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Zeolites were synthesized from paper-sludge ash in different alkali solutions. The ash used in this study has a high-Ca content and a low abundance of Si, in part due to the presence of calcite that is used as a paper filler. The major minerals present in the ash are gehlenite (Ca 2 Al 2 SiO 7 ) and anorthite (CaAl 2 Si 2 O 8 ). Three kinds of alkali solutions (NaOH, KOH, and LiOH) at four different concentrations (1, 2, 3, and 4 M ) were reacted with paper-sludge ash at 90 °C for 24 h. Powder X-ray diffraction showed that hydroxysodalite (Na 6 Al 6 Si 6 O 24 ·8H 2 O) and zeolite Linde F (KAlSiO 4 ·1.5H 2 O) had formed in NaOH and KOH solutions, respectively, and that anorthite had dissolved in these alkaline solutions, whereas gehlenite had remained unaffected. In the LiOH solution, both anorthite and gehlenite dissolved, and various minerals, including Li-ABW zeolite (Li 4 Al 6 Si 6 O 16 ·4H 2 O), hydrocalumite [Ca 2 Al(OH) 6 (Cl, OH)·3H 2 O], tobermorite [Ca 5 Si 6 O 16 (OH) 2 ·4H 2 O], katoite [Ca 3 Al 2 (SiO 4 )(OH) 8 ], and portlandite [Ca(OH) 2 ] formed. The products of mineral synthesis from paper-sludge ash by reaction in alkaline solutions strongly depend on the specific alkali present.

Paper sludge ash was partially converted into zeolites by reaction with 3M NaOH solution at 90 degrees C for 24 h. The paper sludge ash had a low abundance of Si and significant Ca content, due to the presence of calcite that was used as a paper filler. Diatomite was added to the NaOH solution to increase its Si content in order to synthesize zeolites with high cation exchange capacity. Diatomite residue was filtered from solution before addition of ash. The original ash without addition of diatomite yielded hydroxysodalite with a cation exchange capacity ca. 50 cmol/kg. Addition of Si to the solution yielded Na-P1 (zeolite-P) with a higher cation exchange capacity (ca. 130 cmol/kg). 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 capacity for PO(4)(3-) removal from solution as a function of Ca(2+) content, suggesting the formation of an insoluble Ca-phosphate salt. The product with Na-P1 exhibits the ability to remove NH(4)(+) as well as PO(4)(3-) from solution in concentrations sufficient for application in water purification. Both NH(4)(+) and PO(4)(3-) removal showed little variation with pH between 5 and 9. Alternative processing methods of zeolite synthesis, including the addition of ash to an unfiltered Si-NaOH solution and addition of a dry ash/diatomite mixture to NaOH solution, were tested. The third process yielded materials with lower cation exchange capacity due to formation of hydroxysodalite. The second process results in a product with relatively high cation exchange capacity, and reduces the number of processing steps necessary for zeolite synthesis.

Recent efforts to actively recycle paper have caused the amount of papermaking sludge to increase steadily each year, with current estimates of over 3,000,000 tons discharged annually throughout Japan. The Nippon Telegraph and Telephone Corporation has achieved success in converting ash derived from incinerated papermaking sludge into a new porous material with high cation exchange capacity by reacting this ash in an alkali solution. This paper reports some application of the new material to environmental conservation, such as improvement of water quality and admixture in concrete.