Preventing decomposition of sodium cyanide compositions

Abstract

The invention relates to a method for reducing the decomposition of an aqueous sodium cyanide solution by passing an inert gas through the aqueous sodium cyanide solution to remove carbon dioxide from the solution, and / or storing the aqueous sodium cyanide solution under inert gas or vacuum. The invention also relates to a method for reducing the decomposition of a sodium cyanide slurry, a sodium cyanide paste or a solid sodium cyanide composition. The method stores the sodium cyanide paste, the sodium cyanide slurry or the solid sodium cyanide composition under inert gas or vacuum.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 337,231, filed on May 2, 2022, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to a method for reducing the decomposition of sodium cyanide aqueous solution.

[0004] The present invention also relates to a method for reducing the decomposition of sodium cyanide slurry, sodium cyanide paste or solid sodium cyanide composition. Background Art

[0005] Sodium cyanide is produced by absorbing hydrogen cyanide gas into an aqueous sodium hydroxide solution or by reacting liquefied hydrogen cyanide with an aqueous sodium hydroxide solution. Sodium cyanide is a commodity chemical used in the mining industry to extract gold and silver from ores. Sodium cyanide is sold either as an aqueous solution (usually between 25% and 35% sodium cyanide by weight) or as a solid (between 97% and 99% purity). Aqueous sodium cyanide slurries are also used. For example, see US 4,902,301. Over time, the formation of contaminants (including sodium carbonate and sodium formate) reduces the amount of sodium cyanide in solution. It is believed that these contaminants are produced by the reaction of cyanide in solution with dissolved carbon dioxide and / or carbon dioxide absorbed from the atmosphere.

[0006] In the production of sodium cyanide, contaminants such as sodium carbonate and sodium formate are known impurities. See US 4,847,062. Other patents describe separation techniques for these impurities. See US2010 / 0296995 and US 3,273,959. These techniques generally relate to the production of sodium cyanide solids, because the newly formed pure solution can be used as a feed component and can be processed immediately. However, these techniques are capital intensive and are only temporary, because carbonate and formate contaminants will continue to form after separation, whether the sodium cyanide is in the form of a solid, paste or slurry or in the form of a solution.

[0007] The formation of these contaminants not only makes the storage of solid sodium cyanide problematic, it also affects the delivery of the solution, as customers will see less cyanide than was discharged by the production facility. Significant amounts of sodium cyanide can be lost from the solution during storage and transportation. Additionally, degradation of the product can produce ammonia, which is toxic and harmful to those who come into contact with it.

[0008] Therefore, there is a need for a method of reducing the accumulation of contaminants in sodium cyanide compositions by reducing the amount of cyanide lost to degradation, thereby allowing the production and delivery of a high purity sodium cyanide product. Summary of the invention

[0009] The present invention relates to a method for reducing the amount of sodium cyanide lost due to degradation. The method significantly reduces the accumulation of contaminants in the sodium cyanide composition, thereby allowing the production and delivery of a high purity sodium cyanide product. The present invention eliminates the need for capital intensive separation processes.

[0010] Description of the invention

[0011] The present invention relates to a method for reducing the decomposition of an aqueous sodium cyanide solution. The present invention also relates to a method for reducing the decomposition of cyanide in an aqueous sodium cyanide slurry, an aqueous sodium cyanide paste or a solid sodium cyanide composition. The aqueous medium is preferably water itself. The method of the present invention reduces the decomposition of cyanide by more than 50%, more than 70%, more than 90% or more than 95%, and preferably substantially prevents the decomposition.

[0012] The method of the present invention comprises the following steps: passing an inert gas through the aqueous sodium cyanide solution to remove carbon dioxide from the solution, and / or storing the aqueous sodium cyanide solution under an inert gas or under vacuum. In one embodiment of the present invention, the inert gas is bubbled through the aqueous sodium cyanide solution. When the solution is stored under vacuum, the pressure in the container, at least during storage, is a reduced pressure below atmospheric pressure.

[0013] The aqueous sodium cyanide solution or solid sodium cyanide can contain any amount of sodium cyanide. Commercial-scale aqueous sodium cyanide solutions contain about 15wt.% to 45wt.% sodium cyanide, more typically about 25wt.% to 35wt.% sodium cyanide. Inert gases are any gases that are generally considered to be inert in chemical reactions. These gases include, but are not limited to, gases selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen and mixtures thereof. Any gas that does not react with cyanide or does not cause cyanide to decompose can also be an inert gas for the purposes of the present invention.

[0014] Inert gas can be bubbled through the aqueous sodium cyanide solution using methods known in the art. Using the methods of the present invention, preferably all or substantially all (e.g., >50%, >60%, >70%, >80%, >90%, >95%, >96%, >97%, >98%, >99%, >99.9%) of the carbon dioxide is removed from the solution or the surrounding atmosphere. Sufficient carbon dioxide should be removed to prevent decomposition, or at least to minimize decomposition.

[0015] Inert gas can be bubbled through the sodium cyanide solution through an ejector / injector under the liquid surface. This process can be completed at multiple locations in the sodium cyanide production process, including but not limited to an absorption tower, a separation vessel, a sodium cyanide recirculation line, and a sodium cyanide product to a storage line. The present invention can also be implemented by injecting inert gas through a solution contained in a storage container, or by the solution when loaded into a transport container, or by the solution in a transport container. After dissolved carbon dioxide is removed from the solution, carbon dioxide should preferably be removed from the interface between the solution and the gas (i.e., the head space of the container holding the solution). This can be completed by creating a vacuum (by means of a steam ejector or otherwise) or by introducing an inert gas to cover the solution stored in process equipment, storage containers, and transport containers.

[0016] When an aqueous sodium cyanide solution or sodium cyanide in solid form is stored under an inert gas, an inert gas is introduced into the headspace of the container containing the solution. This can be done by bubbling the inert gas through the solution or by introducing the inert gas directly into the headspace. Sufficient inert gas should be used to preferably replace carbon dioxide-containing gases in the headspace or dissolved in the aqueous solution, or to reduce the concentration of carbon dioxide in the headspace, thereby preventing or minimizing decomposition.

[0017] According to the method of the present invention, carbon dioxide is removed from the sodium cyanide aqueous solution to obtain an aqueous sodium cyanide solution containing an inert gas and substantially free of carbon dioxide or an aqueous sodium cyanide solution stored under an inert gas. These are different embodiments of the present invention. Preferably, the sodium cyanide aqueous solution is a solution containing an inert gas and substantially free of carbon dioxide and stored under an inert gas.

[0018] The present invention also provides a method for reducing the decomposition of sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide. These methods store sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide under an inert gas or under a vacuum. The inert gas used in these methods is the same as the above-mentioned inert gas. Sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide usually contain about 25wt.% to 100wt.% sodium cyanide. Generally, sodium cyanide paste or sodium cyanide slurry is a water-based paste or slurry. Before forming a paste or slurry, before mixing with sodium cyanide, carbon dioxide is removed from the water-containing portion by bubbling with an inert gas. As mentioned above, these methods of the present invention produce sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide stored under an inert gas or under a vacuum, each of which is a different embodiment of the present invention.

[0019] When sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide are stored under vacuum, the pressure in the container, at least during storage, is a reduced pressure below atmospheric pressure. Using methods known in the art, an inert gas can be bubbled through the water-containing portion. Using the method of the present invention, preferably all or substantially all (e.g., >50%, >60%, >70%, >80%, >90%, >95%, >96%, >97%, >98%, >99%, >99.9%) carbon dioxide is removed from sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide or the surrounding atmosphere. Sufficient carbon dioxide should be removed to prevent decomposition, or at least to minimize decomposition. By creating a vacuum (by means of a steam ejector or otherwise) or by introducing an inert gas to cover the solution stored in the process equipment, storage container and transport container to remove carbon dioxide.

[0020] According to the method of the present invention, carbon dioxide is removed from sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide to obtain sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide containing inert gas and substantially free of carbon dioxide, or sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide stored under inert gas. These are different embodiments of the present invention. Preferably, sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide contains inert gas and substantially free of carbon dioxide and is stored under inert gas.

[0021] The present invention also relates to a method for preparing sodium cyanide slurry or sodium cyanide paste in an aqueous system. The method comprises the following steps: passing an inert gas through an aqueous solvent to remove carbon dioxide, combining sodium cyanide with an aqueous solvent that removes carbon dioxide to form an aqueous sodium cyanide slurry or an aqueous sodium cyanide paste, optionally dehydrating the aqueous sodium cyanide slurry or aqueous sodium cyanide paste to remove water from the slurry or paste, and / or storing the aqueous sodium cyanide slurry or aqueous sodium cyanide paste under an inert gas or under vacuum. In one embodiment of the invention, the inert gas is bubbled through an aqueous sodium cyanide solution. The aqueous solvent is preferably water itself. As described above with respect to the sodium cyanide aqueous solution, the inert gas can be bubbled through the aqueous system via an ejector / injector.

[0022] Inert gas is any gas that is generally considered to be inert in chemical reactions. These gases include, but are not limited to, gases selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen and mixtures thereof. Any gas that does not react with cyanide or does not cause cyanide decomposition may also be an inert gas for the purposes of the present invention. When sodium cyanide paste or sodium cyanide slurry is stored under vacuum, the pressure in the container, at least during storage, is a reduced pressure below atmospheric pressure.

[0023] The invention also relates to an aqueous sodium cyanide solution containing an inert gas and being substantially free of carbon dioxide. The aqueous sodium cyanide solution is stored under an inert gas or under vacuum.

[0024] The invention also relates to an aqueous sodium cyanide solution stored under an inert gas or under vacuum.

[0025] The invention also relates to sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide stored under inert gas or under vacuum.

[0026] Exemplary embodiments of the present invention:

[0027] E1. A method for reducing the decomposition of an aqueous sodium cyanide solution, comprising the steps of:

[0028] passing an inert gas through an aqueous sodium cyanide solution to remove carbon dioxide from the solution, and / or

[0029] Store aqueous sodium cyanide solutions under inert gas or under vacuum.

[0030] E2. A method for reducing the decomposition of an aqueous sodium cyanide solution, comprising the steps of:

[0031] Store aqueous sodium cyanide solutions under inert gas or under vacuum.

[0032] E3. The method described in E1 or E2, wherein the inert gas is selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen and mixtures thereof.

[0033] E4. The method described in any one of E1-E3, wherein the aqueous sodium cyanide solution contains 15 wt.% to 45 wt.% sodium cyanide or the aqueous sodium cyanide solution contains 25 wt.% to 35 wt.% sodium cyanide.

[0034] E5. The method described in any one of E1-E4, wherein the aqueous solvent of the sodium cyanide aqueous solution is water.

[0035] E6. The method described in any one of E1-E5, wherein the decomposition of the aqueous sodium cyanide solution is reduced by more than 50%, more than 70%, more than 90% or more than 95%.

[0036] E7. A method as described in any of E1-E5, wherein decomposition of the aqueous sodium cyanide solution is substantially prevented.

[0037] E8. A method as described in any one of E1-E7, wherein when the aqueous sodium cyanide solution is stored under vacuum, the pressure is lower than atmospheric pressure.

[0038] E9. The method described in any of E1-E8, wherein all or substantially all (e.g., >50%, >60%, >70%, >80%, >90%, >95%, >96%, >97%, >98%, >99%, >99.9%) of the carbon dioxide is removed from the solution.

[0039] E10. The method of any one of E1-E9, wherein the inert gas is bubbled through a subsurface ejector or syringe.

[0040] E11. The method described in E10, wherein the bubbling occurs in an absorption tower, a separation vessel, a sodium cyanide recycle line, or a sodium cyanide product to storage pipeline.

[0041] E12. The method of E10, wherein the bubbling occurs in the storage container, when loading into the transport container, or in the transport container.

[0042] E13. A method as described in any of E1-E12, wherein carbon dioxide is removed from the interface between the solution and the gas.

[0043] E14. A method as described in any of E1-E13, wherein the carbon dioxide is removed using an inert gas blanket or vacuum.

[0044] E15. A method as described in any of E1-E14, wherein sufficient inert gas is used to replace the carbon dioxide-containing gas in the head space or dissolved in the aqueous sodium cyanide solution.

[0045] E16. The method of any of E1-E14, wherein sufficient inert gas is used to reduce the concentration of carbon dioxide in the head space.

[0046] E17. The method described in any one of E1-E16, wherein the obtained aqueous sodium cyanide solution contains an inert gas and is essentially free of carbon dioxide.

[0047] E18. The method described in any one of E1-E16, wherein the obtained aqueous sodium cyanide solution is stored under an inert gas.

[0048] E19. The method described in any one of E1-E16, wherein the obtained aqueous sodium cyanide solution contains an inert gas, is essentially free of carbon dioxide, and is stored under an inert gas.

[0049] E20. The method of any one of E1-E19, wherein an inert gas is bubbled through an aqueous sodium cyanide solution.

[0050] E21. A method for reducing the decomposition of sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide, comprising the following steps:

[0051] Store sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide under inert gas or under vacuum.

[0052] E22. The method described in E21, wherein the inert gas is selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen and mixtures thereof.

[0053] E23. The method of E21 or E22, wherein the sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide contains 25 wt.% to 100 wt.% sodium cyanide.

[0054] E24. The method of any one of E21-E23, wherein the sodium cyanide paste is an aqueous sodium cyanide paste.

[0055] E25. The method of any one of E21-E23, wherein the sodium cyanide slurry is an aqueous sodium cyanide slurry.

[0056] E26. The method described in any one of E24 or E25, wherein the aqueous solvent of the aqueous sodium cyanide paste and the aqueous sodium cyanide slurry is water.

[0057] E27. A method as described in any of E24-E26, wherein carbon dioxide is removed from the aqueous portion by bubbling with an inert gas before forming an aqueous sodium cyanide paste or an aqueous sodium cyanide slurry and before mixing with sodium cyanide.

[0058] E28. A method as described in any one of E21-E27, wherein the decomposition of sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide is reduced by more than 50%, more than 70%, more than 90% or more than 95%.

[0059] E29. A method as described in any of E21-E27, wherein decomposition of sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide is substantially prevented.

[0060] E30. The method described in any one of E21-E29, wherein the sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide is stored under vacuum and the pressure is lower than atmospheric pressure.

[0061] E31. The method described in any of E21-E30, wherein all or substantially all (e.g., >50%, >60%, >70%, >80%, >90%, >95%, >96%, >97%, >98%, >99%, >99.9%) of the carbon dioxide is removed from the sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide.

[0062] E32. A method as described in any of E21-E31, wherein the carbon dioxide is removed using an inert gas blanket or vacuum.

[0063] E33. The method described in any one of E21-E32, wherein the obtained sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide contains an inert gas and is essentially free of carbon dioxide.

[0064] E34. The method described in any one of E21-E32, wherein the obtained sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide is stored under an inert gas.

[0065] E35. The method described in any one of E21-E32, wherein the obtained sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide contains an inert gas, is essentially free of carbon dioxide, and is stored under an inert gas.

[0066] E36. A method for preparing sodium cyanide slurry or sodium cyanide paste in an aqueous system, comprising the following steps:

[0067] Passing an inert gas through an aqueous solvent to remove carbon dioxide,

[0068] combining the sodium cyanide with an aqueous solvent from which carbon dioxide is removed to form an aqueous sodium cyanide slurry or paste, optionally dehydrating the aqueous sodium cyanide slurry or paste to remove water from the slurry or paste, and / or

[0069] The aqueous sodium cyanide slurry or aqueous sodium cyanide paste is stored under inert gas or under vacuum.

[0070] E37. The method of E36, wherein the aqueous solvent is water.

[0071] E38. The method described in E36 or E37, wherein the inert gas is selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen and mixtures thereof.

[0072] E39. The method described in any one of E36-E38, wherein when the aqueous sodium cyanide slurry or the aqueous sodium cyanide paste is stored under vacuum, the pressure is lower than atmospheric pressure.

[0073] E40. The method described in any of E36-E39, wherein all or substantially all (e.g., >50%, >60%, >70%, >80%, >90%, >95%, >96%, >97%, >98%, >99%, >99.9%) carbon dioxide is removed from the aqueous system.

[0074] E41. The method of any one of E36-E40, wherein the inert gas is bubbled through a subsurface ejector or syringe.

[0075] E42. The method of any of E36-E41, wherein carbon dioxide is removed from the interface between the solution and the gas.

[0076] E43. A method as described in any of E36-E42, wherein the carbon dioxide is removed using an inert gas blanket or vacuum.

[0077] E44. The method described in any one of E36-E43, wherein the obtained aqueous sodium cyanide slurry or aqueous sodium cyanide paste contains an inert gas and is essentially free of carbon dioxide.

[0078] E45. The method described in any one of E36-E43, wherein the obtained aqueous sodium cyanide slurry or aqueous sodium cyanide paste is stored under an inert gas.

[0079] E46. The method of any one of E36-E43, wherein the obtained aqueous sodium cyanide slurry or aqueous sodium cyanide paste contains an inert gas, is essentially free of carbon dioxide, and is stored under an inert gas.

[0080] E47. The method of any one of E36-E46, wherein an inert gas is bubbled through an aqueous sodium cyanide solution.

[0081] E48. An aqueous solution of sodium cyanide containing an inert gas and being substantially free of carbon dioxide.

[0082] The aqueous sodium cyanide solution described in E49.E48 is stored under inert gas or under vacuum.

[0083] E50. Aqueous sodium cyanide solution stored under inert gas or under vacuum.

[0084] E51. Sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide stored under inert gas or under vacuum. Example

[0085] Example 1

[0086] In a closed but not completely sealed beaker, nitrogen was bubbled through about 250 mL of a sodium cyanide solution ("Test") for 30 minutes, and then a nitrogen blanket was applied. The solution was then placed under a heat load at or about 100° C. for 24 hours. This was compared to a baseline control solution ("Control"), which had the same heat load applied but without the nitrogen bubbling and blanketing steps.

[0087] As shown in Table 1 below, the results show a 74% reduction in cyanide loss. The initial concentration of the solution was 340 g / L, and the loss in the control sample corresponded to 34%, which was significantly greater than the 9% loss in the test sample.

[0088] Table 1

[0089]

[0090] Example 2: Effect of solution concentration

[0091] In a closed but not sealed system, about 250 mL of a second solution with reduced sodium cyanide concentration ("Low Concentration") was subjected to a similar process as the control, where a heat load was applied for 24 hours at about 100° C. This was compared to a control solution ("Control"), which had the same heat load applied but without the bubbling and covering steps.

[0092] As shown in Table 2 below, the results show equal losses of cyanide in the high concentration (Control) and low concentration (Low Concentration) solutions. It can be concluded that changes in cyanide concentration have little effect on the loss of sodium cyanide during its decomposition.

[0093] Table 2

[0094]

Claims

1. A method for reducing the decomposition of sodium cyanide aqueous solution, comprising the following steps: passing an inert gas through an aqueous sodium cyanide solution to remove carbon dioxide from the solution, and / or Store aqueous sodium cyanide solutions under inert gas or under vacuum.

2. A method for reducing the decomposition of sodium cyanide aqueous solution, comprising the following steps: Store aqueous sodium cyanide solutions under inert gas or under vacuum.

3. The method according to claim 1, wherein the inert gas is selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen and mixtures thereof.

4. The method according to claim 2, wherein the inert gas is selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen and mixtures thereof.

5. The method according to claim 1, wherein the sodium cyanide aqueous solution contains 15 wt.% to 45 wt.% sodium cyanide or the sodium cyanide aqueous solution contains 25 wt.% to 35 wt.% sodium cyanide.

6. The method according to claim 2, wherein the sodium cyanide aqueous solution contains 15 wt.% to 45 wt.% sodium cyanide or the sodium cyanide aqueous solution contains 25 wt.% to 35 wt.% sodium cyanide.

7. The method of claim 1, wherein the decomposition of the aqueous sodium cyanide solution is reduced by more than 90%.

8. The method of claim 2, wherein the decomposition of the aqueous sodium cyanide solution is reduced by more than 90%.

9. The method of claim 1, wherein all or substantially all of the carbon dioxide is removed from the solution.

10. The method of claim 2, wherein all or substantially all of the carbon dioxide is removed from the solution.

11. A method for reducing the decomposition of sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide, comprising the following steps: Store sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide under inert gas or under vacuum.

12. The method of claim 11, wherein the inert gas is selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen, and mixtures thereof.

13. The method of claim 11, wherein the sodium cyanide paste, sodium cyanide slurry or solid sodium cyanide comprises 25 wt.% to 100 wt.% sodium cyanide.

14. The method of claim 11, wherein the decomposition of the aqueous sodium cyanide solution is reduced by more than 90%.

15. A method for preparing sodium cyanide slurry or sodium cyanide paste in an aqueous system, comprising the following steps: Passing an inert gas through an aqueous solvent to remove carbon dioxide, combining the sodium cyanide with an aqueous solvent from which carbon dioxide is removed to form an aqueous sodium cyanide slurry or an aqueous sodium cyanide paste, Optionally dehydrating the aqueous sodium cyanide slurry or aqueous sodium cyanide paste to remove water from the slurry or paste, and / or The aqueous sodium cyanide slurry or aqueous sodium cyanide paste is stored under an inert gas or under a vacuum.

16. The method of claim 15, wherein the inert gas is selected from the group consisting of nitrogen, argon, methane, natural gas, hydrogen, water vapor, helium, ammonia, oxygen, and mixtures thereof.

17. An aqueous solution of sodium cyanide comprising an inert gas and being substantially free of carbon dioxide.

18. The sodium cyanide aqueous solution according to claim 17, which is stored under an inert gas or under vacuum.

19. A sodium cyanide aqueous solution stored under an inert gas or under vacuum.

20. A sodium cyanide paste, sodium cyanide or solid sodium cyanide, wherein the sodium cyanide paste, sodium cyanide or solid sodium cyanide is stored under an inert gas or under vacuum.

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