Formation Of Silicic Acid Research Articles

Leaching characteristics of Sc-enriched, Fe-depleted acidic slags

Scandium is currently classified as a critical raw material for the European Union, and several research projects focus on the search for new sources to supply to its expected increasing demand. The Kiviniemi mafic intrusion in Finland is a potential primary source for Sc; at Kiviniemi, Sc occurs mainly within the lattices of ferrous silicates, clinopyroxene and amphibole. Some of the main challenges in leaching of Kiviniemi-type feed material are related to either the complexity of Fe and Ti separation from Sc-containing solutions or a possible gelation problem when leaching a material with a high SiO2 content. According to preliminary beneficiation tests, direct acid leaching of the Kiviniemi feed material was not successful mainly due to extensive leaching of Fe from the ferrous concentrate. Therefore, a processing scenario with conventional magnetic separation followed by pyrometallurgical reduction of the FeO component to tackle the Fe issue prior hydrometallurgical stage was studied in the previous parts of our project. Leaching experiments in this study focus on the possibilities to extract Sc from low-FeO, Sc2O3-enriched amorphous slag. Both a synthetic slag and slags produced from Kiviniemi concentrates were submitted to H2SO4-based leaching experiments applying dry digestion, H2O2-assisted leaching, and high-pressure acid leaching (HPAL). The formation of silicic acid (gelation) under acidic conditions was avoided with all these methods. With H2O2-assisted leaching, efficiencies reached 40–50%, whereas leaching with dry digestion was very limited. With HPAL, the leaching efficiency remained at 30–45% under experimental conditions of 2.5 M H2SO4, 60 bar, and 150 °C. These levels of leaching efficiencies are due to an amorphous structure and high SiO2 content of the slag. Future options for hydrometallurgical processing of Kiviniemi-type slags could include controlled cooling of the slag to produce crystalline structures, combined potentially with further chemical modification to enable selectivity for leaching.

Biodegradation model of porous silicon nanoparticles

Development of porous silicon-based drug delivery systems for theranostics requires a precise control of their biodegradation. Thus, we propose a model for the biodegradation of porous silicon nanoparticles (PSi NPs) based on a diffusion equation combined with Nernst-Brunner mass transfer equation describing the dissolution of silicon and formation of silicic acid (SA). The spatiotemporal distributions of PSi NP porosity and SA concentration were calculated. The model was successfully applied to fitting a great variety of experimental data on more than 10 factors influencing the PSi NP biodegradation kinetics, such as the morphology of PSi NPs, surface composition, properties of surrounding media and protective coating layer. Two principal regimes were found out for systems with either diffusion or dissolution dominating over each other. The results of simulations revealed the values of several important parameters, which are hard to be measured experimentally.

A self-lubricated Si incorporated hydrogenated amorphous carbon (a-C:H) film in simulated acid rain

Hydrogenated amorphous carbon (a-C: H) films show high friction and wear in aqueous solution, especially in simulated acid rain, which restrict their application. This problem can be solved by doping Si in the film. Therefore, the influence of the Si content on the composition, structure, mechanical and tribological properties were investigated by various methods in this work. Results show that the contents of SiC bonds and sp3C, including sp3CH and sp3CH2 as well as the surface roughness increase with increasing Si content in the film. Furthermore, films with higher Si content (>8.33 at.%) show better tribological properties in the simulated acid rain. The self-lubricated behaviors are attributed to the adequate content of Si can form silicic acid at the counterface under low applied load and short sliding time in the simulated acid rain. Additionally, the tribological behaviors of the film are mainly depended on the formation of silicic acid instead of graphitization of the film.

Heterogeneous Equilibria in the System MHSiUO6·nH2O-Aqueous Solution (M = Li, Na, K)

The aqueous solutions of mineral-like compounds MHSiUO6·nH2O (M = Li, Na, K) at 298 K were studied. A quantitative model of a crystalline uranosilicate-aqueous solution system was derived from the solubility data and was used to calculate the solubility products and Gibbs formation functions of these compounds. The Gibbs energies of formation of silicic acid and other ionic and molecular Si(IV) species in solution were also calculated. The solubility of uranosilicates in aqueous solutions outside the experimentally studied range was predicted.

ケイ酸の生成とその熟成に及ぼす四塩化炭素の添加効果

ケイ酸の生成とその熟成に及ぼす四塩化炭素の添加効果