A method for treating scheelite heated tailings using boiler tail gas containing CO2

Abstract

The present invention discloses a method for treating scheelite heating and concentrating tailings by using boiler tail gas containing CO2. In this method, the tail gas containing CO2 discharged from the boiler during the scheelite heating and concentrating process is introduced into a reaction vessel through a pressure pump, where it interacts with the scheelite heating and concentrating tailings wastewater after primary precipitation. The CO2 dissolves in water to form carbonic acid, consuming OH in the wastewater. ‑ , reduce the alkalinity of wastewater; CO3 released by carbonic acid dissociation 2‑ With Ca in water 2+ Mg 2+ The reaction forms carbonate precipitation, which reduces the hardness of the tailings wastewater; the dissociated H + With SiO3 2‑ Combined with silicate colloids, the silicate colloids co-precipitate carbonates and fine suspended solids through a bridging effect. Finally, the precipitate is rapidly pneumatically floated out through dwarf flotation columns, reducing the hardness and alkalinity of the tailings wastewater, removing silicate ions and suspended solids, and enabling the continued reuse of the tailings wastewater. This also fixes CO2, reducing greenhouse gas emissions, and replacing conventional treatment processes for silicon-containing alkaline wastewater, such as the lime and acid addition processes, reducing wastewater treatment costs and achieving a green and efficient waste treatment solution.

Description

Technical Field

[0001] The present invention relates to a method for treating flotation tailings with CO2, and in particular to a method for treating scheelite heated tailings by utilizing boiler tail gas containing CO2. Background Art

[0002] Thermal concentration is the most common process for treating scheelite with high calcareous gangue content. This process exploits the differences in the rates at which water glass desorbs collectors from the surface of scheelite and calcareous gangue at high temperatures to maximize the floatability differences between different calcium-containing minerals, thereby producing high-quality scheelite concentrate. This process consumes large amounts of water glass, resulting in an elevated pH in the scheelite concentrate tailings and the presence of high levels of silicate, making them difficult to settle and the wastewater difficult to reuse.

[0003] At present, the main treatment methods for silicon-containing alkaline wastewater are: ① Chemical precipitation: by adding chemical reagents such as sulfuric acid, calcium chloride, and quicklime, the pH value of the wastewater is lowered to form a precipitate of silicate, which is then separated by precipitation. ② Ion exchange: Use ion exchange resins to remove silicon and other impurities in the wastewater. ③ Membrane separation technology: Use membrane separation technologies such as nanofiltration or reverse osmosis to effectively remove silicon and other dissolved components in the wastewater. ④ Biological treatment: For some organosilicon wastewater, biological treatment methods can be used to use microorganisms to decompose organosilicon. ⑤ Deep treatment: After preliminary treatment, deep treatment technologies such as activated carbon adsorption and ozone oxidation can be used to further purify the wastewater. Based on treatment costs and treatment effects, chemical precipitation is widely used in the treatment of industrial silicon-containing alkaline wastewater.

[0004] Industrial production often uses acid or lime treatment to treat heated scheelite tailings. The high consumption of acid and lime significantly increases recovery and processing costs, placing pressure on companies. Conventional carbon capture technologies, including afforestation, underground storage, subsea storage, and carbon conversion, currently suffer from low carbon capture efficiency and a long road to industrial application. Summary of the Invention

[0005] To address the aforementioned issues in the prior art, the present invention aims to provide a method for treating scheelite tailings using CO₂-containing boiler exhaust. This method utilizes CO₂ from industrial exhaust gas to treat scheelite tailings, reducing wastewater treatment costs and enabling carbon capture, contributing to the achievement of the "dual carbon" goals.

[0006] In order to achieve the above technical objectives, the present invention provides the following technical solutions:

[0007] The present invention provides a method for treating scheelite heated tailings using boiler tail gas containing CO2, comprising the following steps:

[0008] 1) Pump the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; then discharge the sediment into the tailings pond and the overflow into the reaction vessel;

[0009] 2) The CO2-containing boiler tail gas is pressurized to a pressure of P≥25 psi, and then pumped into a reaction vessel to fully react with the overflow. During the reaction, the overflow water is stirred to form co-precipitated particles;

[0010] 3) After the reaction is completed, sodium oleate is added to the reaction vessel to improve the hydrophobicity of the co-precipitated particles. The co-precipitated particles are then pneumatically floated out of the flotation column and discharged into the tailings pond. The tailings discharged from the flotation column are the treated tailings water, which is returned to the heating and concentration system for recycling.

[0011] In step 1), the overflow has a high pH value and contains a large amount of difficult-to-sediment suspended solids, silicate, calcium and magnesium ions and other impurities.

[0012] Preferably, in step 2), the CO₂-containing boiler tail gas is pressurized by a pressure pump to raise the tail gas pressure to 25 to 600 psi. Pressurizing the tail gas can increase the reaction rate of CO₂ with silicate, hydroxide, and calcium and magnesium ions in the overflow, increase the depth of reaction, and make wastewater treatment more efficient. However, excessive pressure has little effect on improving reaction efficiency and increases treatment costs.

[0013] Preferably, in step 2), during the process of the CO2-containing boiler exhaust gas and the overflow fully reacting, the CO2 in the exhaust gas dissolves in water to form carbonic acid, and then gradually dissociates into hydrogen ions and carbonate ions, and the hydrogen ions react with the hydroxide ions in the overflow to neutralize, thereby reducing the pH value of the overflow; further, the hydrogen ions react with the silicate ions in the overflow to form silicate colloid; the carbonate ions react with the calcium ions and magnesium ions in the overflow to form carbonate precipitates; under the bridging effect of the silicate colloid, the silicate colloid and the carbonate precipitate and other suspended matter and metal ions in the overflow form co-precipitated particles.

[0014] Preferably, in step 2), the reaction time is 10 to 35 minutes.

[0015] Preferably, in step 2), the overflow water is stirred at a stirring speed of 30 to 90 r / min.

[0016] Preferably, in step 3), the amount of sodium oleate added is 600 to 2000 g / m 3 (g / m 3 The agent is relative to 1m 3 amount of overflow added).

[0017] Preferably, in step 3), the diameter-to-height ratio of the dwarfed flotation column is 1:3 to 1:7.5; the air inlet pressure of the flotation column during the flotation process ranges from 0.2 to 0.4 MPa. The use of air flotation can speed up the treatment efficiency of wastewater. The use of dwarfed flotation columns can avoid the formation of short-circuit flow in the column, which makes it difficult for some particles in the wastewater to float out, reduces the treatment effect, and affects reuse. The air inlet pressure of the flotation column is maintained within a reasonable range. If the air pressure is too low, the co-precipitated particles will be difficult to float, and if the air pressure is too high, the co-precipitated particles will be easily dispersed.

[0018] This invention not only processes heated scheelite tailings, but also captures carbon and rapidly processes and reuses the selected wastewater. Its main principles are:

[0019] 1. pH Adjustment: After primary sedimentation separates the easily settleable particles in the tailings, pressurized CO2-containing boiler exhaust gas is introduced into the tailings overflow water, which contains a large amount of suspended solids, silicates, and high alkalinity, to form carbonic acid (H2CO3). Carbonic acid reacts with the alkaline components in the wastewater, lowering the pH value of the water and thus neutralizing the excessive alkalinity.

[0020] 2. Formation of carbonate precipitation: As the pH value decreases, the silicate dissolved in the water will react with the hydrogen ions dissociated from the carbonate to form silicate colloid. The dissociated carbonate reacts with calcium ions and magnesium ions to form calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) precipitation, removing the inevitable ions in the wastewater. This process can also help remove other harmful substances in the wastewater, such as heavy metal ions, because these substances can also precipitate with the generated carbonate; under the bridging effect of silicate colloid, silicate colloid forms co-precipitated particles with carbonate precipitate and other suspended matter and metal ions.

[0021] 3. Fast treatment cycle: The flotation method is used to overcome the problem of slow natural sedimentation rate of silicon-containing wastewater. Sodium oleate is added to enhance the hydrophobicity of the surface of the co-precipitated particles. Then, a dwarf flotation column is used to quickly separate the co-precipitated particles under appropriate air pressure.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] In the present invention, the tail gas containing CO2 discharged from the boiler during the heating and beneficiation of scheelite is introduced into the reaction vessel through a pressure pump, and interacts with the tailings wastewater (mainly silicon-containing alkaline wastewater containing fine suspended matter) after the primary precipitation. The CO2 dissolves in water to form carbonic acid, which consumes OH in the wastewater. - , reduce the alkalinity of wastewater; CO3 released by carbonic acid dissociation 2- With Ca in water 2+ Mg 2+ The reaction forms carbonate precipitation, which reduces the hardness of the tailings wastewater; the dissociated H + With SiO3 2-Combined, silicate colloid is formed, and silicate colloid causes carbonate and fine suspended matter to co-precipitate through bridging effect. Finally, the precipitate is quickly pneumatically floated out through dwarf flotation columns to reduce the hardness and alkalinity of the tailings wastewater, remove silicate ions and suspended matter, and achieve the purpose of continued reuse of the tailings wastewater; at the same time, CO2 is fixed, greenhouse gas emissions are reduced, and conventional treatment processes for silicon-containing alkaline wastewater such as lime method and acid addition method are replaced, reducing wastewater treatment costs, treating waste with waste, and being green and efficient. In addition, the operation process of this method is relatively simple, and it is also combined with flotation method to accelerate the rapid separation of difficult-to-sediment materials in the tailings, thereby improving the treatment efficiency of scheelite tailings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The process flow chart for treating scheelite tailings by heating and concentrating using boiler tail gas containing CO2;

[0025] Figure 2 Schematic diagram of dwarf flotation column. DETAILED DESCRIPTION

[0026] The present invention uses the CO2-containing tail gas generated by the boiler during the scheelite thermal separation process to treat the tailings of the scheelite thermal separation process, and compares the implementation effect of the invention under different conditions. The CO2-containing tail gas generated by the boiler here refers to the tail gas emitted by burning natural gas.

[0027] Example 1

[0028] 1) Pumping the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; testing showed that the overflow contained 6450 ppm of Si, 590 ppm of Ca+Mg, and a pH of 13.70;

[0029] The CO2-containing tail gas generated by the boiler during the heating and selection process of scheelite is introduced into the pressure pump to pressurize the tail gas and increase the pressure of the tail gas to 25psi.

[0030] 2) The pressurized tail gas is pumped into a reaction vessel to fully react with the overflow water of the heated and concentrated scheelite tailings that has undergone primary precipitation. The overflow water is stirred during the reaction at a stirring speed of 60 r / min and a reaction time of 30 min to generate co-precipitated particles;

[0031] 3) After the reaction is completed, add 2000g / m 3 The sodium oleate was added to increase the hydrophobicity of the coprecipitated particles. Then, a dwarf flotation column (diameter-to-height ratio D:H = 1:3) was used to rapidly pneumatically float the coprecipitated particles out of the tailings pond. The tailings from the flotation column were treated and returned to the heated concentration system for recycling. The column inlet pressure during the flotation process was 0.4 MPa. The treatment results are shown in Table 1.

[0032] Table 1 Comparison of different treatment effects

[0033] Treatment process Si content / ppm Hardness (Ca+Mg) / ppm pH Overflow (raw water) 6450 590 13.70 Example 1 26 53 7.15 <![CDATA[Add H2SO4 (Comparative Example 1)]]> 25 552 6.04 Add quicklime (Comparative Example 2) 390 407 11.88

[0034] As shown in Table 1, Example 1 achieved the best treatment results, not only removing the vast majority of silicates but also effectively reducing the hardness of the tailings water, bringing the slurry pH close to the natural pH of water. Conventional treatment methods, such as adding sulfuric acid, were unable to remove the inevitable ions, resulting in a low pH. Adding quicklime produced the worst silicate removal results, and the return water maintained a relatively high pH.

[0035] Example 2

[0036] 1) Pumping the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; testing showed that the overflow contained 4623 ppm Si, 678 ppm Ca+Mg, and a pH of 12.97;

[0037] The CO2-containing tail gas generated by the boiler during the heating and selection process of scheelite is introduced into the pressure pump to pressurize the tail gas and increase the pressure of the tail gas to 100psi.

[0038] 2) The pressurized tail gas is pumped into a reaction vessel to fully react with the overflow water from the primary precipitated scheelite tailings. The overflow water is stirred during the reaction at a speed of 30 r / min and a reaction time of 10 minutes to form co-precipitated particles.

[0039] 3) After the reaction is completed, add 600g / m 3 The sodium oleate was added to increase the hydrophobicity of the coprecipitated particles. A dwarf flotation column (diameter-to-height ratio D:H = 1:7.5) was then used to rapidly pneumatically float the coprecipitated particles out of the tailings pond. The tailings from the flotation column were treated and returned to the heated concentration system for recycling. The column inlet pressure during the flotation process was 0.2 MPa. The treatment results are shown in Table 2.

[0040] Example 3

[0041] This embodiment is substantially the same as embodiment 2, with the only difference being that the tail gas pressure is 300 psi. The treatment results are shown in Table 2.

[0042] Example 4

[0043] This embodiment is substantially the same as embodiment 2, with the only difference being that the tail gas pressure is 600 psi. The treatment results are shown in Table 2.

[0044] Table 2 Comparison of effects of different exhaust pressures

[0045]

[0046] As shown in Table 2, if the exhaust gas from the boiler is not pressurized, its treatment efficiency will be greatly reduced. If the exhaust gas pressure is further increased after reaching a certain pressure, the improvement in treatment effect will not be obvious.

[0047] Example 5

[0048] 1) Pumping the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; testing showed that the overflow contained 5135 ppm Si, 459 ppm Ca+Mg, and a pH of 13.02;

[0049] The CO2-containing tail gas generated by the boiler during the heating and beneficiation process of scheelite is introduced into the pressure pump to pressurize the tail gas to increase the pressure to 50psi;

[0050] 2) The pressurized tail gas is pumped into a reaction vessel to fully react with the overflow water from the primary precipitated scheelite tailings. The overflow water is stirred during the reaction at a speed of 30 r / min and a reaction time of 15 minutes to form co-precipitated particles.

[0051] 3) After the reaction is completed, add 1200g / m 3 The sodium oleate was added to increase the hydrophobicity of the coprecipitated particles. A dwarf flotation column (diameter-to-height ratio D:H = 1:6) was then used to rapidly pneumatically float the coprecipitated particles out of the tailings pond. The tailings from the flotation column were treated and returned to the heated concentration system for recycling. The column inlet pressure during the flotation process was 0.3 MPa. The treatment results are shown in Table 3.

[0052] Example 6

[0053] This embodiment is substantially the same as embodiment 5, except that the reaction time is 25 min. The treatment results are shown in Table 3.

[0054] Example 7

[0055] This embodiment is substantially the same as embodiment 5, except that the reaction time is 35 min. The treatment results are shown in Table 3.

[0056] Table 3 Comparison of effects of different reaction times

[0057]

[0058] As shown in Table 3, when the reaction time is insufficient, a large amount of silicate and calcium and magnesium ions remain. When the reaction time of the tail gas exceeds 15 minutes, the reaction time of the tail gas and overflow water is further extended, and the treatment effect is basically the same.

[0059] Example 8

[0060] 1) Pumping the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; testing showed that the overflow contained 5043 ppm Si, 705 ppm Ca+Mg, and a pH of 12.97;

[0061] The CO2-containing tail gas generated by the boiler during the heating and selection process of scheelite is introduced into the pressure pump to pressurize the tail gas and increase the pressure of the tail gas to 100psi.

[0062] 2) The pressurized tail gas is pumped into a reaction vessel to fully react with the overflow water from the primary precipitated scheelite tailings. The overflow water is stirred during the reaction at a speed of 30 r / min and a reaction time of 10 minutes to form co-precipitated particles.

[0063] 3) After the reaction is completed, add 1000g / m 3 The sodium oleate was added to increase the hydrophobicity of the coprecipitated particles. A dwarf flotation column (diameter-to-height ratio D:H = 1:7.5) was then used to rapidly pneumatically float the coprecipitated particles out of the tailings pond. The tailings from the flotation column were treated and returned to the heated concentration system for recycling. The column inlet pressure during the flotation process was 0.4 MPa. The treatment results are shown in Table 4.

[0064] Example 9

[0065] This embodiment is substantially the same as embodiment 8, except that the stirring speed is 60 r / min. The treatment results are shown in Table 4.

[0066] Example 10

[0067] This embodiment is substantially the same as embodiment 8, except that the stirring speed is 90 r / min. The treatment results are shown in Table 4.

[0068] Table 4 Comparison of effects of different stirring speeds

[0069]

[0070] As shown in Table 4, when there is no stirring, the calcium ions, magnesium ions and silicate ions do not react completely, and a large amount of residues remain. When the stirring speed is increased to 30r / min, further increasing the stirring speed has no obvious effect on the treatment.

[0071] Example 11

[0072] 1) Pumping the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; testing showed that the overflow contained 5781 ppm Si, 811 ppm Ca+Mg, and a pH of 13.74;

[0073] The CO2-containing tail gas generated by the boiler during the heating and beneficiation process of scheelite is introduced into the pressure pump to pressurize the tail gas to increase the pressure to 50psi;

[0074] 2) The pressurized tail gas is pumped into a reaction vessel to fully react with the overflow water from the primary precipitated scheelite tailings. The overflow water is stirred at a speed of 45 r / min and the reaction time is 15 minutes to form co-precipitated particles.

[0075] 3) After the reaction is completed, add 800g / m 3 The sodium oleate was added to increase the hydrophobicity of the coprecipitated particles. A dwarf flotation column (diameter-to-height ratio D:H = 1:7.5) was then used to rapidly pneumatically float the coprecipitated particles out of the tailings pond. The tailings from the flotation column were treated and returned to the heated concentration system for recycling. The column inlet pressure during the flotation process was 0.3 MPa. The treatment results are shown in Table 5.

[0076] Example 12

[0077] This embodiment is basically the same as embodiment 11, except that the amount of sodium oleate used is 1200 g / m 3 The processing results are shown in Table 5.

[0078] Table 5 Comparison of the effects of different sodium oleate dosages

[0079]

[0080] As shown in Table 5, without the addition of sodium oleate, the coprecipitated particles struggled to float effectively and remained dispersed in the overflow water. When the sodium oleate dosage was insufficient, some coprecipitated particles remained in the overflow water, and the treatment effect remained unsatisfactory. When the sodium oleate dosage exceeded the optimum level, the treatment effect did not improve further. Due to the alkaline nature of sodium oleate, the pH at the end of the flotation column slightly increased.

[0081] Example 13

[0082] 1) Pumping the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; testing showed that the overflow contained 6081 ppm Si, 676 ppm Ca+Mg, and a pH of 13.23;

[0083] The CO2-containing tail gas generated by the boiler during the heating and selection process of scheelite is introduced into the pressure pump to pressurize the tail gas and increase the pressure of the tail gas to 100psi.

[0084] 2) The pressurized tail gas is pumped into a reaction vessel to fully react with the overflow water from the primary precipitated scheelite tailings. The overflow water is stirred during the reaction at a speed of 30 r / min and a reaction time of 10 minutes to form co-precipitated particles.

[0085] 3) After the reaction is completed, add 1200g / m 3 The sodium oleate was added to increase the hydrophobicity of the coprecipitated particles. A dwarf flotation column (diameter-to-height ratio D:H = 1:7.5) was then used to rapidly pneumatically float the coprecipitated particles out of the tailings pond. The tailings from the flotation column were treated and returned to the heated concentration system for recycling. The column inlet pressure during the flotation process was 0.4 MPa. The treatment results are shown in Table 6.

[0086] Table 6 Comparison of the effects of flotation columns with different diameter-to-height ratios

[0087]

[0088] It can be seen from Table 6 that when the diameter height of the flotation column is relatively small, a short-circuit flow is formed inside the column, and a small amount of co-precipitated particles will still remain in the flotation column and accumulate to a certain extent before flowing out with the tail of the discharge; when the diameter height is relatively large, the flotation column loses its sorting effect, and a large amount of co-precipitated particles cannot flow out in time with the upwelling airflow, but remain in the flotation column and flow out with the tail of the discharge.

[0089] Example 14

[0090] 1) Pumping the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; testing showed that the overflow contained 4757 ppm Si, 623 ppm Ca+Mg, and a pH of 13.19;

[0091] The CO2-containing tail gas generated by the boiler during the heating and selection process of scheelite is introduced into the pressure pump to pressurize the tail gas and increase the pressure of the tail gas to 80psi.

[0092] 2) The pressurized tail gas is pumped into a reaction vessel to fully react with the overflow water from the primary precipitated scheelite tailings. The overflow water is stirred during the reaction at a speed of 30 r / min and a reaction time of 15 minutes to form co-precipitated particles.

[0093] 3) After the reaction is completed, add 800g / m 3 The sodium oleate was added to increase the hydrophobicity of the coprecipitated particles. A dwarf flotation column (diameter-to-height ratio D:H = 1:7.5) was then used to rapidly pneumatically float the coprecipitated particles out of the tailings pond. The tailings from the flotation column were treated and returned to the heated concentration system for recycling. The column inlet pressure during the flotation process was 0.4 MPa. The treatment results are shown in Table 7.

[0094] Table 7 Comparison of the effects of different flotation column inlet pressures

[0095]

[0096] It can be seen from Table 7 that when the air inlet pressure of the flotation column is high, some co-precipitates that are not tightly bound are dispersed and remain in the flotation column, resulting in a decrease in the treatment effect; when the air inlet pressure of the flotation column is insufficient, some large-sized co-precipitates will also remain in the flotation column.

Claims

1. A method for treating scheelite heated tailings using boiler tail gas containing CO2, comprising the following steps: 1) Pump the heated scheelite tailings into a primary sedimentation tank for sedimentation to obtain sediment and overflow; then discharge the sediment into the tailings pond and the overflow into the reaction vessel; 2) The CO2-containing boiler tail gas is pressurized to a pressure of P≥25 psi, and then pumped into a reaction vessel to fully react with the overflow. During the reaction, the overflow water is stirred to form co-precipitated particles; 3) After the reaction is completed, sodium oleate is added to the reaction vessel to increase the hydrophobicity of the co-precipitated particles. The co-precipitated particles are then pneumatically floated out of the dwarf flotation column and discharged into the tailings pond. The tailings discharged from the flotation column are the treated tailings water, which is returned to the heating and concentration system for recycling.

2. The method according to claim 1, characterized in that In step 2), the boiler tail gas containing CO2 is pressurized by a pressure pump to increase the pressure of the tail gas to 25 to 600 psi.

3. The method according to claim 1, characterized in that In step 2), the reaction time is 10 to 35 minutes.

4. The method according to claim 1, wherein In step 2), the overflow water is stirred at a stirring speed of 30 to 90 r / min.

5. The method according to claim 1, wherein In step 2), during the process of the CO2-containing boiler exhaust gas and the overflow fully reacting, the CO2 in the exhaust gas dissolves in water to form carbonic acid, and then gradually dissociates into hydrogen ions and carbonate ions. The hydrogen ions react with the hydroxide ions in the overflow to neutralize, thereby reducing the pH value of the overflow; further, the hydrogen ions react with the silicate ions in the overflow to form silicate colloid; the carbonate ions react with the calcium ions and magnesium ions in the overflow to form carbonate precipitates; under the bridging effect of the silicate colloid, the silicate colloid and the carbonate precipitate as well as other suspended matter and metal ions in the overflow form co-precipitated particles.

6. The method according to claim 1, wherein In step 3), the amount of sodium oleate added is 600 to 2000 g / m 3 .

7. The method according to claim 1, characterized in that In step 3), the diameter-to-height ratio of the dwarf flotation column is 1:3 to 1:7.

5.

8. The method according to claim 1, characterized in that In step 3), the air inlet pressure of the flotation column during the flotation process ranges from 0.2 to 0.4 MPa.

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