Dynamic adsorption of fluoride,iron and manganese in underground water of mining area by Srp/HAP

To address the problem of excessive fluorine,iron,and manganese pollution associated with groundwater in mining areas,a composite adsorbent of serpentineloaded hydroxyapatite (Srp/HAP) was prepared using a wet chemical co-precipitation method,and the synchronous adsorption performance of Srp/HAP on F-,Fe2+,and Mn2+ was investigated using dynamic adsorption tests to examine the effects of adsorption bed height,flow rate,and inlet water concentration on the penetration process.Adams Bohart and Thomas model fitting and microscopic characterization by SEM,EDS,XRD,BET,and FT-IR were used to analyze the adsorption mechanism of Srp/HAP on F-,Fe2+,and Mn2+.The results show that the prepared Srp/HAP composite adsorbent particles are compact,which not only has a sheetlike curled structure on the surface of Srp,but also solves the problem of agglomeration on the surface of HAP.After loading,the specific surface area and pore volume of the particles are significantly increased,and they have a better surface.The pore structure facilitates the simultaneous adsorption and removal of fluorine,iron and manganese.The total adsorption volume of the adsorption column increases with the increase in the height of the bed column’s mass transfer zone and the initial concentration of the three ions.The dynamic column has the highest dynamic adsorption capacity for the ions at a feed water flow rate of 4 ml/min.Additionally,the large and small flow rates are not conducive to the dynamic adsorption of the composite adsorbent.When the adsorbent filling height is 15 cm and the inlet water flow rate is 4 mL/min,the dynamic column has the maximum dynamic adsorption capacity of F-,Fe2+ and Mn2+ with initial concentrations of 5,20,and 5 mg/L are respectively 1.567,7.008 and 1.615 mg/g.The adsorption kinetic characteristics of F-,Fe2+ and Mn2+by Srp/HAP can be better described by the Thomas model.Microscopic analysis shows that the adsorption process includes surface physical adsorption and chemical adsorption,and chemical adsorption is mainly manifested by ion exchange and surface complexation.F- partly replaces OH- in HAP,Fe2+ and Mn2+ replace Mg2+ in Srp,so that F-,Fe2+ and Mn2+ are mainly present on the surface of composite particles as Fe3Si2(OH)4O5,Mn3Si2(OH)4O5,Ca5(PO4)3F compounds exist,and PO3-4 on the surface of HAP crystals may also complex with Fe2+ and Mn2+.The serpentineloaded hydroxyapatite composite particles can be used as excellent adsorbents for the treatment of groundwater containing fluorine,iron,and manganese ions in mining areas.