Membrane treatment process for arsenic-containing wastewater of mine

Abstract

The invention provides a mine arsenic-containing wastewater membrane treatment process, which belongs to the technical field of wastewater treatment, and comprises the following steps: 1, removing heavy metal ions in wastewater; step 2, carrying out dynamic electric flocculation treatment on the wastewater; step 3, separating the pre-treated wastewater by an electric field cooperating with a three-stage membrane to obtain concentrated water; and 4, carrying out resourceful treatment on the concentrated water. According to the method, heavy metal ions are removed in the early stage, then floating objects, oil dirt and the like are removed through dynamic electric flocculation, blocking of follow-up membrane treatment is avoided, efficient and rapid arsenic absorption is achieved through follow-up three-stage membrane treatment, drained water meets related standard requirements, high-toxicity wastewater is converted into safe building materials, and waste is turned into wealth.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly to a membrane treatment process for arsenic-containing wastewater in mines. Background Art

[0002] Arsenic is a highly toxic non-metallic element, which widely exists in industrial wastewaters such as non-ferrous metallurgy, iron and steel, chemical fertilizer, and sulfuric acid industries, and is recognized as a class I carcinogen. With the continuous development of industries such as metallurgy, chemical engineering, and materials, and the increasing expansion of the arsenic-containing product market, the discharge and pollution problems of arsenic-containing wastewater will affect the ecological balance of the human living environment and endanger human health. Currently, the main methods for removing arsenic from arsenic-containing wastewater are chemical precipitation (neutralization, sulfidation) methods, electrochemistry methods, biological methods, and adsorption methods.

[0003] The chemical precipitation method has a simple process, low investment, convenient operation, and can treat wastewater with a high arsenic content. It is the first choice for enterprises to remove arsenic from wastewater at present. However, a large amount of chemical reagents need to be added during the precipitation treatment process, and the sludge and waste residues generated are prone to cause secondary pollution if stored for a long time. Moreover, the treatment needs to be handed over to qualified enterprises, resulting in a relatively high treatment cost. The electrochemistry method is an efficient, simple, safe, and high-quality method for treating arsenic-containing wastewater, but the energy consumption caused by the treatment is relatively large. Therefore, it is necessary to design a faster arsenic wastewater membrane treatment process that will not cause secondary pollution. Summary of the Invention

[0004] The purpose of the present invention is to provide a membrane treatment process for arsenic-containing wastewater in mines, so as to solve the technical problems of low efficiency and easy secondary pollution in the existing arsenic wastewater treatment processes.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A membrane treatment process for arsenic-containing wastewater in mines, the process comprising the following steps:

[0007] Step 1: First remove heavy metal ions in the wastewater;

[0008] Step 2: Perform dynamic electrocoagulation treatment on the wastewater;

[0009] Step 3: Separate and treat the pretreated wastewater by an electric field cooperating with a three-stage membrane to obtain concentrated water;

[0010] Step 4: Perform resource treatment on the concentrated water.

[0011] Further, the specific process of Step 1 is: First sprinkle lime or sodium hydroxide solution into the wastewater, stir evenly, adjust the pH to 8-9, and remove Cu 2+ , Pb 2+ , Zn 2+Ions are then added, and sulfuric acid is used to adjust the pH to neutral to remove calcium ions, obtaining the mine wastewater with ions removed.

[0012] Further, the specific process of step 2 is as follows: Fe⁺ is released by electrolyzing an iron electrode, and Fe⁺ is anodized to Fe³⁺ at the anode, generating ferric hydroxide colloid. The suspended solids and colloids in the wastewater are removed through adsorption and bridging effects. The electrode reaction produces strongly oxidizing hydroxyl radicals to remove the oil stains flowing into the wastewater due to machinery. Finally, magnetic nanoparticles are added to combine with the coagulation products to form magnetic flocs, and the sludge is separated by a magnetic field. 2 + 2 + 3 +

[0013] Further, in step 3: The three - stage membrane includes a primary electric - field - assisted nanofiltration membrane, a secondary reverse - osmosis membrane, and a tertiary forward - osmosis membrane. The waste liquid passes through the primary electric - field - assisted nanofiltration membrane, the secondary reverse - osmosis membrane, and the tertiary forward - osmosis membrane in sequence. The primary electric - field - assisted nanofiltration membrane is used to intercept As(V). The secondary reverse - osmosis membrane is used for deep desalination and intercepting residual arsenic. The tertiary forward - osmosis membrane uses a seawater - desalination - grade FO membrane to concentrate the concentrated water to TDS≥30,000 mg / L by combining with a draw solution for subsequent resource utilization.

[0014] Further, in the primary electric - field - assisted nanofiltration membrane, the operating pressure is 8 - 12 bar. By applying an electric field, the interception efficiency of the membrane for charged substances is enhanced. As(V) exists in the form of arsenate and is negatively charged. The charged - characteristic surface of the nanofiltration membrane is positively charged, and the negatively charged pollutants are intercepted through electrostatic repulsion.

[0015] Further, for the secondary reverse - osmosis membrane, the operating pressure is 20 - 30 bar, intercepting impurities such as dissolved salts, organic substances, and heavy metals. The secondary reverse - osmosis membrane has an interception rate of Na⁺, Cl⁻, and SO₄²⁻>95%, reducing the total dissolved solids of the produced water, and intercepting pentavalent arsenic through charge repulsion. An ultraviolet lamp is set to irradiate the wastewater, and while irradiating, the wastewater is stirred. The wastewater is oxidized by the ultraviolet lamp to oxidize As(III) to pentavalent arsenic, which is then intercepted by the secondary reverse - osmosis membrane. The produced water meets the discharge standard of 《GB 25467 - 2010》, with As≤0.05 mg / L. + 、Cl - 、SO4 2-

[0016] Further, the tertiary forward - osmosis membrane selects a seawater - desalination - grade FO membrane, selectively intercepting solutes and allowing water molecules to pass through the membrane into the draw - solution side. Driven by the high osmotic pressure of the NaCl draw solution, the NaCl solution generates an osmotic pressure difference through high concentration, pushing the water in the concentrated water to migrate to the draw - solution side. The concentration target of the concentrated water is TDS≥30,000 mg / L.

[0017] ​Further, in step 4, spray drying is carried out for dehydration and preliminary solid-liquid separation. The concentrated water forms droplets through an atomizing nozzle and quickly evaporates water in hot air at 150-300 °C to obtain a dry arsenic-containing solid residue powder. The residue powder is mixed with diatomite for adsorption and carrier fixation. The specific surface area of diatomite reaches 20-50 m 2 / g, containing 80%-90% SiO2, having adsorption and chemical inertness. Finally, it is calcined at a high temperature of 1000 °C. The amorphous SiO2 in diatomite is transformed into crystalline cristobalite at high temperature. AsO4 3- reacts with SiO2 to form arsenic silicate, or combines with Al2O3 in diatomite to form aluminum arsenate. The densification of the diatomite lattice and the mineral encapsulation of arsenic form a dual stable mechanism of physical barrier and chemical bonding.

[0018] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0019] In the present invention, heavy metal ions are removed in the early stage, and then floating substances and oil dirt are removed by dynamic electrocoagulation to avoid obstruction of subsequent membrane treatment. Subsequently, through three-stage membrane treatment, high-efficiency and rapid absorption of arsenic is achieved, the drainage meets the relevant standard requirements, and the highly toxic wastewater is transformed into safe building materials, realizing the transformation of waste into treasure. Description of the Drawings

[0020] Figure 1 is the process flow chart of the present invention. Detailed Embodiments

[0021] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following preferred embodiments are cited with reference to the accompanying drawings to further elaborate on the present invention in detail. However, it should be noted that many details listed in the specification are only for enabling the reader to have a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be realized even without these specific details.

[0022] As Figure 1 shown, a membrane treatment process for mine arsenic-containing wastewater, the process includes the following steps:

[0023] Step 1: First, remove heavy metal ions in the wastewater. First, lime is sprinkled into the wastewater and stirred evenly, and the pH is adjusted to 8-9 to remove Cu 2+ , Pb 2+ , Zn 2+ ions, and then sulfuric acid is added to adjust the pH to neutral to remove calcium ions, obtaining mine wastewater after removing ions.

[0024] Step 2: Carry out dynamic electrocoagulation treatment on the wastewater. By electrolyzing the iron electrode, Fe 2 + is released, and Fe 2 + is anodized to Fe3 +, ferric hydroxide colloid is generated, and suspended solids and colloids in the wastewater are removed through adsorption and bridging effects. Hydroxyl radicals with strong oxidizing properties are generated by the electrode reaction to remove the oil pollution flowing into the wastewater due to the machine. Finally, magnetic nanoparticles are added to combine with the coagulation product to form magnetic flocs, and the sludge is separated by a magnetic field.

[0025] Step 3: The pretreated wastewater is separated and treated by an electric field in cooperation with a three-stage membrane to obtain concentrated water. It is a separation technology that uses high pressure to drive water molecules through a semi-permeable membrane to intercept impurities such as dissolved salts, organic substances, and heavy metals. As a secondary treatment (advanced treatment), its core lies in further removing pollutants that were not completely removed in the primary treatment.

[0026] The three-stage membrane includes a primary electric field-assisted nanofiltration membrane, a secondary reverse osmosis membrane, and a tertiary forward osmosis membrane. The waste liquid passes through the primary electric field-assisted nanofiltration membrane, the secondary reverse osmosis membrane, and the tertiary forward osmosis membrane in sequence. The primary electric field-assisted nanofiltration membrane is used to intercept As(V), the secondary reverse osmosis membrane is used for deep desalination and intercepting residual arsenic, and the tertiary forward osmosis membrane uses a seawater desalination-grade FO membrane to concentrate the concentrated water to TDS≥30,000 mg / L by combining with the draw solution for subsequent resource utilization.

[0027] The operating pressure in the primary electric field-assisted nanofiltration membrane is 8-12 bar. By applying an electric field, the retention efficiency of the membrane for charged substances is enhanced. As(V) exists in the form of arsenate and is negatively charged. The charged characteristic surface of the nanofiltration membrane is positively charged, and negatively charged pollutants are intercepted through electrostatic repulsion.

[0028] The operating pressure of the secondary reverse osmosis membrane is 20-30 bar, which intercepts impurities such as dissolved salts, organic substances, and heavy metals. The secondary reverse osmosis membrane has a retention rate of >95% for Na + , Cl - , SO4 2- , reduces the total dissolved solids of the produced water, and intercepts pentavalent arsenic through charge repulsion. An ultraviolet lamp is set to irradiate the wastewater, and while irradiating, the wastewater is stirred. The wastewater is oxidized by the ultraviolet lamp to oxidize As(III) to pentavalent arsenic, and then it is intercepted by the secondary reverse osmosis membrane. The produced water meets the discharge standard of 《GB25467-2010》, with As≤0.05 mg / L.

[0029] The tertiary forward osmosis membrane selects a seawater desalination-grade FO membrane, selectively intercepts solutes, allows water molecules to pass through the membrane and enter the draw solution side. Driven by the high osmotic pressure of the NaCl draw solution, the NaCl solution generates an osmotic pressure difference through high concentration, pushing the water in the concentrated water to migrate to the draw solution side, and the target for concentrating the concentrated water is TDS≥30,000 mg / L.

[0030] Step 4: Resource treatment of the concentrated water. Spray drying is carried out for dehydration and preliminary solid-liquid separation. The concentrated water forms droplets through an atomizing nozzle and quickly evaporates water in hot air at 150 - 300 °C to obtain a dry arsenic-containing solid residue powder. The residue powder is mixed with diatomite for adsorption and carrier fixation. The specific surface area of diatomite reaches 20 - 50 m 2 / g, containing 80% - 90% SiO2, having adsorption and chemical inertness. Finally, it is calcined at 1000 °C. The amorphous SiO2 in diatomite is transformed into crystalline cristobalite at high temperature. AsO4 3- reacts with SiO2 to form arsenic silicate, or combines with Al2O3 in diatomite to form aluminum arsenate. The densification of the diatomite lattice and the mineral encapsulation of arsenic form a dual stable mechanism of physical barrier and chemical bonding.

[0031] Building materials raw materials: The calcined product incorporated with diatomite can be used to produce bricks, ceramics, and concrete aggregates. Adsorption materials: The calcined diatomite-arsenic composite can be made into an adsorbent for sewage treatment (such as phosphorus removal and heavy metal removal). The compressive strength ≥ 10 MPa (the standard for ordinary building bricks is MU10), and the arsenic leaching amount is lower than the national standard limit (GB 30760-2014 stipulates that the arsenic leaching amount in building materials ≤ 2.0 mg / L).

[0032] Matters not covered in this invention are well-known technologies.

[0033] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A membrane treatment process for arsenic-containing wastewater in mines, characterized in that: The process includes the following steps: Step 1: Remove heavy metal ions in the wastewater first; Step 2: Conduct dynamic electrocoagulation treatment on the wastewater; Step 3: Separate and treat the pretreated wastewater by the electric field in cooperation with a three-stage membrane to obtain concentrated water; Step 4: Conduct resource treatment on the concentrated water.

2. The membrane treatment process for arsenic-containing wastewater in mines according to claim 1, characterized in that: The specific process of Step 1 is as follows: First, lime or sodium hydroxide solution is added to the wastewater and stirred evenly. The pH is adjusted to 8-9 to remove Cu 2 + , Pb 2+ , Zn 2+ ions. Then, sulfuric acid is added to adjust the pH to neutral to remove calcium ions, and the mine wastewater after ion removal is obtained.

3. A membrane treatment process for arsenic-containing wastewater in mines according to claim 1, characterized in that: The specific process of Step 2 is as follows: Fe is released by electrolyzing an iron electrode 2 +, and Fe 2 + is anodized to Fe 3 +, generating ferric hydroxide colloid, which removes suspended solids and colloids in the wastewater through adsorption and bridging actions. Hydroxyl radicals with strong oxidizing properties generated by the electrode reaction remove the oil pollution flowing into the wastewater due to machinery. Finally, magnetic nanoparticles are added to combine with the coagulation products to form magnetic flocs, and the sludge is separated by a magnetic field.

4. A membrane treatment process for arsenic-containing wastewater in mines according to claim 1, characterized in that: In Step 3: The three-stage membrane includes a first-stage electric-field-assisted nanofiltration membrane, a second-stage reverse osmosis membrane, and a third-stage forward osmosis membrane. The waste liquid passes through the first-stage electric-field-assisted nanofiltration membrane, the second-stage reverse osmosis membrane, and the third-stage forward osmosis membrane once. The first-stage electric-field-assisted nanofiltration membrane is used to intercept As(V), the second-stage reverse osmosis membrane is used for deep desalination and intercepting residual arsenic, and the third-stage forward osmosis membrane uses a seawater desalination-grade FO membrane, combines with the draw solution to concentrate the concentrated water to TDS≥30,000 mg / L for subsequent resource treatment.

5. A membrane treatment process for arsenic-containing wastewater in mines according to claim 4, characterized in that: In the first-stage electric-field-assisted nanofiltration membrane, the operating pressure is 8-12 bar. By applying an electric field, the interception efficiency of the membrane for charged substances is enhanced. As(V) exists in the form of arsenate and is negatively charged. The charged characteristic surface of the nanofiltration membrane is positively charged, and negatively charged pollutants are intercepted through electrostatic repulsion.

6. The membrane treatment process for arsenic-containing wastewater in mines according to claim 4, characterized in that: The operating pressure of the second-stage reverse osmosis membrane is 20 - 30 bar, which intercepts impurities such as dissolved salts, organic matters, and heavy metals. The second-stage reverse osmosis membrane has a rejection rate of >95% for ionic salts such as Na + , Cl - , SO4 2- , reduces the total dissolved solids of the produced water, and intercepts pentavalent arsenic through charge repulsion. An ultraviolet lamp is set to irradiate the wastewater, and during the irradiation process, stirring is carried out simultaneously. The wastewater is oxidized by the ultraviolet lamp to oxidize As(III) to pentavalent arsenic, and then it is intercepted by the second-stage reverse osmosis membrane. The produced water meets the discharge standard of 《GB 25467-2010》, with As ≤ 0.05 mg / L.

7. A membrane treatment process for arsenic-containing wastewater in mines according to claim 4, characterized in that: The third-stage forward osmosis membrane selects a seawater desalination-grade FO membrane, selectively intercepts solutes, allows water molecules to pass through the membrane and enter the draw solution side. Driven by the high osmotic pressure of the NaCl draw solution, the NaCl solution generates an osmotic pressure difference through high concentration, promotes the migration of water in the concentrated water to the draw solution side, and the concentration target of the concentrated water is TDS≥30,000 mg / L.

8. A membrane treatment process for arsenic-containing wastewater in mines according to claim 4, characterized in that: In step 4, spray drying is carried out for dehydration and preliminary solid-liquid separation. The concentrated water forms droplets through an atomizing nozzle and quickly evaporates water in hot air at 150-300 °C to obtain a dry arsenic-containing solid residue powder. The residue powder is mixed with diatomite for adsorption and carrier fixation. The specific surface area of diatomite reaches 20-50 m 2 / g, containing 80%-90% SiO2, having adsorption and chemical inertness. Finally, it is calcined at a high temperature of 1000 °C. The amorphous SiO2 in diatomite is transformed into crystalline cristobalite at high temperature. AsO4 3- reacts with SiO2 to form arsenic silicate, or combines with Al2O3 in diatomite to form aluminum arsenate. The densification of the diatomite lattice and the mineral encapsulation of arsenic form a dual stable mechanism of physical barrier and chemical bonding.

Images