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The influence of solution pH on gyrolite adsorption capacity of Zn 2+ ions has been examined. Adsorption experiments were carried out in the thermostatic adsorber by stirring 1 g of gyrolite in 100 ml of Zn(NO 3 ) 2 solution containing 0.3 g/dm 3 of Zn 2+ ions. Duration of adsorption at 25 °C temperature was 0.5, 1, 3, 5, 10, 25, 60, 120 min. It was found that adsorption process in alkaline solution proceed faster and more efficiently as in acidic because after 30 s 95 % of Zn 2+ ions (28.50 mg Zn 2+ /g) intercalated in to gyrolite structure, whereas in acidic medium -68 % of Zn 2+ ions (20.43 mg Zn 2+ /g). Substitution reaction was found typical for gyrolite in the alkaline solution because 82 % zinc ions participated in ion exchange reaction and other part of these ions were present in gyrolite according to an addition interaction. Cation exchange mechanism proceeded differ in acidic solution because all zinc ions participated only in ion exchange reaction. The adsorption process in alkaline solution folowed by a pseudo-second order model and suggest that it is a process of chemosorption. Gyrolite recrystallized in to gyrolite gel and C-S-H(I) when reaction medium is acidic meanwhile in alkaline medium intercalated zinc ions do not affect the structural properties of gyrolite.

A B S T R A C TThe effect of gyrolite structure properties on Zn 2+ ion adsorption in an alkaline solution was determined. Gyrolite was synthesized for 32, 48, 72, 120, and 168 h at 200˚C from a stoichiometric composition (molar ratio of C/S = 0.66) of the initial CaO and SiO 2 ·nH 2 O mixtures. It was established that gyrolite does not regroup into related compounds, when the hydrothermal synthesis duration was varied from 32 to 168 h, although its structure changed as the duration of the synthesis was prolonged. Also, the adsorption capacity of gyrolite for Zn 2+ ions depends on the structural properties of the adsorbent. By prolonging the duration of synthesis from 32 h to 168 h, the adsorption capacity of gyrolite decreased from 99% (29.92 mg Zn 2+ /g) to 93% (27.91 mg Zn 2+ /g). It was found that the adsorption reactions are not reversible processes, and follow by a pseudo-second-order model. X-ray diffraction analysis showed that the crystal structure of gyrolite remained stable after the adsorption processes.