Mineral Mimetic Material Sr-Exchanged Sitinakite of Different Crystallinity: Phase Transformations during Heat Treatment and the Strength of SR Fixation in a Ceramic Matrix.

A simple method for the direct transformation of Sr-exchanged titanosilicate with the sitinakite structure (IONSIV) into ceramic material through cold pressing and subsequent sintering at 1100 °C for 4 h is presented. The temperature transformation of Sr-exchanged sitinakite showed the stages of recrystallization of the material with the formation of Sr-Ti phases matsubaraite (Sr4Ti5[Si2O7]2O8), jeppeite (SrTi6O13), tausonite (SrTiO3), and rutile. Leaching experiments showed the efficiency of fixation of Sr cations in a ceramic matrix; extraction into water does not exceed 0.01% and desorption in 1 M HNO3 solution is only 0.19% within three days. The leaching rates of immobilized Sr demonstrate the structural integrity of the formed phases in the ceramic (2.8 × 10-5-1.0 × 10-5 g/(m2·day). The decrease in the crystallinity of the initial Na-sitinakite, which is achieved by reducing the synthesis temperature from 250 to 210 °C, does not affect the sorption capacity and the fixation of cations in the ceramic matrix. The obtained results confirm the prospect of using inexpensive precursors, titanium ore enrichment waste, for the synthesis of sorption materials.

The analcime-bearing rock immobilized microalgae: Stress resistance, psychrotolerance, phenol removal.

The development of synergetic biogeocomplices for biodegradation of recalcitrant organic pollutants is an urgently needed to achieve the environmental sustainability. The biogeosorbent based on the analcime-bearing rock immobilized Chlorella vulgaris f. globosa was developed to remove phenol from polluted waterbodies. The microalgae biofilm formation on the ABR resulted in 1.6 × 104 cells/mm2. Stress testing showed that low temperatures up to -30 °C did not adversely affect the cell viability, the dehydrogenase activity of the biogeosorbent exposed was 5.1 mg of formazan/mL. Under phenol-stress conditions, aggregation of suspended cells was observed. The biogeosorbent was more stress resistant than the microalgal suspension, and also reduced the time of exposure and had no secondary waste in comparison with the ABR. After having been treated, phenol removal was found to increase from 70 to 72% for MA, from 27 to 93% for ABR, from 82 to 93% for the biogeosorbent.