It is important for sorption enhanced catalytic processes oc

It is important for sorption-enhanced catalytic processes occurring in an aqueous medium that the MnО2 phase be in a hydrated state. This requirement imposes certain restrictions on the conditions in which this phase can be synthesized, particularly on the CL surface that is sensitive to acidic and alkaline media. The most common technology is aimed at stabilizing a divalent manganese mg115 in the CL matrix with the ion\'s subsequent oxidation [16–18]. Using the MnО4– ion as an oxidant allows to produce a hydrated MnО2 phase with the maximum yield and maximum active oxygen content; however, the behavior of this reaction under heterogeneous synthesis on the CL surface is currently poorly understood. There is a large number of CL-containing rocks of good quality [19, 20], differing in chemical composition, porous structure, and other properties, to be found in Russia; to a significant extent, these differences affect the structure and composition of the resulting MnО2 phase. The goal of this study is in expanding the understanding of structural and morphological properties of the MnО2 phase and the mechanism of its formation on the surfaces of clinoptilolite rocks of different properties.
Experimental procedure The content of the zeolite phase in the samples was determined by the standard thermochemical method [19, 20]. The volume limits of the sorption space (in water) and the (in benzene) were determined by the desiccant method [21]. The volume of the micropores inaccessible to benzene molecules (with pore entrance sizes less than 5.85Å) was defined as
The values of the static sorption capacity , ASLS and АMB, respectively, for the Mn2+ ion, for sodium lauryl sulfate and for methylene blue were found by the static method from solutions with a concentration of 100mg/l, with the solid/liquid ratio of 1:100, and under occasional stirring. The sorption time was 24h, the temperature was 20 ± 1 °C. The mechanical strength of the samples was evaluated as the mechanical degradability MD (wt.%), which was determined by the formula where MS(at) is the mechanical abrasion resistance, determined in accordance with GOST 16188-70 [22]. The chemical strength of the samples was evaluated as the chemical degradability CD (wt.%), which was described by the formula: where RR is the chemical resistance, determined, after the samples were treated with a sodium chloride solution according to GOST R 51641-2000 [23] and subsequently dried, by the sieving method in accordance with GOST 16188-70. The MnO2 content (in the particle volume) was determined by the oxalate method [24]. The synthesis of the MnO2 phase on the surface of the CL rock samples was performed in three stages:
The thickness of the MnO2 phase layer in CL rock particles was determined by linear measurements in the photographed thin sections of these particles, obtained by reflected-light optical microscopy. For this purpose, the MnO2-CL particles were fixed in an epoxy compound; the resulting block was then cut with a diamond micro tool array, ground and polished. The obtained thin sections with the particles were analyzed in reflected visible light using a Biolam-I microscope equipped with a Myscope 130M digital camera (by Webbers). The camera was calibrated by an OMO-1 reflected-light stage micrometer. The morphology of the obtained CL-modified MnO2 samples, as well as the chemical composition of the surface layer of these materials were evaluated by scanning electron microscopy (SEM) using a Supra 55VP device (by Carl Zeiss AG) with an X-MAX X-ray microanalysis detector (Oxford Instruments). The size of the X-ray excitation band in the studied materials was 1.5µm × 1.5µm.
Experimental results The compositions of CL rock samples used in the study before and after modification with MnO2 are listed in Tables 1 and 2. For the purpose of our discussion, the unmodified samples can be divided into two groups by their aluminosilicate contents (see Table 2): the high-silica (the Si/Al ratio lies in the range from 5.16 to 5.60) and the low-silica samples (the Si/Al ratio lies in the range from 4.21 to 4.75). The samples from the Badinskoe and Chuguyevskoe deposits belong to the first group, and the samples from the Sokirnitskoe, Shivyrtuyskoe and Kholinskoe deposits belong to the second one. The high-silica samples are characterized by low sodium content, while the rock sample from the Sokirnitskoe deposit is peculiar in that it contains barium which is not present in any of the other samples; its iron content is also higher than that of the other samples.