Synthesis of zeolites from paper sludge ash and their ability to simultaneously remove NH₄⁺ and PO₄³⁻

Abstract

The objective of this study was to investigate the synthesis of zeolites from paper sludge ash, and to evaluate their applications for water purification to simultaneously remove NH₄ ⁺ and PO₄ ^{3 −} in aqueous solution. Paper sludge ash had a low abundance of Si and a significant Ca content, due to the presence of calcite that was used as paper filler. Na₂SiO₃ was added to the NaOH solution to increase Si content in order to synthesize zeolites with high cation exchange capacity. The original ash without addition of Si yielded hydroxysodalite with a cation exchange capacity of ca. 50 cmol/kg. Addition of Si to the solution yielded Na-P1 (zeolite-P) with a higher cation exchange capacity (ca. 120 cmol/kg). The observed concentrations of Si and Al in the solution during the reaction explain crystallizations of these two phases. The product with Na-P1 could simultaneously remove NH₄ ⁺ and PO₄ ^{3 −} from the solution between pH 4 and 9.

Keywords:

• Paper sludge ash
• cation exchange capacity
• hydroxysodalite
• Na-P1
• water purification
• simultaneous removal of NH₄ ⁺ and PO₄ ³⁻.

Acknowledgments

Analyses of samples by XRD and XRF were carried out at the Instrumentation Center, The University of Kitakyushu.