TWI733515B - Method of synthesizing magnetite crystals from iron-containing solution by fluidized-bed crystallization technology - Google Patents

Abstract

The present invention relates to a method of synthesizing magnetite crystals from iron-containing solution by fluidized-bed crystallization technology. In addition to the high ferrous iron removal efficiency, the method can generate magnetite crystals. By adjusting the operation conditions of reaction pH and section load of ferrous-containing solution, magnetite crystals are formed in the fluidized-bed reactor during the treatment process. The method has a very high application potential because of high treatment efficiency and crystal purity.

Description

Method for synthesizing magnetite crystals from iron-containing solution by fluidized bed crystallization technology

The present invention relates to a method for synthesizing magnetite crystals from iron-containing solutions by using fluidized bed crystallization technology, in particular to a method for removing ferrous iron in the aqueous solution with carbonic acid-dissolved oxygen and generating magnetite crystals.

With the rapid development of science and technology in the past few years, serious environmental pollution, air pollution, and water pollution have followed, causing serious ecological damage. The most serious problem is that a large amount of industrial waste water is discharged randomly due to the rapid industrial development. These industrial waste water contains a lot of heavy metals and inorganic pollutants. If humans eat too much, it may cause diseases and other problems.

Iron usually exists in the form of ferrous or trivalent iron in aqueous solutions. When the amount of ferrous iron in the groundwater is too high, proper pre-treatment is needed to drink it. The traditional treatment of ferrous wastewater uses aeration and an external coagulant to remove the iron content in the aqueous solution. However, the water content of the sludge product after precipitation is very high, and the solid purity is low, which will cause trouble and increase in subsequent treatment. The cost of treating sludge. In recent years, a hydrometallurgical method has been used to treat ferrous iron-containing washing waste liquid, and iron oxides are generated through heating and aeration. However, the product produced by this method has a particle size of microns and particles, which makes subsequent solid-liquid separation difficult. In recent years, fluidized bed crystallization technology for iron removal has received attention. The fluidized bed crystallization iron removal technology not only retains the high efficiency advantages of chemical coagulation precipitation technology, but also greatly reduces the use of chemical agents. In addition, the crystalline beads produced by the fluidized bed crystallization technology have large particle size and low water content. Therefore, there is no need to add flocculants or perform sludge re-dehydration procedures, which can save a lot of costs in waste treatment.

Magnetite is a kind of ferrite magnet, which can be used as a catalyst or adsorbent to remove various organic pollutants, and it is an iron oxide with resource potential. If the ferrous iron can be removed from the wastewater and the commercial value of magnetite (Fe ₃ O ₄ ) can be recovered, the sustainable value of resource reuse can be achieved.

For this reason, the main purpose of the present invention is to provide a method for synthesizing magnetite crystals from iron-containing solutions by using fluidized bed crystallization technology. This method can effectively remove ferrous iron from iron-containing wastewater, and in particular can obtain low Magnetite (ferroferric oxide, Fe ₃ O ₄ ) crystal particles with moisture content have the benefits of reuse and resource utilization.

According to the method for synthesizing magnetite crystals from iron-containing solution by using fluidized bed crystallization technology of the present invention, a fluidized bed reaction tank is first provided. The fluidized bed reaction tank has a lower section and an upper section, and the lower section is provided with a A solution inlet and a medicament inlet, the upper section is provided with a water outlet, and a return line is provided between the lower section and the upper section; the solution containing ferrous iron and the medicament containing the carbonate ion solution are separately flowed from the solution The inlet and the agent inlet are introduced into the fluidized bed reaction tank for mixing reaction, wherein the pH _{e of the} reaction is controlled between 7.0 and 10.0, and the cross-sectional load of the ferrous solution is controlled between 0.4 To 2.0kg/m ² .h; and make the ferrous solution mixed with the agent flow from the lower section of the reaction tank to the upper section of the reaction tank and return to the lower section through the return line for circulation, so that the The ferrous ions in the ferrous solution react with the carbonate ions to form magnetite crystals.

According to the present invention, the cross-sectional load of the ferrous solution is preferably controlled to be less than 1.2 kg/m ^{2 ·} h. In a preferred embodiment, the cross-sectional load is controlled to be between 0.4 and 1.2 kg/m ² .h.

In a preferred embodiment, the acid-base value (pH _e ) of the reaction is controlled between 8.5 and 9.5.

In a preferred embodiment, the agent is a sodium carbonate solution, and the molar concentration ratio of carbonate ions in the sodium carbonate solution to ferrous ions in the ferrous solution is controlled to be between 1.0 and 2.0.

In addition to the advantages of fluidized bed crystallization technology, the method according to the present invention can effectively remove ferrous iron in the iron-containing solution to meet the water quality requirements of the discharged water, and can also recover the commercial value of magnetite (Fe ₃ O ₄ ) is reused as a catalyst or adsorbent to remove various organic pollutants to achieve the benefit of resource utilization.

The other objectives, advantages and features of the present invention will be understood from the detailed description of the following preferred embodiments with reference to the accompanying drawings.

The present invention proposes a method for synthesizing magnetite crystals from iron-containing solutions by using fluidized bed crystallization technology. The method uses crystallization granulation to remove ferrous iron in iron-containing wastewater, and can obtain high-purity magnets Ore (Fe ₃ O ₄ ) crystal particles to have the benefit of reuse and resource utilization.

Referring to FIG. 1, the method of the present invention first provides a fluidized bed reaction tank 10, the reaction tank 10 has a tubular lower section 12 and a tubular upper section 14. The lower section 12 is provided with a solution inlet 16 and a medicine inlet 18, the upper section 14 is provided with a water outlet 20, and a return line 22 is provided between the lower section 12 and the upper section 14. In this embodiment, the bottom of the lower section 12 of the reaction tank 10 has a conical shape, which helps to disperse the reflux flow evenly. An acid-base value (pH value) detector 24 is provided at the water outlet 20 to monitor the acid-base value (pH _e ) of the flowing water, and at the same time, a water sample is collected for water quality analysis. Next, use the pumps 26 and 28 to introduce the ferrous solution (for example, ferrous sulfate, FeSO4) 30 and the agent 32 (solution containing carbonate ions) into the reaction from the solution inlet 16 and the agent inlet 18, respectively. Mix in the lower section 12 of the tank 10. Next, the ferrous-containing solution 30 mixed with the medicine 32 flows from the lower stage 12 to the upper stage 14. After that, the ferrous-containing solution 30 mixed with the medicine 32 flows back to the lower stage 12 via the return line 22 for circulation, so that the iron-containing solution 30 is circulated. The ferrous ions in the ferrous solution 30 and the carbonate ions in the agent 32 undergo a granulation reaction, and the treated water can flow out from the top of the reaction tank 10. In this embodiment, the medicament 32 provides a sodium carbonate (Na ₂ CO ₃ ) solution as a stabilizer and buffer solution. The carbonate ions in the sodium carbonate solution and the ferrous ions in the ferrous solution 30 are used to produce poor solubility. Salts, and use the characteristics of the granulation reaction to control the supersaturation in an appropriate range, and react in the fluidized bed reaction tank 10 to generate magnetite crystals, and remove the ferrous iron in the ferrous solution 30.

According to the method of the present invention, the reaction pH (pH _e ) and the cross-sectional load (L) of the ferrous solution will affect the ferrous ion removal rate (iron removal rate, TR) and particle stability in the ferrous solution 30, respectively. After the granulation rate (crystallization rate, CR). According to the test results, the pH value (pH _e ) of the reaction should be controlled between 7.0 and 10, preferably between 8.5 and 9.5; the cross-sectional load (L) of the ferrous solution should be controlled to be less than 2.0 kg/m ² . h, preferably between 0.4 to 1.2 kg/m ² .h. Furthermore, in the method of the present invention, the ferrous-containing solution 30 and the medicament 32 can be introduced into the reaction tank 10 and mixed to form iron oxide particles as a support under the condition of operating or not operating the reflux. Provide sufficient surface area for growing crystals to facilitate the attachment of newly generated crystal particles to regenerate new particles, avoiding gelatinous precipitation with a large amount of water.

Referring to Figure 2, which shows the feed concentration of the ferrous solution containing 100, 300, 500 mg-Fe/L, respectively, the molar concentration ratio of the carbonate ion of the agent to the ferrous ion of the ferrous solution ( CO ₃ ^2- /Fe ²⁺ ) is 1.2, the feed flow rate and reflux flow rate of the ferrous solution and the medicament are respectively controlled to 50 mL/min, and the upstream velocity U of the reaction tank 10 is 28.6 m/hr1. The effect of different reaction pH (pH _e ) on crystallization rate (CR%) and iron removal rate (TR%). It can be observed from Figure 2 that when the pH _{e is} higher than 6, both the iron removal rate and the crystallization rate (TR and CR) in the wastewater increase, and when the pH _{e is} between pH 8.0 and pH 10.0, its The TR value remains flat, and the removal rate is as high as 95%. However, CR tends to rise slowly. When the pH _{e is} between pH 7.0 and pH 10.0, the crystallization rate is higher, reaching more than 70%. When the pH _{e is} between pH 7.5 and pH 9.5, the crystallization rate (CR%) can reach 75-80%. When the pH _{e is} greater than 9.5, the iron removal rate still maintains a gentle and high removal efficiency, but the crystallization rate decreases. When the pH _{e is} less than 7.0, both the iron removal rate and the crystallization rate (TR and CR) are low. It is found through experiments that high crystallization rate and removal efficiency can be obtained when the acid-base value (pH _{e) in the reaction tank is controlled between 7.0 and 10.0.} Furthermore, it can be observed from Figure 3 that when the pH _{e is} higher than 6, the removal rate of carbonate radicals drops sharply, and reaches a negative removal value when the _{pH e is greater than 9.} At a high pH _e value, the solubility of carbon dioxide increases rapidly with the increase of pH value. Dissolved carbon dioxide can be converted into carbonate and bicarbonate, and increase the amount of carbonate in the system.

Referring to Figure 4, it shows that the feed concentration of the ferrous solution is 200ppm, the pH value (pH _e ) of the reaction is 7-8 and 8.5-9.5, respectively, and the upstream velocity U of the reaction tank 10 is 28.6m/hr to produce Under the operating conditions of 150mL/min total flow rate, the change of the cross-sectional load (L) of the ferrous solution has the effect on the crystallization rate (CR%) and the iron removal rate (TR%). It can be observed from Fig. 4 that under the operating conditions where the cross-sectional load is lower than 2.0kg/m ² .h, the better crystallization rate (CR%) can be achieved when the _{pH e is in the range of 7-8 and 8.5-9.5.} And iron removal rate (TR%). However, when the cross-sectional load is higher than 1.2kg/m ² .h, the crystallization rate drops rapidly from about 80%, but the iron removal rate remains close to 100%. Operating under low cross-sectional load, the concentration of ferrous iron that needs to be processed per unit time and unit cross-sectional area in the reaction tank is not high, so a high crystallization rate can be maintained. Experiments have found that the cross-sectional load (L) of the ferrous solution is controlled between 0.4 and 1.2kg/m ² .h and the reaction acid-base value (pH _e ) is between 8.5-9.5, and the highest ferrous iron can be obtained. Ion removal efficiency and crystallization rate.

It can be seen from the above results that the present invention adopts fluidized bed crystallization technology to adjust the water quality conditions, including the pH _{e of the} reaction and the cross-sectional load of the ferrous solution. It meets the discharge water standard, and recovers magnetite crystals that can be used as catalysts or adsorbents for effective reuse. That is, under _{the operating conditions where the pH e of the} reaction is controlled between 8.5 and 9.5, the obtainable crystallization rate (CR%) and iron removal rate (TR%) are 80% and 99%, respectively , And under the operating conditions that the cross-sectional load is less than 1.2 kg/m ² .h, the achievable crystallization rate (CR%) and iron removal rate (TR%) are about 82% and close to 100%, respectively. _{In addition, the pH e} of the reaction in this case is controlled between 7.0 and 10, which can avoid the formation of iron hydroxide (such as goethite), resulting in high purity of magnetite crystals. , Favorable for subsequent processing applications.

In the foregoing specification, the present invention is only described in terms of specific embodiments, but various changes or modifications can still be made according to the characteristics of the present invention. Therefore, obvious substitutions and modifications that can be made by those familiar with the art will still be incorporated into the scope of the claimed patent of the present invention.

10: Reaction tank

12: Lower paragraph

14: Upper paragraph

16: Solution inlet

18: Medicine inlet

20: water outlet

22: Return line

24: pH detector

26: Pump

28: Pump

30: solution containing ferrous iron

32: Pharmacy

FIG. 1 is a schematic diagram of a fluidized bed reaction tank according to an embodiment of the present invention.

Figure 2 is a diagram showing the relationship between the change of the reaction acid-base value (pH _e ) on the crystallization rate (CR%) and the iron removal rate (TR%) in the homogeneous granulation step of the fluidized bed.

Figure 3 is a diagram showing the relationship between changes in the _{pH value (pH e} ) of the reaction on the removal rate of carbonate during the homogeneous granulation step of the fluidized bed.

Figure 4 is a diagram showing the relationship between the change in the cross-sectional load (L) of the ferrous solution on the crystallization rate (CR%) and the iron removal rate (TR%) in the homogeneous granulation step of the fluidized bed.

10: Reaction tank

12: Lower paragraph

14: Upper paragraph

16: Solution inlet

18: Medicine inlet

20: water outlet

22: Return line

24: pH detector

26: Pump

28: Pump

30: solution containing ferrous iron

32: Pharmacy

Claims (5)

A method for synthesizing magnetite crystals from iron-containing solutions using fluidized bed crystallization technology includes: providing a fluidized bed reaction tank, which has a lower section and an upper section, and the lower section is provided with a solution inlet and a medicament The inlet, the upper section is provided with a water outlet, and a return line is provided between the lower section and the upper section; the medicine containing the ferrous iron solution and the carbonate ion solution are separately separated from the solution inlet and the medicine inlet The mixed reaction is introduced into the fluidized bed reaction tank, wherein the reaction acid-base value (pH _e ) is controlled between 7.0 and 10.0, and the cross-sectional load of the ferrous solution is controlled between 0.4 and 2.0kg/m ² . h between; and the ferrous solution mixed with the medicament flows from the lower section of the reaction tank to the upper section of the reaction tank and returns to the lower section through the return line for circulation, so that the ferrous solution in the ferrous solution The iron ions react with the carbonate ions to form magnetite crystals. The method described in item 2 of the scope of the patent application, wherein the cross-sectional load is controlled between 0.4 and 1.2 kg/m ² .h. The method described in item 1 of the scope of patent application, wherein the acid-base value (pH _e ) of the reaction is controlled between 8.5 and 9.5. The method described in item 1 of the scope of patent application, wherein the agent is a sodium carbonate solution. According to the method described in item 5 of the scope of patent application, the feed molar concentration ratio of the carbonate ion of the agent to the ferrous ion of the ferrous solution is controlled between 1.0 and 2.0.

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