Method for removing magnetic foreign matters in industrial boric acid or borax, high-purity boric acid and application

Abstract

The invention belongs to the technical field of preparation of high-purity boric acid, and discloses a method for removing magnetic foreign matters in industrial boric acid or borax, high-purity boric acid and application. The preparation method comprises the following steps: heating and dissolving raw material industrial boric acid or borax sample powder and deionized water, cooling, and marking as a solution A; adding ammonia water or sodium hydroxide into the solution A, preserving heat and settling for a period of time, and filtering to obtain a first-stage impurity-removed boric acid filtrate marked as a solution B; adding nitric acid, hydrochloric acid or sulfuric acid into the solution B for acidizing, adjusting the pH value, and marking as a solution C; heating and boiling the solution C, adding a complexing agent, preserving heat, stirring and carrying out complexation reaction; marking as a solution D; standing and settling the solution D for a period of time; and carrying out suction filtration to separate the boric acid product from the mother liquor in a solid-liquid phase manner to obtain high-purity boric acid. The preparation method disclosed by the invention is simple in process, mild in production condition and easy to obtain raw materials, and the contents of iron impurities, nickel impurities and chromium impurities in main magnetic foreign matters in the prepared boric acid are relatively low.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of high-purity boric acid, and in particular relates to a method for removing magnetic foreign matter in industrial boric acid or borax, high-purity boric acid and application. Background Art

[0002] Boric acid (H 3 BO 3 ), relative molecular mass 61.83, is a trihydrate of boron oxide, white powdery crystals or triclinic flaky crystals with gloss. It has a greasy feel. It is soluble in water, ethanol, glycerol, ethers and essential oils, and its solubility in water increases with increasing temperature.

[0003] Boric acid is the raw material for manufacturing various boron compounds, such as elemental boron, boron nitride, boron carbide, carbon fiber, borane, fluoroboride and various borates. These borides are widely used in industrial and agricultural production and cutting-edge technology. In addition, boric acid is used in enamel, ceramics, glass, glass fiber, shoe leather, wood preservation, dyes, boron steel and rare metal smelting, and occupies an important position in the national economy.

[0005] At present, the purification methods of boric acid include recrystallization, esterification, ion exchange, electrochemical method, osmotic membrane method, etc. Recrystallization is the process of solid matter precipitating from vapor, solution or molten system in a crystalline state. As an efficient separation and purification method, it is widely used in the purification of boric acid. The recrystallization method sometimes cannot obtain satisfactory purification effect. The crystals formed by impurities in boric acid and the crystals formed by boric acid may form a solid solution. The purity of boric acid produced by recrystallization can generally only reach about 99.5%, which cannot meet the requirements of some special industries such as communication optical fiber, laser crystal, nuclear industry, etc. for the purity of boric acid. The ion exchange method is to use ion exchange resin for impurity separation and other process technologies. Strong acid cation exchange resin can adsorb metal ions in boric acid solution on it, while boron remains in the solution in the form of boric acid. Although the ion exchange method for purifying boric acid has the advantages of high selectivity and good purification effect, its application range is limited due to its small processing capacity and limited mechanical strength. The esterification distillation method is based on the esterification reaction between boric acid and certain substances such as methanol, and then the esterified product combined with boric acid is distilled out, and then high-purity boric acid is obtained by hydrolysis. Pure boric acid can be obtained by the esterification distillation method, but the raw materials used are mostly expensive, the operation is relatively complicated, and impurities are easily introduced during the purification process. In the subsequent purification process, distillation is required. The crystallization process is relatively complicated, the energy consumption is large, and the separation and enrichment of trimethyl borate is slow. These shortcomings restrict the promotion of this method. Electrochemical methods are used to purify boric acid. In this purification system, titanium is used as an anode and graphite is used as a cathode. Direct current is applied between the two electrodes in the boric acid electrolyte to achieve the purpose of purifying boric acid. The electrochemical method for purifying boric acid has the same disadvantages as the ion exchange method, and its application scope is also subject to certain restrictions. The osmotic membrane method refers to a method in which impurities in boric acid are separated by a reverse osmosis membrane at room temperature and under certain pH conditions, and then high-purity boric acid is obtained by evaporation and drying. This method is rarely used in the industry, and the high-purity boric acid produced is used in the cooling system of pressurized water reactors. Metal ion complexing agents refer to organic compounds that can combine with various metal ions to form stable complexes. Complexing agents were originally used mainly for the treatment of metal and metalloid poisoning. Complexing agents are also called chelating agents, chelating dispersants, metal blocking agents, water softeners, etc. in the printing and dyeing industry.

[0006] In industrial production, the complexing effect is often used to achieve the effect of removing impurity metal ions in the mother liquor. According to the principle, complexing agents can generally be divided into two categories: complexing and chelating. For the complexing mechanism, its mechanism of action is to form coordination bonds with metal ions (especially ions with holes in the sub-layer orbital), such as the complexing of ammonia with ions such as copper, iron, cobalt, and nickel. For the chelating mechanism, it can not only provide lone pairs of electrons to form coordination bonds, but also form a relatively stable five-, six-, and seven-membered ring structure with the coordinated metal ions, so that the metal ions enter the chelate ring during the coordination process and passivate, thereby achieving the effect of complexing and impurity removal. In order to obtain a boric acid product with higher purity and fewer impurities, it is sometimes necessary to use a variety of purification methods in combination. Summary of the invention

[0007] In order to overcome the problems existing in the related art, the embodiments disclosed in the present invention provide a method for removing magnetic foreign matter in industrial boric acid or borax, high-purity boric acid and its application.

[0008] The technical scheme is as follows: A method for removing magnetic foreign matter from industrial boric acid or borax comprises:

[0009] S1, mix industrial boric acid or borax sample powder with deionized water in a three-necked flask, heat to dissolve and then cool down, marked as solution A;

[0010] S2, adding ammonia water or sodium hydroxide to solution A, keeping warm and settling, and filtering to obtain a boric acid filtrate, which is marked as solution B;

[0011] S3, adding nitric acid, hydrochloric acid or sulfuric acid to acidify solution B, adjusting the pH, and marking it as solution C;

[0012] S4, after heating solution C to boil, add complexing agent, keep warm and stir for complexing reaction, marked as solution D;

[0013] S5, allowing solution D to settle;

[0014] S6, at a temperature of 70-90°C, filter and separate the boric acid product and the mother liquor into solid-liquid phases to obtain high-purity boric acid.

[0015] In step S1, the mass ratio of industrial boric acid or borax sample powder to deionized water is 1:4 to 1:10.

[0016] In step S1, the heating temperature is 70-80°C; the cooling temperature is 40-50°C.

[0017] In step S2, ammonia water is used as an alkaline additive, and the amount of ammonia water added per kilogram of borax or industrial boric acid is 20 to 60 g;

[0018] Sodium hydroxide is used as an alkali additive, and the amount of sodium hydroxide added to each kilogram of borax or industrial boric acid is 10 to 40 g.

[0019] In step S2, the insulation temperature is 40-50°C and the insulation time is 1-10 hours.

[0020] In step S3, the pH of the solution is adjusted to 2 using nitric acid, hydrochloric acid or sulfuric acid.

[0021] In step S4, the complexing agent added is nicotinic acid or isonicotinic acid; 2 to 20 g of the complexing agent is added per kilogram of borax or industrial boric acid, the insulation temperature is 80 to 90° C., and the complexing reaction time is 20 to 60 min.

[0022] In step S5, the static sedimentation time is 30 to 120 minutes, and the static sedimentation temperature is 70 to 90°C.

[0023] Another object of the present invention is to provide a high-purity boric acid, wherein the high-purity boric acid is prepared by the method for removing magnetic foreign matter from industrial boric acid or borax.

[0024] Another object of the present invention is to provide an application of high-purity boric acid, and to utilize the high-purity boric acid in the smelting of enamel, ceramics, glass, glass fiber, shoe leather, wood preservation, dyes, boron steel and rare metals.

[0025] In combination with all the above technical solutions, the beneficial effects of the present invention are as follows:

[0026] The high-purity boric acid obtained by the treatment method of the present invention has an iron impurity content of less than 0.6ppm, a nickel impurity content of less than 0.5ppm, and a chromium impurity content of less than 0.5ppm among the main magnetic foreign matters. The main content of the high-purity boric acid prepared by the method of the present invention is greater than 99.6%.

[0027] The preparation method of the present invention mainly promotes the precipitation of magnetic metal impurities by adding alkali during the dissolution process. At the same time, the complexing agent introduced in the present invention is also to utilize the nitrogen atoms and oxygen atoms in the complexing agent to bond with the magnetic metal ions to form a stable complex, so as to achieve the purpose of removing magnetic foreign matter in industrial boric acid or borax.

[0028] The preparation method of the invention has simple process, mild production conditions, and readily available raw materials. The iron impurities, nickel impurities, and chromium impurities in the main magnetic foreign matter of the prepared boric acid have low contents, and can meet the national standard level of high-purity boric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the description, serve to explain the principles of the present disclosure;

[0030] Figure 1 The present invention provides a flow chart of a method for removing magnetic foreign matter from industrial boric acid or borax. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0032] Aiming at the current situation that domestic boric acid has many impurities and low quality, especially more magnetic foreign matter. The present invention creatively proposes a series of relatively simple treatment methods, combined with the process of complexing to remove magnetic foreign matter, which can significantly improve the purity of the prepared boric acid and make it reach the international advanced level. The principle of ordinary physical demagnetization of powder is to set an electromagnet or a permanent magnet on the path through which the powder passes to adsorb related magnetic foreign matter. Although this method is simple, it is difficult to remove magnetic foreign matter to below 5ppm. For high-end applications such as glass panels, it is difficult to meet customer needs. Therefore, many manufacturers produce high-end products by importing expensive high-purity boric acid from the United States, Russia, Turkey, Chile, etc. The present invention combines the complexing demagnetization method through a liquid phase process, which can process domestic ordinary industrial boric acid to the standard of high-purity boric acid. The process has strong practical value. The present invention realizes the low-cost processing of industrial boric acid into high-purity boric acid, especially the creative combination of alkali precipitation method and complexing method, which achieves a good effect of removing magnetic foreign matter.

[0033] Embodiment 1, as Figure 1 As shown, the method for removing magnetic foreign matter in industrial boric acid or borax provided by the embodiment of the present invention comprises:

[0034] S1, mix industrial boric acid or borax sample powder with deionized water in a three-necked flask, heat to dissolve and then cool down, marked as solution A;

[0035] Exemplarily, the addition of industrial boric acid or borax sample powder and deionized water is added in a fixed mass ratio, which is m (industrial boric acid or borax): m (pure water) = 1: (4-10);

[0036] Preferably, the heating temperature is 70-80°C;

[0037] Preferably, the cooling temperature is 40-50°C;

[0038] In the present invention, heating is performed during the process of dissolving industrial boric acid in order to increase the dissolution rate of industrial boric acid or borax in water, and cooling is performed after the dissolution is completed in order to solve the problem of ammonia gas escape when introducing ammonia water in the subsequent step.

[0039] S2, adding ammonia water or sodium hydroxide to solution A, keeping warm and settling, and filtering to obtain a boric acid filtrate, which is marked as solution B;

[0040] For example, if ammonia water is used as the base additive in step S2, the amount of ammonia water added is 20 to 60 g (NH 3 .H 2 O) / kg (borax or industrial boric acid);

[0041] Preferably, the amount of ammonia added is 30 to 50 g (NH 3 .H 2 O) / kg (borax or industrial boric acid). If sodium hydroxide is used as the alkali additive, the amount of sodium hydroxide added is 10-40g (sodium hydroxide) / kg (borax or industrial boric acid);

[0042] Preferably, the amount of sodium hydroxide added is 15 to 30 g (sodium hydroxide) / kg (borax or industrial boric acid);

[0043] Optionally, the insulation temperature is 40-50°C;

[0044] Optionally, the holding time is 1 to 10 hours;

[0045] In the present invention, the purpose of introducing ammonia water or sodium hydroxide is to increase the concentration of hydroxide in the dissolving process and promote the precipitation of magnetic metal impurities.

[0046] S3, adding nitric acid, hydrochloric acid or sulfuric acid to acidify solution B, adjusting the pH, and marking it as solution C;

[0047] Exemplarily, in step S3, nitric acid, hydrochloric acid or sulfuric acid is used to adjust the pH of the solution to 2;

[0048] In the present invention, the pH value of the solution is adjusted to 2 using nitric acid, hydrochloric acid or sulfuric acid in order to promote the crystallization of the subsequent product, high-purity boric acid.

[0049] S4, after heating solution C to boil, add complexing agent, keep warm and stir for complexing reaction, marked as solution D;

[0050] Exemplarily, the complexing agent added in step S4 is nicotinic acid, isonicotinic acid or other pyridine hydroxy derivatives;

[0051] Optionally, the complexing agent is added in an amount of 2 to 20 g / kg (borax or industrial boric acid);

[0052] Preferably, the amount of the complexing agent added is 5 to 18 g / kg (borax or industrial boric acid);

[0053] Optionally, the insulation temperature is 80-90°C;

[0054] Optionally, the complexation reaction time is 20 to 60 minutes;

[0055] Preferably, the complexation reaction time is 30 to 50 minutes;

[0056] In the present invention, the complexing agent is introduced to utilize the nitrogen atoms and oxygen atoms in the complexing agent to bond with the magnetic metal ions to form a stable complex, so as to achieve the purpose of removing magnetic foreign matter in industrial boric acid or borax.

[0057] S5, allowing solution D to settle;

[0058] Optionally, in step S5, the static sedimentation time is 30 to 120 minutes; the static sedimentation temperature is 70 to 90° C.;

[0059] S6, filtering at a temperature of 70 to 90° C. to separate the boric acid product and the mother liquor into solid-liquid phases to obtain high-purity boric acid;

[0060] Optionally, the filtration temperature in step S6 is 70-90°C.

[0061] Example 2, titration method to detect the main content of boric acid (according to the national standard, after dissolving the boric acid, adding mannitol and indicator, titrating with sodium hydroxide to determine the H 3 BO 3 content);

[0062] ICP was used to test the content of magnetic foreign matter impurities of iron, nickel and chromium in boric acid (the boric acid sample was dissolved in dilute acid and then measured by inductively coupled plasma atomic emission spectrometry).

[0063] The method for removing magnetic foreign matter from industrial boric acid or borax provided by an embodiment of the present invention comprises:

[0064] Take 1kg industrial boric acid sample in a reaction vessel, add 5kg pure water, stir and heat to 75℃ to dissolve, then cool to 45℃, add 35g ammonia water, keep warm at 45℃ for 2h and filter to obtain a section of impurity-removed boric acid filtrate, then add hydrochloric acid to adjust the pH of the section of impurity-removed boric acid filtrate to 2. Heat and boil the section of impurity-removed boric acid filtrate adjusted to pH 2, add 8g nicotinic acid complexing agent, keep warm and stir at 85℃ for complexing reaction for 35min, then let the reaction solution stand and settle at 85℃ for 50min, then filter at 85℃ to obtain a high-purity boric acid product. The method of Example 2 can increase the purity of industrial boric acid with a main content of 99.6% to 99.9%, and each magnetic foreign body element can be reduced to 0.5ppm, as shown in Table 1, meeting the requirements of national standard high-purity boric acid.

[0065] Table 1 National Standard High Purity Boric Acid Requirements

[0066] Test items Industrial Boric Acid High purity boric acid National standard high purity boric acid Main content 99.6％ 99.9％ ＞99.6％ Fe(ppm) 3.67 0.45 0.5 Ni(ppm) 2.81 0.3 0.5 Cr(ppm) 5.58 Not detected 0.5 Co(ppm) 6.23 0.29 0.5 Mn(ppm) 0.185 Not detected 0.1

[0067] Embodiment 3, the method for removing magnetic foreign matter in industrial boric acid or borax provided by the embodiment of the present invention comprises:

[0068] Take 1kg industrial boric acid sample in a reaction vessel, add 6kg pure water, stir and heat to 75℃ to dissolve, then cool to 42℃, add 20g sodium hydroxide, keep warm at 42℃ for 2h and filter to obtain a section of impurity-removed boric acid filtrate, then add hydrochloric acid to adjust the pH of the section of impurity-removed boric acid filtrate to 2. Heat and boil the section of impurity-removed boric acid filtrate adjusted to pH 2, add 8g nicotinic acid complexing agent, keep warm and stir for complex reaction at 85℃ for 35min, then let the reaction solution stand and settle at 85℃ for 50min, then filter at 85℃ to obtain a high-purity boric acid product. The method of Example 3 can increase the purity of industrial boric acid with a main content of 99.6% to 99.9%, and each magnetic foreign matter element can be reduced to 0.5ppm, as shown in Table 2, meeting the requirements of national standard high-purity boric acid.

[0069] Table 2 meets the national standard high purity boric acid requirements II

[0070] Test items Industrial Boric Acid High purity boric acid National standard high purity boric acid Main content 99.6％ 99.9％ ＞99.6％ Fe(ppm) 3.67 0.35 0.5 Ni(ppm) 2.81 0.2 0.5 Cr(ppm) 5.58 Not detected 0.5 Co(ppm) 6.23 0.32 0.5 Mn(ppm) 0.185 Not detected 0.1

[0071] Embodiment 4, the method for removing magnetic foreign matter in industrial boric acid or borax provided by the embodiment of the present invention comprises:

[0072] Take 1kg borax sample in a reaction vessel, add 6kg pure water, stir and heat to 78℃ to dissolve, then cool to 48℃, add 20g sodium hydroxide, keep warm at 48℃ for 2h and filter to obtain a section of impurity-removed boric acid filtrate, then add hydrochloric acid to adjust the pH of the section of impurity-removed boric acid filtrate to 2. Heat and boil the section of impurity-removed boric acid filtrate with pH adjusted to 2, add 8g nicotinic acid complexing agent, keep warm and stir complex reaction at 85℃ for 35min, then let the reaction solution stand and settle at 85℃ for 50min, then filter at 85℃ to obtain a high-purity boric acid product. The method of Example 4 can improve the purity of the borax sample with a main content of 99.5% to 99.9%, and each magnetic foreign body element can be reduced to 0.5ppm, as shown in Table 3, meeting the requirements of national standard high-purity boric acid.

[0073] Table 3 National Standard High Purity Boric Acid Requirements

[0074] Test items Borax High purity boric acid National standard high purity boric acid Main content 99.5％ 99.9％ ＞99.6％ Fe(ppm) 5.69 0.37 0.5 Ni(ppm) 5.75 0.3 0.5 Cr(ppm) 6.91 0.34 0.5 Co(ppm) 8.36 0.26 0.5 Mn(ppm) 0.364 Not detected 0.1

[0075] Embodiment 5, the method for removing magnetic foreign matter in industrial boric acid or borax provided by the embodiment of the present invention comprises:

[0076] Take 1kg borax sample in a reaction vessel, add 8kg pure water, stir and heat to 74℃ to dissolve, then cool to 44℃, add 25g sodium hydroxide, keep warm at 44℃ for 4h and filter to obtain a section of impurity-removed boric acid filtrate, then add hydrochloric acid to adjust the pH of the section of impurity-removed boric acid filtrate to 2. Heat and boil the section of impurity-removed boric acid filtrate with pH adjusted to 2, add 12g isonicotinic acid complexing agent, keep warm and stir complex reaction at 88℃ for 45min, then let the reaction solution stand and settle at 88℃ for 60min, then filter at 88℃ to obtain a high-purity boric acid product. The method of Example 5 can improve the purity of the borax sample with a main content of 99.5% to 99.9%, and each magnetic foreign body element can be reduced to 0.5ppm, as shown in Table 4, meeting the requirements of national standard high-purity boric acid.

[0077] Table 4 National Standard High Purity Boric Acid Requirements

[0078] Test items Borax High purity boric acid National standard high purity boric acid Main content 99.5％ 99.9％ ＞99.6％ Fe(ppm) 5.69 0.29 0.5 Ni(ppm) 5.75 0.18 0.5 Cr(ppm) 6.91 0.26 0.5 Co(ppm) 8.36 0.39 0.5 Mn(ppm) 0.364 Not detected 0.1

[0079] Example 6: High-purity boric acid is prepared by the method for removing magnetic foreign matter from industrial boric acid or borax in Examples 1-5. The high-purity boric acid is used in enamel, ceramics, glass, glass fiber, shoe leather, wood preservation, dyes, boron steel and rare metal smelting.

[0080] Comparative example: Compare the effects of removing magnetic foreign matter by three different methods: ① using a traditional powder remover, ② using alkali precipitation method alone, and ③ using alkali precipitation and complexation method at the same time.

[0081] Among them, the traditional iron remover selected the GY-XZ-159 type 14,000 GS rotary iron remover produced by Guangmou Magnetic Electric Company. The precipitation method refers to the first half of Example 5, and the steps before complexation iron removal are carried out. The combined method is carried out completely with reference to Example 5. After treatment by three different methods, it can be seen that the alkali precipitation and complexation methods have the best effect.

[0082] Table 5 Comparison results of different methods

[0083]

[0084] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for removing magnetic foreign matter from industrial boric acid or borax, characterized in that: The method includes: S1, mix industrial boric acid or borax sample powder with deionized water in a three-necked flask, heat to dissolve and then cool down, marked as solution A; S2, adding ammonia water or sodium hydroxide to solution A, keeping warm and settling, and filtering to obtain a boric acid filtrate, which is marked as solution B; S3, adding nitric acid, hydrochloric acid or sulfuric acid to acidify solution B, adjusting the pH, and marking it as solution C; S4, after heating solution C to boil, add complexing agent, keep warm and stir for complexing reaction, marked as solution D; S5, allowing solution D to settle; S6, at a temperature of 70-90°C, filter and separate the boric acid product and the mother liquor into solid-liquid phases to obtain high-purity boric acid.

2. The method for removing magnetic foreign matter from industrial boric acid or borax according to claim 1, characterized in that: In step S1, the mass ratio of industrial boric acid or borax sample powder to deionized water is 1:4 to 1:

10.

3. The method for removing magnetic foreign matter from industrial boric acid or borax according to claim 1, characterized in that: In step S1, the heating temperature is 70-80°C; the cooling temperature is 40-50°C.

4. The method for removing magnetic foreign matter from industrial boric acid or borax according to claim 1, characterized in that: In step S2, ammonia water is used as an alkaline additive, and the amount of ammonia water added per kilogram of borax or industrial boric acid is 20 to 60 g; Sodium hydroxide is used as an alkali additive, and the amount of sodium hydroxide added to each kilogram of borax or industrial boric acid is 10 to 40 g.

5. The method for removing magnetic foreign matter from industrial boric acid or borax according to claim 1, characterized in that: In step S2, the insulation temperature is 40-50°C and the insulation time is 1-10 hours.

6. The method for removing magnetic foreign matter from industrial boric acid or borax according to claim 1, characterized in that: In step S3, the pH of the solution is adjusted to 2 using nitric acid, hydrochloric acid or sulfuric acid.

7. The method for removing magnetic foreign matter from industrial boric acid or borax according to claim 1, characterized in that: In step S4, the complexing agent added is nicotinic acid or isonicotinic acid; 2 to 20 g of the complexing agent is added per kilogram of borax or industrial boric acid, the insulation temperature is 80 to 90° C., and the complexing reaction time is 20 to 60 min.

8. The method for removing magnetic foreign matter from industrial boric acid or borax according to claim 1, characterized in that: In step S5, the static sedimentation time is 30 to 120 minutes, and the static sedimentation temperature is 70 to 90°C.

9. A high-purity boric acid, characterized in that: The high-purity boric acid is prepared by the method for removing magnetic foreign matter from industrial boric acid or borax as described in any one of claims 1 to 8.

10. An application of high-purity boric acid, characterized in that: The high-purity boric acid of claim 9 is used in enamel, ceramics, glass, glass fiber, shoe leather, wood antiseptic, dye, boron steel and rare metal smelting.

Images