PhD defence: Dina Belova

Title: "Surface properties of calcite and chalk: Synthesized and biogenic material"

Abstract
The constantly increasing anthropogenic impact on nature during past decades causes numerous environmental problems such as decreased quality of drinking waters and lack of energy resources. The present work was focused on the investigation of surface properties of synthetic calcite (CaCO3) and biogenic chalk (> 96% CaCO3) in connection with these two current day challenges. We investigated uptake capacity of chalk material and compared it with that of calcite to evaluate the possibility of using chalk for the treatment of drinking waters contaminated by nickel. It was found that chalk has higher ability for nickel removal than calcite, and the removal by chalk is significant even at low pH. We also studied the influence of large organic molecules (polysaccharides) associated with chalk on chalk recrystallization rate. The results show that chalk treatment with oxidizing reagents can remove some part of organic compounds from chalk surface and promote recrystallization. In contrast, the dissolved silica (SiO2) at concentrations below the saturation with respect to amorphous silica was found not able to inhibit calcite recrystallization. Our results show that the interaction between dissolved silica at concentrations used in this study and calcite is very weak. Although, in more concentrated silica solutions, the formation of silica coating on calcite surface was detected. This coating modified calcite surface topography and was found to protect the surface from spontaneous recrystallization in air.