Haipu Successfully Overcomes the Difficult Problem of Advanced Treatment of Fluorine-Containing Wastewater

Characteristics and sources of fluoride containing wastewater treatment

Fluoride is one of the trace elements required by the human body to maintain normal physiological activities. Excessive or insufficient intake of fluoride from the outside can affect health. Long term consumption of water with a fluoride concentration below 1.0 mg/L is prone to dental caries, while on the other hand, long-term consumption of high fluoride water is prone to systemic chronic diseases characterized by fluorosis and fluorosis, and even causes damage to the human brain and nerves. In order to protect the human living environment, the research on fluoride removal from fluorine-containing wastewater treatment is an important task in the fields of environmental protection and hygiene both domestically and internationally.

1. Sources of fluoride pollution

The main source of fluoride pollution in water environment is the discharge of fluorine-containing "three wastes" from industrial production, involving industries such as aluminum electrolysis, steel, cement, bricks and tiles, ceramics, phosphate fertilizers, glass, semiconductors, pharmaceuticals, etc. The common feature of these industries is the use of fluorine-containing minerals as the main or auxiliary raw materials. During their smelting and production processes, fluorine decomposes from minerals and enters the environment, causing fluorine pollution. For example, the electrolytic aluminum industry requires the addition of aluminum fluoride (AlF3) and cryolite (Na3AlF6) in the production process; The fluoride pollution in the steel industry is mainly caused by the addition of fluorite during converter steelmaking, which results in the production of a large amount of fluorine-containing flue gas, dust, metallurgical slag, and wastewater during the smelting process; The fluorine pollution in the phosphate fertilizer industry is due to the presence of fluorine in phosphate rock. When processed by acid method, some of the fluorine escapes as waste gas; In the production of glass, ceramics, cement and other industries, fluorite, cryolite, sodium fluorosilicate and other fluorine-containing raw materials are often added. When fired at high temperatures, a large amount of fluorine pollution is also generated; The semiconductor industry requires the use of hydrofluoric acid, ammonium fluoride, etc. in the etching process, which is the source of fluorine-containing wastewater; Due to the presence of fluorine in coal, the flue gas from coal-fired power plants and other industries (including civilian use) also contains a certain amount of fluorine. Fluorine enters the environment in different forms. Fluorine entering the atmosphere mainly exists in the form of gaseous silicon tetrafluoride (SiF4), hydrogen fluoride (HF), and fluorine-containing dust. Fluorine entering water mainly exists in an ionic state (such as SiF26-). Fluorine entering solid waste exists in stable compound forms such as calcium fluoride (CaF2).

2. Research progress on fluoride containing wastewater treatment technology

At present, fluorine-containing industrial wastewater treated both domestically and internationally has complex and diverse components, and there are various treatment methods available. The commonly used methods include adsorption and precipitation, as well as reverse osmosis, ion exchange resin, electrocoagulation, electrodialysis, and so on.

2.1 Precipitation method

2.1.1 Chemical precipitation method

The chemical precipitation method is to add a certain amount of chemical reagents to fluorine-containing wastewater, so that they can form fluoride precipitates with the fluoride in the wastewater or use co precipitation to adsorb fluoride ions. Then, filtration or natural sedimentation methods are used to separate the precipitate from the water, achieving the purpose of fluoride removal. The most commonly used method is limestone precipitation, and its reaction equation is

Ca2++2F－→CaF2↓

Although the chemical precipitation method is simple and cost-effective, it has the problem of secondary pollution and the treatment effect is not ideal. The fluoride content in the effluent is 15-30 mg/L, which makes it difficult to meet the national first-class discharge standard. In addition, it has defects such as slow sedimentation of sludge, long treatment cycle for large flow discharge, and unsuitability for continuous discharge. This method is generally only used for the pre-treatment of fluoride removal in drinking water, and further treatment is required to meet the national fluoride content standards for drinking water.

2.1.2 Coagulation precipitation method

The coagulation precipitation method is a method of removing fluoride by using F - in water to form complex precipitates with cations such as A13+, Fe3+, Mg2+, etc. The selected coagulants are generally inorganic coagulants such as alum, polyiron, and polyaluminum, as well as organic coagulants, including polyacrylamide and natural high molecular weight compounds (such as cellulose, starch, lignin, and chitosan). Different coagulants have different defluorination effects due to their different mechanisms of action.

In the actual processing, lime is usually used together with alum, that is, lime is first added to form a precipitate, and then alum is added to form Al (OH) 3 for flocculation, and the two work together to achieve a good defluorination effect. The removal efficiency of fluoride is highest when the pH value is between 5.5 and 7.5.

The coagulation precipitation method can treat wastewater with high fluoride content, which is economical, practical, simple in equipment, and easy to operate. However, it has problems such as large dosage of coagulant, generation of difficult to treat waste residue, unstable defluorination effect, increasing trend of sulfate ions after defluorination, and large amount of dissolved aluminum in the treated water.

2.2 Adsorption method

Adsorption method is to remove fluorine-containing wastewater by passing it through a device equipped with a fluorine adsorbent. Fluorine is exchanged with other ions or groups in the adsorbent and left on the adsorbent, while the adsorbent is regenerated to restore its exchange capacity. Due to the fact that adsorption process is a surface reaction based on contact method, adsorption method is usually only suitable for the treatment of low fluoride wastewater, or for the deep treatment of pre treated wastewater with fluoride content reduced to 15-30 mg/L.

The adsorption method has a good effect on the deep treatment of fluorine-containing wastewater, but its practicality is limited due to problems such as bed loss, low adsorption capacity, and complex bed regeneration and regeneration liquid treatment. The main direction of future research on adsorption based fluoride removal is to develop efficient new adsorbents to overcome the shortcomings of traditional adsorbents with small saturation adsorption capacity. In addition, it is necessary to strengthen research on the selectivity of adsorbents, regeneration of adsorbents, and adsorption mechanisms.

2.3 Other methods

In addition to the two main methods for treating fluorine-containing wastewater mentioned above, many researchers have also conducted extensive research in areas such as reverse osmosis, electrocoagulation, ion exchange resin, and electrodialysis. For special fluorine-containing wastewater, some new methods have been applied and achieved good results.

2.3.1 Reverse osmosis method

Reverse osmosis technology is widely used in seawater desalination, ultrapure water preparation, and other fields, but there are few reports on the treatment of fluorine-containing wastewater. The reason is that reverse osmosis technology is a molecular level treatment technology that needs to prevent suspended solids from contaminating the reverse osmosis membrane, and industrial wastewater has numerous impurities, so complex pretreatment is required before treatment. In addition, reverse osmosis equipment is expensive and consumes a large amount of electricity.

2.3.2 Electrocoagulation method

The electrocoagulation method uses the intermediate products of different forms of hydroxides formed during the hydrolysis process of aluminum ions dissolved into the solution by aluminum plate electrodes under the action of a direct current electric field as adsorption media to adsorb F - and fluoride complexes in water. The electrocoagulation method can reduce the F-concentration of low concentration fluorine-containing wastewater to below 2 mg/L. Although the electrocoagulation method has simple equipment and easy operation, it has a high water production cost and poor treatment effect on wastewater with high fluoride content, making it difficult to promote at present.

2.3.3 Ion exchange resin method

The ion exchange resin method utilizes the ion exchange interaction between resin and solution to remove fluoride. The exchange capacity and fluoride removal efficiency of ion exchange resin method are relatively low, and the resin price is expensive and the regeneration cost is high, so there are no industrial examples yet.

2.3.4 Electrodialysis method

Electrodialysis is a type of membrane separation technology, which operates by utilizing the selective permeability of ion exchange membranes to selectively migrate anions and cations in water under the action of an external direct current electric field. Ionic exchange membrane is formed by ion exchange resin, so electrodialysis is actually another application form of ion exchange resin method.

The electrodialysis device is complex, consumes a large amount of electricity, requires high maintenance intensity, and has strict technical requirements for operators. In addition, the presence of high priced metal ions in the water can easily cause membrane poisoning and damage to the electrodes.

There are many methods for treating fluorine-containing wastewater, among which the precipitation method has a simple process and easy operation, but it requires a large amount of chemicals and can cause secondary pollution; Adsorption method has certain treatment effects on various types of wastewater, and the sources of adsorption materials are wide. If it can effectively improve the adsorption capacity of adsorbents and solve the problem of adsorbent regeneration, it should have good development prospects; Other new methods have more complex processes and higher operating costs, and are currently only suitable for the treatment of some special fluorine-containing wastewater. Developing new functional materials and combining various methods to achieve efficient treatment and resource utilization of fluorine-containing wastewater without generating secondary pollution is the future direction of fluorine-containing wastewater treatment technology.

Hepu Fluorinated Wastewater Treatment Plan

Jiangsu Haipu Functional Materials Co., Ltd. is a high-tech enterprise dedicated to the research and development of high-performance adsorbents, catalysts, and their process applications. With a series of independently developed high-performance adsorbents and catalysts as the core, combined with independently developed process technology, Haipu has become a professional solution provider in the fields of environmental governance and resource recycling. At the same time, taking it as our responsibility to help industrial enterprises meet environmental standards and achieve sustainable development through resource utilization, we adopt modular lean production and develop engineering solutions based on research and development data. Relying on independently developed high-performance adsorbents and rigorous and comprehensive process development, Haipu has accumulated many treatment cases in the deep treatment of fluorine-containing wastewater, solving development problems and creating value for many enterprises.

Haipu high-performance adsorbent has the following advantages:

Wide applicability and good practicality

This method can be applied to wastewater concentrations ranging from a few to several hundred ppm, and the adsorption is not affected by the inorganic salts contained in the solution. It can also be applied in non-aqueous systems.

High adsorption efficiency, easy desorption and regeneration

For fluorine-containing wastewater, after adsorption, it can generally meet or approach the discharge standards, with a material adsorption rate of over 95%, without producing secondary pollutants, and can significantly reduce the fluoride content. Common acid-base or organic solvents are used for desorption, and the desorption rate can generally reach over 92%.

Stable performance and long service life

The material has high resistance to oxidation, acid and alkali, and organic solvents, and can be used for a long time below 150 ℃. Under normal circumstances, the annual material loss rate is less than 5%.

Beneficial for comprehensive utilization and turning waste into treasure

The raw material intermediates or products present in wastewater generally have higher prices. The adoption of this method can largely recycle and use, which will generate considerable economic benefits. Usually, the recycling value is equivalent to the daily operating expenses, and some have surplus.

Easy to operate, low energy consumption

Using this technology, the process is simple, no special equipment is required, the technology is easy to master, and the consumption of thermal and electrical energy is relatively low during operation.

Haipu Handling Case

4.1 The 2000t/d fluorine-containing wastewater generated in the production of a certain enterprise in Hunan was treated by the Haipu adsorption process, and the fluoride content in the wastewater was reduced to below 20ppm, thus meeting the requirements for enterprise reuse.

4.2 After treatment with the Haipu adsorption process, the fluoride content in the 600t/d fluorine-containing washing water of a certain enterprise in Shandong is greatly reduced, and no other metal ions or impurity ions that affect reuse are introduced, achieving a removal rate of over 90%.

4.3 A Beijing enterprise's 1500t/d circuit board fluorine-containing washing water is required to be reused without introducing other impurity ions or increasing the TDS of the effluent. After treatment with the Haipu adsorption process, the fluoride content in the water is less than 0.5ppm and meets other customer requirements.