Ferrous chloride wastewater and chlorine tail gas combined treatment method

Abstract

The invention relates to the technical field of environment-friendly chemical industry, in particular to a ferrous chloride waste water and chlorine tail gas combined treatment method, which comprises the following steps: feeding ferrous chloride waste water instead of a sodium hydroxide solution into a tail gas spray tower to absorb chlorine, and reacting ferrous chloride with chlorine to generate ferric trichloride; a ferrous chloride solution and a ferric trichloride solution are evenly mixed according to a certain proportion, the molar ratio of ferrous iron to ferric iron is 1: 2, a sodium hydroxide solution is added for neutralization, the pH is about 13, then stirring, heat preservation and other conditions are carried out, ferroferric oxide without crystal water is generated through a reaction, the filtering performance and the drying performance of neutralized slag precipitation are improved, the slag amount is reduced, and the production cost is reduced. The transportation and smelting economy of the slag is improved, and meanwhile, the chlorine tail gas is also absorbed.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection chemical industry, in particular to a method for treating ferrous chloride wastewater and chlorine tail gas. Background Art

[0002] Titanium tetrachloride is an important intermediate raw material for the production of titanium sponge and titanium dioxide. At present, the production methods of titanium tetrachloride are mainly boiling chlorination method and molten salt chlorination method. In the boiling chlorination method, the iron in the raw titanium slag mainly generates ferrous chloride, which is taken out of the chlorination furnace with titanium tetrachloride. After cyclone dust collection, pulping and filtration, ferrous chloride wastewater is formed. The wastewater is generally neutralized with cheap calcium carbide mud, and after pressure filtration, ferrous hydroxide waste slag and calcium chloride wastewater containing crystal water are obtained. Ferrous hydroxide waste slag contains crystal water and low iron content. The economic benefits of transporting and smelting to recover iron are poor, so it can only be piled nearby. At the same time, the tail gas of the chlorination furnace also contains chlorine, which needs to be absorbed by 30% liquid alkali spraying. Summary of the invention

[0003] The purpose of the present invention is to provide a method for treating ferrous chloride wastewater in combination with chlorine tail gas, so as to solve the problem in the above background technology that ferrous hydroxide waste residue contains crystal water, has low iron content, has poor economic benefits in transporting and smelting to recover iron, and can only be piled nearby.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A method for treating ferrous chloride wastewater and chlorine tail gas, comprising the following steps:

[0006] S10: sending the ferrous chloride wastewater to a tail gas absorption tower to absorb chlorine, and after the absorption is completed, discharging the wastewater to detect the concentrations of divalent iron ions and trivalent iron ions;

[0007] S20: re-detecting the concentrations of ferrous ions and ferric ions in the ferrous chloride wastewater that has not absorbed chlorine;

[0008] S30: calculating the ratio of ferrous chloride wastewater and ferric chloride wastewater absorbing perchlorine, adding a certain amount of ferrous chloride wastewater and ferric chloride wastewater absorbing perchlorine to a mixing tank and mixing them evenly;

[0009] S40: discharge the mixed solution into a neutralization stirring tank, slowly add a 30% sodium hydroxide solution to neutralize and adjust the pH to 12-14;

[0010] S50: The material is discharged into the insulation tank, and the reaction heat is neutralized to heat the material, and the insulation is done for 20 hours;

[0011] S60: After the heat preservation is completed, the material is put into the filter press for filtering, the filter residue is washed with water and filtered again, and the filtrate is prepared with alkaline solution and used again for neutralization in step S30;

[0012] S70: Dry the filter residue and dry the solid to a certain humidity to obtain the final product Fe3O4. The reaction formula is:

[0013] 2FeCl2+Cl2→2FeCl3

[0014] FeCl2+2FeCl3+8NaOH→Fe3O4+8NaCl+4H2O.

[0015] Preferably, the tail gas absorption tower in step S10 is a multi-stage countercurrent absorption tower, and each stage is provided with a spray system.

[0016] Preferably, the method for detecting the concentrations of ferrous ions and ferric ions in the ferrous chloride wastewater that has not absorbed chlorine in step S20 is ion chromatography.

[0017] Preferably, the specific steps of the ion chromatography are:

[0018] S21 injection: the ferric chloride wastewater is introduced into the chromatographic column through the injector;

[0019] S22 ion exchange: In the chromatographic column, the ions in the ferric chloride wastewater are exchanged with the stationary phase to achieve ion separation;

[0020] S23 detection: The separated ions are detected by a detector, and the concentration of the ions is measured to determine the content of each ion in the mixture.

[0021] Preferably, the stationary phase in step S22 is an anion exchange resin or a cation exchange resin.

[0022] Preferably, the amount of ferrous chloride wastewater added in step S30 is 4 t, and the amount of ferric chloride wastewater added after absorbing perchlorine is 7-10 t, so that the molar ratio of divalent iron to trivalent iron is 1:2.

[0023] Preferably, the 30% sodium hydroxide solution in step S40 is added by automatic dropwise control, the pH value of the mixed solution is monitored in real time by an online pH monitor, and the dropping speed of the sodium hydroxide solution is automatically adjusted according to the monitoring result to ensure that the pH value of the mixed solution is stabilized between 12-14.

[0024] Preferably, the heating and insulation temperature in step S50 is 90-100° C., and the insulation time is 15-25 hours.

[0025] Preferably, the filter press in step S60 is a plate and frame filter press, and the pressure range of the plate and frame filter press is 0.5-1.6 MPa.

[0026] Preferably, the filter residue drying equipment in step S70 is a hot air circulation oven, the drying temperature is 90-110° C., and the moisture content of the filter residue after drying is less than 10%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) Resource recovery and utilization: Ferrous chloride wastewater is originally a waste that needs to be treated, but the present invention converts it into a valuable resource for absorbing chlorine to generate ferric chloride solution. This not only reduces the cost of waste treatment, but also realizes the effective recovery and reuse of resources.

[0029] (2) Energy saving and emission reduction: Compared with the traditional method of using sodium hydroxide solution to absorb chlorine, the solution of the present invention avoids the consumption of a large amount of sodium hydroxide, reduces the cost of raw materials, and at the same time reduces energy consumption and carbon dioxide emissions in the production process, meeting the environmental protection requirements of energy saving and emission reduction.

[0030] (3) Product value enhancement: By controlling the mixing ratio of ferrous chloride wastewater and ferric chloride solution, the molar ratio of divalent iron to trivalent iron reaches 1:2, and ferroferric oxide without crystal water is generated through neutralization reaction. Ferroferric oxide is an important magnetic material with broad application prospects, such as electronics, magnetic recording, catalysts and other fields. Therefore, the present invention improves the value of the product and increases economic benefits.

[0031] (4) Optimization of wastewater treatment effect: Small amounts of nickel, chromium, manganese, titanium, aluminum, vanadium and other elements contained in wastewater will form corresponding hydroxide and oxide precipitates during the reaction process. These precipitates can be separated and recovered through processes such as filter presses, further reducing the difficulty and cost of wastewater treatment and improving the wastewater treatment effect.

[0032] (5) Simple and easy process: The process flow of the scheme of the present invention is relatively simple, easy to operate and control. By adjusting the mixing ratio of ferrous chloride wastewater and ferric chloride solution, the amount of sodium hydroxide solution added and other parameters, the reaction conditions and product quality can be conveniently controlled.

[0033] In summary, the scheme of the present invention utilizes ferrous chloride wastewater instead of sodium hydroxide solution to absorb chlorine, which not only realizes resource recovery and reuse, reduces production cost and energy consumption, but also improves the value of the product and the wastewater treatment effect. Therefore, the present invention has significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] Embodiment 1:

[0037] ① The ferrous chloride wastewater was sent to the tail gas absorption tower to absorb chlorine. After the absorption was completed, the ferrous and ferric ion concentrations were tested. The ferrous ion concentration was 9.6 g / L and the ferric ion concentration was 95.6 g / L.

[0038] ② The concentrations of divalent iron and ferric iron in the ferrous chloride wastewater that had not absorbed chlorine were tested again. The concentration of divalent iron was 79.6 g / L, and the concentration of ferric iron was 5.6 g / L.

[0039] ③ Calculate the ratio of ferrous chloride wastewater and ferric chloride wastewater absorbed with perchlorine as 1:2.01, add 4 tons of ferrous chloride wastewater and 8.04 tons of ferric chloride wastewater absorbed with perchlorine into the mixing tank and mix them evenly.

[0040] ④ Drain the mixed solution into the neutralization stirring tank, slowly add 30% sodium hydroxide solution to neutralize and adjust the pH to 12.8;

[0041] ⑤ The material is discharged into the insulation tank. The heat of the neutralization reaction has heated the material to about 94°C. Keep it warm for 20 hours.

[0042] ⑥ After the insulation is completed, the material is pumped into the filter press for filtration, the filter residue is washed with water and filtered again, and the filtrate is prepared with alkali solution and used again in step ③ for neutralization;

[0043] ⑦ Dry the filter residue.

[0044] Embodiment 2:

[0045] ① The ferrous chloride wastewater is pumped to the tail gas absorption tower to absorb chlorine. After the absorption is completed, the concentrations of divalent iron ions and trivalent iron ions are tested. The concentration of divalent iron ions is 2g / L, and the concentration of trivalent iron ions is 80g / L.

[0046] ② Re-test the concentrations of divalent iron and trivalent iron in the ferrous chloride wastewater that has not absorbed chlorine. The concentration of divalent iron is 95g / L, and the concentration of trivalent iron is 3.6g / L.

[0047] ③ Calculate the ratio of ferrous chloride wastewater and ferric chloride wastewater absorbed with perchlorine as 1:2.45, add 4 tons of ferrous chloride wastewater and 9.8 tons of ferric chloride wastewater absorbed with perchlorine into the mixing tank and mix them evenly.

[0048] ④ Drain the mixed solution into the neutralization stirring tank, slowly add 30% sodium hydroxide solution to neutralize and adjust the pH to 13;

[0049] ⑤ The material is discharged into the insulation tank. The heat of the neutralization reaction has heated the material to 90°C. The material is well insulated for about 18 hours.

[0050] ⑥ After the insulation is completed, the material is pumped into the filter press for filtration, the filter residue is washed with water and filtered again, and the filtrate is prepared with alkali solution and used again in step ③ for neutralization;

[0051] ⑦ Dry the filter residue.

[0052] Embodiment 3:

[0053] ① The ferrous chloride wastewater was sent to the tail gas absorption tower to absorb chlorine. After the absorption, the ferrous and ferric ion concentrations were tested. The ferrous ion concentration was 0g / L and the ferric ion concentration was 93g / L.

[0054] ② The concentrations of divalent iron and trivalent iron in the ferrous chloride wastewater that had not absorbed chlorine were tested again. The concentration of divalent iron was 84.4 g / L, and the concentration of trivalent iron was 4.8 g / L.

[0055] ③ Calculate the ratio of ferrous chloride wastewater and ferric chloride wastewater absorbed with perchlorine as 1:1.76, add 4 tons of ferrous chloride wastewater and 7.04 tons of ferric chloride wastewater absorbed with perchlorine into the mixing tank and mix them evenly.

[0056] ④ Drain the mixed solution into the neutralization stirring tank, slowly add 30% sodium hydroxide solution to neutralize and adjust the pH to 13.5;

[0057] ⑤ The material is discharged into the insulation tank. The heat of the neutralization reaction has heated the material to about 96°C. The material is well insulated for about 21 hours.

[0058] ⑥ After the insulation is completed, the material is pumped into the filter press for filtration, the filter residue is washed with water and filtered again, and the filtrate is prepared with alkali solution and used again in step ③ for neutralization;

[0059] ⑦ Dry the filter residue.

[0060] The scheme of the present invention uses ferrous chloride wastewater instead of sodium hydroxide solution to absorb chlorine. Ferrous chloride and chlorine react to generate ferric chloride to obtain ferric chloride solution. Then, the ferrous chloride solution that has not absorbed chlorine and the ferric chloride solution that has absorbed chlorine are mixed evenly in a certain proportion to make the molar ratio of divalent iron to trivalent iron 1:2. Sodium hydroxide solution is added to neutralize it to make its pH ≈ 13, and then it is reacted to generate ferric oxide without crystal water through stirring, heat preservation and other conditions. There are also a small amount of other elements such as nickel, chromium, manganese, titanium, aluminum, vanadium, etc. in the wastewater, which will also participate in the reaction to form corresponding hydroxide and oxide precipitations, which have little effect on the main reaction. The main reaction formula is as follows:

[0061] Original scheme: Wastewater treatment FeCl2+Ca(OH)2→Fe(OH)2+CaCl2

[0062] CaCl2+Na2SO4→CaSO4+2NaCl2

[0063] Tail gas absorption Cl2+2NaOH→NaCl+NaClO+H2O

[0064] The scheme of the present invention: 2FeCl2+Cl2→2FeCl3

[0065] FeCl2+2FeCl3+8NaOH→Fe3O4+8NaCl+4H2O.

[0066] The original scheme treated ferrous chloride wastewater to obtain ferrous hydroxide and calcium chloride wastewater. Ferrous hydroxide contains water of crystallization, has a low iron content and is difficult to filter; the calcium chloride wastewater produced at the same time requires further reaction to produce sodium chloride; and chlorine is absorbed by sodium hydroxide solution, which is costly. The sodium hypochlorite produced by the reaction is pungent, has low purity and cannot be sold and is difficult to handle.

[0067] The scheme of the present invention utilizes a boiling chlorination furnace to produce ferrous chloride wastewater, absorbs chlorine in the tail gas produced by a molten salt chlorination furnace, and saves costs; on the other hand, by controlling the concentration ratio of divalent iron and trivalent iron, magnetic ferroferric oxide is generated by reaction, which does not contain crystal water, improves the filtering performance of waste slag, reduces the amount of slag, and improves the economy of transportation and smelting of waste slag.

[0068] The scheme of the present invention utilizes ferrous chloride wastewater instead of traditional sodium hydroxide solution to absorb chlorine, which has multiple beneficial effects, mainly reflected in the following aspects:

[0069] (1) Resource recovery and utilization: Ferrous chloride wastewater is originally a waste that needs to be treated, but the present invention converts it into a valuable resource for absorbing chlorine to generate ferric chloride solution. This not only reduces the cost of waste treatment, but also realizes the effective recovery and reuse of resources.

[0070] (2) Energy saving and emission reduction: Compared with the traditional method of using sodium hydroxide solution to absorb chlorine, the solution of the present invention avoids the consumption of a large amount of sodium hydroxide, reduces the cost of raw materials, and at the same time reduces energy consumption and carbon dioxide emissions in the production process, meeting the environmental protection requirements of energy saving and emission reduction.

[0071] (3) Product value enhancement: By controlling the mixing ratio of ferrous chloride wastewater and ferric chloride solution, the molar ratio of divalent iron to trivalent iron reaches 1:2, and ferroferric oxide without crystal water is generated through neutralization reaction. Ferroferric oxide is an important magnetic material with broad application prospects, such as electronics, magnetic recording, catalysts and other fields. Therefore, the present invention improves the value of the product and increases economic benefits.

[0072] (4) Optimization of wastewater treatment effect: Small amounts of nickel, chromium, manganese, titanium, aluminum, vanadium and other elements contained in wastewater will form corresponding hydroxide and oxide precipitates during the reaction process. These precipitates can be separated and recovered through processes such as filter presses, further reducing the difficulty and cost of wastewater treatment and improving the wastewater treatment effect.

[0073] (5) Simple and easy process: The process flow of the scheme of the present invention is relatively simple, easy to operate and control. By adjusting the mixing ratio of ferrous chloride wastewater and ferric chloride solution, the amount of sodium hydroxide solution added and other parameters, the reaction conditions and product quality can be conveniently controlled.

[0074] In summary, the scheme of the present invention utilizes ferrous chloride wastewater instead of sodium hydroxide solution to absorb chlorine, which not only realizes resource recovery and reuse, reduces production cost and energy consumption, but also improves the value of the product and the wastewater treatment effect. Therefore, the present invention has significant economic and environmental benefits.

[0075] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for treating ferrous chloride wastewater and chlorine tail gas, characterized in that: The specific steps include: S10: sending the ferrous chloride wastewater to a tail gas absorption tower to absorb chlorine, and after the absorption is completed, discharging the wastewater to detect the concentrations of divalent iron ions and trivalent iron ions; S20: re-detecting the concentrations of ferrous ions and ferric ions in the ferrous chloride wastewater that has not absorbed chlorine; S30: calculating the ratio of ferrous chloride wastewater and ferric chloride wastewater absorbing perchlorine, adding a certain amount of ferrous chloride wastewater and ferric chloride wastewater absorbing perchlorine to a mixing tank and mixing them evenly; S40: discharge the mixed solution into a neutralization stirring tank, slowly add a 30% sodium hydroxide solution to neutralize and adjust the pH to 12-14; S50: The material is discharged into the insulation tank, and the reaction heat is neutralized to heat the material, and the insulation is done for 20 hours; S60: After the heat preservation is completed, the material is put into the filter press for filtering, the filter residue is washed with water and filtered again, and the filtrate is prepared with alkaline solution and used again for neutralization in step S30; S70: Dry the filter residue and dry the solid to a certain humidity to obtain the final product Fe3O4. The reaction formula is: 2FeCl2+Cl2→2FeCl3 FeCl2+2FeCl3+8NaOH→Fe3O4+8NaCl+4H2O.

2. The ferrous chloride wastewater combined with chlorine tail gas treatment method according to claim 1, characterized in that: The tail gas absorption tower in step S10 adopts a multi-stage countercurrent absorption tower, and each stage is provided with a spray system.

3. The ferrous chloride wastewater combined with chlorine tail gas treatment method according to claim 1, characterized in that: The method for detecting the concentrations of ferrous ions and ferric ions in the ferrous chloride wastewater that has not absorbed chlorine in step S20 is ion chromatography.

4. The ferrous chloride wastewater combined with chlorine tail gas treatment method according to claim 1, characterized in that: The specific steps of the ion chromatography are: S21 injection: the ferric chloride wastewater is introduced into the chromatographic column through the injector; S22 ion exchange: In the chromatographic column, the ions in the ferric chloride wastewater are exchanged with the stationary phase to achieve ion separation; S23 detection: The separated ions are detected by a detector, and the concentration of the ions is measured to determine the content of each ion in the mixture.

5. The method for treating ferrous chloride wastewater and chlorine tail gas according to claim 1, characterized in that: In step S22, the stationary phase is an anion exchange resin or a cation exchange resin.

6. The method for treating ferrous chloride wastewater and chlorine tail gas according to claim 1, characterized in that: In step S30, the amount of ferrous chloride wastewater added is 4t, and the amount of ferric chloride wastewater added after absorbing perchlorine is 7-10t, so that the molar ratio of divalent iron to trivalent iron is 1:

2.

7. The method for treating ferrous chloride wastewater and chlorine tail gas according to claim 1, characterized in that: The 30% sodium hydroxide solution in step S40 is added in an automatic dropwise manner, and the pH value of the mixed solution is monitored in real time by an online pH monitor, and the dropping speed of the sodium hydroxide solution is automatically adjusted according to the monitoring result to ensure that the pH value of the mixed solution is stable between 12-14.

8. The method for treating ferrous chloride wastewater and chlorine tail gas according to claim 1, characterized in that: The heating and heat preservation temperature in step S50 is 90-100° C., and the heat preservation time is 15-25 hours.

9. The method for treating ferrous chloride wastewater and chlorine tail gas according to claim 1, characterized in that: The filter press in step S60 is a plate and frame filter press, and the pressure range of the plate and frame filter press is 0.5-1.6 MPa.

10. The method for treating ferrous chloride wastewater and chlorine tail gas according to claim 1, characterized in that: The filter residue drying equipment in step S70 is a hot air circulation oven, the drying temperature is 90-110° C., and the moisture content of the filter residue after drying is less than 10%.

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