Principle and application of polyaluminium chloride (PAC) as a high efficiency fluoride removal agent

1. Principle and chemical mechanism of fluoride removal

Polyaluminum chloride (PAC) is an inorganic polymer compound, and its fluoride removal is mainly realized through the following two mechanisms:

Chemisorption: PAC dissolved in water released aluminum ion (Al³), and combined with fluoride ion (F) to form hydrofluoric acid (HF) intermediate, and then further formed insoluble aluminum fluoride (AlF ₃) precipitation.

Co-precipitation effect: the aluminum hydroxide colloid generated by PAC hydrolysis coats the free fluorine ion through surface adsorption and mesh capture, and finally removes it by solid-liquid separation.

2. Application scenarios and effects

Groundwater purification: For high fluoride areas (fluoride concentration> 1.5 mg/L), PAC can reduce the fluoride content to the national drinking water standard (<1.0 mg/L). For example, in one case, the fluoride concentration was reduced from 14.6mg/L to 0.4-1.0mg/L, and the removal rate reached 75%.

Industrial wastewater treatment: suitable for fluorine-containing chemical wastewater (such as semiconductor, glass etching industry), can be combined with other fluoride removal agents (such as calcium salt) to improve efficiency.

Municipal water supply system: as a pretreatment or in-depth treatment link, to ensure the safety of drinking water, especially in the northern winter, the water temperature should be controlled by> 20℃ to maintain the reactivity.

3. core advantage

High efficiency: Compared with traditional aluminum salt (such as aluminum sulfate), PAC has high charge density and fast flocculation speed, and the fluorine removal efficiency is increased by 30% under the same addition amount.

Economy: the treatment cost is more than 40% lower than that of activated alumina, reverse osmosis and other technologies, and no complex equipment is needed.

Wide adaptability: pH A wide range of application (5.0-9.0), can synchronously remove turbidity, heavy metals and other pollutants.

4. Use the key points and use the optimization direction

Add control: it is recommended to determine the optimal feeding ratio (usually 11-13kg / thousand tons of water) through beaker experiment, and excessive use may lead to excessive aluminum residue.

Optimization of reaction conditions: the pH value is optimal at 6.5-7.6, and the temperature is lower than 20℃ when the temperature is increased.

Composite process development: the CaF ₂ -AlF ₃ double precipitation system can be formed when combined with calcium salt (such as lime), and the fluoride removal rate can reach more than 95%.

5. Environmental protection and economic value

As a key environmental protection material promoted in the 14th Five-Year Plan period, PAC reduces the risk of fluorosis and promotes the development of water treatment industry to the direction of low cost and low energy consumption. Its large-scale production (domestic annual output of more than 180,000 tons) and technology upgrading (such as aluminum hydroxide raw material process) further consolidate the dominant position in the market.

Through multiple action mechanisms and wide applicability, polyaluminum chloride has become one of the most economical and efficient fluoride removal solutions at present. With the application of nano-modification and other technologies in the future, its performance is expected to achieve greater breakthrough.