Physicochemical and adsorption-structural properties of diatomite modified with aluminum compounds

Abstarct A selective sorbent based on the diatomite of local origin modified with aluminum compounds has been studied by the methods of powder X-ray diffraction; FTIR; and differential thermal, adsorption-structural (BET), and chemical analyses. The surface modification of diatomite is carried out by heating it in an NaOH solution and its subsequent treatment with a solution of aluminum salt and ammonia. The amorphous surface silica partially dissolves during the treatment with NaOH and forms an aluminosilicate compound at the addition of an aluminum salt. The obtained material is deposited both on the surface of the diatomite and on the inner surface of the macro- and larger mesopores, which leads to the development of the specific surface area of 81.8 m 2 /g, which is 2.5 times larger than the corresponding value in the initial diatomite (37.5 m 2 /g). The precipitated aluminosilicate compound with the concentration equal to 0.34 g of Al/g of aluminosilicate contributes to the development of a porous structure in the treated diatomite, so the volume of the mesopores increases from 0.029 to 0.079 cm 3 /g and that of the micropores from 0.012 to 0.027 cm 3 /g. The qualitative changes in the composition of the obtained sorbent are confirmed by the emergence of new lines in the X-ray diffraction patterns, which are characteristic for aluminosilicates, and additional peaks in the infrared spectra corresponding to the stretching vibrations of Si-O-Al. The selectivity of the obtained adsorbent with respect to fluoride ions increases significantly, specifically, its adsorption capacity increases from 8.9 to 57.6 mg of F/g at the initial fluorine concentration equal to 0.15 mol/L.