The primary nucleation mechanism of the gypsum in a bulk aqueous medium was identified as a heterogeneous one for 0.05 and 0.03 mol·L⁻¹ CaSO₄·2H₂O solutions and 25 °C. By means of a particle counter and dynamic light scattering (DLS) technique, solid nano/microimpurities were found, and controlled in stock brines for gypsum supersaturated solutions preparation. It is demonstrated that the common procedure of reagent grade 0.10 mol·L^‒1 CaCl₂ and Na₂SO₄ aqueous solutions filtration via 200 nm membranes is capable to reduce the foreign solid microimpurities content (size > 100 nm) from 10⁶ to 10³ units in 1 mL, but fails to affect the more numerous nanofraction (size < 100 nm). Thus, the gypsum nucleation takes place in presence of a significant amount of “nano/microcodust” templates, and has a heterogenous character. The induction time, measured by conductivity for the similar supersaturation levels, reveals a well detectable dependence on nano/microdust concentent: an increasing background particle concentration substantially decreases the induction period at a constant saturation state and temperature, and thus increases the nucleation rate. Therefore, the gypsum nucleation reaction starts tentatively through the fast heterogeneous formation of well-defined, primary nuclei via [Ca²⁺], [SO₄^2‒], and [CaSO₄]^o species sorption on the surface of “nano/microdust” particles. Thus, the “nano/microdust”, naturally occurring in any high purity chemical, plays a key role in sparingly soluble salts nucleation in the bulk aqueous medium.

The textural and structural characteristics of phosphorites from the Polpinsky deposit have been determined. These raw materials are shown to be of siliceous polymineral type and consist mostly of α-quartz, hydroxycarbonate apatite, montmorillonite, and bonschtedtite. The modification dynamics of chemical composition and the textural characteristics (specific surface, pore volume, and pore diameter) of the solid upon the acid decomposition of a phosphorite sample from Polpinsky deposit have been studied. The α-quartz in phosphorites is shown to not experience crystal-structural alterations upon acid decomposition; its pore size does not inhibit the extraction of acid-soluble components, including calcium and phosphorus, from the bulk.

— The effect of physicomechanical factors (drying temperature and compaction pressure) on the specific surface area and total pore volume of size fractions of preground phosphorite from the...

The phase composition of phosphorites from the Polpino deposit (Bryansk oblast, Russia) is studied. The phosphorites are shown to be highly likely to contain α-quartz, phosphate substance, and clay...