Abstract
Paper sludge ash (PSA) typically has a low Si abundance and significant Ca content because of the presence of calcite fillers, which interfere with the zeolitic conversion of PSA. Ca-masking with ethylenediaminetetraacetic acid (EDTA) was used to reduce Ca interference during zeolite synthesis so that a zeolitic product with a high cation exchange capacity (CEC) could be synthesized. Hydroxysodalite, zeolite-P, hydroxycancrinite, tobermorite, and zeolite-A can be synthesized from PSA by an alkali reaction with EDTA. With the addition of EDTA, calcium ions in the solution were trapped by chelation, and the number of zeolitic crystals with low Si/Al (Si/Al = 1), zeolite-A, increased owing to the promotion of the synthesis reaction. A product with a high CEC that has a high zeolite-A content was obtained. The chelating agent can inhibit Ca interference for zeolite synthesis by Ca-masking, and a product with a high zeolite-A content can be obtained from PSA using EDTA.
Highlights
Zeolites are a group of microporous aluminosilicate minerals that are tectosilicates with three-dimensional aluminosilicate structures containing water molecules, alkali, and alkaline earth metals in their structural framework [1,2]
The chemical and mineralogical compositions of the Paper sludge ash (PSA) used in this study are shown in Table 1 and Figure 1, respectively
The interference by Ca content was inhibited by Ca-masking by ethylenediaminetetraacetic acid (EDTA), and a high content of the aluminosilicate gels with higher Si/Al ratios were converted into zeolite-A, zeolite-P, and hydroxysodalite
Summary
Zeolites are a group of microporous aluminosilicate minerals that are tectosilicates with three-dimensional aluminosilicate structures containing water molecules, alkali, and alkaline earth metals in their structural framework [1,2]. In the past few decades, PSA has been used for the synthesis of functional minerals, such as zeolites and tobermorites [39,40] Owing to their ion-exchange properties and unique structures, they are used in various applications such as gas removal and water purification [41,42,43]. We applied acid leaching to reduce the Ca content in calcium-containing ash to synthesize zeolitic materials with high CECs [48,49,50].
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