Method for manufacturing oyster shell waste for removing fluorine from wastewater

Abstract

The present invention relates to a method for manufacturing oyster shell waste for removing fluorine from wastewater, in which calcined oyster shell waste is manufactured in order to remove fluorine from wastewater, the method comprising the steps of: washing and drying oyster shell waste so as to remove salt and foreign substances from the surface of the oyster shell waste; grinding the oyster shell waste having undergone the washing and drying step to a particle diameter of 0.5-1 cm; and calcining, at 900°C for 2 hours, the oyster shell waste having undergone the grinding step.

Description

Method for manufacturing oyster shells to remove fluoride from wastewater

[0001] The present invention relates to a method for manufacturing oyster shells for water treatment capable of removing fluoride from wastewater.

[0002] Fluorine is the only chemical capable of dissolving silicon and is used in various manufacturing industries such as semiconductors, displays, and secondary batteries. When hydrofluoric acid is used in the manufacturing process, fluorine-containing wastewater is generated. Since fluorine wastewater is a highly toxic substance that can lead to paralysis, heart disease, and death if discharged, the permissible discharge levels are strictly regulated to 15 ppm in general areas and 2 ppm or less in water supply areas.

[0003] Meanwhile, oyster farming, a type of coastal aquaculture, generates large quantities of oyster shells, leading to pollution of coastal fishing grounds, issues regarding the management of public waters, and damage to natural landscapes. Research is needed on disposal methods and recycling for oyster shells, which are fishery waste.

[0004] The inventor of the present invention has completed the present invention after conducting long-term research and trial and error on a method of recycling the aforementioned oyster shells to remove fluoride from wastewater as one of the post-removal technologies for treating fluoride in hydrofluoric acid wastewater.

[0005] The present invention aims to provide a method for efficiently removing fluoride from wastewater using calcined oyster shells.

[0006] In addition, the present invention provides a method for manufacturing oyster shells that removes fluoride from wastewater by suggesting optimal conditions, such as calcination temperature and calcination time, during the calcination of oyster shells to improve the efficiency of fluoride removal from wastewater during the calcination of oyster shells.

[0007] Meanwhile, other unspecified objects of the present invention will be further considered to the extent that they can be easily inferred from the following detailed description and effects.

[0008] In order to solve the above problem, the first aspect of the present invention is a method for manufacturing calcined oyster shells to remove fluoride from wastewater, wherein

[0009] A step of washing and drying oyster shells to remove salt and foreign substances from the surface of the oyster shells;

[0010] A step of crushing the oyster shells that have undergone the washing and drying steps described above into particles with a diameter of 0.5 cm to 1 cm;

[0011] A method comprising the step of calcining the oyster shells that have undergone the above-mentioned crushing step at 900℃ for 2 hours,

[0012] The present invention provides a method for manufacturing oyster shells that removes fluoride from wastewater.

[0013] The above firing step is,

[0014] Nitrogen ((N It can be carried out under an atmosphere.

[0015] The above firing step is,

[0016] The oyster shells that have undergone the above crushing step can be fed into a cylindrical rotary furnace having a pre-set angle of inclination to proceed with firing.

[0017] The second aspect of the present invention is a method for removing fluorine by injecting calcined oyster shells into wastewater, wherein

[0018] A method for removing fluoride from wastewater using oyster shells produced by any one of claims 1 to 3, wherein 50g of oyster shells are injected per 1L of wastewater.

[0019] The effects of the present invention are clear. By using the present invention, fluoride can be efficiently removed from wastewater using calcined oyster shells.

[0020] In addition, by specifically presenting the conditions for calcining oyster shells, the efficiency of fluoride removal from wastewater can be improved by using calcined oyster shells.

[0021] Meanwhile, it should be added that even if an effect is not explicitly mentioned here, the effects described in the following specification and the provisional effects expected by the technical features of the present invention are treated as described in the specification of the present invention.

[0022] FIG. 1 illustrates a method for manufacturing oyster shells that removes fluoride from wastewater according to an embodiment of the present invention. It should be noted that the attached drawings are provided as examples for reference to help understand the technical concept of the present invention, and the scope of the present invention is not limited by them.

[0023] In the following description of the present invention, detailed explanations of related known functions are omitted if they are deemed obvious to a person skilled in the art and could unnecessarily obscure the essence of the invention.

[0024] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0025] The following describes an example of a method for manufacturing oyster shells that removes fluoride from wastewater according to the present invention.

[0026] Oyster shells are CaCO It forms a layer mainly containing [material], and organic matter is attached between the layer structures to form a composite structure; the glossy surface of the inner surface of the oyster shell is composed of SiO2. The main component of the oyster shell is CaCO3. It makes up 93.5% of the main components, and Na, Mg, Si, etc. account for trace components.

[0027] When these oyster shells are calcined, CaCO₃ a CaO and CaCO A porous body composed of CaCO3 is formed. As it changes into CaO, CO It is generated, and the generated CO As it flies away, the total mass decreases.

[0028] CaO / CaCO3 generated by calcining oyster shells Porous active shells composed of porous materials have Ca on the surface in an aqueous solution. It forms fluorite (CaF₂) by reacting with F in wastewater. If ) is generated and removed from the wastewater, fluoride can be removed from the wastewater.

[0029] The reaction equation for this is as follows.

[0030] Ca + 2F <-> CaF

[0031]

[0032] As described above, this invention relates to a method for manufacturing oyster shells capable of removing fluoride most efficiently by utilizing the property of calcined oyster shells to remove fluoride from wastewater.

[0033] FIG. 1 shows a method for manufacturing oyster shells that removes fluoride from wastewater according to one embodiment of the present invention.

[0034] Referring to FIG. 1, a method for manufacturing oyster shells to remove fluoride from wastewater includes the steps of washing and drying, grinding, and calcining.

[0035] Salt may remain in oyster shells, and since this residual salt can interfere with fluoride removal, it is desirable to remove it. In addition, foreign substances attached to the surface of the oyster shells are CaCO₃ These foreign substances must also be removed because they hinder the calcination into CaO.

[0036] Thus, the present invention includes a step of washing and drying oyster shells to remove residual salt and foreign substances on the surface of the oyster shells.

[0037] The crushing step involves crushing the oyster shells, which have undergone the washing and drying steps, to a particle size of 0.5 cm to 1 cm. If the size of the oyster shells becomes too large, the space between different oyster shells becomes too large, resulting in wastewater that does not come into contact with the surface of the oyster shells, which may reduce the efficiency of fluoride removal from wastewater using oyster shells.

[0038] In addition, if the oyster shells become too small, it takes too long for wastewater to pass through the spaces between them, leading to reduced economic viability.

[0039] Therefore, it is preferable to manufacture the oyster shells with a particle size of 0.5 cm or more and 1 cm or less. When the particle size of the oyster shells is 0.5 cm or more and 1 cm or less, wastewater passes through the gaps between the oyster shells while sufficiently contacting the surface of the oyster shells.

[0040] The calcination step involves calcining the oyster shells that have undergone the crushing step at 900°C for 2 hours. To determine the optimal temperature and time for efficiently removing fluorine from the oyster shells, the oyster shells were calcined at various temperatures and times.

[0041] Table 1 below shows the mass loss rate measured while calcining oyster shells at 800°C, 900°C, and 1000°C for 1 hour, 2 hours, and 3 hours, respectively.

[0042]

[0043] Classification Temperature (°C) 800 900 1000 Hour (Hr) 113.1 26.3 34.8 225.6 54.5 47.1 427.8 45.3 44.8

[0044]

[0045] As explained earlier, when oyster shells are calcined, CaCO3, which constitutes most of the oyster shell a CaO / CaCO As it transforms into a porous body, its mass decreases. The greater the rate of mass loss, the greater the amount of CaO / CaCO₃. A porous body is formed, and the CaO / CaCO₃ generated at this time Porous materials are used to remove fluoride from aqueous solutions. Therefore, the greater the mass reduction rate, the higher the fluoride removal efficiency from wastewater.

[0046] When fired at 900°C for 1 hour, a weight loss rate of approximately 26% is observed, and when fired for 2 hours or more, the weight loss rate of the oyster shells is 45–50%, indicating that there is no significant difference in the weight loss rate even as the firing time increases. Furthermore, when fired at 1000°C for 1 hour, the weight loss rate increased (approximately 34%) compared to when fired at 900°C for 1 hour; however, when fired for 2 hours or more, the weight loss rate was found to be lower or similar compared to when fired at 900°C. Additionally, when the firing time is 4 hours, a tendency for the weight loss rate to decrease slightly compared to when fired for 2 hours can be observed.

[0047] As can be seen from Table 1 above, the highest mass loss rate was observed when oyster shells were calcined at 900°C for 2 hours. In other words, the most efficient calcination for removing fluoride from wastewater was carried out.

[0048] Meanwhile, the step of calcining oyster shells can be carried out under a nitrogen atmosphere. This involves injecting nitrogen into the kiln to calcine the oyster shells under a nitrogen atmosphere. The rate of mass loss was found to be greater during the calcination of oyster shells under a nitrogen atmosphere compared to calcination under an oxygen atmosphere.

[0049] When oyster shells were calcined at 900°C for 2 hours under an oxygen atmosphere, the mass loss rate was found to be 45.1%, which is significantly lower than the mass loss rate of 54.1% under a nitrogen atmosphere. In other words, when calcining oyster shells, carrying out the oyster shell calcination step under a nitrogen atmosphere can increase the efficiency of fluoride removal from wastewater.

[0050] In the present invention, oyster shells are calcined to obtain CaCO₃ a CaO / CaCO Experiments were conducted under various conditions to verify whether the fluoride removal efficiency of oyster shells actually increases when the weight decreases as the shell changes to a porous body.

[0051] Table 2 below shows the fluoride removal efficiency when oyster shells calcined at 800℃ for 1, 2, and 4 hours were added at varying amounts of 10g, 25g, and 50g per liter of wastewater containing fluoride.

[0052]

[0053] Classification Injection Volume (g / L) 10 25 50 Hours (Hr) 18.7 12.5 14.4 27.3 13.6 18.2 49.2 15.6 16.5

[0054] In addition, Table 3 shows the fluoride removal efficiency when oyster shells calcined at 900℃ for 1, 2, and 4 hours were added at varying amounts of 10g, 25g, and 50g per liter of wastewater containing fluoride.

[0055] With the same amount of oyster shells injected, the fluoride removal rate according to calcination time shows a similar trend, and as the injection amount increases, the total fluoride removal rate increases. Overall, the removal rate is 20% or less, making it unsuitable for use in removing fluoride from wastewater.

[0056]

[0057] Classification Injection Volume (g / L) 10 25 50 Hours (Hr) 15.7 19.2 24.3 249.2 55 83.5 49.4 41.2 61.3

[0058]

[0059] Table 4 shows the fluoride removal efficiency when oyster shells calcined at 1000℃ for 1, 2, and 4 hours were added at varying amounts of 10g, 25g, and 50g per liter of wastewater containing fluoride.

[0060]

[0061] Classification Injection Volume (g / L) 10 25 50 Hours (Hr) 19.6 19.3 29.1 2 29.2 5 2.5 8 1.2 4 16.9 4 1.2 6 9.0

[0062] As can be seen in Tables 2 to 4 above, the highest fluoride removal efficiency is observed when oyster shells are calcined at 900°C for 2 hours. When 50g of oyster shells calcined at 900°C for 2 hours are injected per 1L of wastewater, a maximum fluoride removal efficiency of 83.5% is observed.

[0063] Referring to Tables 1 to 4 above, through the weight loss rate and fluorine removal rate according to the calcination temperature and calcination time of oyster shells, it can be confirmed that calcining oyster shells at 900°C for 2 hours provides the optimal fluorine removal efficiency.

[0064] Meanwhile, the calcination step of the present invention is characterized by introducing oyster shells that have undergone a crushing step into a cylindrical rotary furnace having a predetermined angle of inclination to carry out calcination.

[0065] The reason oyster shells are fed into a cylindrical rotary kiln for firing is that as the kiln rotates, the shells fed inside also rotate, allowing a large quantity of shells to be fired evenly at the same temperature.

[0066] In addition, the cylindrical rotary furnace at this time is formed at an inclined angle so that oyster shells fed from the top move down along the furnace by gravity. Through this inclined cylindrical furnace, the calcination process of the oyster shells can be carried out continuously.

[0067] Furthermore, the firing time of the oyster shells can be controlled by adjusting the inclination angle of the cylindrical rotary kiln at this time. Specifically, increasing the inclination angle causes the oyster shells inside the cylindrical rotary kiln to move quickly, shortening the firing time, while decreasing the inclination angle causes the oyster shells to move slowly, extending the firing time.

[0068] In this way, by adjusting the angle of inclination, the calcination time of oyster shells can be controlled, and the calcination process can be carried out continuously.

[0069] The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it is added once again that the scope of protection of the present invention cannot be limited by obvious changes or substitutions in the technical field to which the present invention belongs.

[0070]

Claims

1. A method for removing fluoride from wastewater using calcined oyster shells, wherein The above-mentioned calcined oyster shell is, A step of washing and drying oyster shells to remove salt and foreign substances from the surface of the oyster shells; A step of crushing the oyster shells that have undergone the washing and drying steps above into particles with a diameter of 0.5 cm to 1 cm; and The method includes the step of calcining the oyster shells that have undergone the crushing step at 900℃ for 2 hours, and The above firing step is, Nitrogen ((N The process is carried out under an atmosphere in which the oyster shells that have undergone the aforementioned crushing step are fed into a cylindrical rotary kiln with a predetermined angle of inclination to perform calcination, and through this calcination, CaCO₃, the main component of the oyster shells CaO / CaCO3 used to remove fluoride Characterized by a decrease in mass as it changes into a porous body, As manufactured by the oyster shell manufacturing method, A method for removing fluoride from wastewater using calcined oyster shells produced by the above-described oyster shell manufacturing method, characterized by injecting 50g of oyster shells per 1L of wastewater. Method to remove fluoride from wastewater

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