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1

Physically and chemically bound H2O in the gyrolite structure

100%

Baltakys K. , Siauciunas R.

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tom Vol. 27, No. 1

255--263

EN

Synthetic pure gyrolite prepared under hydrothermal conditions (32 h, 200 °C) from a stoichiometric composition (CaO/SiO2 = 0.66) of calcium oxide and a fine-grained SiO2onH2O mixture can easily adsorb water vapour. The equilibrium quantity of adsorbed water vapour was estimated from desorption thermograms. It was determined that the thermal effect of desorption is close to the steam-heat of water vapour at temperatures up to 175 °C. This part of water vapour adsorption can be described by a physical adsorption model, only a small quantity of water vapour being chemisorbed. The crystal structure of gyrolite under a pressure of water vapour and at low temperatures (-197 °C) was stable.

2

The sorption of copper ions by gyrolite in alkaline solution

100%

Bankauskaite A. , Baltakys K.

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tom Vol. 27, No. 3

899--908

EN

Sorption of copper ions by synthetic pure gyrolite (CaO/SiO2 = 0.66; 96 h; 200 °C) in alkaline solutions was examined. When the initial concentration of Cu2+ ions is 1 g/dm3, the cation exchange capacity of the gyrolite is 100 mg Cu2+/g after 360 min of sorption at 25 °C. It has been proved that the cation exchange capacity of gyrolite depends on the concentration of copper ions in the Cu(NO3)2 solution, because a fivefold increase of the concentration (from 1.0 to 5.0 g/dm3) reduces the duration of the ion exchange reaction by a factor of three (from 15 min to 5 min). In solutions with higher initial concentrations of Cu2+ ions (10.0 and 20.0 g/dm3), the sorption proceeds more intensively and all the copper ions are adsorbed in 1 min. It should be noted that the cation exchange reactions are reversible in alkaline solution, because nearly 90% of the copper ions are adsorbed in a physical process, while the remaining part of the cation exchange process takes place in a chemical reaction. Furthermore, the crystal structure of gyrolite is stable in alkaline solution. The products of sorption were characterized by X-ray diffraction, thermogravimetry-differential scanning calorimetry and Fourier-transform infrared spectroscopy methods.

3

The influence of gamma-Al2O3 and Na2O on the formation of calcium silicate hydrates in the CaO-quartz-H2O system

100%

Baltakys K. , Siauciunas R.

Materials Science Poland

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2007

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tom Vol. 25, No. 1

185--198

EN

The influence of gamma-Al2O3 and Na2O additives on the formation and sequence of calcium silicate hydrates in the CaO-quartz-H2O system with CaO/SiO2 (C/S) molar ratio equal to 0.66 was determined. The synthesis was carried out in unstirred suspensions. The molar ratios of the primary mixtures were CaO/(SiO2 + Al2O3) = 0.66 and Al2O3/(SiO 2 + Al2O3) = 0 or 0.025. The amount of NaOH, corresponding to 5% of Na2O in the mass of dry material, was added in the form of solution. Due to the low solubility rate of quartz in the CaO-quartz-H2O system with C/S = 0.66 in the temperature range 150-200°C, low-base calcium silicate hydrates (Z-phase, gyrolite, pectolite, and others) do not form even after 72 hours of hydrothermal curing. It has been proved that gamma-Al2O3 and Na2O additives change the reaction mechanisms and composition of intermediate (final) products. In mixtures with Na2O, gyrolite starts to form already at 175°C. It should be noted that in the temperature range 175-200°C the final products are gyrolite and pectolite, and the intermediate compounds are C-S-H(l) and Z-phase. The formation of low-base calcium silicate hydrates in the CaO-quartz-Na2O-H2O system is slowed down when Al 2O3 is added because Al3+ ions stimulate the formation of tobermorite and prevent the formation of pectolite and Z-phas

4

Hydrosodalite ion exchange in saturated Ca(OH)2 solution

80%

Vaičiukyniene D. , Baltakys K. , Kantautas A.

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tom Vol. 27, No. 2

417--426

EN

The possibility of substituting Na+ ions contained in pure hydrosodalite crystal structure with Ca2+ ions in saturated Ca(OH)2 solution has been examined in the temperature range from 25 °C to 95 °C. It was found that temperature strongly influences the hydrosodalite ion exchange: upon increasing temperature only by 5 °C (from 25 to 30 °C) Ca2+ the time required for Ca2+ions to be incorporated within the hydrosodalite crystal structure is reduced by the factor of 3. With the increase of temperature from 45 °C to 65 °C almost all the Ca2+ ions, initially contained in the Ca(OH)2 solution, become incorporated in the hydrosodalite structure after 5 min However, high temperature has an adverse effect on the sorption process (Ca2+ ions will not be incorporated within the hydrosodalite structure before 10 min have elapsed). Partly reversible ion exchange reactions of hydrosodalite are characteristic at temperatures higher than 30 °C). The structure of hydrosodalite crystals remains stable when performing ion exchange reactions at 25-95 °C temperature.