The kinetics of gypsum precipitation, the inhibiting effect of citric acid and its use in the differential precipitation of Mg(OH)2 from CaSO4·2H2O

The crystallization of solids from supersaturated solutions is a source of numerous complications during a range of industrial processes: undesirable precipitates may clog pipelines, foul membranes, contaminate the target compounds of a process, lower the effectiveness of heat-exchange via scale formation, etc. Calcium sulfate dihydrate (CaSO4·2H2O or gypsum) is one of the most common of such solids, therefore during the last decades, numerous studies were dedicated to the investigation of the precipitation kinetics and method development potentially suitable for precipitation control and inhibition. In the experimental work leading to this dissertation, the kinetics of gypsum precipitation was studied in the entire experimentally available concentration range. The impact of citric acid (or citrate ion) on the reaction was investigated in detail including some experiments in unconventional media. The acquired experience was used to optimize the differential precipitation of magnesium hydroxide from gypsum, which provides a promising method to improve the treatments of acidic wastewaters economically and in environmentally friendly way, and could also be useful in desalination processes

Binding of Ca2+ Ions to Alkylbenzene Sulfonates: Micelle Formation, Second Critical Concentration and Precipitation

Anionic surfactants, such as sodium linear alkylbenzene sulfonates (NaLAS), are utilized in various fields, including industry, household, and agriculture. The efficiency of their use in aqueous environments is significantly affected by the presence of cations, Ca2+ and Mg2+ in particular, as they can decrease the concentration of the surfactant due to precipitation. To understand cation–sulfonate interactions better, we study both NaLAS colloidal solutions in the presence of CaCl2 and precipitates forming at higher salt concentrations. Upon addition of CaCl2, we find the surface tension and critical micelle concentration of NaLAS to decrease significantly, in line with earlier findings for alkylbenzylsulfonates in the presence of divalent cations. Strikingly, an increase in the surface tension is discernible above 0.6 g L–1 NaLAS, accompanied by the decrease of apparent micelle sizes, which in turn gives rise to transparent systems. Thus, there appears to be a second critical concentration indicating another micellar equilibrium. Furthermore, the maximum salt tolerance of the surfactant is 0.1 g L–1 Ca2+, above which rapid precipitation occurs yielding sparingly soluble CaLAS2∙2H2O

Sol-Gel Synthesis of Ceria-Zirconia-Based High-Entropy Oxides as High-Promotion Catalysts for the Synthesis of 1,2-Diketones from Aldehyde

Efficient Lewis-acid-catalyzed direct conversion of aldehydes to 1,2-diketones in the liquid phase was enabled by using newly designed and developed ceria–zirconia-based high-entropy oxides (HEOs) as the actual catalysts. The synergistic effect of various cations incorporated in the same oxide structure (framework) was partially responsible for the efficiency of multicationic materials compared to the corresponding single-cation oxide forms. Furthermore, a clear, linear relationship between the Lewis acidity and the catalytic activity of the HEOs was observed. Due to the developed strategy, exclusively diketone-selective, recyclable, versatile heterogeneous catalytic transformation of aldehydes can be realized under mild reaction conditions