A calcium ion enrichment and CO2 reduction method for differentiated energy-saving integration of coal-based solid waste 2 Mineralization method

Abstract

The present application discloses a method for integrating calcium ion enrichment and CO2 reduction by differentiated energy conservation of coal-based solid waste. 2 Mineralization method, which belongs to the safe disposal of coal-based solid waste and CO 2 In the field of mineralization, the method comprises the following steps: uniformly mixing coal gasification slag with hydrochloric acid, performing two-step mechanochemical activation treatment on the slag, filtering to obtain an acidic filtrate; uniformly mixing fly ash with hydrochloric acid, then adding the acidic filtrate, performing two-step mechanochemical activation treatment to obtain a treated product; filtering the treated product to obtain a filtrate, then adjusting the pH to 8.5-9.5 with aqueous ammonia, filtering particulate matter, removing impurities, and obtaining a filtrate enriched with calcium ions; then introducing CO 2 Therefore, this application adopts the above-mentioned coal-based solid waste differentiated energy-saving integrated calcium ion enrichment and CO 2 The mineralization method integrates the treatment processes of coal gasification slag and fly ash, and organically links the treatment processes of different coal-based solid wastes; through the combined treatment of mechanical grinding, chemical activation, heating, etc., the "mechanical force field-chemical-temperature field" is achieved to synergistically enhance the leaching of calcium ions.

Description

Technical Field

[0001] This application belongs to the safe disposal of coal-based solid waste and CO 2 In particular, it involves a calcium ion enrichment and CO 2 Mineralization method. Background Art

[0002] Coal-based solid waste refers to solid waste generated during coal mining, washing and processing. Large amounts of stockpiling not only occupy land area, but also pollute the surrounding environment such as soil, atmosphere and water. Most existing technologies add acid to coal-based solid waste and then use carbon dioxide for mineralization. However, existing technologies cannot optimize the physical property differences of different coal-based solid wastes. At the same time, the treatment of coal gasification slag and fly ash is often carried out independently, lacking effective process integration, and failing to fully utilize the synergistic effects of various treatment methods such as mechanical grinding, chemical activation and heating to improve the leaching rate of calcium ions. Summary of the invention

[0003] The purpose of this application is to provide a calcium ion enrichment and CO2 2 The mineralization method integrates the treatment processes of coal gasification slag and fly ash, and organically links the treatment processes of different coal-based solid wastes; through the combined treatment of mechanical grinding, chemical activation, heating, etc., the "mechanical force field-chemical-temperature field" is achieved to synergistically enhance the leaching of calcium ions.

[0004] The present invention provides a method for integrating calcium ion enrichment and CO2 reduction by using differentiated energy-saving technology of coal-based solid waste. 2 The mineralization method comprises the following steps:

[0005] S1 uniformly mixes coal gasification slag and hydrochloric acid, performs two-step mechanochemical activation treatment on the mixture, and filters the final mechanochemical activation product to obtain an acidic filtrate;

[0006] S2: evenly mixing the fly ash and hydrochloric acid, then adding the acidic filtrate in step S1, and subjecting the obtained solution to a two-step mechanochemical activation treatment to obtain a treated product;

[0007] After the product is treated in S3 and filtered, a filtrate is obtained, and then the pH is adjusted to 8.5-9.5 with aqueous ammonia, and the particulate matter generated in the filtrate after the pH adjustment is filtered to remove impurities, thereby obtaining a filtrate enriched with calcium ions;

[0008] S4 introduces CO into the calcium ion-enriched filtrate 2 To mineralize.

[0009] Preferably, in step S1, when the coal gasification slag and hydrochloric acid are uniformly mixed, the concentration of the hydrochloric acid is 2.5-5 mol / L, and the liquid-solid ratio of the hydrochloric acid to the gasification slag is 2-3 mL / g;

[0010] Preferably, in step S1, the two-step mechanochemical activation treatment process is: the rotation speed of the first stage is 150 r / min and the ball milling time is 30 min; the rotation speed of the second stage is 300 r / min and the ball milling time is 60 min, and the activation temperature of the first stage and the second stage is 50-70°C.

[0011] Preferably, in step S2, when the fly ash and hydrochloric acid are evenly mixed, the concentration of the hydrochloric acid is 1.5-3 mol / L, and the liquid-to-solid ratio of the total hydrochloric acid to the gasified slag is 3-4 mL / g.

[0012] Preferably, in step S2, the two-step mechanochemical activation treatment process is: the rotation speed of the first stage is 150 r / min and the ball milling time is 20 min, the rotation speed of the second stage is 300 r / min and the ball milling time is 40 min, and the activation temperature of the first stage and the second stage is 40-60°C.

[0013] Preferably, in step S4, the mineralization temperature is 30-60°C, the reaction time is 45-90 min, and the CO 2 The gas flow rate is 300-500mL / min.

[0014] Preferably, in step S4, the carbonation efficiency of the mineralized filtrate is above 85%.

[0015] CO 2 When the gas flow rate is 500 mL / min, the mineralization temperature is 60°C, and the mineralization time is 90 minutes, the mineralization efficiency is 99.5%.

[0016] Therefore, this application adopts the above-mentioned coal-based solid waste differentiated energy-saving integrated calcium ion enrichment and CO 2 Mineralization method, has the following beneficial effects:

[0017] (1) Traditional coal-based solid waste treatment methods often ignore the differences in the physical properties of different types of solid waste, resulting in energy waste and low treatment efficiency. This application introduces the energy adaptation concept and designs different activation treatment parameters based on the different physical and chemical properties of coal gasification slag and fly ash, thus achieving efficient energy utilization and significantly reducing overall energy consumption.

[0018] (2) In traditional treatment methods, the treatment of coal gasification slag and fly ash is often carried out independently, lacking organic links and resulting in low resource utilization efficiency. This application innovatively uses the mechanochemical activation filtrate of coal gasification slag for further treatment of fly ash, which not only achieves the organic link between the two different coal-based solid waste treatment processes, but also ensures the efficient use of acid and maximizes the extraction of useful components in solid waste, thereby achieving "dry and clean" and reducing secondary pollution of waste;

[0019] (3) Through the combined treatment of mechanical grinding, chemical activation, heating, etc., the “mechanical force field-chemical-temperature field” is synergistically enhanced to leaching and enrich calcium ions from multi-source coal-based solid waste;

[0020] (4) By changing CO 2 The optimal carbonation conditions of the calcium ion enriched filtrate obtained in the mechanochemical activation of coal-based solid waste are obtained by adjusting the gas introduction rate, reaction temperature, reaction time and other conditions. DETAILED DESCRIPTION

[0021] The present invention provides a method for integrating calcium ion enrichment and CO2 reduction by using differentiated energy-saving technology of coal-based solid waste. 2 The mineralization method comprises the following steps:

[0022] S1 uniformly mixes the coal gasification slag and hydrochloric acid, and performs a two-step mechanochemical activation treatment on them, and filters the final mechanochemical activation product to obtain an acidic filtrate; the concentration of hydrochloric acid is 2.5-5 mol / L, and the liquid-solid ratio of hydrochloric acid to gasification slag is 2-3 mL / g; the process of the two-step mechanochemical activation treatment is: the rotation speed of the first stage is 150 r / min and the ball milling time is 30 min; the rotation speed of the second stage is 300 r / min and the ball milling time is 60 min, and the activation temperature of the first stage and the second stage is 50-70 ° C.

[0023] S2: evenly mix the fly ash and hydrochloric acid, then add the acidic filtrate in step S1, and perform two-step mechanochemical activation treatment on the obtained solution to obtain a treated product; when the fly ash and hydrochloric acid are evenly mixed, the concentration of hydrochloric acid is 1.5-3 mol / L, the liquid-solid ratio of total hydrochloric acid to gasified slag is 3-4 mL / g, and the process of the two-step mechanochemical activation treatment is: the speed of the first stage is 150 r / min and the ball milling time is 20 min, the speed of the second stage is 300 r / min and the ball milling time is 40 min, and the activation temperature of the first stage and the second stage is 40-60°C;

[0024] After the product is treated in S3 and filtered, a filtrate is obtained, and then the pH is adjusted to 8.5-9.5 with aqueous ammonia, and the particulate matter generated in the filtrate after the pH adjustment is filtered to remove impurities, thereby obtaining a filtrate enriched with calcium ions;

[0025] The calcium ion-enriched filtrate of S4 was added to a 500 mL container, and CO was introduced into the calcium ion-enriched filtrate. 2 Mineralization; CO 2 The feeding amount is 300-500 mL / min, the mineralization temperature is 30-60° C., the reaction time is 45-90 min, and the carbonation efficiency of the filtrate after mineralization is more than 85%.

[0026] Example 1

[0027] Pretreatment and mechanochemical activation of S1 coal gasification slag

[0028] 10g of coal gasification slag was first uniformly mixed with hydrochloric acid at a concentration of 2.5mol / L to form a mixture with a liquid-solid ratio of 2mL / g, and then subjected to a two-step mechanochemical activation treatment to enhance its chemical reactivity. In the first stage, the ball mill was operated at a speed of 150r / min for 30 minutes, while in the second stage, the speed was increased to 300r / min and the operation time was extended to 60 minutes. The activation temperature of both stages was controlled at 50°C. The activated product was separated by filtration to obtain an acidic filtrate; the calcium ion leaching rate was 80% in the first stage and 95% in the second stage.

[0029] Pretreatment and mechanochemical activation of S2 fly ash

[0030] 10g of fly ash was mixed with 3mol / L hydrochloric acid, and the acidic filtrate obtained in step S1 was added to form a mixture with a liquid-solid ratio of 3mL / g. The first stage was ball milled at a speed of 150r / min for 20 minutes, and the second stage was ball milled at a speed of 300r / min for 40 minutes. The activation temperature of the two stages was controlled at 60°C. The calcium ion leaching rate was 92% in the first stage and 98% in the second stage.

[0031] Enrichment and purification of S3 calcium ions

[0032] The product after the second mechanochemical activation treatment is filtered to obtain a filtrate. Subsequently, the pH of the filtrate is adjusted to 8.5 using ammonia water to precipitate and remove impurity ions such as aluminum and iron, and the generated particulate matter is removed by filtration to obtain a pure filtrate enriched with calcium ions.

[0033] S4CO 2 Mineralization reaction

[0034] The flow rate was 400 mL / min CO 2 The gas is passed into the calcium ion-enriched filtrate for mineralization reaction, which is carried out at a temperature of 60°C and a reaction time of 75 minutes. In order to convert the calcium ions in the filtrate into calcium carbonate, CO 2 The capture and storage of the mineralized filtrate reaches 97% carbonation efficiency.

[0035] Example 2

[0036] 1 Pretreatment and mechanochemical activation of coal gasification slag

[0037] 10g of coal gasification slag was first uniformly mixed with hydrochloric acid at a concentration of 5mol / L to form a mixture with a liquid-solid ratio of 3mL / g, and then underwent a two-step mechanochemical activation treatment to enhance its chemical reactivity. In the first stage, the ball mill was operated at a speed of 150r / min for 30 minutes, while in the second stage, the speed was increased to 300r / min and the operation time was extended to 60 minutes. The activation temperature of both stages was controlled at 70℃, and the activated product was separated by filtration to obtain an acidic filtrate. The calcium ion leaching rate was 89% in the first stage and 98% in the second stage.

[0038] Pretreatment and mechanochemical activation of S2 fly ash

[0039] 10g of fly ash was mixed with hydrochloric acid having a concentration of 1.5mol / L, and the acidic filtrate obtained in step S1 was added to form a mixture with a liquid-solid ratio of 3mL / g. It was also subjected to mechanochemical activation treatment. The mechanochemical activation treatment was divided into two stages. The first stage was ball milled at a speed of 150r / min for 20 minutes, and the second stage was ball milled at a speed of 300r / min for 40 minutes. The activation temperature of the two stages was controlled at 40°C. The calcium ion leaching rate was 90% in the first stage and 96% in the second stage.

[0040] Enrichment and purification of S3 calcium ions

[0041] The product after the second mechanochemical activation treatment is filtered to obtain a filtrate, and then the pH of the filtrate is adjusted to 9.5 using ammonia water to precipitate and remove impurity ions such as aluminum and iron. The generated particulate matter is removed by filtration to obtain a pure filtrate enriched with calcium ions.

[0042] S4CO 2 Mineralization reaction

[0043] The flow rate was 350 mL / min CO 2 The gas is introduced into the calcium ion-enriched filtrate for mineralization reaction. The mineralization reaction is carried out at a temperature of 50°C and the reaction time is 90 minutes. The carbonation efficiency of the filtrate reaches 92%. Example 3

[0044] 1 Pretreatment and mechanochemical activation of coal gasification slag

[0045] 10g of coal gasification slag was first uniformly mixed with hydrochloric acid at a concentration of 3.5mol / L to form a mixture with a liquid-to-solid ratio of 2.5mL / g. It then underwent a two-step mechanochemical activation treatment to enhance its chemical reactivity. In the first stage, the ball mill was operated at a speed of 150r / min for 30 minutes, while in the second stage, the speed was increased to 300r / min and the operating time was extended to 60 minutes. The activation temperature in both stages was controlled at 60°C, and the activated product was separated by filtration to obtain an acidic filtrate. The calcium ion leaching rate was 86% in the first stage and 97% in the second stage.

[0046] Pretreatment and mechanochemical activation of S2 fly ash

[0047] 10g of fly ash was mixed with hydrochloric acid having a concentration of 2mol / L, and the acidic filtrate obtained in step S1 was added to form a mixture with a liquid-solid ratio of 3.5mL / g. The mixture was also subjected to mechanochemical activation treatment, which was divided into two stages: the first stage was ball milled at a speed of 150r / min for 20 minutes, and the second stage was ball milled at a speed of 300r / min for 40 minutes. The activation temperature of the two stages was controlled at 50°C. The calcium ion leaching rate was 90% in the first stage and 97% in the second stage.

[0048] Enrichment and purification of S3 calcium ions

[0049] The product after mechanochemical activation treatment is filtered to obtain a filtrate. Subsequently, the pH of the filtrate is adjusted to 9 using ammonia water, which helps to precipitate and remove impurity ions such as aluminum and iron. The generated particulate matter is removed by filtration to obtain a pure filtrate enriched with calcium ions.

[0050] S4CO 2 Mineralization reaction

[0051] The flow rate was 300 mL / min CO 2 The gas is passed into the calcium ion-enriched filtrate for mineralization reaction. The mineralization reaction is carried out at a temperature of 30°C and the reaction time is 75 minutes. The calcium ions in the filtrate are converted into calcium carbonate to achieve CO 2 The capture and storage of filtrate reaches 87% carbonation efficiency.

[0052] Example 4

[0053] 10g of coal gasification slag was first uniformly mixed with hydrochloric acid at a concentration of 2.5mol / L to form a mixture with a liquid-solid ratio of 2mL / g, and then subjected to a two-step mechanochemical activation treatment to enhance its chemical reactivity. In the first stage, the ball mill was operated at a speed of 150r / min for 30 minutes, while in the second stage, the speed was increased to 300r / min and the operation time was extended to 60 minutes. The activation temperature of both stages was controlled at 50°C. The activated product was separated by filtration to obtain an acidic filtrate; the calcium ion leaching rate was 80% in the first stage and 95% in the second stage.

[0054] Pretreatment and mechanochemical activation of S2 fly ash

[0055] 10g of fly ash was mixed with 3mol / L hydrochloric acid, and the acidic filtrate obtained in step S1 was added to form a mixture with a liquid-solid ratio of 3mL / g. The first stage was ball milled at a speed of 150r / min for 20 minutes, and the second stage was ball milled at a speed of 300r / min for 40 minutes. The activation temperature of the two stages was controlled at 60°C. The calcium ion leaching rate was 92% in the first stage and 98% in the second stage.

[0056] Enrichment and purification of S3 calcium ions

[0057] The product after the second mechanochemical activation treatment is filtered to obtain a filtrate. Subsequently, the pH of the filtrate is adjusted to 8.5 using ammonia water to precipitate and remove impurity ions such as aluminum and iron, and the generated particulate matter is removed by filtration to obtain a pure filtrate enriched with calcium ions.

[0058] S4CO 2 Mineralization reaction

[0059] The flow rate was 500 mL / min CO 2 The gas is introduced into the calcium ion-enriched filtrate to carry out a mineralization reaction at a temperature of 60° C. for 90 minutes. The carbonation efficiency of the filtrate reaches 99.5%.

[0060] Comparative Example 1

[0061] 10g of coal gasification slag was first uniformly mixed with hydrochloric acid at a concentration of 2.5mol / L to form a mixture with a liquid-solid ratio of 2mL / g, and then subjected to a two-step mechanochemical activation treatment to enhance its chemical reactivity. In the first stage, the ball mill was operated at a speed of 150r / min for 30 minutes, while in the second stage, the speed was increased to 300r / min and the operation time was extended to 60 minutes. The activation temperature of both stages was controlled at 80°C. The activated product was separated by filtration to obtain an acidic filtrate; the calcium ion leaching rate was 74% in the first stage and 88% in the second stage.

[0062] Pretreatment and mechanochemical activation of S2 fly ash

[0063] 10g of fly ash was mixed with 3mol / L hydrochloric acid, and the acidic filtrate obtained in step S1 was added to form a mixture with a liquid-solid ratio of 3mL / g. The first stage was ball milled at a speed of 150r / min for 20 minutes, and the second stage was ball milled at a speed of 300r / min for 40 minutes. The activation temperature of the two stages was controlled at 60°C. The calcium ion leaching rate was 80% in the first stage and 93% in the second stage.

[0064] Enrichment and purification of S3 calcium ions

[0065] The product after the second mechanochemical activation treatment is filtered to obtain a filtrate. Subsequently, the pH of the filtrate is adjusted to 8.5 using ammonia water to precipitate and remove impurity ions such as aluminum and iron, and the generated particulate matter is removed by filtration to obtain a pure filtrate enriched with calcium ions.

[0066] S4CO 2 Mineralization reaction

[0067] The flow rate was 400 mL / min CO 2 The gas is passed into the calcium ion-enriched filtrate for mineralization reaction, which is carried out at a temperature of 60°C and a reaction time of 75 minutes. In order to convert the calcium ions in the filtrate into calcium carbonate, CO 2 The capture and storage of the mineralized filtrate reached a carbonation efficiency of 87%.

[0068] Comparative Example 2

[0069] 10g of coal gasification slag was first uniformly mixed with hydrochloric acid at a concentration of 2.5mol / L to form a mixture with a liquid-solid ratio of 2mL / g, and then subjected to a two-step mechanochemical activation treatment to enhance its chemical reactivity. In the first stage, the ball mill was operated at a speed of 150r / min for 30 minutes, while in the second stage, the speed was increased to 300r / min and the operation time was extended to 60 minutes. The activation temperature of both stages was controlled at 30°C. The activated product was separated by filtration to obtain an acidic filtrate; the calcium ion leaching rate was 74% in the first stage and 83% in the second stage.

[0070] Pretreatment and mechanochemical activation of S2 fly ash

[0071] 10g of fly ash was mixed with 3mol / L hydrochloric acid, and the acidic filtrate obtained in step S1 was added to form a mixture with a liquid-solid ratio of 3mL / g. The first stage was ball milled at a speed of 150r / min for 20 minutes, and the second stage was ball milled at a speed of 300r / min for 40 minutes. The activation temperature of the two stages was controlled at 60°C. The calcium ion leaching rate was 79% in the first stage and 90% in the second stage.

[0072] Enrichment and purification of S3 calcium ions

[0073] The product after the second mechanochemical activation treatment is filtered to obtain a filtrate. Subsequently, the pH of the filtrate is adjusted to 8.5 using ammonia water to precipitate and remove impurity ions such as aluminum and iron, and the generated particulate matter is removed by filtration to obtain a pure filtrate enriched with calcium ions.

[0074] S4CO 2 Mineralization reaction

[0075] The flow rate was 400 mL / min CO 2 The gas is passed into the calcium ion-enriched filtrate for mineralization reaction, which is carried out at a temperature of 60°C and a reaction time of 75 minutes. In order to convert the calcium ions in the filtrate into calcium carbonate, CO 2 The capture and storage of the mineralized filtrate reaches 85% carbonation efficiency.

[0076] This application uses different carbon dioxide flow rates, mineralization temperatures, and mineralization times for analysis, and the other conditions are the same as those in Example 1. The results are shown in Table 1. It can be seen that in the experimental results of Group 2, CO 2 The carbonation rate is relatively high. 2 The amount of gas introduced per unit time has the most significant effect on the carbonation rate. 2 As the amount of gas introduced increases, the carbonation rate continues to increase. However, excessive CO 2 The amount of gas introduced will partially dissolve the calcium carbonate precipitate to form calcium bicarbonate, which is not conducive to the carbonation process.

[0077] Table 1. Effects of various factors on CO 2 Effect of Carbonation Rate

[0078]

[0079] Therefore, the present application provides a method for integrating calcium ion enrichment and CO 2 The mineralization method integrates the treatment processes of coal gasification slag and fly ash, and organically links the treatment processes of different coal-based solid wastes; through the combined treatment of mechanical grinding, chemical activation, heating, etc., the "mechanical force field-chemical-temperature field" is achieved to synergistically enhance the leaching of calcium ions.

[0080] In the description of this specification, the description with reference to the terms "an experimental example", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the experimental example or example are included in at least one experimental example or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same experimental example or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more experimental examples or examples in a suitable manner.

[0081] Finally, it should be noted that the above experimental examples are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred experimental examples, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calcium ion enrichment and CO2 mineralization with differentiated energy-saving integration of coal-based solid waste, characterized in that: The following steps are involved: S1 uniformly mixes coal gasification slag and hydrochloric acid, performs two-step mechanochemical activation treatment on the mixture, and filters the final mechanochemical activation product to obtain an acidic filtrate; S2: evenly mixing the fly ash and hydrochloric acid, then adding the acidic filtrate in step S1, and subjecting the obtained solution to a two-step mechanochemical activation treatment to obtain a treated product; After the product is treated in S3 and filtered, a filtrate is obtained, and then the pH is adjusted to 8.5-9.5 with aqueous ammonia, and the particulate matter generated in the filtrate after the pH adjustment is filtered to remove impurities, thereby obtaining a filtrate enriched with calcium ions; S4 introduces CO2 into the calcium ion-enriched filtrate for mineralization; In step S1, the two-step mechanochemical activation treatment process is as follows: the rotation speed of the first stage is 150 r / min and the ball milling time is 30 min; the rotation speed of the second stage is 300 r / min and the ball milling time is 60 min, and the activation temperature of the first stage and the second stage is 50-70°C; In step S2, the two-step mechanochemical activation treatment process is as follows: the rotation speed of the first stage is 150 r / min and the ball milling time is 20 min, the rotation speed of the second stage is 300 r / min and the ball milling time is 40 min, and the activation temperature of the first stage and the second stage is 40-60°C.

2. The method for calcium ion enrichment and CO2 mineralization of coal-based solid waste with differentiated energy-saving integration according to claim 1 is characterized in that: In the step S1, when the coal gasification slag and the hydrochloric acid are uniformly mixed, the concentration of the hydrochloric acid is 2.5-5 mol / L, and the liquid-to-solid ratio of the hydrochloric acid to the coal gasification slag is 2-3 mL / g.

3. The method for calcium ion enrichment and CO2 mineralization of coal-based solid waste with differentiated energy-saving integration according to claim 1, characterized in that: In step S2, when the fly ash and hydrochloric acid are evenly mixed, the concentration of the hydrochloric acid is 1.5-3 mol / L.

4. The method for calcium ion enrichment and CO2 mineralization of coal-based solid waste with differentiated energy-saving integration according to claim 2 is characterized in that: In step S4, the mineralization temperature is 30-60°C, the reaction time is 45-90 min, and the CO2 gas introduction rate is 300-500 mL / min.

5. The method for calcium ion enrichment and CO2 mineralization of coal-based solid waste with differentiated energy-saving integration according to claim 4 is characterized in that: In step S4, the carbonation efficiency of the mineralized filtrate is above 85%.

6. The method for differentiated energy-saving integrated calcium ion enrichment and CO2 mineralization of coal-based solid waste according to claim 5, characterized in that: When the CO2 gas flow rate was 500 mL / min, the mineralization temperature was 60°C, and the mineralization time was 90 minutes, the mineralization efficiency was 99.5%.

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