This study is devoted to studying the sorption of ¹³⁷Cs on mineral sorbents at a wide pH range, from 2 to 10, as well as to studying sorption mechanisms. In order to obtain the most reliable sorption characteristics, samples of high purity were examined as sorbents: bentonite, glauconite, zeolite, and diatomite. A detailed description of their mineral composition, cation exchange capacity and specific surface of sorbents is given. XRD, XRF, FTIR, SEM, and BET adsorption methods were used for assaying. The sorption and desorption values were identified for each sorbent. As a result of the conducted research, it can be concluded that ¹³⁷Cs sorption mainly occurs through the exchange reaction on zeolite, glauconite and bentonite. The highest cesium Kd was observed on zeolite due to its high CEC and amounted to 4.05 mg/L at pH 7. The higher sorption capacity of glauconite in comparison with bentonite is primarily due to the high layer charge which is mainly localized in tetrahedral sheets, and to the existence of highly selective sorption sites (frayed edge sites) on the glauconite surface. Diatomite showed the lowest sorption capacity provided by the presence of a small quantity of smectite and kaolinite in its composition. The values of desorption increase in the following order: zeolite < bentonite ~ diatomite < glauconite.

This paper deals with adsorption regularities and mechanisms of nonradioactive Cs(I) and Sr(II) analogs on bentonites of different chemical and mineral composition from solutions of Cs and Sr nitrates with pH 3, 7, and 10 units at constant ionic strength. The bentonites were taken from the deposits Taganskoe (T), Dash-Salakhlinskoe (DS), Zyryanskoe (Z), and 10th Khutor (10H). The pH of bentonite aqueous suspensions, T and DS, exceeded 9 units. A less alkaline reaction was observed in bentonite suspensions Z and T with pH 8.94 and 7.70, respectively. Bentonites T and DS contained significant amounts of nonsilicate iron compounds, 1.0 and 0.5%, respectively. The recovery rate of the studied clays from aqueous solutions of Cs(I) and Sr(II) ions in concentrations from 0.25 to 5 mmol/L varied from 50% to 90% and decreased in the following order: “Ta-ganskoe” > “Dash-Salakhlinskoe” > “Zyryanskoe” > “10th Khutor” in the studied pH range. The main mechanism of Cs(I) and Sr(II) sorption in the studied pH range was cation fixation in the form of outer-sphere complexes on planar surfaces resulting from ion exchange. Increasing pH (pH > 6) enhanced pH-dependent positions, which allowed Cs(I) and especially Sr(II) ions to fix on them more firmly as inner-sphere complexes. At pH 9–10, Sr(II) could precipitate in the form of carbonates. The sorption of Cs(I) + and Sr(II) was accompanied by competitive interactions with proton at pH < 6 and Na⁺, Ca²⁺, Mg²⁺, and K⁺ cations at higher pH values. This competition was more apparent at concentrations of Cs(I)and Sr(II) in initial solutions < 0.5 mmol/L. The ability of bentonite T to sorb Cs(I) and Sr(II) in large amounts compared to the other bentonites was determined by high CEC values and charge of smectite T.

The interaction of organic matter with mineral components of the solid phase of soils is the most important process that regulates the cycle and balance of carbon in the biosphere. The adsorption of humic acids on minerals is accompanied by their fractionation in size, composition, and amphiphilicity, thus decreasing their heterogeneity. Despite a strong interest in studying the regularities and mechanisms of the interaction between natural organic matter and layered aluminosilicates, it is necessary to take into account the natural diversity of soil organic matter, adsorption conditions, and mineral composition. This study was designed to investigate the adsorption regularities of fulvic acid (FA) and water-extractable organic matter (WEOM) isolated from horizon H of peaty-podzolic-gleyic soil on kaolinite and muscovite. Sorbates and sorbents were examined by the following methods: high-pressure size exclusion chromatography (HPSEC), high-performance liquid chromatography (HPLC), and potentiometric titration. The specific surface areas of the sorbents were determined by the sorption of N₂ molecules. We found that hydrophobic components of FA and WEOM are mainly adsorbed on mineral surfaces. The adsorption of FA and WEOM on kaolinite and muscovite is followed by decreased hydrophobicity of organic matter and decreased heterogeneity of its amphiphilic properties in an equilibrium solution. At pH levels around 6, sorption of organic matter from FA solution containing 19% and 81% hydrophilic and hydrophobic components, respectively, onto kaolinite and muscovite occurs mainly due to hydrophobic components. Hydrophobic interactions on siloxane surfaces are the main mechanism to fix FA on both minerals. Kaolinite adsorbs slightly more organic carbon per unit area than muscovite. The adsorption of WEOM from a solution with 41% hydrophilic and 59% hydrophobic components results not only from hydrophobic and hydrophilic components but also from hydrophobic and electrostatic interactions and depends on pH. The most hydrophobic fractions of organic matter are adsorbed from the hydrophobic components on the surface of both minerals. Under conditions of the performed experiments at pH < 5, more WEOM is adsorbed on muscovite than on kaolinite.

The fractional composition of aluminum compounds was studied in soil solutions obtained using vacuum lysimeters from loamy podzolic soils on two-layered deposits. The concentration of aluminum was estimated in brooks and a river draining the area with a predominance of these soils. In soil solutions, the concentration of aluminum was experimentally determined in the following compounds: (1) organic and inorganic monomers, (2) stable complexes with HAs and FAs together with polymers, and (3) the most stable complexes with HAs and FAs together with fine-crystalline and colloidal compounds. The total Al concentration in soil solutions from forest litter was 0.111–0.175 mmol/l and decreased with depth to 0.05 mmol/l and lower in solutions from the IIBD horizons. More than 90% of the Al in the solutions was bound into complexes with organic ligands. Some amount of Al in solution could occur in aluminosilicate sols. The translocation of Al complexes from the litter through the AE horizon to the podzolic horizon was accompanied by an increase in the ratio between the Al concentration in fraction 2 and the C concentration in the solution. The concentrations of Al_tot in the surface waters varied in the range from 0.015 to 0.030 mmol/l. Most of the Al came to the surface waters from the litter and AE horizons and partially from the podzolic horizon due to the lateral runoff along the waterproof IIBD horizon. Approximate calculations showed that the recent annual removal of Al from the AE and E horizons with the lateral runoff was 7 to 560 mg (3–21 mmol) from 1 m².

The profile distributions of aluminum extracted by the Tamm and Bascomb reagents and of the exchangeable aluminum were studied in soils of automorphic, transitive, and accumulative positions in the landscapes of the southern taiga. In the mineral horizons of the gleyic peaty-podzolic soils developed on poorly drained flat surfaces and in the floodplain soils, the distribution of oxalate- and pyrophosphate-soluble aluminum has a strongly pronounced accumulative character. In the podzolic soils of the automorphic positions and slopes, an eluvial-illuvial distribution was characteristic with the maximal aluminum content in the podzolic horizons. The strong differentiation of the upper part of the profile in the automorphic podzolic soils in terms of the Al content in the Tamm and Bascomb extracts is mainly related to an increase of the pedogenic chlorite content upon the transition from the AE to the E horizon. In the podzolic horizons of these soils, aluminum can accumulate in the form of proto-imogolite structures. The exchangeable aluminum displays an accumulative type of distribution. On the basis of calculating the reserves of the different aluminum compounds, two main accumulative zones for the mobile compounds of this element were recorded in the soils of the landscapes studied: the E horizon in the automorphic podzolic soils, where Al accumulates as soil chlorite or, probably, as proto-imogolite, and the A1 horizon of the floodplain soils, where Al accumulates in aluminoorganic complexes.

The sorption of Cu²⁺ onto bentonite modified with Al Keggin cations and humic acid from CuCl₂ solutions at pH 4.5 was studied. Modification of Na-bentonite with Al Keggin cations was found to result in an increase in the basal spacing of montmorillonite from 1.29 nm for N-form to 1.85 and 1.78 nm for HAl₁₃ and Al₁₃ forms respectively, in a reduction of CEC (cation exchange capacity) and in the formation of additional sites with a variable charge with pH_PZC 4.2. Al₁₃-bentonite is not affected by heat. Under the conditions of the experiments at pH of 4.5 Na-bentonite adsorbs more Cu²⁺ from CuCl₂ solutions then Al₁₃ forms of bentonites. The main mechanism of copper sorption on Na-bentonite is the cation exchange Cu²⁺–Na⁺. The reduction of CEC of Na-bentonite after modification with Al Keggin cations leads to a decrease in the Cu²⁺ sorption. pH-dependent sorption sites on Al₁₃-bentonites have a pH_PZC of 4.2 and, therefore, under conditions of the experiment have positive charge which prevents Cu²⁺ sorption. Na-bentonite adsorbs more humic acid solution (HA) then Al₁₃-bentonite and the proportion of adsorbed HA remains constant over the entire concentration range. Treatment of the Al₁₃-bentonite with HA leads to the formation of the additional sorption sites. The amount of sorbed Cu²⁺ and the percentage of their extraction from solutions by HAAl₁₃-bentonite is similar to those values for Na-bentonite.