Abstract
UDC 541.183
This article considers the adsorption potential of a natural (D1) and structural-chemical modified (DMA) diatomites in removing fluorine ions from solutions with high concentrations of the latter (0.3 mol/l) under static conditions at room temperature. The influence of different parameters such as pH, initial concentration of fluorine, sorbent mass, the surface charge density of the particles were examined so as to understand the adsorption properties of sorbents with respect to fluorine. It is shown that the pH of the solution plays a crucial role in the removal of fluorine from the solution. An efficient removal of fluorine takes place at a pH of 4.5–5.5. In equilibrium conditions, at the saturation of the DMA surface with fluoride ions, its adsorption capacity reaches 1160 mg F/g of the sorbent at the initial fluorine concentration in water of 0.035 mol/l. That is 5.5 times higher than with an unmo-dified sample – D1. The adsorption isotherms of F on the samples of diatomite have been obtained; equilibrium adsorption data were modeled using a two-step Langmuir model. The experimental results were shown to be in good agreement with the adsorption of F calculated by the model: the correlation coefficient R2 is 0.9952 for the sample D1 and 0.9687 for the DMA. The mechanism of F adsorption on the samples has been studied. An XRD and chemical analysis, FTIR-spectroscopy and potentiometric titration data, as well as the experiments on adsorption – desorption showed that in the diatomite – NaF-H2O system there is the physical adsorption, ion exchange, and chemical bonding of the fluorine ions with the sorbents surface active sites – low soluble compounds of fluorine with Al on the DMA and Ca on the D1 (AlF3, Na3AlF6, CaF2).
Keywords: diatomite, modification, adsorption, fluorine, modeling, adsorption mechanism.