Research on industrial application of coagulation and adsorption combined with fluorine removal technology in fluorine-containing mine water

Stratigraphy status in western China is classified as high-fluorine formations.Coal mining activities lead to the fluorine migration from formations to groundwater,which causes the groundwater and mining drainage to exceed the fluorine concentration.In order to solve the problem of fluorine pollution in water,the emission limit of fluoride in mine drainage in Inner Mongolia mining areas was set up less than 1 mg/L which results in huge environmental protection difficulties.In this study,an accessible defluorination method addresses pointing at low fluoride discharge limit requirements and large quantity of wastewater treatment in mining industry.Practical technical route is proposed by combining polyaluminum chloride coagulation precipitation and hydroxyapatite adsorption,which can be dismantled in-situ treatment based on original mining water treatment plants.The results proves that:①35.%Al2O3 PACl as a defluorination reagent shows high defluorination rate (91.37%) and the residual fluoride concentration is less than 1 mg/L,only 0.6 mg/L;②the results of adsorption ability experiments show that the Pseudo-Second order kinetic model can better describe the adsorption of F- onto hydroxyapatite particles surface,and the adsorption isotherm of F- adsorption conforms to the Freundlich model,that is,the mainly adsorption principle is a multilayer chemical adsorption by the replacement of OH- and F.The dynamic adsorption experiments show that under 2 BV/h hydraulic conditions,the breakthrough point appears after 54 BV,and the alkali as the regenerating solution recovers comparable adsorption capacity as fresh adsorbents after 5 times regeneration.The regeneration solution is recommended to use 1.5% or 2% NaOH.PACl coagulation and hydroxyapatite adsorption cascade defluorination process is economical,which moreover can effectively avoid problems of the significant TDS increase owing to overdosing and the fluoride concentration over discharge due to fluoride fluctuations of influent.