Method for recovering precious metal from low-concentration waste liquid

Abstract

The invention discloses a microfluid reaction method for efficiently recovering precious metals from low-concentration waste liquid, which adopts sodium sulfide or hydrogen sulfide as a vulcanizing agent, the sodium sulfide or hydrogen sulfide and the low-concentration waste liquid are jointly injected into a microfluid reactor in a microfluid form, and a rapid vulcanization reaction is realized in a micron-sized channel. And the reacted mixture flows into an intermediate tank and is filtered and separated to obtain sulfide concentrate with the noble metal content of 0.5-3.15%, and the recovery rate of the noble metal exceeds 99.5%. The system adopts modular design, parameters such as flow velocity, reaction temperature, pH value and the like can be adjusted according to the characteristics of the waste liquid, the optimal reaction pH range is 2.0-6.0, and the temperature is controlled to be 20-80 DEG C. The method has the advantages of small equipment size, low energy consumption, high automation degree and the like, and is suitable for treating the waste liquid containing gold, silver, platinum, palladium and other precious metals generated in the precious metal smelting and electroplating industry. According to the method, the dosage of the vulcanizing agent can be reduced by 15-20%, the amount of generated waste residues is reduced by 50% or above, and remarkable economic and environmental benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the field of precious metal recovery technology, and in particular to a microfluidic reaction method for efficiently recovering precious metals from low-concentration waste liquid (1-10 mg / L). The method is suitable for treating wastewater containing precious metals such as gold (Au), silver (Ag), platinum (Pt), and palladium (Pd) generated in industries such as precious metal production and electroplating. Background Art

[0002] Precious metals (such as gold, silver, platinum, and palladium) are widely used in industries such as electronics, electroplating, chemicals, and pharmaceuticals due to their excellent physical and chemical properties. However, industrial production processes generate large amounts of wastewater containing precious metals. These wastewaters typically contain low concentrations of precious metals (1-10 mg / L), but direct discharge not only wastes resources but also causes serious environmental pollution. Therefore, efficient recovery of precious metals from low-concentration wastewaters is of great economic and environmental significance.

[0003] Currently, the commonly used precious metal recovery methods in industry mainly include chemical precipitation, ion exchange, adsorption, solvent extraction and electrolysis. However, these methods all have limitations to varying degrees when treating low-concentration wastewater: 1. Chemical precipitation: Chemical precipitation is one of the most traditional methods for precious metal recovery. It usually uses sodium sulfide (Na2S) or hydrogen sulfide (H2S) as a precipitant to precipitate precious metal ions into sulfides. However, this method has the following problems when treating low-concentration wastewater: (1) Low reaction efficiency: Due to the low concentration of precious metals, the precipitation reaction rate is slow, usually taking several hours or even longer to complete, and the precipitation is incomplete, and the recovery rate is usually less than 95%; (2) High reagent consumption: In order to ensure the precipitation effect, it is often necessary to add excessive amounts of sulfiding agents (usually 1.5-2 times the theoretical amount), which increases operating costs and may introduce secondary pollution; (3) Large amount of waste residue: A large amount of sludge containing heavy metals will be generated during the sedimentation process, which is difficult to handle and may cause secondary loss of precious metals.

[0004] 2. Ion exchange method: The ion exchange method uses the selective adsorption characteristics of resin to recover precious metals and is suitable for low-concentration wastewater. However, its disadvantages include: (1) Resin is easily contaminated: impurity ions in the waste liquid (such as Fe³⁺, Cu²⁺, etc.) will compete with precious metals for adsorption sites, reducing the adsorption capacity and life of the resin; (2) High regeneration cost: The resin needs to be regenerated regularly with strong acid or strong base solution, which is not only complicated to operate, but also produces a large amount of acid and alkali wastewater; (3) Slow processing speed: The dynamic adsorption process usually requires a long contact time, making it difficult to achieve continuous and efficient recovery.

[0005] 3. Adsorption method: Adsorption method (such as activated carbon adsorption) is simple to operate, but has the following problems: (1) Poor selectivity: Activated carbon has low adsorption selectivity for precious metals, especially in complex wastewater recovery; (2) Limited adsorption capacity: The adsorption efficiency is low at low concentrations, and after adsorption saturation, high-temperature incineration or chemical desorption is required to recover precious metals, which consumes a lot of energy and easily causes precious metal loss.

[0006] 4. Solvent extraction: Solvent extraction is suitable for high-concentration precious metal solutions, but performs poorly in low-concentration wastewater: (1) Low mass transfer efficiency: At low concentrations, the contact area between the two phases is insufficient, the extraction rate is slow, and multi-stage extraction is required to achieve the ideal recovery rate; (2) Loss of organic phase: The extractant is easily emulsified or dissolved in the aqueous phase, resulting in increased costs and environmental pollution.

[0007] 5. Electrolysis: Electrolysis can directly recover metal elements, but it is only suitable for high-concentration wastewater (>100 mg / L) and has problems such as high energy consumption and electrode passivation.

[0008] In summary, traditional precious metal recovery methods (such as chemical precipitation, ion exchange, and activated carbon adsorption) suffer from low efficiency, long reaction times, high reagent consumption, and large amounts of waste residue when treating low-concentration wastewater. Therefore, a method for recovering precious metals from wastewater with efficient mass transfer, rapid reaction, and low energy consumption is urgently needed. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for enriching and recovering precious metals from low-concentration waste liquid with high mass transfer efficiency, rapid reaction, low energy consumption, and the ability to effectively combine microfluidic reaction and sulfide precipitation technology.

[0010] To achieve the above object, the technical solution adopted by the present invention is: a method for recovering precious metals from low-concentration waste liquid, comprising the following steps: (1) Low-concentration waste liquid containing precious metals and a sulfiding agent are co-injected into a microfluidic reactor in the form of microfluids; (2) Rapid sulfurization reaction occurs within the micron-scale channel to generate precious metal sulfides; (3) The mixture after the reaction flows into the middle tank and is separated by filtration to obtain a sulfide concentrate with a precious metal content of 0.5-2.0%, and a precious metal recovery rate of ≥99.5%; The content of precious metals in the low-concentration waste liquid containing precious metals is 1-10 mg / L, and the sulfiding agent is one of sodium sulfide and hydrogen sulfide.

[0011] Furthermore, the reaction channel size of the microfluidic reactor is 10-500 μm, and the reaction time is ≤30 seconds.

[0012] Furthermore, the amount of the sulfiding agent added is 1.0-1.5 times the molar amount of the noble metal in the waste liquid.

[0013] Furthermore, the optimal pH range of the sulfurization reaction is 2.0-6.0, and the reaction temperature is controlled at 20-80°C.

[0014] Furthermore, the flow rate of the microfluidic reactor is controlled at 0.1-10 mL / min, and the reaction pressure is 0.1-1.0 MPa.

[0015] Furthermore, the precious metal includes one or more of gold (Au), silver (Ag), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), and iridium (Ir).

[0016] Furthermore, the volume of the microfluidic reactor is ≤500 mL, and the energy consumption is reduced by more than 40% compared with the traditional precipitation method.

[0017] The core technology of the present invention is: (1) Using a microfluidic reactor, low-concentration wastewater and sulfiding agent (sodium sulfide or hydrogen sulfide) can be quickly mixed and reacted in a micron-scale channel, greatly improving the mass transfer efficiency; (2) Ensure high efficiency and selectivity of precious metal sulfide precipitation by optimizing reaction parameters (pH 2.0-6.0, temperature 20-80°C, flow rate 0.1-10 mL / min); (3) After the reaction, the mixture flows into the middle tank and is separated into solid and liquid to obtain precious metal sulfide concentrate (precious metal content 0.5-2.0%) with a recovery rate of ≥99.5%; This method utilizes microfluidics technology to significantly enhance the mass transfer process, shortening the sulfidation reaction time to less than 1 / 10 that of traditional methods and increasing reaction efficiency by over 30%. The system utilizes a modular design, allowing parameters such as flow rate, reaction temperature, and pH to be adjusted according to the characteristics of the wastewater. The optimal reaction pH range is 2.0-6.0, and the temperature is controlled between 20-80°C. This method offers advantages such as small equipment size (reactor volume <500mL), low energy consumption (energy consumption reduced by over 40%), and a high degree of automation. It is particularly suitable for treating wastewater containing precious metals such as gold, silver, platinum, and palladium generated in the precious metal smelting and electroplating industries. Compared with traditional precipitation methods, this method can reduce the amount of sulfiding agent used by 15-20% and reduce the amount of waste residue generated by over 50%, offering significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1The present invention is a process flow chart of a method for recovering precious metals from low-concentration waste liquid. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to specific examples: Example

[0020] See the attached figure. The conditions are: gold plating waste liquid from a certain factory, containing an Au concentration of 5 mg / L, pH=3.0, and a flow rate of 2 mL / min; the sulfiding agent is Na2S solution (molar ratio of Au:Na2S=1:1.2); the reaction conditions are a microfluidic reactor (channel size 100μm), a temperature of 50°C, and a reaction time of 20 seconds; the Au recovery rate is 99.72%, and the Au content of the sulfide concentrate is 1.21%. Example

[0021] See the attached figure. The conditions are: a certain silver-plating waste liquid, Ag concentration of 8 mg / L, pH = 4.5, flow rate 5 mL / min; the sulfiding agent is H2S gas (molar ratio Ag:H2S = 1:1.1); the reaction conditions are a microfluidic reactor (channel size 200μm), temperature 30℃, reaction time 15 seconds; Ag recovery rate is 99.64%, and the Ag content of the sulfide concentrate is 1.85%. Example

[0022] See the attached figure. Conditions: treatment of wastewater from a precious metal hydrometallurgical plant, with a Pt concentration of 3 mg / L, a Pd concentration of 2 mg / L, and a Rh concentration of 5 mg / L in the wastewater, pH=2.5, and a flow rate of 6 mL / min; the sulfiding agent is a Na2S solution (molar ratio Pt / Pd / Rh:Na2S=1:3.6); the reaction conditions are a microfluidic reactor (channel size 200 μm), a temperature of 70°C, and a reaction time of 10 seconds; the Pt / Pd / Rh recovery rate is 99.53%, and the Pt / Pd / Rh content of the sulfide concentrate is 1.62%. Example

[0023] See the attached figure. Conditions: treatment of wastewater from a precious metal hydrometallurgical plant, with an Ir concentration of 3 mg / L and a Ru concentration of 6 mg / L in the wastewater, pH=3.5, and a flow rate of 3 mL / min; the sulfiding agent is a Na2S solution (molar ratio Ir / Ru:Na2S=1:2.5); the reaction conditions are a microfluidic reactor (channel size 150 μm), a temperature of 50°C, and a reaction time of 15 seconds; the Ir / Ru recovery rate is 99.53%, and the Ir / Ru content of the sulfide concentrate is 1.91%. Example

[0024] See the attached figure. Conditions: treatment of wastewater from a precious metal hydrometallurgical smelter, with a Pd concentration of 4 mg / L, a Rh concentration of 1 mg / L, a Pt concentration of 2 mg / L, a Ir concentration of 3 mg / L, and a Ru concentration of 5 mg / L in the wastewater, pH=4.0, and a flow rate of 5 mL / min; the sulfiding agent is an H2S solution (molar ratio Pd / Rh / Pt / Ir / Ru:H2S=1:5.6); the reaction conditions are a microfluidic reactor (channel size 300 μm), a temperature of 60°C, and a reaction time of 30 seconds; the Pd / Rh / Pt / Ir / Ru recovery rate is 99.52%, and the Pd / Rh / Pt / Ir / Ru content in the sulfide concentrate is 3.15%.

Claims

1. A method for recovering precious metals from low-concentration waste liquid, characterized in that: The following steps are involved: (1) Low-concentration waste liquid containing precious metals and a sulfiding agent are co-injected into a microfluidic reactor in the form of microfluids; (2) Rapid sulfurization reaction occurs within the micron-scale channel to generate precious metal sulfides; (3) The mixture after the reaction flows into the middle tank and is separated by filtration to obtain a sulfide concentrate with a precious metal content of 0.5-2.0%, and a precious metal recovery rate of ≥99.5%; Wherein, the content of precious metals in the low-concentration waste liquid containing precious metals in step (1) is 1-10 mg / L, and the sulfiding agent is one of sodium sulfide or hydrogen sulfide.

2. The method for recovering precious metals from low-concentration waste liquid according to claim 1, wherein: The reaction channel size of the microfluidic reactor is 10-500 μm, and the reaction time is ≤30 seconds.

3. The method for recovering precious metals from low-concentration waste liquid according to claim 1, characterized in that: The amount of the sulfiding agent added is 1.0-1.5 times the molar amount of the noble metal in the waste liquid.

4. The method for recovering precious metals from low-concentration waste liquid according to claim 1, wherein: The optimal pH range of the sulfurization reaction is 2.0-6.0, and the reaction temperature is controlled at 20-80°C.

5. The method for recovering precious metals from low-concentration waste liquid according to claim 1, characterized in that: The flow rate of the microfluidic reactor is controlled at 0.1-10 mL / min, and the reaction pressure is 0.1-1.0 MPa.

6. The method for recovering precious metals from low-concentration waste liquid according to claim 1, characterized in that: The precious metal includes one or more of gold (Au), silver (Ag), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), and iridium (Ir).

7. The method for recovering precious metals from low-concentration waste liquid according to claim 1, characterized in that: The volume of the microfluidic reactor is ≤500 mL, and the energy consumption is reduced by more than 40% compared with the traditional precipitation method.

Images