A method for treating tin smelting waste acid wastewater and intermediate slag

Abstract

The application discloses a treatment method of tin smelting waste acid sewage and intermediate slag, and comprises the following specific steps: (1) after limestone is added into tin smelting waste acid sewage to adjust the pH value to 10-11, solid-liquid separation is carried out to obtain first arsenic-containing gypsum slag and first filtrate; (2) the first filtrate is subjected to an oxidation reaction, iron salt is added and stirring reaction is carried out, then solid-liquid separation is carried out to obtain second arsenic-containing gypsum slag and second filtrate, and the second filtrate can be discharged or recycled; (3) the first arsenic-containing gypsum slag, the second arsenic-containing gypsum slag and pyrite are uniformly mixed and then sent into a fuming furnace for treatment; the method can realize stable and standard discharge or recycling of the waste acid sewage and harmless utilization of the intermediate slag.

Description

Technical Field

[0001] This invention relates to the field of pollution control technology in non-ferrous smelting, specifically to a method for treating waste acid and intermediate slag from tin smelting. Background Technology

[0002] The acidic wastewater generated by tin smelters mainly originates from the scrubbing of flue gas in the acid production workshop, as well as cleaning wastewater from the sulfuric acid treatment area and other acidic wastewater from other sites. This wastewater is characterized by large volume, heavy color, high acidity, complex forms, and high toxicity, containing sulfuric acid, fluorine, arsenic, and their compounds. Traditional tin smelting wastewater treatment methods, such as sulfidation-lime neutralization, have proven ineffective in achieving stable arsenic and acid emissions that meet standards or for recycling.

[0003] The intermediate slag produced from the waste acid wastewater generated by tin smelters cannot be effectively utilized. Most enterprises currently still use the method of unified stockpiling to treat arsenic-containing gypsum slag (arsenic-calcium slag). However, stockpiling has high requirements for site conditions and high site construction and maintenance costs. Over the years, the stockpiling will continuously occupy land area and also pose the risk of polluting surrounding water resources and damaging the ecological environment.

[0004] Therefore, providing a safe, environmentally friendly, and efficient method for treating tin smelting wastewater and intermediate slag is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to propose a method for treating waste acid and intermediate slag from tin smelting. This method can achieve stable discharge or recycling of waste acid, and can also achieve the harmless utilization of intermediate slag (arsenic-containing gypsum slag).

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for treating tin smelting wastewater and intermediate slag includes the following specific steps:

[0008] (1) After adding limestone to the tin smelting wastewater to adjust the pH value to 10-11, solid-liquid separation was performed to obtain the first arsenic-containing gypsum residue and the first filtrate.

[0009] (2) The first filtrate is oxidized and iron salt is added and stirred to react. The solid and liquid are separated to obtain the second arsenic-containing gypsum residue and the second filtrate. The second filtrate can be discharged or recycled.

[0010] (3) Mix the first arsenic-containing gypsum slag, the second arsenic-containing gypsum slag and pyrite and then send them into the fuming furnace for treatment.

[0011] Preferably, the solid-liquid separation is performed using plate and frame filtration.

[0012] This invention uses plate and frame filter press for solid-liquid separation, which has high separation efficiency and produces arsenic-containing gypsum slag with low moisture content, calcium sulfate content of 50-70%, and moisture content of 15-20%. The arsenic-containing gypsum slag can be directly fed into the fuming furnace without drying.

[0013] Preferably, the stirring time for adjusting the pH value in step (1) is 20-30 min.

[0014] This invention involves adding an excessive amount of limestone to acidic wastewater to ensure SO4 levels are controlled. 2- All precipitates were formed, and the pH of the solution was adjusted to make it alkaline, in preparation for further arsenic removal.

[0015] Preferably, the oxidant used in the oxidation reaction in step (2) is ozone.

[0016] Preferably, the stirring time in step (2) is 20-30 min.

[0017] Preferably, the iron salt in step (2) is at least one of FeCl3, Fe2(SO4)3 and FeSO4;

[0018] The amount of iron salt added is calculated based on the pure iron content of the iron salt, with an iron-arsenic mass ratio of (1.5-2.0):1.

[0019] This invention oxidizes the filtrate and adds iron salts to oxidize free arsenic or trivalent arsenic into pentavalent arsenic, which then reacts with limestone to form Ca3(AsO3)2 and Fe(AsO4)3 precipitates. 2- The ions are oxidized and hydrolyzed to form ferric hydroxide. In an alkaline environment with a pH of 10-11, the surface area of ​​the ferric hydroxide colloid increases, and its adsorption capacity is enhanced, which can adsorb and co-precipitate impurities such as Ca3(AsO3)2 and Fe(AsO4)3. The arsenic-containing gypsum residue filtered out has a Ca3(AsO3)2 and Fe(AsO4)3 content of more than 75% and a moisture content of 15-30%.

[0020] Preferably, in step (3), the total amount of the first arsenic-containing gypsum slag and the second arsenic-containing gypsum slag is in a mass ratio of 1:(3-5) to the pyrite, and the feeding rate is 2-8t / h into the fuming furnace for treatment.

[0021] This invention involves feeding the arsenic-containing gypsum slag produced together with pyrite into a fuming furnace. The pyrite is fed into the fuming furnace during the highest temperature stage of sulfidation and volatilization, which provides a good dissociation temperature for Ca3(AsO3)2, Fe(AsO4)3, and CaSO4. The calcium oxide and ferrous oxide produced by dissociation are the main components of the fuming furnace slag, which can effectively form slag. The sulfur produced is reintroduced into the acid production system in the form of SO2, and the arsenic is enriched as As2O3 in the bag filter dust collector.

[0022] Preferably, the feeding speed in step (3) is 2-8 t / h.

[0023] Preferably, the temperature of the fumigation furnace in step (3) is 1200-1450℃ and the silica content is 0.8-1.2.

[0024] This invention employs a fumigation furnace under a weakly reducing atmosphere at 1200-1450℃ to perform fumigation and sulfidation treatment on arsenic-containing gypsum slag in conjunction with pyrite. The mass ratio of the total amount of arsenic-containing gypsum slag to the mass of pyrite is 1:(3-5). Arsenic is efficiently cracked and volatilized into the flue dust, while the arsenic content of the slag after fumigation and sulfidation is basically below 0.5%. After water quenching, the slag forms granular solids. Due to the unique compositional characteristics of tin smelting slag, the arsenic content in tin smelting slag is relatively stable, and its toxicity leaching index consistently meets the standards for use in domestic cement plants. Therefore, it is one of the main raw materials for cement production. This invention achieves the purpose of harmless disposal of gypsum slag produced from tin smelting wastewater treatment, avoiding potential environmental pollution and resource waste caused by the stockpiling of arsenic-containing gypsum slag. This invention achieves the harmless disposal of arsenic-containing gypsum produced from wastewater treatment, and also achieves centralized disposal of arsenic in wastewater.

[0025] The above-described treatment method is applied to acidic wastewater from tin smelting.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) In the process of treating acidic wastewater by lime-iron salt method, ozone is added to significantly improve the arsenic removal effect, the desulfurization rate can reach more than 99.5%, and the arsenic removal rate can reach more than 98%.

[0028] (2) This invention makes full use of the existing equipment in tin smelting plants, such as fuming furnaces, filter presses, and ozone generators, which can reduce cost input;

[0029] (3) This invention avoids the problem of long-term stockpiling of arsenic-containing gypsum slag (arsenic-calcium slag), which occupies land and pollutes the environment, and saves the construction and maintenance costs of stockpiling sites;

[0030] (4) This invention recovers valuable element arsenic and also forms an open path for arsenic in the tin smelting system, which can reduce the output of intermediate products in the tin refining process and save production costs.

[0031] (5) The SO2 produced by the decomposition of arsenic-containing gypsum slag can be used as a sulfiding agent for the volatilization of sulfidation in the fuming furnace, which can replace part of the pyrite and reduce the input of pyrite. The decomposed FeO and CaO are important components of the slag. The input of arsenic-containing gypsum slag will not have any negative impact on the fuming furnace. The slag produced can be used to make cement after water quenching, saving production costs. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0033] Figure 1 The present invention provides a flow chart of a method for treating tin smelting wastewater and intermediate slag. Detailed Implementation

[0034] Embodiments of the present invention are described below, examples of which are shown in the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0035] Raw material source: Waste acid from a tin smelter was used as the research object. The main components were sulfuric acid 12.1%, arsenic ions 850 mg / L, and fluorine 265 mg / L. The treatment capacity was 200 m³ / day. 3 Taking acidic wastewater as an example, the total arsenic content of the acidic wastewater is 170 kg;

[0036] Example 1

[0037] like Figure 1 This invention provides a method for treating tin smelting wastewater and intermediate slag, specifically including the following steps:

[0038] (1) Limestone was added to the neutralization reaction tank of tin smelting waste acid, and stirred for 20 minutes at room temperature. When the pH value was 10-11, the addition of limestone was stopped. After plate and frame filter, the first arsenic-containing gypsum slag and the first filtrate were obtained.

[0039] (2) The first filtrate is introduced into the oxidation reaction tank. The agitator in the oxidation tank is turned on, and ozone is introduced from the bottom of the tank. The ozone flow rate is set to 1.0 m³ / s. 3 / h, after turning on the ozone, FeSO4 is added to the solution. Calculated based on the mass of pure iron in the iron salt, the FeSO4 with an iron-arsenic mass ratio of 1.5:1 is added. That is, the required mass of iron is 1.5 × 170 kg = 255 kg, and the required weight of FeSO4 is 255 × 152 / 56 = 692.1 kg. Stir for 23 minutes, and after filtration by a filter press, the second arsenic-containing gypsum residue and the second filtrate are obtained. The second filtrate contains almost zero sulfuric acid, 0.004 g / L of arsenic ions, and 0.001 g / L of fluoride ions. It can be directly discharged or recycled.

[0040] (3) The first and second arsenic-containing gypsum slags (containing 10-15% S, 20-25% Ca, and 5-10% As) and pyrite are mixed evenly at a mass ratio of 1:3 and fed into the fuming furnace at a rate of 2 t / h. The temperature of the fuming furnace is controlled at 1200℃ and the silica content is 0.8. The slag is formed in the furnace during the sulfidation and volatilization stage, producing flue dust containing 54% tin and 2.75% arsenic. The flue gas contains 10000-11000 mg / m³ of SO2. 3 The slag is sent to the acid production system to produce acid, and after being discharged from the fuming furnace and quenched in water, it is sent to the cement plant to make cement.

[0041] This technology significantly improves arsenic removal efficiency, achieving a desulfurization rate of up to 99.5% and an arsenic removal rate of up to 98%.

[0042] Example 2

[0043] like Figure 1 This invention provides a method for treating tin smelting wastewater and intermediate slag, specifically including the following steps:

[0044] (1) Limestone was added to the neutralization reaction tank of tin smelting waste acid, and stirred for 25 minutes at room temperature. When the pH value was 10-11, the addition of limestone was stopped. After plate and frame filter, the first arsenic-containing gypsum slag and the first filtrate were obtained.

[0045] (2) The first filtrate is introduced into the oxidation reaction tank. The agitator in the oxidation tank is turned on, and ozone is introduced from the bottom of the tank. The ozone flow rate is set to 1.2 m³ / s. 3 / h, after turning on the ozone, add FeSO4 and FeCl3 with a pure iron mass ratio of 1:1 to the solution. Calculate the required iron mass ratio of 1.7:1 for FeSO4 and FeCl3. The required iron mass is 1.7 × 170 kg = 289 kg. Therefore, the required weights of FeSO4 and FeCl3 with a mass ratio of 1:1 are 289 / 2 × 152 / 56 = 392.2 kg and 289 / 2 × 162.5 / 56 = 419.3 kg, respectively. Stir for 23 minutes, and filter using a filter press to obtain the second arsenic-containing gypsum residue and the second filtrate. The second filtrate contains almost zero sulfuric acid, 0.003 g / L of arsenic ions, and 0.0005 g / L of fluoride ions. It can be directly discharged or recycled.

[0046] (3) The first and second arsenic-containing gypsum slags (containing 10-15% S, 20-25% Ca, and 5-10% As) and pyrite are mixed evenly at a mass ratio of 1:4 and fed into a fuming furnace at a rate of 3 t / h. The temperature of the fuming furnace is controlled at 1250℃ and the silica content is 1.0. The slag is formed in the furnace during the sulfidation and volatilization stage, producing flue dust containing 55% tin and 2.8% arsenic. The flue gas contains 10000-11000 mg / m³ of SO2. 3The slag is sent to the acid production system to produce acid, and after being discharged from the fuming furnace and quenched in water, it is sent to the cement plant to make cement.

[0047] This technology significantly improves arsenic removal efficiency, achieving a desulfurization rate of up to 99.7% and an arsenic removal rate as high as 98.3%.

[0048] Example 3

[0049] like Figure 1 This invention provides a method for treating tin smelting wastewater and intermediate slag, specifically including the following steps:

[0050] (1) Limestone was added to the neutralization reaction tank of tin smelting waste acid, and stirred for 30 minutes at room temperature. When the pH value was 10-11, the addition of limestone was stopped. After plate and frame filter, the first arsenic-containing gypsum slag and the first filtrate were obtained.

[0051] (2) The first filtrate is introduced into the oxidation reaction tank. The agitator in the oxidation tank is turned on, and ozone is introduced from the bottom of the tank. The ozone flow rate is set to 1.3 m³ / h. 3 / h, after turning on ozone, add FeSO4, FeCl3 and Fe2(SO4)3 with a pure iron mass ratio of 1:1:3 to the solution. Calculate the required iron mass by adding FeSO4 and FeCl3 with an iron-arsenic mass ratio of 2.0:1. That is, the required iron mass is 2.0 × 170 kg = 340 kg. Then the required pure iron mass ratio of FeSO4, FeCl3 and Fe2(SO4)3 are 340 / 5 × 152 / 56 = 184.6 kg, 340 / 5 × 162.5 / 56 = 197.3 kg and 340 / 3 × 406 / 112 = 410.8 kg respectively. Stir for 23 minutes, and filter with a filter press to obtain the second arsenic-containing gypsum residue and the second filtrate. The second filtrate contains almost zero sulfuric acid, 0.0025 g / L of arsenic ions, and 0.0008 g / L of fluoride ions. It can be directly discharged or recycled.

[0052] (3) The first and second arsenic-containing gypsum slags (containing 10-15% S, 20-25% Ca, and 5-10% As) and pyrite are mixed evenly at a mass ratio of 1:5 and fed into the fuming furnace at a rate of 7t / h. The temperature of the fuming furnace is controlled at 1300℃ and the silica content is 1.1. The slag is formed in the furnace during the sulfidation and volatilization stage, producing flue dust containing 58% tin and 3.0% arsenic. The flue gas contains 10000-11000 mg / m³ of SO2. 3 The slag is sent to the acid production system to produce acid, and after being discharged from the fuming furnace and quenched in water, it is sent to the cement plant to make cement.

[0053] This technology significantly improves arsenic removal efficiency, achieving a desulfurization rate of up to 99.8% and an arsenic removal rate as high as 98.5%.

[0054] Comparative Example 1, without ozone oxidation

[0055] A method for treating tin smelting wastewater and intermediate slag specifically includes the following steps:

[0056] (1) Limestone was added to the neutralization reaction tank of tin smelting waste acid, and stirred for 20 minutes at room temperature. When the pH value was 10-11, the addition of limestone was stopped. After plate and frame filter, the first arsenic-containing gypsum slag and the first filtrate were obtained.

[0057] (2) The first filtrate is introduced into the oxidation reaction tank without ozone. FeSO4 is added directly to the solution with an iron-arsenic mass ratio of 1.5:1. The required iron mass is 1.5 × 170 kg = 255 kg. The required FeSO4 mass is 255 × 152 / 56 = 692.1 kg. After stirring for 23 min, the second arsenic-containing gypsum residue and the second filtrate are obtained after filtration by a filter press. The second filtrate contains almost zero sulfuric acid, 0.004 g / L of arsenic ions, and 0.001 g / L of fluoride ions. It can be directly discharged or recycled.

[0058] (3) The first and second arsenic-containing gypsum slags (containing 10-15% S, 20-25% Ca, and 5-10% As) and pyrite are mixed evenly at a mass ratio of 1:3 and fed into the fuming furnace at a rate of 2 t / h. The temperature of the fuming furnace is controlled at 1200℃ and the silica content is 0.8. The slag is formed in the furnace during the sulfidation and volatilization stage, producing flue dust containing 52% tin and 2.5% arsenic. The flue gas contains 10000-11000 mg / m³ of SO2. 3 The slag is sent to the acid production system to produce acid, and after being discharged from the fuming furnace and quenched in water, it is sent to the cement plant to make cement.

[0059] This technology can achieve a desulfurization rate of 71% and an arsenic removal rate of 80%.

[0060] Comparative Example 1: Treatment of acidic wastewater under different pH control conditions

[0061] A method for treating tin smelting wastewater and intermediate slag specifically includes the following steps:

[0062] (1) Limestone was added to the neutralization reaction tank of tin smelting waste acid, and stirred for 20 minutes at room temperature. When the pH value was 7-8, the addition of limestone was stopped. After plate and frame filter, the first arsenic-containing gypsum slag and the first filtrate were obtained.

[0063] (2) The first filtrate is introduced into the oxidation reaction tank without ozone. FeSO4 is added directly to the solution with an iron-arsenic mass ratio of 1.5:1. The required iron mass is 1.5 × 170 kg = 255 kg. The required FeSO4 mass is 255 × 152 / 56 = 692.1 kg. After stirring for 23 min, the second arsenic-containing gypsum residue and the second filtrate are obtained after filtration by a filter press. The second filtrate contains almost zero sulfuric acid, 0.004 g / L of arsenic ions, and 0.001 g / L of fluoride ions. It can be directly discharged or recycled.

[0064] (3) The first and second arsenic-containing gypsum slags (containing 10-15% S, 20-25% Ca, and 5-10% As) and pyrite are mixed evenly at a mass ratio of 1:3 and fed into the fuming furnace at a rate of 2 t / h. The temperature of the fuming furnace is controlled at 1200℃ and the silica content is 0.8. The slag is formed in the furnace during the sulfidation and volatilization stage, producing flue dust containing 52% tin and 2.55% arsenic. The flue gas contains 10000-11000 mg / m³ of SO2. 3 The slag is sent to the acid production system to produce acid, and after being discharged from the fuming furnace and quenched in water, it is sent to the cement plant to make cement.

[0065] This technology can achieve a desulfurization rate of 68% and an arsenic removal rate of 78%.

[0066] The embodiments of the present invention have been shown and described above. These embodiments are exemplary, and those skilled in the art can make changes to the above examples within the technical scope of the present invention.

Claims

1. A method for treating tin smelting wastewater and intermediate slag, characterized in that, The specific steps include the following: (1) After adding limestone to the tin smelting wastewater to adjust the pH value to 10-11, solid-liquid separation was performed to obtain the first arsenic-containing gypsum residue and the first filtrate. (2) The first filtrate is subjected to an oxidation reaction, and iron salt is added and stirred to react. The solid and liquid are separated to obtain the second arsenic-containing gypsum residue and the second filtrate. The second filtrate can be discharged or recycled. The iron salt in step (2) is at least one of FeCl3, Fe2(SO4)3 and FeSO4. The amount of iron salt added is calculated based on the amount of pure iron in the iron salt, and the iron-arsenic mass ratio is (1.5-2.0):

1. The oxidant used in the oxidation reaction is ozone. (3) Mix the first arsenic-containing gypsum slag, the second arsenic-containing gypsum slag and pyrite and then send them into the fuming furnace for treatment.

2. The method for treating tin smelting wastewater and intermediate slag according to claim 1, characterized in that, The solid-liquid separation is performed using plate and frame filtration.

3. The method for treating tin smelting wastewater and intermediate slag according to claim 1, characterized in that, The stirring time for adjusting the pH value in step (1) is 20-30 min.

4. The method for treating tin smelting wastewater and intermediate slag according to claim 1, characterized in that, The stirring time in step (2) is 20-30 minutes.

5. The method for treating tin smelting wastewater and intermediate slag according to claim 1, characterized in that, Step (3) The total amount of the first arsenic-containing gypsum slag and the second arsenic-containing gypsum slag is in the mass ratio of the pyrite to 1:(3-5).

6. The method for treating tin smelting wastewater and intermediate slag according to claim 1, characterized in that, The feeding speed in step (3) is 2-8 t / h.

7. The method for treating tin smelting wastewater and intermediate slag according to claim 1, characterized in that, The temperature of the fumigation furnace in step (3) is 1200-1450℃ and the silica content is 0.8-1.

2.

8. The application of the treatment method according to any one of claims 1-7 in tin smelting wastewater.

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