A process for the recovery and resource utilization of wastewater and waste gas generated during silver powder production.

Abstract

This invention discloses a process for the recovery and resource utilization of wastewater and waste gas generated during silver powder production. It effectively recovers and treats four types of wastewater generated during silver powder production: organic-free ammonium nitrate wastewater, organic-free sodium nitrate wastewater, sodium nitrate wastewater containing organic matter, and ammonium nitrate wastewater containing both organic matter and sodium nitrate. The invention effectively recovers and treats all four main types of wastewater and two types of waste gas generated during silver powder production, converting them all into the necessary production materials such as ammonia, concentrated nitric acid, dilute nitric acid, and sodium hydroxide, thus achieving complete recovery and utilization of all wastewater and waste gas.

Description

Technical Field

[0001] This invention relates to the field of wastewater and waste gas treatment technology in silver powder production, specifically a process for the recovery and resource utilization of wastewater and waste gas generated during silver powder production. Background Technology

[0002] There are many methods for producing silver powder, but they mainly involve two steps. The first step is to react silver ingots with concentrated nitric acid to produce silver nitrate and nitrogen oxides. The second step involves using ammonia water and different reducing agents and additives to produce silver powder with different crystal forms and particle sizes. This process generates inorganic ammonium nitrate wastewater and ammonium nitrate and sodium nitrate wastewater containing organic matter. Due to the different reducing agents and additives used, the resulting wastewater and waste gas vary, but they can generally be categorized as follows: gaseous nitrogen oxides, ammonia, ammonium nitrate wastewater, and sodium nitrate and ammonium nitrate wastewater containing organic matter. A treatment method is needed to address these wastewater and waste gas emissions.

[0003] Therefore, a process for the recovery and resource utilization of wastewater and waste gas generated during silver powder production is proposed to address the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a process for the recovery and resource utilization of wastewater and waste gas generated during silver powder production. This process effectively recovers and treats four types of wastewater generated during silver powder production: ammonium nitrate wastewater (free of organic matter), sodium nitrate wastewater (free of organic matter), sodium nitrate wastewater (containing organic matter), and ammonium nitrate wastewater (containing both organic matter and sodium nitrate), as well as two types of waste gas: waste ammonia and waste nitrogen oxides. The wastewater and waste gas are converted into raw materials needed for silver powder production: high-concentration ammonia water, high-concentration nitric acid, and high-concentration sodium hydroxide. While removing pollution from the wastewater and waste gas, the process also achieves complete resource utilization of the wastewater and waste gas. Simultaneously, the wastewater is also recycled into pure water for resource utilization. The specific operation steps are as follows:

[0005] Step 1: Under alkaline conditions, ammonia water and sodium nitrate solution are prepared from ammonium nitrate wastewater containing no organic matter by ammonia stripping. The residual ammonia nitrogen in the sodium nitrate solution is completely removed by a hydrophobic membrane. The prepared sodium nitrate solution is then converted into low-concentration sodium hydroxide and nitric acid by bipolar membrane electrodialysis. The prepared ammonia water and low-concentration sodium hydroxide and nitric acid are then recovered and utilized as resources.

[0006] Step 2: The sodium nitrate solution in the organic-free sodium nitrate wastewater is concentrated. The prepared sodium nitrate solution is then converted into low-concentration sodium hydroxide and nitric acid by bipolar membrane electrodialysis. The low-concentration sodium hydroxide and nitric acid are then recovered and utilized as resources. The remaining ultra-low concentration sodium nitrate solution is concentrated and refluxed through reverse osmosis.

[0007] Step 3: The organic matter in the wastewater containing sodium nitrate and ammonium nitrate is removed by catalytic oxidation, and ammonia nitrogen is removed by passing through a hydrophobic membrane under alkaline conditions. During the ammonia nitrogen removal process, dilute nitric acid is added to the absorption side to obtain ammonium nitrate solution and sodium nitrate solution. The obtained ammonium nitrate solution is then recycled and utilized in Step 1 above. The obtained sodium nitrate solution is processed in Steps 1 and 2 to extract sodium hydroxide, and nitric acid is recovered and utilized.

[0008] Step 4: The waste ammonia gas produced is absorbed by pure water under negative pressure to obtain ammonia water for reuse in production;

[0009] Step 5: The waste nitrogen oxide gas produced is oxidized and absorbed by pure water to produce low-concentration nitric acid for reuse in production.

[0010] Specifically, the alkaline conditions in steps one and three refer to the conditions where sodium hydroxide is present and pH > 11.

[0011] Specifically, the ammonia water with a concentration >20% prepared in steps one and four is recycled for production.

[0012] Specifically, the low-concentration sodium nitrate from steps one, two, and three is concentrated into a sodium nitrate solution via reverse osmosis and reused in the bipolar membrane electrodialysis step of the sodium nitrate solution from steps one and two. The low-concentration sodium hydroxide with a concentration of 7% is concentrated into a high-concentration sodium hydroxide with a concentration greater than 20% and reused in production. The low-concentration nitric acid with a concentration of 7% is concentrated and refined into a high-concentration nitric acid with a concentration of 65% and reused in production. A small amount of sodium nitrate is reused in the bipolar membrane electrodialysis step of the sodium nitrate solution from steps one and two. The pure water produced by reverse osmosis is reused in production.

[0013] Specifically, the catalytic oxidation process of wastewater containing organic matter sodium nitrate and ammonium nitrate in step three, as well as the oxidation of waste nitrogen oxides and pure water absorption process in step five, all require the use of an ozone generator to provide high-concentration ozone as an oxidant.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. This invention effectively recovers and treats four main types of wastewater generated during silver powder production: wastewater containing no organic matter (ammonium nitrate), wastewater containing no organic matter (sodium nitrate), wastewater containing organic matter (sodium nitrate), and wastewater containing organic matter (sodium nitrate and ammonium nitrate), as well as two types of waste gas (ammonia and nitrogen oxides). All of these wastewater and waste gas are converted into raw materials such as ammonia, concentrated nitric acid, dilute nitric acid, and sodium hydroxide, which are required for silver powder production. This ensures that all wastewater and waste gas are fully recovered and utilized as resources.

[0016] 2. No ions or organic matter other than nitric acid, sodium hydroxide, ozone, and pure water are added in the process of this invention. This ensures that the final product of this invention is completely free of other impurities and that the product can be completely and recycled in production with high quality.

[0017] 3. This invention separates the treatment of wastewater without organic matter and wastewater containing organic matter generated during the silver powder production process, avoiding cross-contamination between different water quality treatment processes and reducing investment and operating costs.

[0018] 4. This invention transforms silver powder production from a heavily polluting process into a green one, generating no wastewater, waste gas, or solid waste. The raw material for silver powder production is silver ingots, and the product is silver powder. The use of other auxiliary raw materials such as ammonia, nitric acid, sodium hydroxide, and pure water is completely closed-loop, reducing the procurement of auxiliary raw materials to almost zero. This avoids the environmental impact of wastewater, waste gas, and solid waste generated by the original production process, greatly reduces the transportation risks of hazardous chemicals, and generates significant social benefits.

[0019] 5. In addition to its application in the electronics field, silver powder is also widely used in the solar energy industry, which is of great practical significance for the solar energy industry to replace imported silver powder and promote the development of the solar energy industry. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0021] As attached Figure 1 As shown, this invention provides a process for the recovery and resource utilization of wastewater and waste gas generated during silver powder production. This process effectively recovers and utilizes four types of wastewater generated during silver powder production: organic-free ammonium nitrate wastewater, organic-free sodium nitrate wastewater, sodium nitrate wastewater containing organic matter, and organic-containing sodium nitrate and ammonium nitrate wastewater, as well as two types of waste gas: waste ammonia and waste nitrogen oxides. The specific operation steps are as follows:

[0022] Step 1: Under alkaline conditions, ammonia water and sodium nitrate solution are prepared from organic-free ammonium nitrate wastewater by ammonia stripping. Residual ammonia nitrogen in the sodium nitrate solution is completely removed through a hydrophobic membrane. The prepared ammonia water is recycled for production. The prepared sodium nitrate solution is converted into low-concentration sodium hydroxide and nitric acid by bipolar membrane electrodialysis. The residual low-concentration sodium nitrate (1%) is concentrated into a 10% sodium nitrate solution by reverse osmosis and reused in the sodium nitrate solution bipolar membrane electrodialysis step. The 7% sodium hydroxide is concentrated into a 20% sodium hydroxide solution and reused in production. The 7% low-concentration nitric acid is concentrated and purified into a 65% high-concentration nitric acid solution and reused in production. A small amount of sodium nitrate is reused in the sodium nitrate solution electrodialysis step. The pure water produced by reverse osmosis is reused in production.

[0023] Step 2: Concentrate the sodium nitrate solution from the organic-free sodium nitrate wastewater. The prepared sodium nitrate solution is then converted into low-concentration sodium hydroxide and nitric acid via bipolar membrane electrodialysis. The residual 1% ultra-low concentration sodium nitrate is concentrated into a 10% sodium nitrate solution via reverse osmosis and reused in the sodium nitrate solution bipolar membrane electrodialysis step. The 7% low concentration sodium hydroxide is concentrated into a 20% high concentration sodium hydroxide solution and reused in production. The 7% low concentration nitric acid is concentrated and refined into a 65% high concentration nitric acid solution and reused in production. A small amount of sodium nitrate is reused in the sodium nitrate solution electrodialysis step. The pure water produced by reverse osmosis is reused in production.

[0024] Step 3: The wastewater containing organic matter such as sodium nitrate and ammonium nitrate is subjected to catalytic oxidation to remove organic matter. Taking vitamin C as an example, but not limited to vitamin C, it also includes other organic matter and organic additives used for reduction. The reaction formula is as follows:

[0025] C6H8O6 + O3 → CO2 + H2O

[0026] Sodium hydroxide is added to the wastewater to remove organic matter, and ammonia nitrogen is removed through a hydrophobic membrane under alkaline conditions. Dilute nitric acid is added during the ammonia nitrogen removal process to obtain ammonium nitrate solution and sodium nitrate solution. The obtained ammonium nitrate solution is mixed with organic-free ammonium nitrate wastewater and fed into the ammonia stripping step to produce ammonia water for reuse in production. The obtained sodium nitrate solution is then subjected to bipolar membrane electrodialysis to produce low-concentration sodium hydroxide and nitric acid. The residual ultra-low concentration sodium nitrate is concentrated into a sodium nitrate solution via reverse osmosis and reused in the sodium nitrate solution bipolar membrane electrodialysis step. The material reaction formula is:

[0027] NaNO3 (high concentration) → HNO3 (7%) + NaOH (7%) + NaNO3 (trace amount)

[0028] A 7% low-concentration sodium hydroxide solution is concentrated to a 20% high-concentration sodium hydroxide solution for reuse in production. A 7% low-concentration nitric acid solution is concentrated and refined to a 65% high-concentration nitric acid solution for reuse in production. A small amount of sodium nitrate is reused in the sodium nitrate solution electrodialysis step. The material reaction formula is:

[0029] HNO3 (7%) + NaNO3 (trace amount) → HNO3 (65%) + NaNO3 (20%) + H2O (condensate reuse)

[0030] Step 4: The waste ammonia gas produced is absorbed by pure water under negative pressure to obtain ammonia water, and the prepared ammonia water is recycled for use in production;

[0031] Step 5: The generated waste nitrogen oxide gas is oxidized and absorbed by pure water to produce low-concentration nitric acid for reuse in production. The material reaction formula is as follows:

[0032] NO + O3 + H2O → HNO3

[0033] Specifically, the catalytic oxidation process of wastewater containing organic sodium nitrate and ammonium nitrate in step three, as well as the oxidation of waste nitrogen oxide gas and pure water absorption process in step five, all require the use of an ozone generator to provide high-concentration ozone as an oxidant. Using ozone as an oxidant eliminates the need to add other impurities.

[0034] The main feature of this invention is that, apart from using ozone, NaOH, and HNO3, no other substances are added, which ensures the purity of the high-concentration NaOH and HNO3 substances reused by the system. Since no impurities are added, the long-term stable and continuous operation of this process can be guaranteed.

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

Claims

1. A process for the recovery and resource utilization of wastewater and waste gas generated during silver powder production, characterized in that: Effective recovery and resource utilization were achieved for four types of wastewater generated during silver powder production: organic-free ammonium nitrate wastewater, organic-free sodium nitrate wastewater, sodium nitrate wastewater containing organic matter, and organic-containing sodium nitrate and ammonium nitrate wastewater, as well as two types of waste gas: waste ammonia and waste nitrogen oxides. The specific operational steps are as follows: Step 1: Under alkaline conditions, ammonia water and sodium nitrate solution are prepared from organic-free ammonium nitrate wastewater by ammonia stripping. Residual ammonia nitrogen in the sodium nitrate solution is completely removed through a hydrophobic membrane. The prepared sodium nitrate solution is then converted into low-concentration sodium hydroxide and nitric acid by bipolar membrane electrodialysis. The prepared ammonia water and low-concentration sodium hydroxide and nitric acid are recovered and utilized as resources. The remaining ultra-low concentration sodium nitrate solution is concentrated and refluxed through reverse osmosis. Step 2: Extract the sodium nitrate solution from the organic-free sodium nitrate wastewater. The prepared sodium nitrate solution is then converted into low-concentration sodium hydroxide and nitric acid by bipolar membrane electrodialysis. The low-concentration sodium hydroxide and nitric acid are then recovered and utilized as resources. The remaining low-concentration sodium nitrate solution is concentrated and refluxed through reverse osmosis. Step 3: The organic matter in the wastewater containing sodium nitrate and ammonium nitrate is removed by catalytic oxidation, and ammonia nitrogen is removed by passing through a hydrophobic membrane under alkaline conditions. During the ammonia nitrogen removal process, dilute nitric acid is added to the absorption side to obtain ammonium nitrate solution and sodium nitrate solution. The obtained ammonium nitrate solution is then recycled and utilized in Step 1 above. The obtained sodium nitrate solution is processed in Steps 1 and 2 to extract sodium hydroxide, and nitric acid is recovered and utilized. Step 4: The produced waste ammonia gas is absorbed by pure water under negative pressure to obtain ammonia water; Step 5: The generated waste nitrogen oxide gas is oxidized by ozone and absorbed by pure water to produce low-concentration nitric acid for resource recovery and reuse in production; The low-concentration sodium nitrate from steps one, two, and three is concentrated into a high-concentration sodium nitrate solution via reverse osmosis and reused in the bipolar membrane electrodialysis step of the sodium nitrate solution from steps one and two. The low-concentration sodium hydroxide is concentrated into a high-concentration sodium hydroxide solution and reused in production. The low-concentration nitric acid is concentrated and refined into a high-concentration nitric acid solution and reused in production. A small amount of sodium nitrate is reused in the bipolar membrane electrodialysis step of the sodium nitrate solution from steps one and two.

2. The process for wastewater and waste gas recovery and resource utilization generated during silver powder production according to claim 1, characterized in that: The alkaline conditions in steps one and three refer to the complete removal of residual ammonia nitrogen from the sodium nitrate solution through a hydrophobic membrane in the presence of sodium hydroxide.

3. The process for wastewater and waste gas recovery and resource utilization generated during silver powder production according to claim 1, characterized in that: The ammonia water prepared in steps one and four is recycled and reused in production.

4. The process for wastewater and waste gas recovery and resource utilization generated during silver powder production according to claim 1, characterized in that: In step three, the catalytic oxidation process to remove organic matter from wastewater containing organic matter such as sodium nitrate and ammonium nitrate, as well as the oxidation of waste nitrogen oxides and the absorption of pure water in step five, all require the use of an ozone generator to provide ozone as an oxidant.

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