Preparation and properties of potassium aluminosilicate prepared from the waste solution of selectively leached calcined kaolinite

Amorphous aluminosilicates containing large amounts of potassium were prepared from the waste solution remaining after the preparation of mesoporous γ-alumina from kaolinite by selective leaching. The solution was neutralized using 3 mol/l nitric acid at pH≈5.5, producing a precipitate, which was aged in the mother solution for 0.5, 2, 8 and 24 h. After calcination at 350 °C for 4 h, the product was characterized by XRD, XRF, 27Al and 29Si MAS NMR, FTIR, NH3 TPD and N2 adsorption methods. The chemical composition of the amorphous product varies between (65.6–68.1) wt.% SiO2, (18.3–20.1) wt.% Al2O3 and (13.1–13.8) wt.% K2O in dry base. The pore size distributions show a sharp peak at 1.85 nm and a broad peak corresponding to pores up to 10 nm in radius. Increasing the aging time caused an increase in the larger particles, evidenced in the pore size distribution data by a decrease in the first peak and a broadening of the second peak. The porous properties of the samples showed little change with aging times, the surface area reducing from 377 to 360 m2/g during aging up to 24 h.