Hydrothermal Synthesis of Zeolite A Using Blast Furnace Slag

Abstract

Alkali hydrothermal synthesis of zeolite A using blast furnace (BF) slag was investigated. The preliminary experiment was conducted in use of synthetic slag consisting of SiO 2 , Al 2 O 3 , and CaO powders, and it was made clear that the most optimum slag compositions to synthesize zeolite A were the molar ratio of Si to Al (Si/Al) of 1 and reduction of CaO content down to 15 mass%, and that hydrothermal treating conditions were the temperature range from 328 to 358 K, NaOH solution of 1 M (ϭmol/L) and the ratio of the volume of NaOH solution to total mass of slag (V sol /W slag ) of 15 (mL/g). It was also found that synthetic slag with such a higher content of CaO as 40 % resulted in formation of tobermorite and hydrogarnet. In the experiment using BF slag, zeolite A could be successfully synthesized by optimizing both conditions of the compositions of raw material powders and hydrothermal treatment as noted above, where optimization of the compositions of raw material powders such as Si or Al content were performed by the suitable amount of addition of SiO 2 powder or NaAlO 2 powder as a source of Si and Al. The ball milling type reaction vessel containing numerous small SiC balls which was first adopted in this hydrothermal treating study was confirmed to be very effective for acceleration of synthetic reaction rate, shortening markedly the time period needed for fully synthesis of zeolite A. Temperature dependence of heat capacity of zeolite A powder synthesized in use of BF slag was measured after absorption of vapor at the ambient temperature, showing endothermic behavior with the peak at the temperature of around 473 K.

Alkali Hydrothermal Synthesis of Zeolite A Using Oxide By-products

“…It is concluded that the reason why the heat of water adsorption of the product was greater than the predicted value is that the Si/Al ratio of the synthesized zeolite A is less than that of commercial zeolite A. Further, not only the formation of zeolite A but also that of tobermorite and hydrogarnet, which had a certain heat storage capacity, 6) was detected. This is also one of reasons why the products have greater heats of water adsorption.…”

“…From the previous study, 6) it was found that the decrease of CaO content in raw material powders in use of BF slag was essentially needed to synthesize zeolite A. Under the optimum conditions, the addition ratio of BF slag has to be controlled less than 30% of the raw materials.…”

“…However, they did not report on the alkali hydrothermal synthesis of zeolite A. We have previously 6) reported the synthesis of zeolite A using water-quenched BF slag. The synthesis of zeolite A was carried out using BF slag, SiO 2 , and NaAl 2 O 4 , where BF slag was used to adjust the composition of the raw material.…”

“…As previously described, the major product obtained by the direct synthesis of zeolite A under high ratio of solution to powder material was sodalite. 6) Many researchers have investigated the transformation of zeolite A to sodalite. Subotic et al 16) reported that zeolite A transformed to zeolite P in 1 mol/L NaOH solution and to hydroxysodalite under high concentrations of NaOH.…”

Preparation of Porous Ceramics by the Hydrothermal Reaction of Blast Furnace Slag for Use in a Water-retentive Material

“…Hydrothermal treatments of BF slag have been applied in the production of heat storage material and high strength building material with additives. [1][2][3][4] In addition, the authors have studied the hydrothermal reaction of the slag for preparing functional materials.…”