Kestutis Baltakys

A study on the intercalation of heavy metal ions in a wastewater by synthetic layered inorganic adsorbents

AbstractThis study examined the intercalation mechanism of Co2+, Ni2+, Zn2+, Mn2+ and Fe3+ ions into synthetic layered inorganic adsorbents—hydrotalcite and gyrolite under different conditions. It was observed that the process parameters above depend on the chemical nature of both solutions and adsorbents. An extremely high and selective uptake of Fe3+ ions was observed in both cases (~98–99%). The selectivity sequence of studied metal ions by gyrolite can be written as follows: Co2+ > Zn2+/Mn2+/Ni2+ > Fe3+, while with calcined hydrotalcite: Co2+/Ni2+/Mn2+ > Zn2+ > Fe3+. It was determined that, during simultaneous adsorption, the intercalation of heavy metal ions into the structure of gyrolite or calcined hydrotalcite proceeds differently, because the amount of adsorbed Mex+ ions is higher than the amount of leached Ca2+ and Mg2+ ions, resulting in the occurrence of two types of chemical reactions – substitution and addition. It should be noted that almost all heavy metal ions (~99.84%) are chemisorbed by...

The Synthesis of α-C2S Hydrate Substituted with Al3+ Ions in Mixture with CaO/SiO2 = 1.75

The parameters of α-C2SH substituted with Al3+ ions hydrothermal synthesis was determined. α-C2SH was synthesized in the primary mixtures with CaO/(SiO2+Al2O3) = 1.75 and Al2O3/(SiO2+Al2O3) = 0; and 0.025. The hydrothermal synthesis has been carried out in unstirred suspensions under saturated steam pressure in argon atmosphere at 175 °C temperature for 4; 8; 16; 24; 48; 72 hours by applying extra argon gas (10 bar). It was determined that in unstirred CaO–SiO2·nH2O–H2O suspensions, the additive of Al2O3 changes the formation mechanism of synthesis products as well as their stability during the isothermal curing. It should be noted that in the mixtures with Al2O3, within 4 hours of isothermal curing at 175 °C all Al3+ ions were incorporated in the synthesis products structure. However, Al2O3 additive has negative influence on the formation of calcium silicate hydrates because even after 24 h of isothermal curing quite intensive diffraction peaks of unreacted portlandite were identified. When hydrothermal synthesis is extended to 48 hours, Ca (OH)2 fully reacted and dibasic calcium silicate hydrates start dominate in the products.

The Effect of Synthetic Hydrated Calcium Aluminate Additive on the Hydration Properties of OPC

The effect of synthetic CAH (130°C; 8 h; CaO/(SiO2 + Al2O3) = 0.55; Al2O3/(SiO2 + Al2O3) = 0.1, 0.15) with different crystallinity on the hydration kinetics of OPC at early stages of hydration was investigated. Also, the formation mechanism of compounds during OPC hydration was highlighted. It was determined that the synthetic CAH accelerated the initial reaction and shortened the induction period. Also, the second and third exothermic reactions begun earlier, and, during the latter reaction, the higher values of the heat flow were obtained in comparison with pure OPC samples. At later stages of hydration, synthetic CAH affect the OPC hydration as the usual pozzolanic additives; moreover, the larger values of cumulative heat were reached. It should be noted that the nature of synthetic CAH samples accelerated the dissolution of gypsum and stimulates the earliest C3S hydration.