TWI644857B - Method of synthesizing homogeneous zinc-containing crystals by using fluidized-bed crystallization technology - Google Patents

Abstract

This invention relates to a process for the synthesis of homogeneous zinc-containing crystals by fluidized bed crystallization techniques. This method not only has the high efficiency of removing zinc ions in wastewater, but also reduces the use of chemicals. Again, this method does not require the use of a heterogeneous support in a fluidized bed reaction tank. The water quality conditions are adjusted, including the pH value of the reaction, the molar ratio of the carbonate to the zinc feed, and the initial zinc concentration. The fluidized bed homogenous crystallization system recovers the crystal particles of the zinc salt to remove zinc ions from the wastewater. The treatment efficiency obtained by the method is high and the purity of the crystal particles is high, and has high utilization potential.

Description

Method for synthesizing homogeneous zinc-containing crystal by fluidized bed crystallization technique

The invention relates to a method for synthesizing homogeneous zinc-containing crystals by a fluidized bed crystallization technique, in particular to a method for removing and recovering zinc from zinc-containing wastewater by fluidized bed crystallization granulation.

With the rapid development of science and technology over the past few years, serious environmental pollution, air pollution, and water pollution have caused serious damage to the ecology. The most serious of these is due to the rapid industrial development, a large amount of industrial wastewater is arbitrarily discharged. These industrial wastewaters contain a lot of heavy metals and inorganic pollutants, etc., if human consumption is too much, it may cause diseases and other problems.

The techniques for removing zinc from wastewater are mainly: coagulation sedimentation method, sulfurization precipitation method, electrolysis method, ion exchange method, adsorption method, biosorption method and the like. At present, the method of removing zinc in wastewater is mainly selected by chemical coagulation precipitation method. Chemical coagulation sedimentation is the use of a precipitant, by adding an alkali solution to adjust the appropriate pH value, reacting with zinc ions to form a solid precipitation solution, and with the addition of a polymer flocculant, to achieve the purpose of zinc removal by a coprecipitation mechanism. Although chemical coagulation and sedimentation has simple operation and good zinc removal effect, it needs to add a large amount of chemicals in the zinc removal process, and the solid waste produced by the solid waste has high moisture content (ie, zinc sludge with high water content), which has an impact on the environment. The purity of the solid is low, which also causes trouble and harm to the subsequent solid-liquid separation and recovery. In addition, the traditional treatment program removes heavy metal technology from water, which requires horizontally connected fast mixing tanks, slow mixing tanks, sedimentation tanks, and sludge dewatering machines. The required space is large and the amount of sludge generated is large, which has a considerable impact on the environment. Large, which in turn increases the trouble and burden of sludge treatment.

In order to improve the problem of chemical coagulation, a technique for recovering high-concentration metals in wastewater by using a fluidized bed crystallization procedure has been proposed, and the obtained high-concentration metal particles can be reused compared to conventional chemistry. Coagulation not only reduces costs, but also maintains the environment and reduces the hassle of tube disposal.

The processing apparatus of the "fluidized bed crystallization procedure" mainly comprises a reaction tank (i.e., a fluidized bed) having a support therein. The waste water to be treated flows upward from the bottom of the reaction tank, so that the support fluidizes at a certain upward flow speed, and the reaction tank is connected with a chemical inlet for feeding the medicament, so that the pollutants in the waste water are in the fluidized bed. The support is crystallized to remove anions or metal ions in the wastewater, and the reusable metal particles are recovered. However, the conventional "fluidized bed crystallization program" is wrong! The reference source cannot be found. It is necessary to add, for example, cerium or brick powder to the reaction vessel to carry out crystallization, thereby causing the carrier component to be contained in the metal crystal, and the purity of the crystal is not good, which adversely affects the value of reuse. In addition, there is currently no related art for removing and recovering zinc from wastewater using fluidized bed crystallization techniques.

Accordingly, the main object of the present invention is to provide a method for synthesizing homogeneous zinc-containing crystals by a fluidized bed crystallization technique, which can not only replace chemical coagulation to achieve an excellent zinc removal effect, but also adopts homogeneous nucleation. The crystallization technology results in a high purity of the zinc-containing crystals, which is beneficial for subsequent processing applications of zinc recovery.

According to an embodiment of the present invention, the method for synthesizing homogeneous zinc-containing crystals by a fluidized bed crystallization technique comprises: providing a fluidized bed reaction tank having a lower section and an upper section, wherein the lower section is provided with a solution a flow port and a medicament inlet port, the upper section is provided with a water outlet, and a drain line is provided between the lower section and the upper section, the reaction tank does not have a heterogeneous support; and the zinc-containing solution and the granulation agent are separately The solution inlet is mixed with the chemical inlet into the fluidized bed reaction tank, wherein the granulating agent is carbonate, phosphate or hydroxide, and the molar concentration of the granulating agent relative to the zinc ion of the zinc-containing solution The ratio is controlled between 1.0 and 2.0; the zinc-containing solution mixed with the granulating agent flows from the lower portion of the reaction tank to the upper portion of the reaction tank; and the zinc-containing solution in which the granulating agent is mixed is refluxed through the reflux line The lower stage is cycled, and the pH value (pH _e ) of the reaction in the reaction tank is controlled to be between 7 and 9, so that the zinc ions in the zinc-containing solution are reacted with the granulating agent to produce homogeneous zinc-containing crystal particles.

In a preferred embodiment, the initial concentration of zinc in zinc-containing solution is controlled between 100-300 mg / L, and the pH of the reaction vessel reaction (pH _e) controlled between 7-8, the fluid The homogenization granulation process of the chemical bed is maintained at an appropriate pH to obtain a higher zinc ion removal rate and crystallization rate.

In a preferred embodiment, the pH value of the granulating agent is controlled between 10 and 11, the hydraulic retention time (HRT) is controlled between 10 and 50 min, and the cross-sectional load control of the zinc-containing solution is controlled. Between 0.1 and 5 kg m ^-2 h ^-1 to increase the zinc ion removal rate and crystallization rate.

Other objects, advantages and features of the present invention will become apparent from

The invention provides a method for synthesizing homogeneous zinc-containing crystals by fluidized bed crystallization technology, which utilizes granulation to remove and recover zinc in a zinc-containing solution (for example, zinc-containing wastewater), thereby reducing chemical agents. The use of the support does not require the use of the support, and the obtained zinc-containing crystals have high purity, which is advantageous for subsequent processing applications. Furthermore, the method of the present invention can treat (but not limited to) wastewater having a zinc content of 50-500 mg/L, and effectively remove the zinc content to an average concentration of 0.5 mg/L or less. Thus, the present invention The method is most suitable for the treatment of heavy metal-containing wastewater or other zinc-containing wastewater generated in the electroplating or steel industry processes, thereby solving the pollution problem.

Referring to Figure 1, the process of the present invention first provides a fluidized bed reaction tank 10 having a tubular lower section 12 and a tubular upper section 14, the upper section 14 having an outer diameter greater than the outer diameter of the lower section 12. The lower section 12 is provided with a solution inlet 16 and a medicament inlet 18, the upper section 14 is provided with a water outlet 20, and a lower return line 22 is formed between the lower section 12 and the upper section 14. In the present embodiment, the bottom portion of the lower portion 12 of the reaction tank 10 has a conical shape to facilitate uniform dispersion of the return flow force. A pH value detector 24 is provided at the water outlet 20 to monitor the pH value of the reaction in the reaction tank 10 (i.e., pH _e of the outflow solution), and a water sample is collected for water quality analysis. Next, the zinc-containing solution (for example, zinc-containing wastewater) 30 and the granulating agent 32 are separately introduced into the lower portion 12 of the reaction tank 10 from the solution inlet port 16 and the drug inlet port 18 by using the two pumps 26 and 28. . Next, the zinc-containing solution 30 mixed with the granulation agent 32 flows from the lower stage 12 to the upper stage 14, and thereafter, the zinc-containing solution 30 in which the granulation agent 32 is mixed is returned to the lower stage 12 via the return line 22 to The circulation is performed so that the zinc ions in the zinc-containing solution 30 are granulated with the granulation agent 32. In the present embodiment, the granulating agent 32 is a carbonate (for example, sodium carbonate or sodium hydrogencarbonate), and a zinc carbonate ion in the zinc-containing solution 30 is used to generate a poorly soluble salt, and the characteristics of the granulation reaction are utilized. The supersaturation is controlled to an appropriate range to react in the fluidized bed reaction tank 10 to form homogeneous zinc carbonate and zinc hydroxide crystals to remove zinc ions in the zinc-containing solution 30. In other possible embodiments, the granulating agent 32 is a phosphate (eg, sodium phosphate, sodium hydrogen phosphate) or a hydroxide (eg, sodium hydroxide). The use of carbonate, phosphate or hydroxide (hydroxygen) as granulation agent 32 has the common property of reducing the solubility of zinc to produce crystals, but the use of carbonate as granulation agent 32 does not cause eutrophication. It is harmless to the environment.

According to the method of the present invention, the pH value (pH _e ) of the reaction in the reaction tank 10, the feed molar concentration ratio of the granulating agent to the zinc ion of the zinc-containing solution (C _CO3 /C _Zn ), and the zinc-containing solution 30 The initial zinc concentration and the initial static bed height (the height of the particles accumulated in the reactor when the fluidized bed is at rest) will affect the zinc ion removal rate (zinc removal efficiency) in the zinc-containing solution 30 and the crystallization after the particles are stabilized, respectively. Rate (granulation efficiency). According to the test result, the pH of the reaction within reaction vessel 10 (pH _e) controlled between 7-9, the feed molar concentration of zinc ions was zinc granulation agent relative ratio (C _CO3 / C _Zn) control Between 1.0 and 2.0, the initial zinc concentration of the zinc-containing solution is controlled between 100 and 300 mg/L, and a better crystallization ratio (CR%) and zinc removal efficiency (TR%) are obtained. Further, in the method of the present invention, the zinc-containing solution 30 and the granulating agent 32 may be introduced into the reaction tank 10 to be mixed or not to produce a homogeneous zinc-containing crystal particle as a support. In order to provide sufficient crystal growth surface area to facilitate the adhesion of newly formed crystal particles to regenerate new particles, to avoid the formation of gelatinous precipitates containing a large amount of water, the particle bed height is controlled at 0.25 of the length of 12 tubes in the lower part of the reaction tank. Between -0.75. In this embodiment, the lower section of the reaction vessel 12 has a length of about 80 cm and the particle bed height is controlled between 20 and 60 cm.

Referring to Fig. 2, it is shown that the initial zinc concentration of the zinc-containing solution is 300 mg/L, and the molar ratio of the granulating agent (carbonate) to the zinc ion of the zinc-containing solution is (C _CO3 / C _Zn ) is 1.2. The effect of the pH value of the granulation agent 32 on the crystallization rate (CR%) and the zinc removal efficiency (TR%) in the operating conditions. It has been found through experiments that the pH value (pH) of the granulation agent 32 can be obtained when the pH value of the granulation agent 32 is controlled between 10 and 11 and the crystallization rate is higher than 90%. When controlled at 10.6, the zinc ion removal rate and the crystallization rate after particle stabilization are optimal (about 96% zinc removal efficiency and crystallization rate), and when the pH value of the granulation agent 32 is controlled above 11 At (11.2), the zinc ion removal rate and the crystallization rate after the particles are stabilized are relatively low. Further, it is found from FIG. 3, the pH of the reaction within the reaction tank 10 (i.e., the pH of effluent solution pH _e) granulating agent can vary with pH (CO ₃ pH). When the pH value (pH) of the granulation agent 32 was controlled at 10.6, the pH value (pH _e ) of the reaction in the corresponding reaction tank 10 was 8.0. When the effluent solution pH (pH _e) is controlled between 7-9, homogeneous granules, can fluidized bed process maintained at an appropriate pH, to afford a higher rate of crystallization and removal of zinc ions.

Referring to Figure 4, there is shown that the granulation agent (carbonate) is relatively zinc-containing solution in an operating condition in which the initial zinc concentration of the zinc-containing solution is 300 mg/L and the pH value of the granulation agent 32 is 10.6. The effect of the change in the molar concentration of zinc ions (C _CO3 /C _Zn ) on the crystallization rate (CR%) and the zinc removal efficiency (TR%). It has been found through experiments that the ratio of the molar concentration of the granulating agent (carbonate) to the zinc ion of the zinc-containing solution (ie, the molar ratio of the carbonate ion to the zinc ion of the feed) is controlled to be between 1.0 and 2.0. A zinc removal efficiency and a crystallization ratio of more than 90% are obtained, and when the granulation agent (carbonate) is controlled at 1.2 by the feed molar ratio (C _CO3 /C _Zn ) of the zinc ion of the zinc-containing solution, the zinc ion The removal rate and the crystallization rate after particle stabilization are optimal (about 96% zinc removal efficiency and crystallization rate), and when the granulation agent is compared with the zinc ion solution of the zinc solution, the molar concentration ratio (C _CO3 /C _Zn) When the control is at 1 or less, the zinc ion removal rate and the crystallization rate after the particles are stabilized are relatively low. Further, it is found from FIG. 5, the effluent solution pH (pH _e) is also fed with a solution of granulating agent molar concentration ratio of the relative zinc (C _CO3 / C _Zn) changes. When the zinc into the solution of granulation agent relative to zinc ion molar concentration ratio of feed (C _CO3 / C _Zn) controlled at 1.2, the corresponding effluent solution pH (pH _e) is 7.9, this pH ( At pH _e ), a large amount of zinc carbonate and zinc hydroxide crystals are obtained to remove zinc ions in the zinc-containing wastewater, and a high crystallization ratio is obtained.

Referring to Fig. 6, there is shown an operating condition in which the feed molar ratio (C _CO3 /C _Zn ) of the zinc ion of the granulating agent to the zinc-containing solution is 1.2 and the pH value (pH) of the granulating agent 32 is 10.6. The effect of the initial zinc concentration (mg/L) of the zinc-containing solution on the crystallization rate (CR%) and the zinc removal efficiency (TR%). It has been found that when the initial zinc concentration of the zinc-containing solution is controlled between 100-300 mg/L, the zinc removal efficiency and crystallization rate are higher than 90%, and the initial zinc concentration of the zinc-containing solution is controlled at 300 mg. When /L, the crystallization rate of zinc ion particles is the best (about 96% crystallization rate). When the initial zinc concentration of zinc-containing solution is controlled at 100 mg/L, the zinc removal efficiency is the best (99.9% of the removal). Zinc efficiency), and when the initial zinc concentration of the zinc-containing solution is controlled at 500 mg/L, the zinc ion removal rate and the crystallization rate after the particles are stabilized are relatively low. Further, it can be seen from Fig. 7 that the pH value (pH _e ) of the effluent solution changes with the initial zinc concentration (mg/L) of the zinc-containing solution. When the initial concentration of zinc in the zinc-containing solution is controlled to 300 mg / L, the corresponding effluent solution pH (pH _e) is 7.9, this pH (pH _e), the large number of available zinc carbonate hydroxide Zinc crystals are used to remove zinc ions from zinc-containing wastewater and give high crystallization rates.

As described above, according to the method of the present invention, the molar ratio of the molar ratio of the granulating agent to the zinc ion of the zinc-containing solution (C _CO3 /C _Zn ) is 1.2, and the pH value (pH _e ) of the reaction in the reaction vessel 10 is as follows. For the initial zinc concentration of 8.0 and zinc solution controlled at 100 mg / L operating conditions, 99.9% zinc removal efficiency can be obtained, while in the zinc solution, the initial zinc concentration is controlled at 300 mg / L operating conditions, A crystallinity of 96.7% was obtained. Furthermore, the final residual zinc concentration in the effluent was 0.15 mg/L, which was completely within the limits specified by EPA and WHO (5.0 mg/L). In addition, the hydraulic retention time (HRT) and the cross-sectional load L _{Zn of the} zinc-containing solution also affect the zinc ion removal rate in the zinc-containing solution 30 and the granulation rate after the particles are stabilized. It has been found that the hydraulic retention time (HRT) is controlled between 10 and 50 min, and the cross-sectional load of the zinc-containing solution (ie, the zinc ion flux through the cross-sectional area of the reaction tank 10, L) is controlled between 0.1 and 5 kg m ^- When between ² h ^-1 , high zinc ion removal rate and crystallization rate can be obtained.

From the above results, it is understood that the present invention employs a fluidized bed homogenization crystallization technique to adjust the water quality conditions including the pH value (pH _e ) of the reaction in the reaction tank 10, and the granulation agent (carbonate ion, phosphate ion or hydroxide ion). Compared with the zinc concentration of the zinc ion solution, the molar concentration ratio of the zinc ion solution, the initial zinc concentration of the zinc-containing solution, and the initial high static bed temperature, the zinc-containing wastewater can be rectified to achieve high-efficiency removal of zinc ions in water to meet the discharge. The water standard and the recovery of zinc-containing crystals are effectively reused. Furthermore, the method of the present invention adopts a homogeneous nucleation crystallization technique, and does not require the prior addition of a heterogeneous support in the fluidized bed reaction tank, so that the obtained zinc-containing crystals have high purity, which is advantageous for subsequent processing applications. Therefore, the method of the invention can not only replace the chemical coagulation to achieve an excellent treatment effect, but also avoid the defects of the traditional chemical or biological methods, and achieve the purpose of product resource, and has the advantages of high efficiency, low cost, no sludge, and the like. .

In the foregoing specification, the invention has been described in terms of a particular embodiment, and various changes or modifications may be made in accordance with the features of the invention. Therefore, obvious substitutions and modifications may be made by those skilled in the art, and will still be incorporated in the scope of the claimed invention.

10‧‧‧Reaction tank

12‧‧‧ lower section

14‧‧‧上段

16‧‧‧ solution inlet

18‧‧‧Pharmaceutical inflow

20‧‧‧Water outlet

22‧‧‧Return line

24‧‧‧pH detector

26‧‧‧

28‧‧‧

30‧‧‧Zinc containing solution

32‧‧‧Plasting Agent

1 is a schematic view of a fluidized bed reaction tank in accordance with an embodiment of the present invention.

2 is a graph showing the relationship between the crystallization rate (CR%) and the zinc removal efficiency (TR%) relative operating time in the fluidized bed homogenization granulation step under the operating conditions of the pH value of different granulating agents. Figure.

Figure 3 is a graph showing the relationship between the pH value of different granulating agents and the corresponding pH value of the effluent solution (pH _e ) versus crystallization rate (CR%) and zinc removal efficiency (TR%).

Figure 4 is a diagram showing the crystallization rate (CR%) versus the zinc removal efficiency (TR%) under the operating conditions of different granulation agents relative to the feed molar concentration of the zinc-containing solution in the fluidized bed homogeneous granulation step. Diagram of operating time.

Figure 5 shows different granulating agent based zinc solution relative molar concentration ratio of the feed and the corresponding effluent solution pH (pH _e) For the crystallization rate (CR%) in addition to the relationship between the efficiency of zinc (TR%) Effect Figure.

Figure 6 is a graph showing the relationship between crystallization rate (CR%) and zinc removal efficiency (TR%) versus operating time for operating conditions of different zinc-containing solutions in a fluidized bed homogeneous granulation step.

Figure 7 is a graph showing the relationship between the initial zinc concentration of different zinc-containing solutions and the corresponding pH value of the effluent solution (pH _e ) versus crystallization rate (CR%) and zinc removal efficiency (TR%).

Claims (7)

A method for synthesizing homogeneous zinc-containing crystals by a fluidized bed crystallization technique, comprising: providing a fluidized bed reaction tank having a lower section and an upper section, the lower section being provided with a solution inlet port and a medicament inlet port, The upper section is provided with a water outlet, and there is a return line between the lower section and the upper section, and the reaction tank does not have a heterogeneous support; the zinc-containing solution and the granulating agent are separately introduced from the solution inlet port and the medicament inlet port. Mixing in a fluidized bed reaction tank, wherein the granulating agent is carbonate, phosphate or hydroxide, and the molar ratio of the granulating agent to the zinc ion of the zinc-containing solution is controlled to be between 1.0 and 2.0, wherein The pH value of the granulating agent is controlled between 10 and 11; the zinc-containing solution mixed with the granulating agent flows from the lower portion of the reaction tank to the upper portion of the reaction tank; and the granulating agent is mixed The zinc-containing solution is refluxed to the lower stage through the reflux line for circulation, and the pH value (pH _e ) of the reaction in the reaction tank is controlled to be between 7 and 9, so that the zinc ion in the zinc-containing solution and the granulating agent are controlled. Reaction to produce homogeneous zinc-containing crystals . A method for synthesizing a homogeneous zinc-containing crystal by a fluidized bed crystallization technique as described in claim 1, wherein the initial zinc concentration of the zinc-containing solution is controlled to be between 100 and 500 mg/L. The patentable scope of the application of paragraph 1 to the fluidized bed method of crystallization the homogeneous synthesized crystals of zinc, the reaction vessel wherein the reaction pH (pH _e) controlled between 7-8. A method for synthesizing a homogeneous zinc-containing crystal by a fluidized bed crystallization technique as described in claim 1, wherein the ratio of the granulating agent to the zinc ion of the zinc-containing solution is 1.2, the granulating agent The pH value was 10.6 and the initial zinc concentration of the zinc solution was 100 mg/L. As described in the first paragraph of the patent application, the fluidized bed crystallization technique is used to synthesize homogeneous A method for zinc crystals, wherein a molar ratio of a granulating agent to a zinc ion of a zinc-containing solution is 1.2, a pH value of a granulating agent is 10.6, and an initial zinc concentration of the zinc solution is 300 mg/L. . A method for synthesizing a homogeneous zinc-containing crystal by a fluidized bed crystallization technique as described in claim 1, wherein the zinc-containing solution and the granulating agent are first mixed in the reaction tank to produce a homogeneous zinc-containing crystal particle. Body, and the initial static bed height of the control particles is between 0.25-0.75 of the length of the lower section of the reaction tank. A method for synthesizing homogeneous zinc-containing crystals by a fluidized bed crystallization technique as described in claim 1, wherein the hydraulic retention time (HRT) is controlled between 10 and 50 minutes, and the cross-sectional load of the zinc-containing solution is controlled. Between 0.1 and 5 kg m ^-2 h ^-1 .