Aluminum agent fluorine removal potential risk non-aluminum technology to lead a new chapter

近日，Nanjing University张孝林副教授课题组以Formation of aluminum-fluoride complexes compromises defluoridation efficiency of aluminum-based coagulation为题，Published in the leading journal Environmental Science & In Technology (link: http://doi).org/10.1021/acs.est.4c04722), this study revealed the risk and mechanism of chemical method and aluminum materials in deep defluorination of industrial wastewater, which can provide theoretical guidance and methodological reference for the analysis of the form and total amount of fluoride in industrial wastewater。

The rapid development of strategic emerging industries such as photovoltaic, semiconductor, new energy vehicles and fluorine chemical industry has made human activities an important source of fluorine pollution in water bodies。It is estimated that billions of tons of fluorine-containing wastewater are produced in China every year, posing a serious threat to the water environment and human health。In recent years, with the upgrading of industrial wastewater fluoride discharge standards to surface water quality standards (Class I-III water :≤1 mg/L, Class IV-V water :≤1).5 mg/L), the demand for deep defluoridation of industrial wastewater has become increasingly prominent。

In view of the strong coordination ability between aluminum and fluorine, a large number of aluminum salt coagulant precipitators or aluminum-loaded adsorption resins have been selected for deep defluorination of industrial wastewater。Although there are still problems such as large overdosage of precipitating agents and lack of long-term stability of adsorbents, a large number of studies and engineering practices have shown that fluoride can be reduced to 1~1.Below 5 mg/L。However, recently, the research group of Associate Professor Zhang Xiaolin of Nanjing University found that due to the excessive precipitation agent and the loss of adsorbent, the residual aluminum in water will cause some fluorine to remain in the form of fluoro-aluminum complex。This results in a hidden danger that cannot be ignored: under environmental changes (such as pH fluctuations, salinity increases) or time, these complex fluorine may re-dissociate into free fluorine, resulting in the deterioration of water quality again。

The research group combined modern analytical methods such as 19F/23Al nuclear magnetic resonance spectroscopy (NMR) and electrospray mass spectrometry (ESI-MS)，Proving that fluoride in treated effluent is free fluorine (F-), Exchangeable fluorine (Exchangeable F), EF) and Non-exchangeable F, Three main forms of NEF exist。Experimental data show that even when the initial free fluorine content is very low (less than 0.5 mg/L), but over time, EF and NEF are gradually converted to free fluorine, resulting in a concentration of 2-3 mg/L within 48 hours, posing a potential threat to water safety。

Figure: Residual fluorine form after chemical coagulation treatment(a)And detection method(b)示意，Fluorine morphology distribution in photovoltaic wastewater after coagulation treatment(c)Transform with...(d)

Based on the above research, NTU Environmental research and development team through detailed research on the production process, targeted solutions, innovation iteration:

Increase the promotion of low aluminum and zero aluminum defluorination technology

Considering the instability of reversible transformation of fluorine-aluminum complexes, and the low or zero aluminum defluorination technology may become a new trend of environmental protection, NTU environmental protection research and development team has developed innovative materials such as strong coordination and precipitation special defluorination agents, collaborative precipitation defluorination technology and equipment, and zirconia-loaded nano-adsorption resins, which have been successfully applied in a number of projects。In view of the stronger coordination capacity between zirconium and fluorine, and its chemical stability is far greater than that of aluminum, so it can form non-exchangeable fluoride or fluorine precipitation with fluorine, effectively avoiding secondary pollution caused by the loss of zirconium, and opening up a safer and more efficient new path for the deep defluorination of industrial wastewater。

Nanomaterial deep defluorination equipment is more reliable

Over the years，Ntu Environmental Protection works closely with Nanjing University to jointly tackle key problems，To meet the needs of deep defluorination of industrial wastewater，After more than 10 years of continuous research and development，The deep defluorination equipment of industrial wastewater with nano-adsorption materials as the core can not only reduce the fluoride in various wastewater stably to less than 1 mg/l，And can significantly reduce operating costs。At present, the relevant technology has treated 60 million tons of fluorine-containing wastewater, and it is continuously promoted and applied。