Identification and Evaluation of NaOH Hydrothermal-Treated Na-Ca-Si-Al Glass.

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  • Ｎａ‐Ｃａ‐Ｓｉ‐Ａｌ系ガラスのＮａＯＨ水熱反応による生成物の同定と評価
  • Na Ca Si Alケイ ガラス ノ NaOH スイネツ ハンノウ ニ ヨル セイセイブツ ノ ドウテイ ト ヒョウカ

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Abstract

Wasted glassy materials such as coal fly ash, fused garbage slag or aqua-crashed furnace slag are generally classified into two groups in terms of a product of a hydrothermal treatment in NaOH solution (zeolite synthesis process). One group is materials from which zeolites will be crystallized well, and the other is those from which zeolites will be hardly crystallized. Coal fly ash belongs to the former group, and fused garbage slag and aqua-crashed furnace slag the latter. The zeolite synthesis process can be divided into two stages. In the 1st stage, Si and Al are dissolved from glass to the solution. In the 2nd stage, the dissolved Si and Al are gathered in the vicinity of glass surface and crystallized to zeolite. The second group (fused garbage slag and aqua-crashed furnace slag) is characterized by high content of CaO. It has been thought that the high content of Ca0 will prevent the dissolution of Si in the 1st stage, resulting in inhibition for subsequent crystallization of zeolites in the 2nd stage. In this study, validity of this general speculation was examined in terms of a change in amount of Al, Si and Ca in the glass and solution at the hydrothermal condition, being compared with a theoretical calculation based on the molecular orbital method.<BR>The Na-Ca-Si-Al glasses with the composition range of Na2O+Ca0≥40 mass% were prepared, and then they were subjected to the hydrothermal treatment in 2 M NaOH solution. The zeolite species, NaP1, was dominantly synthesized from glasses in the composition range of CaO<10 mass%. Calcium silicate hydrate or calcium aluminosilicate hydrate, CS (A) H, became dominant in the product from glasses in the range of Ca0> 10 mass%. It was found that the formation of CS (A) H, as well as NaP1 and hydroxy-sodalite, possibly affected the cation exchange capacity (CEC) value. Cross-sectional microanalysis of the glass surface and quantitative analysis of the hydrothermal media after the treatment of the glass of 30 mass% CaO revealed that the Al component was selectively dissolved into the solution and the Si component fairly remained in the glass. Also, the theoretical calculation supported the analytical results, in which Al-0 bond would be weaker than Si-O bond in Al-O-Si bonding when Al was tetrahedral and Na+ and CaOH+ coexisted. As a result, we proposed the reaction phase model on the alkali hydrothermal treatment of high Ca0-content glass, in which the reaction phase of tight calcium silicate bonding covers upon the glass surface.

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