Synthesis of Zeolitic Material from Paper Sludge Ash Using Diatomite

Abstract

Paper sludge ash (PSA) was partially converted into zeolites by reaction with 3 M NaOH solution at 90°C for 24 h. The PSA had a low abundance of Si and significant Ca content, due to the presence of calcite that was used as paper filler. Diatomite, which contains amorphous silica and dissolves easily in alkali solution, was mixed with the ash, and then added to the NaOH solution to increase its Si content during alkali reaction and thus synthesize zeolites with high cation exchange capacity (CEC). The original ash without addition of diatomite yielded hydroxysodalite with CEC ca. 0.5 mmol/g. Addition of diatomite to the ash yielded zeolite-P with a higher CEC (ca. 1 mmol/g). The observed concentrations of Si and Al in the solution during the reaction explain the crystallization of these two phases. The reaction products were tested for their adsorption capacity for nutrients from liquid fertilizer, such as K+, NH4+ and PO43−. The product with zeolite-P exhibits high ability to adsorb these nutrients from liquid fertilizer, which is desirable for application in soil improvement.