Adsorption of Bichromate and Arsenate Anions by a Sorbent Based on Bentonite Clay Modified with Polyhydroxocations of Iron and Aluminum by the "Co-Precipitation" Method.

The physicochemical properties of natural bentonite and its sorbents were studied. It has been established the modification of natural bentonites using polyhydroxoxides of iron (III) (mod.1_Fe_5-c) and aluminum (III) (mod.1_Al_5-c) by the "co-precipitation" method led to changes in their chemical composition, structure, and sorption properties. It was shown that modified sorbents based on natural bentonite are finely porous (nanostructured) objects with a predominance of pores of 1.5-8.0 nm in size. The modification of bentonite with iron (III) and aluminum compounds by the "co-precipitation" method also leads to an increase in the sorption capacity of the obtained sorbents with respect to bichromate and arsenate anions. A kinetic analysis showed that, at the initial stage, the sorption process was controlled by an external diffusion factor, that is, the diffusion of the sorbent from the solution to the liquid film on the surface of the sorbent. The sorption process then began to proceed in a mixed diffusion mode when it limited both the external diffusion factor and the intra-diffusion factor (diffusion of the sorbent to the active centers through the system of pores and capillaries). To clarify the contribution of the chemical stage to the rate of adsorption of bichromate and arsenate anions by the sorbents under study, kinetic curves were processed using equations of chemical kinetics (pseudo-first-order, pseudo-second-order, and Elovich models). It was found that the adsorption of the studied anions by the modified sorbents based on natural bentonite was best described by a pseudo-second-order kinetic model. The high value of the correlation coefficient for the Elovich model (R2 > 0.9) allows us to conclude that there are structural disorders in the porous system of the studied sorbents, and their surfaces can be considered heterogeneous. Considering that heterogeneous processes occur on the surface of the sorbent, it is natural that all surface properties (structure, chemical composition of the surface layer, etc.) play an important role in anion adsorption.

Biodegradation of an organoselenium compound to elemental selenium by Lentinula edodes (shiitake) mushroom.

The present paper reports for the first time the transformation of an organic selenium compound into red selenium (Se), which causes the intense red pigmentation of Lentinula edodes (shiitake mushroom) mycelia. The biotransformation of 1,5-diphenyl-3-selenopentanedione-1,5 (diacetophenonyl selenide, preparation DAPS-25) was studied in liquid- and solid-phase cultures of L. edodes. In liquid culture medium, a red color develops in the mycelium at initial DAPS-25 concentrations equal to or higher than 0.1 mmol/l. The intensity and initiation time of coloration is Se concentration-dependent. Semiquantitative data obtained by physicochemical methods on the extent of Se and acetophenone production suggest that L. edodes is able to absorb and/or destruct this organic Se xenobiotic.