Method for treating complex arsenic-containing and sulfur-containing industrial acidic wastewater

Abstract

The invention relates to a method for treating complex industrial acid wastewater containing arsenic and sulfur, and belongs to the field of environmental protection. The invention relates to a method for treating complex arsenic-containing and sulfur-containing industrial acid wastewater, which comprises the following process steps of: adding a small amount of water into ferric salt for dissolving, mixing with neutralized return water, and stirring for reaction to obtain iron agent slurry; the iron agent slurry is subjected to standing sedimentation, supernate and sedimentation underflow are obtained, the supernate serves as new return water to be recycled, and the sedimentation underflow is the iron agent; the obtained iron agent is dissolved in the to-be-treated complex arsenic-containing and sulfur-containing industrial acid wastewater, then lime is added into the to-be-treated complex arsenic-containing and sulfur-containing industrial acid wastewater for a neutralization arsenic removal reaction, solid-liquid separation is conducted after the reaction is finished, neutralization slag and neutralization return water are obtained, and the neutralization return water is circulated to be used for preparing the iron agent. According to the method, the iron agent is prepared from the neutralized return water, OH <-> in the neutralized return water is effectively utilized, the iron agent sedimentation underflow is added into the complex arsenic-containing and sulfur-containing industrial acid wastewater, waste heat resources in industrial production are effectively utilized, the arsenic removal efficiency is improved, and the energy loss is reduced.

Description

Technical Field

[0001] The invention relates to a method for treating complex arsenic- and sulfur-containing industrial acidic wastewater, and belongs to the field of environmental protection. Background Art

[0002] Arsenic is often associated with gold, copper, lead, tin, nickel, cobalt, zinc and other minerals in the form of sulfides. Arsenic-containing non-ferrous metals and precious metal sulfide ores will release a large amount of arsenic-containing waste during the mining and smelting process. Among them, the pretreatment processes such as pressurized oxidation, biological oxidation, roasting, etc. of arsenic-containing gold mines and the acid production process of arsenic-containing pyrites will produce a large amount of complex arsenic-containing and sulfur-containing industrial acidic wastewater. Complex arsenic-containing and sulfur-containing industrial acidic wastewater is characterized by high output, complex composition and strong toxicity. Therefore, it must be de-arsenicized before it can be discharged or reused. The lime iron salt method has the advantages of high arsenic removal rate, low cost and simple operation, and has been widely used in industry.

[0003] The principle of the lime iron salt method is to add lime to the complex arsenic-containing and sulfur-containing industrial acidic wastewater for neutralization, and then add iron salt and oxidant for arsenic removal. The conventional lime iron salt method uses iron salt to add iron salt and aerate during the neutralization process of complex arsenic-containing and sulfur-containing industrial acidic wastewater. In this process, Fe 2+ Oxidized to Fe 3+ , Fe 3+ During the neutralization process, hydrolysis occurs, and the resulting colloidal iron hydroxide has a huge active surface, which adsorbs arsenic and arsenic compounds to produce a coprecipitation effect, thereby achieving the effect of arsenic removal. However, this iron supplementation method requires the addition of aeration equipment, and a large amount of lime is used, resulting in a large amount of arsenic slag.

[0004] Feng Zhibing and others invented a process for treating arsenic-containing wastewater, using the "hydrogen peroxide + iron salt" method to remove arsenic. The iron supplementation method is to add iron salt and hydrogen peroxide to the neutralized filtrate, and use compressed air for full aeration and oxidation. This method requires the addition of an oxidant, hydrogen peroxide, and the need to blow in compressed air for oxidation, which increases costs.

[0005] Du Dongyun and others invented a three-stage lime iron salt method to treat high-arsenic and high-cadmium waste acid. The iron supplementation method is to add ferrous sulfate to the supernatant after the first stage of neutralization at a molar ratio of iron to arsenic of 4:1, aerate continuously for 60 minutes, with a gas-liquid ratio of 1.2:1, and then add flocculant anionic polyacrylamide for coagulation and precipitation to remove arsenic. This method requires aeration and the addition of additional flocculants, which increases the equipment cost and reagent cost. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a method for treating complex arsenic-containing and sulfur-containing industrial acidic wastewater by iron supplementation and arsenic removal, using waste heat and neutralization return water to make iron agent, realizing secondary utilization of resources; eliminating the aeration process, reducing equipment costs and energy consumption; improving arsenic removal efficiency while reducing slag volume. Compared with traditional methods, the treatment method proposed in this article has the advantages of simple operation, economy and environmental protection.

[0007] A method for treating complex arsenic-containing and sulfur-containing industrial acidic wastewater comprises the following process steps:

[0008] (1) adding a small amount of water to dissolve the iron salt, mixing it with neutralized return water, stirring and reacting, and obtaining an iron agent slurry; allowing the iron agent slurry to settle to obtain a supernatant and a sedimentation underflow, wherein the supernatant is reused as new return water, and the sedimentation underflow is the iron agent;

[0009] (2) dissolving the iron agent obtained in step (1) in the complex arsenic-containing and sulfur-containing industrial acidic wastewater to be treated, and then adding lime thereto to carry out a neutralization and arsenic removal reaction. After the reaction is completed, solid-liquid separation is performed to obtain neutralization slag and neutralization return water, and the neutralization return water is recycled to be used for preparing the iron agent in step (1).

[0010] In the method of the present invention, the neutralization return water is wastewater after heavy metal ions are removed, and the pH value is 11±0.5.

[0011] In the method of the present invention, the neutralization return water source is the neutralization return water generated after treating complex arsenic-containing and sulfur-containing industrial acidic wastewater using the lime iron salt method or directly using the neutralization return water on site of the enterprise.

[0012] In the method of the present invention, in the step (1), the pH value of the supernatant is 7-8.

[0013] In the method of the present invention, in step (1), the supernatant can be returned to other processes as new return water, such as preparing ore slurry, washing the ground, or it can be directly discharged under the premise of meeting the discharge requirements.

[0014] In the method of the invention, in step (1), the main component of the iron agent is ferric hydroxide.

[0015] In the method of the invention, in step (2), the neutralized slag is calcium sulfate slag containing heavy metal ions.

[0016] In the method of the present invention, when the iron agent is mixed with the complex arsenic-containing and sulfur-containing industrial acidic wastewater to be treated in step (2), the original temperature of the wastewater is directly utilized, and the waste heat of the wastewater is utilized. According to the existing working conditions, the temperature of the complex arsenic-containing and sulfur-containing industrial acidic wastewater is 40-50°C.

[0017] In the method of the present invention, the neutralization return water initially used comes from the neutralization return water obtained by the traditional lime iron salt method or the neutralization return water on site of the enterprise. After the process flow involved in the first steps (1) and (2) is completed, the neutralization return water produced in step (2) can meet the reaction requirements of step (1), and the entire process can be circulated, and the neutralization return water can be recycled.

[0018] The lime iron salt method of the present invention is an existing technology for treating complex arsenic-containing and sulfur-containing industrial acidic wastewater in the prior art. Specifically, the lime iron salt method is: adding lime and iron salt to complex arsenic-containing and sulfur-containing industrial acidic wastewater, reacting for 6 to 7 hours at a stirring speed of 500 to 700 r / min, and performing solid-liquid separation after the reaction to obtain neutralized slag and neutralized return water with a pH of 11±0.5.

[0019] Among them, the aeration (air) flow rate is 20-30m 3 / h; the amount of lime added is calculated based on the molar ratio of the effective calcium oxide content in the lime and the sulfate in the wastewater of 2.0 to 2.5, and the amount of iron salt added is calculated based on the molar ratio of iron to arsenic in the wastewater of 2 to 3:1.

[0020] In the method of the present invention, the lime is one or more of calcium oxide, calcium hydroxide, or carbide slag, limestone slag, etc. with calcium oxide or calcium hydroxide as the main component.

[0021] In the method of the present invention, the iron salt is ferrous sulfate.

[0022] In the method of the present invention, in the step (1), a small amount of water is added to dissolve the iron salt, wherein the amount of water used is sufficient to ensure that the iron salt is completely dissolved, and the obtained iron salt solution is mixed with neutralization return water.

[0023] Furthermore, in the step (1), the amount of iron salt added is determined by the pH of the neutralized return water after addition being 7-8; the stirring speed is 600-800 r / min, the reaction time is 30-90 min; and the sedimentation time is 30-60 min. In the method of the present invention, the pH value of the complex arsenic-containing and sulfur-containing industrial acidic wastewater is 0.5-1.5, the iron-arsenic molar ratio is <1, the sulfate content is 30-60 g / L, and the wastewater temperature is 40-50°C.

[0024] Furthermore, the complex arsenic- and sulfur-containing industrial acidic wastewater is derived from arsenic- and sulfur-containing industrial acidic wastewater produced during the pressurized oxidation pretreatment process of arsenic-gold mines, the acid-making process of pyrite roasting, and the neutralization and sulfidation treatment of metallurgical industrial wastewater.

[0025] Furthermore, in the step (2), in the neutralization and arsenic removal reaction, the amount of lime added is calculated based on the molar ratio of the effective calcium oxide content in the lime to the sulfate ion in the wastewater of 1.5 to 2.0, the reaction time is 1 to 2 hours, and solid-liquid separation is performed after the reaction is completed. The pH value of the obtained neutralization return water is 11±0.5.

[0026] Furthermore, in the step (2), the obtained iron agent is added to the complex arsenic-containing and sulfur-containing industrial acidic wastewater to be treated, and is stirred for 30 to 60 minutes at a stirring speed of 500 to 700 r / min to dissolve.

[0027] Furthermore, in the step (2), the amount of the iron agent added is calculated based on a molar ratio of iron to arsenic in the wastewater of 2 to 3:1.

[0028] The beneficial effects of the present invention are as follows: the present invention first utilizes the alkalinity of the neutralized return water to react with iron salt to prepare an iron agent, and then utilizes the temperature of the complex arsenic-containing and sulfur-containing industrial acidic wastewater to dissolve the iron agent to form a lime iron salt arsenic removal system. The present invention can not only reduce the pH value of the return water and realize the reuse of the neutralized return water to meet the emission standards, but also cleverly utilizes the waste heat of the waste acid instead of aeration oxidation.

[0029] The present invention uses the neutralization return water to prepare the iron agent, which effectively utilizes the OH in the neutralization return water. — , the iron agent sedimentation underflow is added to the complex arsenic-containing and sulfur-containing industrial acidic wastewater, which effectively utilizes the waste heat resources in industrial production and reduces energy loss. The present invention improves the iron supplementation method of the traditional lime iron salt method, and can achieve ferrous oxidation without additional oxidation operation, thereby reducing the equipment investment cost. The present invention is simple and efficient to operate, can greatly reduce the process operation cost, and realizes the recycling of resources at the same time, with significant economic benefits, social benefits and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a flow chart of a method for treating complex arsenic-containing and sulfur-containing industrial acidic wastewater by supplementing iron and removing arsenic. DETAILED DESCRIPTION

[0031] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0032] The test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0033] A method for treating complex arsenic-containing and sulfur-containing industrial acidic wastewater, such as Figure 1 shown.

[0034] Experimental raw material 1: Arsenic-containing low-iron acid wastewater produced during the pressurized oxidation pretreatment process of arsenic-containing gold ore, wherein pH = 1.5, iron-arsenic molar ratio is 0.5, arsenic concentration is 100 mg / L, sulfate content is 30 g / L, and wastewater temperature is 50°C.

[0035] Experimental raw material 2: Arsenic-containing low-iron acid wastewater produced in the process of pyrite roasting and acid production, with pH = 0.5, iron-arsenic molar ratio of 0.8, arsenic concentration of 500 mg / L, sulfate content of 60 g / L, and wastewater temperature of 40°C.

[0036] The experimental raw material 1 was treated by lime iron salt method to prepare neutralized return water. The specific steps are as follows: 1000 mL of experimental raw material 1 was taken, and lime (effective calcium oxide content was 90%) was added thereto. The amount of lime added was 38.9 g / L (n(CaO) / n(SO4 2- )=2)), stirring speed is 600r / min, aeration flow rate is 25m 3 / h, reaction time 7h, after the reaction is completed, solid-liquid separation is carried out to obtain neutralization backwater with a volume of 900mL and a pH of 11. The obtained neutralization backwater is used for the preparation of the iron agent in Example 1.

[0037] In the following examples, experimental raw materials 1 and experimental raw materials 2 must be used under conditions that ensure the corresponding temperatures.

[0038] Example 1

[0039] (1) Preparation of iron agent: 0.74 g of ferrous sulfate heptahydrate was dissolved in 10 mL of water with an iron-to-arsenic molar ratio of 2, and added into 500 mL of neutralization return water (pH = 11). The mixture was stirred at a stirring speed of 600 r / min for 45 min and then allowed to settle for 45 min to obtain a supernatant and a sedimentation underflow. The pH value of the supernatant was 8 and could be discharged or returned as return water to the pressure oxidation process of arsenic-containing gold ore. The sedimentation underflow was the iron agent.

[0040] (2) Neutralization reaction: Take 1000 mL of experimental raw material 1, add the iron agent prepared above, stir at a stirring speed of 600 r / min for 45 min, and then add lime (effective calcium oxide content of 90%), the amount of lime added is 38.9 g / L (n(CaO) / n(SO4 2- )=2)), continue stirring the reaction for 1.5h, perform solid-liquid separation after the reaction is completed, and obtain neutralization slag and neutralization return water (890mL), the pH value of the neutralization return water is 10.5, the arsenic concentration is reduced to 0.4mg / L, and the arsenic removal rate is greater than 99.5%. The neutralization return water can continue to use step (1) to prepare iron agent and be recycled.

[0041] Example 2

[0042] (1) Preparation of iron agent: 0.93 g of ferrous sulfate heptahydrate was dissolved in 10 mL of water with an iron-arsenic molar ratio of 2.5, and added to 500 mL of the neutralized return water produced in Example 1. The mixture was stirred at a stirring speed of 700 r / min for 30 min and then allowed to settle for 30 min to obtain a supernatant and a sedimentation underflow. The supernatant had a pH value of 7 and could be discharged or returned as return water to the arsenic-containing gold ore pressure oxidation process. The sedimentation underflow was the iron agent.

[0043] (2) Neutralization reaction: Take 1000 mL of experimental raw material 1, add the iron agent prepared above, stir at a stirring speed of 700 r / min for 30 min, and then add lime (effective calcium oxide content is 90%), the amount of lime added is 29.18 g / L (n(CaO) / n(SO4 2- )=1.5)), continue stirring the reaction for 2h, and perform solid-liquid separation after the reaction to obtain neutralized slag and neutralized return water (850mL). The pH value of the neutralized return water is 11.5, the arsenic concentration is reduced to 0.31mg / L, and the arsenic removal rate is greater than 99.5%. The neutralized return water can continue to use step (1) to prepare the iron agent and be recycled.

[0044] Example 3

[0045] (1) Preparation of iron agent: 1.11 g of ferrous sulfate heptahydrate was dissolved in 10 mL of water with an iron-to-arsenic molar ratio of 3, and added to 400 mL of the neutralization return water produced in Example 2. The mixture was stirred at a stirring speed of 800 r / min for 90 min and then allowed to settle for 60 min to obtain a supernatant and a sedimentation underflow. The pH value of the supernatant was 7.5, and the supernatant could be discharged or returned as return water to the arsenic-containing gold ore pressure oxidation process. The sedimentation underflow was the iron agent.

[0046] (2) Neutralization reaction: 1000 mL of experimental raw material 1 was added with the iron agent prepared above, stirred at a stirring speed of 650 r / min for 60 min, and then lime (effective calcium oxide content of 90%) was added, and the amount of lime added was 29.18 g / L (n(CaO) / n(SO4 2- )=1.5)), continue stirring the reaction for 1h, perform solid-liquid separation after the reaction is completed, and obtain neutralization slag and neutralization return water (830mL), the pH value of the neutralization return water is 10.8, the arsenic concentration is reduced to 0.31mg / L, and the arsenic removal rate is greater than 99.5%. The neutralization return water can continue to use step (1) to prepare iron agent and be recycled.

[0047] Example 4

[0048] (1) Preparation of iron agent: 5.56 g of ferrous sulfate heptahydrate was dissolved in 20 mL of water with an iron-to-arsenic molar ratio of 3, and added to 800 mL of the neutralization return water produced in Example 3. The mixture was stirred at a stirring speed of 600 r / min for 90 min and then allowed to settle for 60 min to obtain a supernatant and a sedimentation underflow. The pH value of the supernatant was 7.5 and could be discharged or returned as return water to the arsenic-containing gold ore pressure oxidation process. The sedimentation underflow was the iron agent.

[0049] (2) Neutralization reaction: Take 1000 mL of experimental raw material 2, add the iron agent prepared above, stir at a stirring speed of 700 r / min for 30 min, and then add lime (effective calcium oxide content of 88%), the amount of lime added is 79.55 g / L (n(CaO) / n(SO4 2- )=2)), continue stirring the reaction for 1h, perform solid-liquid separation after the reaction is completed, and obtain neutralization slag and neutralization return water (850mL), the pH value of the neutralization return water is 11.2, the arsenic concentration is reduced to 0.24mg / L, and the arsenic removal rate is greater than 99.5%, and the neutralization return water can continue to use step (1) to prepare iron agent and be recycled.

[0050] Example 5

[0051] (1) Preparation of iron agent: 3.72 g of ferrous sulfate heptahydrate was dissolved in 15 mL of water with an iron-arsenic molar ratio of 2, and added to 800 mL of the neutralization return water produced in Example 4. The mixture was stirred at a stirring speed of 800 r / min for 30 min and then allowed to settle for 30 min to obtain a supernatant and a sedimentation underflow. The pH value of the supernatant was 8.0, which could be discharged or returned as return water to the pyrite roasting acid production process. The sedimentation underflow was the iron agent.

[0052] (2) Neutralization reaction: Take 1000 mL of experimental raw material 2, add the iron agent prepared above, stir at a stirring speed of 500 r / min for 30 min, and then add lime (effective calcium oxide content is 88%), the amount of lime added is 59.66 g / L (n(CaO) / n(SO4 2- )=1.5)), continue stirring the reaction for 1.8h, and after the reaction is completed, perform solid-liquid separation to obtain neutralized slag and neutralized return water (850mL). The pH value of the neutralized return water is 11.2, and the arsenic concentration is reduced to 0.44mg / L. The arsenic removal rate is greater than 99.5%. The neutralized return water can continue to be used in step (1) to prepare the iron agent and be recycled.

[0053] Comparative Example 1

[0054] The experimental raw material 2 was treated by lime iron salt aeration oxidation method. The specific steps are as follows: 1000 mL of experimental raw material 2 was taken, and lime (effective calcium oxide content was 88%) was added thereto. The amount of lime added was 99.45 g / L (n(CaO) / n(SO4 2-)=2.5)), stirring speed is 700r / min, aeration flow rate is 30m 3 / h, reaction time 7h, after the reaction is completed, solid-liquid separation is carried out to obtain neutralized backwater with a volume of 800mL and a pH of 11.

[0055] By comparison, the neutralization time required for treating experimental raw material 2 using the present invention is 3.3 to 4 hours, while the lime iron salt method requires 7 hours. Therefore, the arsenic removal efficiency of the present invention is higher; in addition, the present invention does not require an aeration device, is simpler to operate, and has lower energy consumption.

Claims

1. A method for treating complex arsenic-containing and sulfur-containing industrial acidic wastewater, comprising the following process steps: (1) adding a small amount of water to dissolve the iron salt, mixing it with neutralized return water, stirring and reacting, and obtaining an iron agent slurry; allowing the iron agent slurry to settle to obtain a supernatant and a sedimentation underflow, wherein the supernatant is reused as new return water, and the sedimentation underflow is the iron agent; (2) dissolving the iron agent obtained in step (1) in the complex arsenic-containing and sulfur-containing industrial acidic wastewater to be treated, and then adding lime thereto to carry out a neutralization and arsenic removal reaction. After the reaction is completed, solid-liquid separation is performed to obtain neutralization slag and neutralization return water, and the neutralization return water is recycled to be used for preparing the iron agent in step (1).

2. The method according to claim 1, characterized in that In the step (1), the neutralization return water source is the neutralization return water generated after treating complex arsenic-containing and sulfur-containing industrial acidic wastewater using the lime iron salt method or directly using the neutralization return water on site of the enterprise.

3. The method according to claim 2, characterized in that The lime iron salt method is as follows: adding lime and iron salt to complex arsenic-containing and sulfur-containing industrial acidic wastewater, reacting for 6 to 7 hours at a stirring speed of 500 to 700 r / min, and performing solid-liquid separation after the reaction to obtain neutralized slag and neutralized return water with a pH of 11±0.

5. Among them, the aeration flow rate is 20~30m 3 / h; the amount of lime added is calculated based on the molar ratio of the effective calcium oxide content in the lime and the sulfate in the wastewater of 2.0 to 2.5, and the amount of iron salt added is calculated based on the molar ratio of iron to arsenic in the wastewater of 2 to 3:

1.

4. The method according to claim 1, characterized in that: The lime is one or more of calcium oxide, calcium hydroxide, or carbide slag, limestone slag, etc. with calcium oxide or calcium hydroxide as the main component; the iron salt is ferrous sulfate.

5. The method according to claim 1, characterized in that In the step (1), the amount of iron salt added is determined by the pH of the neutralized return water after addition being 7 to 8; the stirring speed is 600 to 800 r / min, the reaction time is 30 to 90 min; and the sedimentation time is 30 to 60 min.

6. The method according to claim 1, characterized in that The complex arsenic- and sulfur-containing industrial acidic wastewater has a pH value of 0.5 to 1.5, an iron-arsenic molar ratio of <1, a sulfate content of 30 to 60 g / L, and a wastewater temperature of 40 to 50°C.

7. The method according to claim 1, characterized in that The complex arsenic- and sulfur-containing industrial acidic wastewater comes from the arsenic- and sulfur-containing industrial acidic wastewater produced during the pressurized oxidation pretreatment process of arsenic-gold mines, the acid-making process of pyrite roasting, and the neutralization and sulfurization treatment processes of metallurgical industrial wastewater.

8. The method according to claim 1, characterized in that In the step (2), in the neutralization and arsenic removal reaction, the amount of lime added is calculated based on the molar ratio of the effective calcium oxide content in the lime and the sulfate ion in the wastewater of 1.5 to 2.0, the reaction time is 1 to 2 hours, and solid-liquid separation is performed after the reaction is completed. The pH value of the obtained neutralization return water is 11±0.

5.

9. The method according to claim 1, characterized in that: In the step (2), the obtained iron agent is added to the complex arsenic-containing and sulfur-containing industrial acidic wastewater to be treated, and is stirred for 30 to 60 minutes at a stirring speed of 500 to 700 r / min to dissolve.

10. The method according to claim 1, characterized in that In the step (2), the amount of the iron agent added is calculated based on a molar ratio of iron to arsenic in the wastewater of 2 to 3:1.

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