Fluoride removal equipment is generally used to remove fluoride from groundwater (well water) when the fluoride content exceeds the standard. Fluoride is an essential trace element in the human body. When the fluoride content in water is between 1.0-1.5mg/L, long-term consumption has a slight adverse effect on the human body; When the fluoride content in water exceeds 1.5mg/L, long-term consumption can lead to dental fluorosis and skeletal fluorosis. Therefore, the fluoride content in drinking water should not exceed 1.0mg/L, and in special circumstances should not exceed 1.5mg/L. In addition to the activated alumina adsorption method, coagulation precipitation method, and electrodialysis method, there are also reverse osmosis method, electrocoagulation method, bone carbon method, and other fluorine removal processes. According to the survey, the most commonly used defluorination processes in groundwater and deep well water treatment projects, such as general tap water projects and rural safe drinking water projects, are the activated alumina adsorption method and the newly developed bone charcoal method in recent years. The electrodialysis method and reverse osmosis method are more commonly used in quality based water supply projects.

2. Overview of defluorination equipment

The fluoride removal equipment developed by our company adopts multifunctional fluoride removal filter material, which can effectively remove fluoride ions from water and reduce it to the standard of drinking water. At the same time, it also has a certain removal effect on other harmful ions in water such as iron, manganese, heavy metals, ammonia nitrogen, and turbidity, and no excessive substances are dissolved. The filter material can be regenerated repeatedly and has a lifespan of up to 30 years.

Multi functional defluorination filter material, made of imported non-metallic crystal core materials and high-quality silicate materials, is composite through specific high-temperature physical activation and chemical reaction. Its significant characteristics include high porosity, large specific surface area, ion exchange, adsorption, catalysis, acid resistance, heat resistance, radiation resistance and other high-quality properties.

3. Working principle of defluorination equipment

After adsorbing aluminum ions, the defluorination filter material forms hydroxyl complex ion groups on the surface and pores. The fluoride ions F - in water exchange with the OH - in the multifunctional defluorination filter material, achieving the goal of defluorination with a removal rate of>95%. The total reaction equation is as follows:

nF—+F.FAInOH—=F.FAlnF—+nOH—

F. F composite molecular sieve structure: The multifunctional fluoride removal filter material is a framework like structure of hydrated aluminosilicate minerals, mainly containing Na, Ca, and a few metals such as Sr, Ba, K, Mg, etc. F. The chemical composition of F is usually represented by the following formula: (Na, K) x (Mg, Ca, Sr, Ba) y {Al (x+2y) Si [n - (x+2y)] O2n}? mH2O， Abbreviation MxDy-R. Among them, M represents monovalent cations Na and K; D represents divalent cations Mg, Ca, Sr, Ba; R represents the zeolite framework {Al (x+2y) Si [n - (x+2y)] O2n}? mH2O。

The structure of multifunctional defluorination filter material is generally composed of a three-dimensional silicon (aluminum) oxygen lattice, and its basic unit is a silicon oxygen tetrahedron [SiO4] formed by the arrangement of four oxygen ions around silicon as the center.

If the silicon in the silicon oxygen tetrahedron is replaced by aluminum ions, an aluminum oxygen tetrahedron is formed. Aluminum is+3 valent, so one of the oxygen ions in the four vertices of the aluminum oxygen tetrahedron cannot be neutralized, resulting in a negative charge. In order to neutralize its electrical properties, metal cations are added accordingly. Silicon oxygen tetrahedra and aluminum oxygen tetrahedra are connected to each other through their corner tops, forming various shapes of three-dimensional silicon (aluminum) oxygen lattice structures, namely multifunctional fluorine removal filter material structures. Due to the diverse connection methods of silicon (aluminum) oxygen tetrahedra, many pores and channels have been formed in the multifunctional fluorine removal filter material structure.

The holes and channels inside the multi-functional defluorination filter material structure are usually filled with water molecules, which can be removed at a specific temperature. The holes and channels left after removal become sponge or foam like structures with adsorption properties.

In order to balance the charge in the multifunctional defluorination filter material structure, alkali metal or alkaline earth metal ions that enter the crystal structure of the multifunctional defluorination filter material can be replaced by other ions. As one of the main components of multifunctional fluoride removal filter materials, alumina has hydrolysis properties similar to aluminum salts. The hydrolysis of aluminum salts and the positive charge of aluminum colloids provide a theoretical basis for the adsorption of highly electronegative fluoride ions. After specific high-temperature modification and chemical activation, the multifunctional fluoride removal filter material has high selective exchange performance for fluoride ions. The multifunctional fluoride removal filter material after absorption can be regenerated with a desorbent and reused repeatedly.

4. Operation characteristics of fluoride removal equipment for drinking groundwater

(1) The pH value of the raw water is within 8.0, and there is no need to adjust the pH.

(2) Has better stability. After the first regeneration of defluorination materials such as activated alumina, the defluorination energy not only decreases, but also accelerates with the increase of production cycle; Multi functional defluorination filter material, during the first ten production cycles, the energy increases once every regeneration until it stabilizes.

(3) The effluent quality is good. Activated alumina and other materials can only remove fluoride and cannot comprehensively improve water quality; Multi functional defluorination filter material can comprehensively improve water quality. Activated alumina effluent has the problem of increased or even exceeded aluminum ions, while multifunctional fluoride removal filter media does not have this problem. Aluminum ions can cause premature hardening of the cardiovascular system, leading to stroke, hemiplegia, and brain dementia.

(4) Strong anti-interference ability. Activated alumina, hydroxyapatite, and other materials that come into contact with iron, manganese, and high hardness water will quickly decrease in particle size, turn yellow in color, and have difficulty recovering their functions after regeneration, and may even fail after two or three cycles. The multifunctional fluorine removal filter material is basically not affected by poor water quality and can remove interfering substances together.

(5) Easy to operate and manage. The management of activated alumina and other materials is difficult, and if not handled properly, they may become ineffective due to compaction; The multifunctional defluorination filter material does not have the problem of clogging. Even if it is not used for several years, it can be cleaned before use to restore its original adsorption capacity.

5. Mechanism of fluoride removal by filter media

To characterize the chemical reaction process and simplify the discussion, several conditions are assumed:

(1) K+in aluminum potassium solution can undergo complete exchange with MxDy;

(2) Al3+in aluminum potassium sulfate solution undergoes hydrolysis in the most advanced first-order hydrolysis state (K=1 × 10-5), namely Al3++H2O Al (OH) 2++H+;

(3) Represent the total charge of MxDy by (MxDy)+.

After special physical and chemical modifications, the multifunctional defluorination filter material is activated by aluminum potassium sulfate solution. The (MxDy)+, which is maintained by positive charges in the multifunctional defluorination filter material, is exchanged by K+and has strong polarity. The hydroxyl complex Al (OH) 2+of aluminum, which is rich in positive charges, transfers the charge of K+during the exchange process as a special hydrated cation, and adsorbs on the surface of the multifunctional defluorination filter material. SO42- coordinates with the hydroxyl complex of aluminum to maintain electricity balance. The reaction process is represented as:

MxDy—R+ K+ + Al3+ + SO42- +H2O→R—K? Al（OH）SO4 +（MxDy）+ +H+

When the multifunctional defluorination filter comes into contact with fluorine-containing raw water, the highly electronegative F - will replace SO42-. At the same time, MxDy in the fluorine-containing water enters the pores of the multifunctional defluorination filter and undergoes a certain degree of exchange with K+in the pores of the multifunctional defluorination filter. The reaction is expressed as:

R—K? Al（OH）SO4 +2F-+（MxDy）+→MxDy—R? Al（OH）F2 + K+ + SO42-

Parameter table of defluorination equipment:

Project/Model	Water production rate (m3/h)	Tank diameter (mm)	Main equipment weight (Kg)	Water supply population
HCF-1	4～6.5	￠1000	900	1600
HCF-2	8~12	￠1400	2300	3200
HCF-4	13~20	￠1800	3500	5400
HCF-5	16~25	￠2000	4000	6400
HCF-6	20~36	￠2400	4900	8000
HCF-7	28~40	￠2600	5400	11000
HCF-8	35~50	￠2800	6000	13000
HCF-9	45~60	￠3000	6700	16000