A novel effective sorbent for the extraction of antimony(III) from rice straw has been generated, having a specific surface area of 470 m(2)/g. The material was subjected to a series of analyses, including scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction analysis, and FT-IR spectroscopy. The sorption properties relative to Sb(III) ions were characterised in dynamic conditions in a column experiment. The total dynamic exchange sorption capacity of 113.92 mg/g renders this material suitable for use as a permeable reactive barrier (sorption barrier) with the objective of protecting soils from antimony contamination. To identify the optimal conditions for soil protection, the chemical composition, acid-base properties, and sorption parameters of soils of varying types were characterised. The sorption properties of the soils were determined in static conditions to obtain the sorption isotherm. The maximal sorption capacity was identified for the soil sample with low base saturation and a high organic component content, a finding that was corroborated by DTA analysis. The results of the column experiment with layers of soil and aluminosilicate sorbent indicate the promising use of the new sorbent as a sorption barrier for the effective protection of soils from antimony contamination.

The paper presents the results of the study of sorption of antimony(III) from aqueous solutions by potassium aluminosilicates obtained from rice straw and husks. The chemical composition, structure and physicochemical characteristics of the obtained biogenic samples were established. The sorption kinetics of Sb(III) ions by potassium aluminosilicates was investigated using diffusion and chemical kinetics models. It is shown that the rate of antimony sorption process on the studied aluminosilicates is limited by the mixed -diffusion process, as well as by the stage of chemical interaction of antimony cations with the sorbent surface. It is shown that in the concentration range of 0.017-0.1 mmol/l the adsorption process of Sb(III) by natural materials is determined by chemical interaction with the surface of samples and obeys the Freundlich model, which indicates the heterogeneity of the sorbent surface. The influence of the solution medium on the sorption of antimony(III) by aluminosilicates has been investigated. It is shown that the adsorbent surface has a positive charge in acidic medium and a negative charge in neutral medium. The sorption activity for all sorbents decreases with increasing pH of the solution. The desorption of Sb(III) depends on the contact time of the sorbent with the solution and on the solution medium, and the desorption is higher in neutral medium. The results show that potassium aluminosilicates obtained from rice straw and husks are promising materials for the removal of antimony(III) from aqueous solutions. These studies allow us to give recommendations on the choice of materials for purification of solutions from Sb(III) ions, expanding the range of currently used natural sorbents based on plant raw materials, as well as to solve an urgent environmental and economic problemthe utilization of rice production waste.

Samples of sodium aluminosilicates obtained by hydrolytic deposition using rice straw of different varieties as silicon-containing raw materials were studied. The morphology of the particles was determined by scanning electron microscopy, the specific surface area (362–470 m2/g) was measured, IR spectra were recorded, and the chemical and phase composition of the samples was determined. The sorption properties of the obtained materials with respect to lead ions have been studied, the sorption capacity is 199–550 mg/g. An organic component was found and isolated in the samples, which is formed as a result of the deposition of aluminosilicates from rice straw hydrolysates, its composition was determined by thermogravimetry and IR spectroscopy. The effect of the organic component on the sorption capacity of plant-derived aluminosilicates has been investigated. The proposed sorption mechanism has been established. The approach used makes it possible to obtain aluminosilicates with a high sorption capacity, as well as safely dispose of rice straw.

Using rice straw as a source of silicon, a new composite material containing wollastonite CaSiO3, silicon dioxide SiO2, and an organic component (cellulose and lignin) was obtained. It is shown that calcination up to 1200°C leads to crystallization of SiO2 in the form of quartz and cristobalite, while the bulk density increases from 2.48 to 3.01 g/cm3. Using IR spectroscopy, the features of crystallization processes during calcination were studied, as were the morphology of particles and the nature of their surface. It is shown that the reflection coefficient in the visible range and the whiteness for biogenic calcium silicate are higher than for wollastonite obtained from reagents and reaches 98.9

An effective sorption material for the immobilization of cobalt radionuclides into highly safe and reliable solid-state matrices is proposed. The resulting silicate sorbent CaSiO3 had an amorphous mesoporous structure (ABET 53 m2/g) and a sorption capacity Co ions of 3.32 mmol/g. The physico-chemical characteristics of the CaCoSi2O6 sample obtained after Co2+ ions sorption were studied using XRD, N2 and Ar adsorption-desorption, SEM-EDX and TG/DTA methods. Solid-state silicate matrices characterized by high density values (2.86-3.16 g/cm3), compressive strength (150-637 MPa) and Vickers microhardness (1.80-5.25 GPa) were obtained by spark plasma sintering (SPS). The sample obtained at 1000 degrees C had the lowest values of Co2+ ions leaching (RCo ~10-7 g/(cm2xday)) and diffusion coefficient (De 1.73 x10-17 cm2/s) from silicate matrices. Thus, the obtained CaCoSi2O6 silicate matrices saturated with Co ions comply with the regulatory requirements of GOST R 50926-96 and ANSI/ANS 16.1 for 60Co immobilization. (c) 2022 Elsevier B.V. All rights reserved.

A new approach to the use of rice straw as a difficult-to-recycle agricultural waste was proposed. Potassium aluminosilicate was obtained by spark plasma sintering as an effective material for subsequent immobilization of 137Cs into a solid-state matrix. The sorption properties of potassium aluminosilicate to 137Cs from aqueous solutions were studied. The effect of the synthesis temperature on the phase composition, microstructure, and rate of cesium leaching from samples obtained at 800–1000 °C and a pressure of 25 MPa was investigated. It was shown that the positive dynamics of compaction was characteristic of glass ceramics throughout the sintering. Glass ceramics RS-(K,Cs)AlSi3O8 obtained by the SPS method at 1000 °C for 5 min was characterized by a high density of ∼2.62 g/cm3, Vickers hardness ∼ 2.1 GPa, compressive strength ∼231.3 MPa and the rate of cesium ions leaching of ∼1.37 × 10−7 g cm−2·day−1. The proposed approach makes it possible to safe dispose of rice straw and reduce emissions into the atmosphere of microdisperse amorphous silica, which is formed during its combustion and causes respiratory diseases, including cancer. In addition, the obtained is perspective to solve the problem of recycling long-lived 137Cs radionuclides formed during the operation of nuclear power plants into solid-state matrices.

Functional silicon-containing materials—silicon–carbon product, high-purity amorphous silicon dioxide, sodium aluminosilicate, and iron-containing magnetoactive composite material with specific surface area from 56.7 to 470 m 2 /g—have been obtained from agricultural wastes (rice husk and straw). Chemical and phase composition of obtained samples have been determined, particle morphology has been established by scanning electron microscopy, specific surface area has been measured, IR spectra have been recorded. The possibility to use the obtained materials for the removal of antimony ions from aqueous solutions has been studied. It has been found that sodium aluminosilicate and iron-containing composite materials based on biogenic silica show high capacity toward antimony ions: 596 and 386 mg/g, respectively. Used approach, in the first place, allows one to reclaim safely rice straw and husk and to reduce atmospheric emission of microdisperse amorphous silica SiO 2 resulting from their open combustion and causing respiratory diseases. In the second place, the study enables purification of natural and technogeneous wastewaters contaminated by antimony(III), which form on the sites of antimony rock deposits on their decay and mining.

— Solutions of SbF 3 and NaSbF 4 (50 and 100 mg/L) were found to have a toxic effect on soil microflora. At the final concentration of 50 mg/L, bacteria and microscopic fungi were detected sporadically in the nutrient medium (MPA). At 100 mg/L, bacterial growth in the studied soils was completely suppressed. Microscopic fungi were found to be more resistant to the action of the studied compounds. Addition of 0.1 M sodium dihydrophosphate (NaH 2 PO 4 ) solution to SbF 3 or NaSbF 4 solutions resulted in a 5.7‒6.9-fold decrease in the concentration of dissolved Sb 3+ ions. However, this solution still had a toxic effect on the number of soil microorganisms. In contrast to reagent purification, the method of sorption extraction of Sb(III) was shown to be efficient. A solution containing 5000 mg/L antimony, which was used to dilute the soil suspension, completely suppressed the growth of microflora. After sorption treatment, the concentration of antimony decreased to 201.3 mg/L, and growth of microorganisms was noted.

The paper presents an original method for the template synthesis of biomimetic porous composites using polyferrophenylsiloxane (PFPS) and the skeleton of the sea urchin Strongylocentrotus intermedius as a structuring template. The study aimed to form an organosilicon base of a composite with an inverted structure relative to the original structure of the sea urchin shell with a period of structure movement of about 20 µm and ceramic composites fabrication with the silicate base with an average pore size distribution of about 10 μm obtained by the reaction of PFPS with the inorganic base of the sea urchin test under conditions of calcination at 1000 °C followed by acid etching. The composition and morphology of the obtained composites were investigated by IR, XRD, XPS, EDX, and SEM techniques and by mercury porosimetry; the parameters of the porous structures depend on the selected methods of their synthesis. The proposed method is of fundamental importance for developing methods for the chemical synthesis of new biomimetics with a unique porosity architecture based on environmentally friendly natural raw materials for a vast practical application.

A comparative study of the microscopic morphology and chemical characteristics of spicules of Hexactinellids (Hexactinellida) with different structural features of the skeletons, as well as the freshwater Baikal sponge belonging to the class of common sponges (Demospongia), was carried out. The trace element composition of sponge spicules was determined by X-ray fluorescence spectrometry. The spicules of siliceous sponges contain many elements, arranged in decreasing order of concentration: Si, Ca, Fe, Cl, K, Zn, and others. It was shown that the surface layer of sea sponges contains mainly carbon (C), oxygen (O), and to a lesser extent nitrogen (N), silicon (Si), and sodium (Na). The spicules of the studied siliceous sponges can be divided into two groups according to the phase composition, namely one containing crystalline calcium compounds and one without them. Analysis of infrared absorption spectra allows us to conclude that the sponges Euplectella aspergillum, E. suberia and Dactylocalyx sp. contain silica partially bound to the organic matrix, while the silica skeleton of the sponges of the other group (Schulzeviella gigas, Sericolophus sp., Asconema setubalense, Sarostegia oculata, Farrea sp. and Lubomirskia baicalensis sp.) practically does not differ from the precipitated SiO2. This comparative study of the chemical composition of the skeletons of marine Hexactinellids and common freshwater sponge allows us to conclude that there are no fundamental differences in the chemical composition of spicules, and all of them can be used as a starting material for creating new composite silicon–organic functional materials.

The present work shows results of studying acid-base properties of the surface by the methods of pH-metry and Hammett of amorphous silicon dioxide from rice husks and straw obtained by various schemes: oxidative firing; oxidative roasting with preliminary treatment with 0.1 M hydrochloric acid solution; precipitation from alkaline solutions. The samples obtained by the thermal method contain impurities of alkali, alkaline earth metals, aluminum, and aluminum and practically do not contain water. The composition of the deposited samples contains a small fraction of impurities (0.05%) and water - from 8.2 to 10.2%. The pH value of an aqueous suspension of silicon dioxide has a neutral, alkaline or acidic environment depending on the content of impurities of alkali and alkaline earth metals. Distribution of acid-base centers on the surface of the samples is nonmonotonic and heterogeneous, and manifests itself in discreteness with a fairly clear differentiation of sorption bands with maxima of different intensities corresponding to a certain pKa value. Distribution curves of the adsorption centers of the indicators on the surface of the samples of amorphous silicon dioxide are similar to each other. There are four types of active centers on their surface: acidic Lewis (pKa + 16.80), Bransted main (pKa +7.15 and +9.45) and acid (pKa + 2.50). The number of active centers depends on the preparation scheme and is determined by the content of impurity elements and water in the oxide samples.

Magnetic sorbents show promise in technologies for they can be removed with a magnet after sewage waters are decontaminated. Sol–gel strategy was implemented to manufacture new cost-efficient composite sorbents based on cobalt ferrite, vermiculite, and alkaline rice husks hydrolyzate. An alkaline solution of the rice husks hydrolyzate was added with a suspension of Co[Fe 2 O 4 ] nanoparticles, and then neutralized with vermiculite suspension in 12% hydrochloric acid. The thus-manufactured magnetic sorbents were characterized by X-ray powder diffraction, IR and positron annihilation spectroscopy. Their physical and chemical characteristics were determined by low-temperature nitrogen physisorption as well as by adsorption of Methylene Blue dye in solution. The morphology of composites was identified by means of scanning electron microscopy. The bulk and surface elemental compositions of samples were found by energy dispersive fluorescent analysis. The magnetic saturation and coercivity of the samples were measured in the range of 0 to 2500 Oe fields. Sorbent particles were easily separated from solutions with a magnet. The sorbents showed high adsorption capacity with respect to Methylene Blue dye. The effect of the sodium phenyl siliconate template on the magnetic properties of the composites was elucidated.

To isolate silicon-containing products from plant materials, the reaction of interaction of rice husks with triethanolamine and ethylene glycol have been investigated. The effect of pretreatment of raw materials and the reaction conditions on the yield of soluble products containing silicon has been studied. It has been shown that the highest enrichment of rice husks with silicon occurs upon its treatment with concentrated hydrochloric acid and the Schweitzer's reagent. The highest degree of silicon extraction (69%) was achieved at using native rice husks and vanadyl acetylacetonate as a catalyst. The resulting solution contained silicon in the form of silatrane fragments. In order to isolate a silicon-containing product from the ethylene glycol solution, which would have the prospect of practical use and the maximum silicon yield, the heterofunctional polycondensation method was applied. It has appeared to be possible to isolate solid products using acetylacetonates of trivalent and tetravalent metals, which formed metal siloxanes. The structure of the obtained compounds has been confirmed by the element and X-ray diffraction analysis, as well as by the IR spectroscopy. When using rice husk chaffs as a silicon source, the product of the reaction with ethylene glycol and triethanolamine has appeared to be an irregular copolymer comprising amorphous silicon dioxide fragments and cyclic fragments similar in structure to that of silatranes. The application of metal acetylacetonates has made it possible to isolate silicon derivatives in the form of organometallic siloxanes. Тhe yield of metalsiloxanes increased in the sequence Zr < Fe < Al. Apparently, this was due to formation of lattice structures in the case of trivalent aluminum and iron, while zirconium had two remaining acetylacetonate groups and, in this case, its functionality was lower than for trivalent metals, which was confirmed by the spectral data.

Biosilica-based adsorbents prepared from rice husk, sequentially modified with polymeric polyamines and carboxyarsenazo were proposed for the preconcentration of 13 lanthanides, La, Sc, and Y. It is shown that the proposed adsorbent quantitatively extracted rare earth elements (REEs) from solutions with pH 3.5-6.5. Carrying out adsorption at pH 3.5-4.5 allows the quantitative separation of rare earth elements from accompanying ions of non-ferrous, alkaline and alkaline-earth metals. A procedure for solid-phase extraction followed by mass spectrometric determination (SPE-ICP-MS) of REEs has been developed, which includes passing of 100 mL of the analyzed solution (pH 4) through a column with the adsorbent at a flow rate of 1 mL min-1, elution of REEs with 5 mL 1 M HNO3 (a preconcentration factor of 20) and subsequent determination of elements in the eluate by inductively coupled plasma mass spectrometry (ICP-MS). The accuracy of the results was confirmed by the recovery test of spiked samples and by analysis of a Certified Reference Material. The limit of detection was 0.04-10.9 ng L-1. The procedure was used for determination of REEs in lignites from Krasnoyarsk Krai (Russia) and fumarole sediment from Kudryavy volcano of the Greater Kuril Chain (Sakhalin Oblast, Russia).

Based on biogenic silica, a number of magnetoactive composite sorbents of Fex(O,OH)(y)/SiO2 composition with 2.4-29.8% of Fe2O3 was obtained by deposition and impregnation. The morphology and character of the distribution of nanoscale iron oxide particles in the silica matrix were studied by scanning and transmission electron microscopy. By varying the composition and methods of preparation, samples with different magnetic properties were synthesized. Acid-base properties of the surface and sorption activity with respect to the aqueous solutions of methylene blue were studied. The combination of magnetic properties, sorption capacity up to 96.5 mg/g and surface area values up to 293 m(2)/g made suitable the obtained composites to be used as adsorbents.

Sodium and potassium aluminosilicates samples are synthesized from solutions formed via the alkaline hydrolysis of rice straw. The fabricated samples are characterized by means of X-ray diffraction analysis and IR-spectroscopy, and their elemental composition, particle morphology, specific surface area, and thermal properties are determined. The sorption properties of the synthesized aluminosilicates with respect to Cs+ ions are investigated under static conditions. Kinetic curves and sorption isotherms are provided and a sorption kinetic model is described.

— We have demonstrated the possibility of preparing nanostructured, X-ray amorphous sodium aluminosilicate with a specific surface area of 364 m 2 /g using an alkaline rice straw hydrolysate. Its Cs + sorption properties have been studied under static conditions in solutions with various salt compositions (seawater and nitrate solutions).

Using rice straw of various varieties of the Far Eastern selection as a source of silicon, a number of samples of sodium aluminosilicates with a Si:Al ratio from 1.02 to 1.56 were synthesized. For the obtained samples, the elemental and phase composition was found, the thermal properties were investigated. The morphology of aluminosilicates was studied: the particle size varies from 0.2 to 50 μm with a maximum distribution of about 10 μm, the specific surface area is 364 m2/g. The acid-base properties of the surface of aluminosilicates are characterized by pH-metry methods and the Hammett indicator method, the nature of the distribution of adsorption centers on the surface is established. The sorption capacity of the obtained samples, determined with respect to methylene blue (MB), is from 31.9 to 103.9 mg/g. By varying the synthesis conditions, it was shown that the greatest sorption capacity with respect to MB is achieved at the time of hydrolysis of the original rice straw for 60 minutes. It is shown that the sorption of Cs+ ions in the obtained samples is described by the Langmuir model. The sorption properties with respect to Cs+ ions from aqueous solutions with different salt background were studied.