Method for recovering valuable elements in multi-metal arsenic acid wastewater

Abstract

The invention relates to a method for recovering valuable elements in multi-metal arsenic acid wastewater. The method comprises the following steps: detecting the content of metal elements; mixed precipitation of copper, arsenic, gold and silver; purifying the acidic mother liquor to remove iron; preparing high-quality gypsum; two-stage leaching of harmful element arsenic; and curing arsenic. Through reasonable cooperation of sodium hydrosulfide and 25 # black powder, copper and arsenic ions and micro-fine particle gold and silver in the acid wastewater are fully precipitated, and the recovery rate of target components is greatly increased; then, two-stage leaching arsenic removal is carried out on the precipitate by means of an acidic wastewater stock solution or by supplementing copper sulfate at the same time, and high-quality gold-silver-copper concentrate can be obtained on the premise that the use amount of copper sulfate is reduced; the filtered iron-containing acid mother liquor is subjected to iron removal and gypsum preparation to obtain high-quality gypsum and ferric hydroxide, the intermediate product ferric hydroxide is directly used for arsenic removal of the arsenic-containing acid mother liquor, under the synergistic effect of the intermediate product ferric hydroxide and lime milk, the harmful element arsenic can be efficiently removed, and comprehensive recovery and harmless treatment of valuable elements in the acid wastewater are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrometallurgy, and particularly relates to a method for recovering valuable elements from multi-metal arsenic-containing acidic wastewater. Background Art

[0002] A large amount of multi-metal arsenic-containing acidic wastewater is generated during the production process of non-ferrous metal smelting enterprises. The properties of this type of acidic wastewater are complex, and with different production processes, the components contained are often quite different. Generally, arsenic in the acidic wastewater is precipitated as gypsum slag through wet arsenic precipitation or arsenic filter cake is obtained through sulfide arsenic precipitation for treatment. However, the valuable metals in this type of wastewater are not recycled. With the development and utilization of mineral resources and the continuous rise of the international gold price, the recovery of valuable metals such as gold, silver, and copper in wastewater has attracted increasing attention. Especially for the wastewater generated from the washing or acid leaching treatment of multi-metal sulfide ore roasting slag containing gold to extract gold and silver, the recovery value of its valuable elements is relatively high. Gold and silver in this type of waste liquid exist in the form of fine particles, while copper, arsenic, iron, etc. exist in the form of ions. Due to their different existing forms, it is difficult to comprehensively and effectively recycle valuable metals.

[0003] Currently, the main precipitation recovery methods for this type of wastewater include the lime-ferric salt method, the sulfide method, etc. For the valuable metals and harmful elements in the precipitation slag, methods such as hydrometallurgy, pyrometallurgy smelting, and flotation are used for recovery and reduction of hazards. These methods all have more or less deficiencies and defects in application. Either the valuable components cannot be effectively recovered, or secondary pollution is generated again, seriously affecting the natural environment. (1) Lime method: Using the calcium hydroxide produced by the hydrolysis of lime to react with arsenate ions to form calcium arsenate precipitation. To improve the arsenic removal effect, the pH value generally needs to be controlled at 9 - 10.5. In this environment, other valuable metals are prone to form coprecipitation, producing a large amount of sediment, with a low recovery rate of valuable metals and high subsequent treatment costs; (2) Ferric salt method: A large amount of ferric hydroxide colloid particles are generated under the condition of a pH value of 3 - 5.4 by ferric ions, so as to adsorb and coprecipitate arsenate ions. The valuable components in this method will also coprecipitate and cannot be effectively recovered; (3) Sulfide flotation method: Using a sulfiding agent to precipitate valuable metal ions and then recovering them by flotation method, and then treating the flotation tail liquid or tailings. This method will also cause arsenic in the waste liquid to be sulfidized and floated into the product together, resulting in unqualified products, and the flotation effect of fine particles into bubbles is poor, with a low recovery rate. In addition, the process flow is long, the investment is large, affecting the economic benefits of enterprises; (4) Pyrometallurgy smelting: Pyrometallurgy smelting is used to remove arsenic and recover valuable metals, with a complex process, high cost, and serious secondary environmental pollution; (5) Cyanide leaching method: Using cyanide to react with gold and silver to form soluble complexes, so that gold and silver enter the solution, thereby realizing the extraction of gold and silver. This method requires the use of highly toxic reagent cyanide, not only with high reagent costs, low gold and silver leaching rates, difficult recovery of copper, but also the cyanide slag produced faces the environmental problem of secondary pollution.

[0004] In order to overcome the deficiencies and defects existing in the prior art, the present invention provides a method for recovering valuable elements from multi-metal arsenic acidic wastewater, aiming to economically and environmentally recover valuable metals from arsenic acidic wastewater. Summary of the Invention

[0005] The present invention provides a method for recovering valuable elements from multi-metal arsenic acidic wastewater. This method is aimed at gold-containing multi-metal arsenic acidic wastewater. By adding sodium hydrosulfide, copper and arsenic ions are precipitated. After the reaction is complete, a small amount of No. 25 black medicine is added to enhance the hydrophobicity of fine-grained gold and silver, so that fine-grained gold and silver, copper and arsenic are co-precipitated. The acidic mother liquor separated by filtration is de-ironed (generating iron hydroxide) and then high-purity gypsum is prepared. The precipitate is subjected to two-stage leaching for arsenic removal to obtain a gold, silver and copper concentrate and an arsenic-containing mother liquor. The arsenic-containing mother liquor is sequentially added with iron hydroxide and lime for arsenic removal and purification treatment, thus realizing the harmless treatment of acidic wastewater and the comprehensive recovery of valuable elements. Its technical solutions include: (1) Detection of metal element content: Take a certain amount of multi-metal arsenic acidic wastewater to be treated and respectively measure the contents of copper, arsenic, gold, silver and iron therein; (2) Mixed precipitation of copper, arsenic, gold and silver: Add a 20% sodium hydrosulfide solution to the acidic wastewater and stir for precipitation to precipitate copper and arsenic ions. After stirring for 15 minutes, add No. 25 black medicine and stir for 2 - 4 minutes to enhance the hydrophobicity of fine-grained gold and silver, so that fine-grained gold and silver co-precipitate with copper and arsenic, and then perform thickening and filtration separation to obtain a mixed precipitate containing copper, arsenic, gold and silver and an acidic mother liquor; (3) Purification and iron removal of acidic mother liquor: After stirring the acidic mother liquor obtained in step (2) with air for 5 - 10 minutes, add a 10% sodium hydroxide solution, control the pH value at 3 - 4, stir for 10 - 20 minutes, and then perform thickening and filtration separation to obtain iron hydroxide and an iron-removed mother liquor; (4) Preparation of high-quality gypsum: Add 10% lime milk to the iron-removed mother liquor obtained in step (3), control the pH value at 7 - 7.5, stir for 15 minutes, and then perform thickening and filtration separation to obtain high-quality gypsum and dischargeable purified water; (5) Two-stage leaching of harmful element arsenic: (5-1) First-stage leaching for arsenic removal: Add a certain amount of multi-metal arsenic acidic wastewater or simultaneously supplement copper sulfate to the mixed precipitate containing copper, arsenic, gold and silver obtained in step (2) for first-stage leaching for arsenic removal, leach for 1.5 - 2 hours, and then perform thickening and filtration separation to obtain a gold and silver precipitate and an arsenic-containing acidic mother liquor I; Secondary arsenic removal by leaching: Add a certain amount of multi-metal arsenic-containing acidic wastewater or simultaneously supplement copper sulfate to the gold and silver precipitate obtained from the primary arsenic removal by leaching for secondary arsenic removal by leaching. The leaching time is 0.5 - 1 hour, and then thickening and filtration separation are carried out to obtain high-quality gold, silver, and copper concentrate and arsenic-containing acidic mother liquor II; (6) Solidification treatment of arsenic: After combining the arsenic-containing acidic mother liquor I and II obtained in step (5), add the ferric hydroxide obtained in step (3), stir for 10 - 15 minutes, then add 10% lime milk, control the pH value at 7 - 7.5, stir for 10 - 15 minutes, and then carry out thickening and filtration separation to obtain arsenic-containing slag and dischargeable purified water.

[0006] Furthermore, in step (2), sodium hydrosulfide is added according to 1.2 - 1.4 times the theoretical cumulative dosage of the chemical reaction equations Cu 2+ +S 2- =CuS and 2H 3 AsO 3 +3S 2- +6H + =As 2 S 3 ↓+6H 2 O.

[0007] Furthermore, the dosage of No. 25 black medicine in step (2) is 10 g / m 3 .

[0008] Furthermore, in step (5), when performing primary arsenic removal by leaching, the addition amount of multi-metal arsenic-containing acidic wastewater or simultaneously supplementing copper sulfate is added according to 0.8 - 0.9 times the theoretically calculated copper amount of the chemical reaction equations 3Cu 2+ +3As 2 S 3 +6H 2 O=3CuS+3H 3 AsO 4 +3SO 2 .

[0009] Furthermore, in step (5), when performing secondary arsenic removal by leaching, the addition amount of multi-metal arsenic-containing acidic wastewater or simultaneously supplementing copper sulfate is added according to 0.2 - 0.3 times the theoretically calculated copper amount of the chemical reaction equations 3Cu 2+ +3As 2 S 3 +6H 2 O=3CuS+3H 3 AsO 4 +3SO 2 , and the copper concentration in the solution is controlled to be 2 - 3 times that of the copper concentration in the primary leaching solution.

[0010] Advantages of the present invention: In the method of the present invention, firstly, through the reasonable combination of sodium hydrosulfide and No. 25 black powder, copper, arsenic ions and fine-grained gold and silver in acidic wastewater are fully precipitated, which can greatly improve the recovery rate of target components; then, two-stage leaching and arsenic removal of the precipitate are carried out by means of the original acidic wastewater solution or by supplementing copper sulfate at the same time, and high-quality gold, silver and copper concentrates can be obtained on the premise of reducing the dosage of copper sulfate; the iron-containing acidic mother liquor filtered out is processed to obtain high-quality gypsum and iron hydroxide after iron removal and gypsum preparation, and then the intermediate product iron hydroxide is directly used for arsenic removal treatment of arsenic-containing acidic mother liquor. Under the synergistic effect with lime milk, harmful element arsenic can be efficiently removed, truly realizing the comprehensive recovery of valuable elements in acidic wastewater and harmless treatment. Moreover, the recovery quality and recovery rate of each valuable element are remarkable, fully realizing the maximization of resource value. The treated wastewater also meets the industrial wastewater discharge standard, which is beneficial to reducing the environmental pollution risk and has good economic and environmental benefits. Brief Description of the Drawings

[0011] Figure 1 is a flow chart of a method for recovering valuable elements from multi-metal arsenic-containing acidic wastewater of the present invention. Detailed Embodiments

[0012] In order to make the technical problems and technical solutions solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Embodiment 1

[0013] Raw material 1#: A multi-metal arsenic-containing acidic wastewater with a solution pH of 1.8, and the metal element contents are: arsenic 512 mg / L, copper 1650 mg / L, gold 0.15 mg / L, silver 0.048 mg / L, and iron 4700 mg / L.

[0014] As Figure 1 shown, the present invention is used to recover valuable elements from the multi-metal arsenic-containing acidic wastewater. The specific technical solutions include: (1) Detection of metal element contents: Take a certain amount of multi-metal arsenic-containing acidic wastewater to be treated, and measure the contents of copper, arsenic, gold, silver and iron therein respectively; (2) Mixed precipitation of copper, arsenic, gold and silver: Add 20% sodium hydrosulfide solution to the acidic wastewater and stir for precipitation to precipitate copper and arsenic ions. After stirring for 15 minutes, add 10 g / m of No. 25 black powder 3 , stir for 2 - 4 minutes to strengthen the hydrophobicity of fine-grained gold and silver, so that fine-grained gold and silver co-precipitate with copper and arsenic, and then carry out thickening and filtration separation to obtain a mixed precipitate containing copper, arsenic, gold and silver and an acidic mother liquor; during this process, sodium hydrosulfide is in accordance with the chemical reaction equation Cu 2++S 2- =CuS and 2H 3 AsO 3 +3S 2- +6H + =As 2 S 3 ↓ + 6H 2 Add at 1.2 - 1.4 times the theoretical cumulative dosage of O.

[0015] (3) Purification of acidic mother liquor to remove iron: After introducing air and stirring for 5 - 10 minutes into the acidic mother liquor obtained in step (2), add 10% sodium hydroxide solution, control the pH value at 3 - 4, stir for 10 - 20 minutes for the reaction, and then perform thickening and filtration separation to obtain iron hydroxide and iron-removed mother liquor; (4) Preparation of high-quality gypsum: Add 10% lime milk to the iron-removed mother liquor obtained in step (3), control the pH value at 7 - 7.5, stir for 15 minutes for the reaction, and then perform thickening and filtration separation to obtain high-quality gypsum and dischargeable purified water; (5) Two-stage leaching of harmful element arsenic: First-stage arsenic removal by leaching: Add a certain amount of multi-metal arsenic-containing acidic wastewater or simultaneously supplement copper sulfate to the mixed precipitate containing copper, arsenic, gold, and silver obtained in step (2) for first-stage arsenic removal by leaching. The addition amount of the multi-metal wastewater or simultaneously supplemented copper sulfate is added according to 0.8 - 0.9 times the theoretically calculated copper amount in the chemical reaction equation 3Cu 2+ + 3As 2 S 3 + 6H 2 O = 3CuS + 3H 3 AsO 4 + 3SO 2 Add according to 0.8 - 0.9 times the theoretically calculated copper amount, leach for 1.5 - 2 hours, and then perform thickening and filtration separation to obtain a precipitate containing gold and silver and acidic arsenic-containing mother liquor I; Second-stage arsenic removal by leaching: Add a certain amount of multi-metal arsenic-containing acidic wastewater or simultaneously supplement copper sulfate to the precipitate containing gold and silver obtained from the first-stage arsenic removal by leaching for second-stage arsenic removal by leaching. The addition amount of the multi-metal wastewater or simultaneously supplemented copper sulfate is added according to 0.2 - 0.3 times the theoretically calculated copper amount in the chemical reaction equation 3Cu 2+ + 3As 2 S 3 + 6H 2 O = 3CuS + 3H 3 AsO 4 + 3SO 2 Add according to 0.2 - 0.3 times the theoretically calculated copper amount, and control the copper concentration in the solution to be 2 - 3 times that of the first-stage leaching solution. The leaching time is 0.5 - 1 hour, and then perform thickening and filtration separation to obtain high-quality gold, silver, and copper concentrate and acidic arsenic-containing mother liquor II; (6) Solidification treatment of arsenic: After combining the arsenic-containing acidic mother liquors I and II obtained in step (5), add the iron hydroxide obtained in step (3), stir for 10 - 15 minutes, then add 10% lime milk, control the pH value at 7 - 7.5, stir for 10 - 15 minutes, and then perform thickening, filtration and separation to obtain arsenic-containing slag and dischargeable purified water.

[0016] The test results obtained are as follows: copper concentrate with a gold grade of 27.64 g / t, a silver grade of 9.75 g / t, and a copper grade of 40.85%, and the recovery rates of gold, silver, and copper are 77.99%, 78.25%, and 95.38% respectively. Example 2

[0017] Raw material 2#: A multi-metal arsenic-containing acidic wastewater with a solution pH = 2.2, and the metal element contents are: arsenic 486 mg / L, copper 1130 mg / L, gold 0.18 mg / L, silver 0.075 mg / L, and iron 5100 mg / L.

[0018] As Figure 1 shown, the present invention is implemented on this complex platinum-palladium concentrate, and the specific steps are as follows: As Figure 1 shown, the present invention is used for the recovery of valuable elements from this multi-metal arsenic-containing acidic wastewater, and the specific technical solution includes: (1) Detection of metal element contents: Take a certain amount of multi-metal arsenic-containing acidic wastewater to be treated, and respectively measure the contents of copper, arsenic, gold, silver and iron therein; (2) Mixed precipitation of copper, arsenic, gold and silver: Add 20% sodium hydrosulfide solution to the acidic wastewater and stir for precipitation to precipitate copper and arsenic ions. After stirring for 15 minutes, add 10 g / m of No. 25 black medicine 3 , stir for 2 - 4 minutes to strengthen the hydrophobicity of fine-grained gold and silver, so that fine-grained gold and silver co-precipitate with copper and arsenic, and then perform thickening, filtration and separation to obtain a mixed precipitate containing copper, arsenic, gold and silver and an acidic mother liquor; in this process, sodium hydrosulfide is added according to 1.2 - 1.4 times the theoretical cumulative dosage of the chemical reaction equation Cu 2+ +S 2- =CuS and 2H 3 AsO 3 +3S 2- +6H + =As 2 S 3 ↓+6H 2 O.

[0019] (3)Purification and iron removal of acidic mother liquor: After introducing air and stirring the acidic mother liquor obtained in step (2) for 5 - 10 minutes, add 10% sodium hydroxide solution, control the pH value at 3 - 4, stir for 10 - 20 minutes for the reaction, and then perform thickening and filtration separation to obtain iron hydroxide and iron-removed mother liquor; (4)Preparation of high-quality gypsum: Add 10% lime milk to the iron-removed mother liquor obtained in step (3), control the pH value at 7 - 7.5, stir for 15 minutes for the reaction, and then perform thickening and filtration separation to obtain high-quality gypsum and dischargeable purified water; (5)Two-stage leaching of harmful element arsenic: First-stage arsenic removal by leaching: To the mixed precipitate containing copper, arsenic, gold and silver obtained in step (2), add a certain amount of multi-metal arsenic-containing acidic wastewater or supplement copper sulfate simultaneously for first-stage arsenic removal by leaching. The addition amount of the multi-metal wastewater or the supplemented copper sulfate is added according to 0.8 - 0.9 times the theoretically calculated copper amount. Leach for 1.5 - 2 hours, and then perform thickening and filtration separation to obtain a precipitate containing gold and silver and arsenic-containing acidic mother liquor I; 2+ +3As 2 S 3 +6H 2 O=3CuS+3H 3 AsO 4 +3SO 2 The addition amount of the multi-metal wastewater or the supplemented copper sulfate is added according to 0.8 - 0.9 times the theoretically calculated copper amount. Leach for 1.5 - 2 hours, and then perform thickening and filtration separation to obtain a precipitate containing gold and silver and arsenic-containing acidic mother liquor I; Second-stage arsenic removal by leaching: Add a certain amount of multi-metal arsenic-containing acidic wastewater or supplement copper sulfate simultaneously to the precipitate containing gold and silver obtained from the first-stage arsenic removal by leaching for second-stage arsenic removal by leaching. The addition amount of the multi-metal wastewater or the supplemented copper sulfate is added according to 0.2 - 0.3 times the theoretically calculated copper amount, and control the copper concentration in the solution to be 2 - 3 times that of the first-stage leaching solution. Leach for 0.5 - 1 hour, and then perform thickening and filtration separation to obtain high-quality gold, silver and copper concentrate and arsenic-containing acidic mother liquor II; 2+ +3As 2 S 3 +6H 2 O=3CuS+3H 3 AsO 4 +3SO 2 The addition amount of the multi-metal wastewater or the supplemented copper sulfate is added according to 0.2 - 0.3 times the theoretically calculated copper amount, and control the copper concentration in the solution to be 2 - 3 times that of the first-stage leaching solution. Leach for 0.5 - 1 hour, and then perform thickening and filtration separation to obtain high-quality gold, silver and copper concentrate and arsenic-containing acidic mother liquor II; (6)Solidification treatment of arsenic: After combining the arsenic-containing acidic mother liquors I and II obtained in step (5), add the iron hydroxide obtained in step (3), stir for 10 - 15 minutes for the reaction, then add 10% lime milk, control the pH value at 7 - 7.5, stir for 10 - 15 minutes for the reaction, and then perform thickening and filtration separation to obtain arsenic-containing slag and dischargeable purified water.

[0020] The test results obtained are copper concentrate with a gold grade of 26.89 g / t, a silver grade of 10.25 g / t, and a copper grade of 38.96%, and the recovery rates of gold, silver, and copper are 78.30%, 77.19%, and 94.92% respectively.

[0021] It can be seen from the above embodiments that by using the method described in the present invention to treat multi-metal acidic wastewater, valuable elements such as gold, silver, and copper in it can be comprehensively recovered. The gold recovery rate can reach about 78%, the silver recovery rate can reach about 78%, and the copper recovery rate can reach about 95%. The comprehensive utilization of resources is truly realized. At the same time, the intermediate product ferric hydroxide can be used for arsenic removal treatment of wastewater to ensure the up-to-standard discharge of this type of acidic wastewater, truly realizing harmless treatment, reducing the risk of environmental pollution, and having good economic and environmental benefits.

[0022] The present invention has been described in detail through specific and preferred embodiments above. However, those skilled in the art should understand that the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for recovering valuable elements from polymetallic arsenic acid wastewater, characterized in that: The steps include: (1) Detection of metal element content: Take a certain amount of polymetallic arsenic acid wastewater to be treated and determine the contents of copper, arsenic, gold, silver and iron therein respectively; (2) Mixed precipitation of copper, arsenic, gold and silver: add 20% sodium hydrosulfide solution to acidic wastewater for stirring and precipitation. After stirring for 15 minutes, add 25# black medicine and stir for 2 to 4 minutes to make fine particles of gold and silver co-precipitate with copper and arsenic. Then, thicken and filter to obtain a mixed precipitate containing copper, arsenic, gold and silver and an acidic mother liquor. (3) Purification of the acidic mother liquor to remove iron: After passing air into the acidic mother liquor obtained in step (2) and stirring for 5 to 10 minutes, a 10% sodium hydroxide solution is added, the pH value is controlled at 3 to 4, the stirring reaction time is 10 to 20 minutes, and then the solution is concentrated and filtered to obtain iron hydroxide and iron removal mother liquor; (4) Preparation of high-quality gypsum: Add 10% lime milk to the iron removal mother liquor obtained in step (3), control the pH value to 7-7.5, stir and react for 15 minutes, then thicken and filter to obtain high-quality gypsum and purified water that can be discharged; (5) Two-stage leaching of harmful element arsenic: Primary leaching and arsenic removal: adding a certain amount of polymetallic arsenic acid wastewater or copper sulfate to the mixed precipitate containing copper, arsenic, gold and silver obtained in step (2) to perform primary leaching and arsenic removal, leaching for 1.5 to 2 hours, and then concentrating and filtering to obtain a gold and silver precipitate and an arsenic acid mother liquor I; Secondary leaching and arsenic removal: a certain amount of polymetallic arsenic acid wastewater or copper sulfate is added to the gold-silver precipitate obtained by primary leaching and arsenic removal for secondary leaching and arsenic removal. The leaching time is 0.5 to 1 hour, followed by thickening and filtration separation to obtain high-quality gold-silver-copper concentrate and arsenic acid mother liquor II; (6) Arsenic solidification treatment: After combining the arsenic-containing acid mother liquors I and II obtained in step (5), add the iron hydroxide obtained in step (3), stir the reaction for 10 to 15 minutes, then add 10% lime milk, control the pH value at 7 to 7.5, stir the reaction for 10 to 15 minutes, and then concentrate and filter to obtain arsenic-containing slag and purified water that can be discharged.

2. The method for recovering valuable elements from polymetallic arsenic acid wastewater according to claim 1, characterized in that: In step (2), sodium hydrosulfide is reacted according to the chemical reaction equation Add 1.2 to 1.4 times the theoretical cumulative amount.

3. The method for recovering valuable elements from polymetallic arsenic acid wastewater according to claim 1 or 2, characterized in that: The amount of 25# black medicine added in step (2) is 10g / m 3 .

4. The method for recovering valuable elements from polymetallic arsenic acid wastewater according to claim 1, characterized in that: In step (5), the amount of copper sulfate added to the polymetallic arsenic acid wastewater or the copper sulfate added simultaneously during the primary leaching and arsenic removal is calculated according to the chemical reaction equation: Add 0.8 to 0.9 times the theoretical amount of copper.

5. The method for recovering valuable elements from polymetallic arsenic acid wastewater according to claim 1 or 4, characterized in that: In step (5), the amount of copper sulfate added to the wastewater containing polymetallic arsenic or the copper sulfate added at the same time during the secondary leaching and arsenic removal is calculated according to the chemical reaction equation: 0.2 to 0.3 times of the theoretically calculated amount of copper is added, and the copper concentration of the solution is controlled to be 2 to 3 times the copper concentration of the primary leaching solution.

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