CaCO₃ precipitation is physical-chemical basis of biomineral formation of hard tissue (shells, skeletons) in marine calcifying organisms (=biomineralization). Processes controlling biomineralization are still not fully clarified, so the study of influence of pH on basic processes of CaCO₃ precipitation should contribute to better understanding of biomineralization under climate change. This paper reports on the effect of initial pH (pH₀) and type of stirring (mechanical and magnetical) on spontaneous precipitation and phase composition, size and morphology of spontaneously precipitated CaCO₃ formed at the identical initial supersaturation, ionic strength and a(Ca²⁺)/a(CO₃²⁻) ratio. The initial pH varied in a range 8.50 ≤ pH₀ ≤ 10.50 and included values relevant for mimicking the conditions related to biomineralization in marine organisms. In all systems two CaCO₃ polymorphs were found: calcite and/or vaterite. The increase of pH₀ favoured the formation of rhombohedral calcite no matter the type of stirring. This was exclusively influenced by the systems’ pH₀ (other relevant initial parameters were identical). Furthermore, increase of pH₀ caused change of vaterite morphology from cauliflower-like spheroids to regular spherulites. The mechanically stirred systems produced larger calcite and vaterite particles and higher content of calcite.

High-energy ball milling has been employed for mechanochemical treatment of TiO2 and ZrO2, thus facilitated the solid-state reaction toward ZrTiO4. The ceramics with different degrees of porosity were prepared by 8 h sintering of thus prepared nanopowder precursor at 1100, 1200, 1300 and 1400 °C. The solid-state reaction was completed after sintering at 1200 °C. The correlation between the structure of ZrTiO4 ceramic (ZT) at the nano-scale and its electric response at different humidities was studied. Highly porous ZT ceramics sintered at 1100 and 1200 °C showed significant difference in electrical conductivity depending on atmosphere conditions indicating promising application as humidity sensors

Tošići-Dujići bauxite deposit, situated in Dalmatian inlands, Croatia, contains minor remaining bauxite reserves. The deposit lies on Lower Eocene foraminiferal limestone and is covered by Upper Eocene Promina sediments. Bauxite samples were analyzed for textural, mineralogical, and geochemical features in order to determine absolute REE abundances and their relation to mineralogy, as well as to devise the origin of REE enrichment and to trace weathering and bauxitization paths of the parent material. The samples show total REE abundances up to 3500 mg/kg with significant HREE enrichment in some cases. All samples are gibbsitic with hematite and anatase as major phases. Kaolinite occurs in most of the samples, and goethite, böhmite, and nordstrandite are minor phases. Monazite-(Ce) and xenotime-(Y) were identified as detrital REE minerals as well as authigenic florencite-(Ce). In the REE most abundant sample, REE are most likely bound to Fe- and Ti-oxide phases as suggested by correlation analysis. Chemical weathering proxies show intensive weathering. Geochemical and textural data imply that the REE enrichment is influenced by intensive weathering (CIA 97.87–99.26) of detrital material, and also by possible deposition/redeposition of residual material potentially derived and mobilized from various sedimentary rocks of the area.

Structural stability of nanostructured titanates was investigated for further processing and possible applications. With the aim to investigate their mechanochemical stability we applied highenergy ball milling and studied induced phase transitions. Hydrogen titanates having two different morfologies, microcrystals and nanotubes, were taken into consideration. During mechanochemical treatment of both morphologies, we observed the phase transition from hydrogen titanate to TiO2 anatase and then to TiO2 rutile. Anatase to rutile phase transition occurred without appearance of intermediate high pressure TiO2 II typically observed in the case of mechanochemical treatment of TiO2. In the case of microcrystals, phase transition from hydrogen titanate to anatase starts after longer milling time than in the case of nanotubes, which is explained by larger particles sizes of crystalline powder. On the contrary, further phase transition from anatase to rutile was occurred faster in crystalline powder than in the case of nanotubes. The sequence of phase transitions was studied by Raman spectroscopy and X-ray powder diffraction, while morphology and crystal structure at nanoscale were analyzed by high resolution electron microscopy