Cationic reaction of transition metals with synthetic crystalline calcium sillicates

The action uptake reactions of transition metals of Mn, Fe, Co, Ni, Cu, Zn, Pb, Cd and Hg with some synthetic crystalline calcium silicates such as xonotlite, gyrolite and Beta-wollastonite were studied. The total cations uptake reaction appeared to be a factor combining both partial exchange Ca[2+] - M[2+]and precipitation of M[2+] as carbonates, hydroxy carbonates, hydroxy nitrates or hydroxides during the course of reaction. It was difficult to delineate the extent of the former reaction from the latter. These cations; have negative effect, on basic crystallinity of the solids, Beta-wollastonite was considered the most stable one. The total amounts in meq. of ions up taken by these solids have been found in a descending order : xonotlite > gyrolite > Beta-wollastonite

Physico-chemical studies on hydrothermal characteristics of calcite-rich clays

Marl-clay deposits containing 30% CaCO3 from Sinai, Egypt, were calcined at different temperatures between 800C to 950C for 30 min. The processed briquettes from these powders were hydrothermally treated at 202C [16 atm] for 4 hours. The evaluation and assessment of the treated specimens were achieved through the determination of their physical properties and the phases developed by XRD, IR- spectroscopy, SEM and chemical analysis. The thermochemistry of these phases were followed using DSC and TG technique. A correlation between the determined properties and the developed phases were also discussed. The results encountered in this investigation indicated that the physical properties of the hydrothermally treated bodies are improved with increasing the precalcination temperature. Also, the data encourage the utilization of this technique [autoclaving] in production of building units from lime-rich clays as is followed in sand lime bricks industry without any additives

Hydrothermal crystallization and crystal growth of 7-sio from rice husk silica ash in alkaline solutions

White pure and active amorphous silica was prepared from rice husk with 99.96% purity by acid leaching and pyrolysis. This silica could be crystallized into prismatic microcrystalline alpha-Sio2 [77-88nm] under hydrothermal conditions [215 °C = 20 atm. press.] from alkaline solutions. The maximum yield of alpha-Sio2 was obtained at 0.6 molar ratio of NaOH / Sio2 which reduced to 0.2 in the presence of A13+ and /or B3+ traces. This is due to the formation of silicalite crystals [considered to be a polymorph of sio2]. It has been found that transition metal cations in the reaction media affects the degree of alpha-Sio2 crystallization in the order: Fe3+> Ni2+> Cr3+> amorphous Sio2> Co2+> Cu2+> Mn2+> Zn2-> Zr4+ > La3+. Both mechanism of alpha-Sio2, silicalite growth and ions incorporation were discussed