations in the structure. In this case, an increase in the sorption activity of modified samples is observed. Despite the fact that, as can be seen from table 2, the processing of the starting material with a 10% solution of sulfuric acid leads to a decrease in the absorption capacity of clay in relation to Cu ²⁺ cations by more than 20%, in relation to Fe ³⁺ cations by about 30%.

Examples 2 and 3 show that a 2-fold increase in the concentration of the modifying agent practically does not change the sorption activity of the modified samples, which is explained by the almost identical content of Li cations - 0.8 wt%.

The concentration of the modifying agent used in example 1 leads to a decrease in the content of Li ⁺ cations in the product to 0.5 wt.% And, as a result, to a decrease in the absorption capacity of the product with respect to the samples presented and described in examples 2 and 3. However, in relation to the initial and acid-treated samples of montmorillonite clay, an increase in the absorption capacity by several times was observed.

Thus, the proposed method allows to obtain a product with significantly improved absorption characteristics to cations of heavy metals with a low consumption of reagent by preliminary acid treatment and reducing the time of the modification process. High absorption characteristics allow the use of these modification products as sorption-active materials for the purification of natural, drinking and industrial waters contaminated with heavy metals.

Table 1 The chemical composition of the original montmorillonite clay, wt.% SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ TiO ₂ MgO CaO K ₂ O Na ₂ O p.p.p. Σ 56.08 18.39 4.35 0.72 2.54 4,50 2.19 4.16 7.50 100.43 table 2 Comparative absorption capacity of clay samples with respect to Cu ²⁺ and Fe ^{3+ cations} Sample Absorption capacity, mg / g Cu ²⁺ Fe ³⁺ Source 1.70 3.90 Treated with 10% H ₂ SO ₄ 1.20 2.80 Modified with a ratio of ^∗ 1: 0.36: 3.6 40,20 24.50 Modified with a ratio of ^∗ 1: 0.18: 3.6 41.40 39.60 Modified with a ratio of ^∗ 1: 0.09: 3.6 7.90 7.60

∗ The ratio of solid (clay): modifying agent (LiOH): water is indicated.

Claims (3)

1. A method of modifying montmorillonite clay, comprising reacting a solid material with a modifying agent - lithium hydroxide, washing with distilled water and drying, characterized in that the initial solid material is pretreated with 10% sulfuric acid solution, dried at 20-500 ° C, when modifying the mass ratio of clay: modifying agent: water is chosen equal to 1: (0.09-0.36): 3.6. 2. The method according to claim 1, characterized in that the modification process is carried out at a temperature of 80-100 ° C for 5-7 hours 3. The method according to claim 1, characterized in that the modified clay is dried at a temperature of 20-200 ° C.