Showing papers on "Vermiculite published in 2021"

Expanded vermiculite as an alternative adsorbent for the dysprosium recovery

Abstract: Background Dysprosium (Dy) is a critical resource for developing high-tech green energies, and its growing demand implying the need to recover it from secondary sources. Due to the known stability, availability, and high cation exchange capacity, adsorption on vermiculite can be promisor for this purpose. Methods This work evaluated the dysprosium adsorption and desorption on expanded vermiculite through experiments of equilibrium, thermodynamic, and reuse cycles. Also, the regenerated material was characterized regarding morphological, compositional, thermal, superficial aspects. Significant findings The equilibrium data achieved high adsorption capacities (0.9 mmol/g), and the sigmoidal isotherms indicated a first layer saturation and progressive surface precipitation, which may favor a Dy selective sorption. The process is feasible and spontaneous, endothermic, and classified as physisorption, advantageous for facilitating dysprosium desorption. From the reusability experiments, high efficiencies of adsorption (99%) and desorption (94%) were reached during five cycles, indicating the effective regeneration of the adsorbent and recovery of the adsorbate using a source of magnesium as eluent (magnesium nitrate hexahydrate solution). The characterization analyzes corroborated the stability and the renewability of the adsorbent. Thus, the material shows a high adsorption capacity and an easy regeneration compared to other complex adsorbents, giving the vermiculite an expressive potential for future applications in rare earth metals recovery.

Rhizosphere drives biotite-like mineral weathering and secondary Fe–Si mineral formation in Fe Ore tailings

Abstract: Pioneer plants play an important role in eco-engineering Fe ore tailings into soil for sustainable mine site rehabilitation. However, root-driven mineral weathering and secondary mineral formation remain poorly understood in tailings, despite being prerequisites for aggregate formation and pedogenesis. The present study aimed at characterizing the direct role of plant roots in tailing mineral weathering and secondary mineral formation in a compartmented cultivation system. It was found that root activities accelerated the weathering of biotite-like minerals via Fe(II) oxidation coupled with Fe(III) and Si dissolution. Numerous nanosized Fe–Si short-range-ordered (SRO) minerals and vermiculite were neoformed in the tailings after root interactions, as revealed by various microspectroscopic analyses. The Fe–Si-SRO minerals may have resulted from co-precipitation of dissolved Fe(III) and Si on mineral surfaces under alkaline and circumneutral pH conditions. Among the three plant species, Sorghum spp. (Gramineae plant) root developed most extensively in the tailings, possibly leading to more efficient mineral weathering and secondary mineral formation than Atriplex amnicola (halophyte plant) and Acacia chisholmii (leguminous plant). Overall, the study has elucidated the rhizosphere effects on tailing mineral (biotite dominant) weathering and secondary Fe–Si mineral formation, justifying pioneer plant roles in eco-engineering Fe ore tailings into soil.

A novel vermiculite/ vegetable polyurethane resin-composite for thermal insulation eco-brick production

Abstract: Affordable houses with thermal insulation materials are an efficient and creative solution for needy populations in regions where high temperatures are a public health and economic problem. In this sense, the present work had as objective to present, produce, and evaluate composites of raw vermiculite (RV) or expanded vermiculite (EV) in a vegetable polyurethane resin (VPR) matrix as thermal insulation eco-bricks. First, RV and EV were characterized by thermogravimetry (TG/DTG), X-ray fluorescence spectrometry (XRF), and scanning electron microscopy (SEM) coupled to energy-dispersive X-ray spectroscopy (EDX). Second, VPR was analyzed by TG/DTG. Then, materials were mixed and conformed into bricks in concentrations of 70, 80, and 90 wt % of raw vermiculite, and also 70, 80, 90 wt % of expanded vermiculite. The produced bricks were submitted to an alterability test with immersion into chemical reagents (ASTM D 543), humid atmosphere attack (NBR 8095), UV exposure (ASTM G 53), compressive test (ASTM D 695), physical indexes (NBR 12766), thermal insulation test, and TG/flammability test (ASTM D 635). Analysis of Variance (ANOVA) derived by a mixed 2 and 3-level design was utilized. Only 70% raw vermiculite passed NBR 8492 (soil-cement brick - dimensional analysis, compressive strength determination and water absorption - test method) and for this reason, was chosen for prototype production. Vermiculite react more with acid solutions. Vermiculite incorporation improves thermal stability and flame retardancy. 70 wt % RV brick was able to reduce 65% of the temperature, with good compressive strength (4.12 MPa) and low specific mass (1.47 g cm−3).

Does calcium carbonate influence clay mineral transformation in soils developed from slope deposits in Southern Poland

Abstract: Literature reported that soils characterized by heterogeneity would reveal the different direction of clay minerals transformation. Hence, in this study, four soils developed on menilite shales slope deposits were investigated to test if the clay minerals transformations in soils with varied calcium carbonate distribution would show multidirectional paths of clay mineral weathering, or if transformation of secondary phases in such stratified materials would reveal only one trajectory. The separated clay fractions were analysed using X-ray diffractometry and Fourier-transform infrared spectroscopy. Geochemical analyses were performed using ICP-ES and ICP-MS after sample fusion with lithium borate and an alloy dissolution with nitric acid. Calcium carbonate did not influence the composition and transformation of clay minerals. Despite the fact that soils were characterized by different content and distribution of calcium carbonate within the solum and additionally indicated various morphological features, the mineralogical composition of clay fraction was very uniform. Among the secondary phases, chlorite, illite, vermiculite, kaolinite and mixed phases illite-smectite and vermiculite-chlorite were detected in all horizons. The uniform composition of the clay minerals in the studied soils suggested that mass movement, which controlled the formation of slope covers, was probably of a similar character and intensity across the whole of the slope. Furthermore, it seems that the pedogenesis in all soils proceeded on the same scale of advancement. This was indicated by a similar degree of weathering of soil material and lack of depth-dependent weathering in the profiles, confirmed by values of weathering indices (CIA and ICV) as well as by micromorphologically visible, highly weathered coarse fragments. Moreover, weak intensity of the illuviation process within the homogeneous substrate could have resulted in the very uniform composition of clay minerals in the studied soils.

Vermiculite Filler Modified with Casein, Chitosan, and Potato Protein as a Flame Retardant for Polyurethane Foams

Abstract: In this study, polyurethane (PU) composite foams were modified with 2 wt.% of vermiculite fillers, which were themselves modified with casein, chitosan, and potato protein. The impact of the fillers on selected properties of the obtained composites, including their rheological (foaming behavior, dynamic viscosity), thermal (temperature of thermal decomposition stages), flame-retardant (e.g., limiting oxygen index, ignition time, heat peak release), and mechanical properties (toughness, compressive strength (parallel and perpendicular), flexural strength) were investigated. Among all the modified polyurethane composites, the greatest improvement was noticed in the PU foams filled with vermiculite modified with casein and chitosan. For example, after the addition of modified vermiculite fillers, the foams’ compressive strength was enhanced by ~6–18%, their flexural strength by ~2–10%, and their toughness by ~1–5%. Most importantly, the polyurethane composites filled with vermiculite filler and modified vermiculite fillers exhibited improved flame resistance characteristics (the value of total smoke release was reduced by ~34%, the value of peak heat release was reduced by ~25%).

Replacement of Natural Sand with Expanded Vermiculite in Fly Ash-Based Geopolymer Mortars

Abstract: Increasing the thermal insulation of building components to reduce the thermal energy loss of buildings has received significant attention. Owing to its porous structure, using expanded vermiculite as an alternative to natural river sand in the development of building materials would result in improvement of the thermal performance of buildings. This study investigates the properties of fly ash (FA)-based geopolymer mortars prepared with expanded vermiculite. The main aim of this study was to produce geopolymer mortar with lower thermal conductivity than conventional mortar for thermal insulation applications in buildings. A total of twelve batches of geopolymers were prepared for evaluating their different properties. The obtained results show that, at a given FA and expanded vermiculite content, the geopolymers prepared with a 10 molar NaOH solution exhibited a higher flowability, water absorption and porosity, as well as a lower dry unit weight, compressive strength, ultrasound pulse velocity and thermal conductivity compared with those prepared with a 15 molar NaOH solution. As is also shown, the geopolymers containing expanded vermiculite (15%) developed a lower flowability (~6%), dry unit weight (~6%), compressive strength (~7%), ultrasound pulse velocity (~6%) and thermal conductivity (~18%), as well as a higher apparent porosity (~6%) and water absorption (~9%) compared with those without expanded vermiculite at a given FA content and NaOH concentration. The findings of this study suggest that incorporating expanded vermiculite in FA-based geopolymer mortar can provide eco-friendly and lightweight building composites with improved sound and thermal insulation properties, contributing toward the reduction of the environmental effects of waste materials and conservation of natural sand.

Investigation of materials for reactive permeable barrier in removing cadmium and chromium(VI) from aquifer near a solid domestic waste landfill

Abstract: The sorption characteristics of raw and biofilm-coated materials: vermiculite, lightweight expanded clay aggregate (LECA), perlite, zeolite, and shungite toward Cd and Cr(VI) ions were investigated to evaluate the possibility of their use as filtration barrier in the aquifer near a solid domestic waste landfill. The effectiveness of Cr(VI) removal by the raw materials changed in the following order: shungite > zeolite > perlite > vermiculite > LECA and for Cd: zeolite > shungite > vermiculite > perlite > LECA. After biofilm formation on the surface of the materials, the sorption capacity increased in some (perlite, LECA), while in others (zeolite) it was reduced. Four kinetic models were used to describe the experimental data. Mechanisms of metal removal were proposed: for Cr(VI), a characteristic combination of sorption processes was suggested, while the removal of Cd ions could occur by ion exchange and by complexation on the surface of the sorbent. Cr(VI) reduction by living bacterial cells forming a biofilm on the sorbent surface was assessed.

Spray-coated barrier coating on copper based on exfoliated vermiculite sheets

Abstract: High-temperature barrier coatings protect metals and alloys from oxidization, delay property degradation and increase their service lifetime. Here we demonstrate a vermiculite clay-based oxidation-resistant coating on metal, using copper as an example. Dispersions of few-layer vermiculite sheets with lateral dimension in the range of microns to tens of microns are obtained in a two-step mechanical–chemical exfoliation approach, using vermiculite mineral as the starting material. The dispersion of these high aspect ratio two-dimensional sheets can be directly spray-coated on Cu foils to form a continuous and transparent thermal barrier film without the need for any binder materials. After heating in air at 400 °C for 24 h, vermiculite protected Cu foils did not show any significant sign of oxidation or degradation in mechanical and electrical properties, while uncoated Cu foils were completely destroyed.

Extended release of 6-aminopenicillanic acid by silanol group functionalized vermiculite

Abstract: The present study aimed to improve capability of vermiculite for extended release ofdrug such as: 6-Aminopenicillanic acid (6-APA). For this purpose, functionalization of vermiculite (VMT) was done...

Chitosan coated - porous low expansion vermiculite for efficient removal of cesium from radioactive wastewater

Abstract: Radioactive elements have very important applications in practical life and work. The long-lived 137Cs has a half-life of 30.2 years, it is easily absorbed by the human body. At present, the treatment methods of 137Cs are mainly adsorption, ion exchange, co-precipitation and membrane separation technology. Among them, the adsorption method is widely used because of its low cost and easy availability, and with the continuous upgrading and improvement of the removal methods, the removal cost is also rising, so it is important to develop inexpensive and high removal rate adsorbent materials. Based on this, porous adsorbents made of pre‑sodiumed low expansion vermiculite modified by urea porogenesis and polyglutamic acid covalent grafting followed by chitosan coating had been used to remove Cs+. The proposed adsorbent was successfully applied for radioactive Cs removal to be used as the potential candidate in Fukushima nuclear wastewater treatment. It showed that the porous expanded vermiculite modified with low swelling, with urea as porogen and polyglutamic acid added to increase the negative charge vacancies on the expanded vermiculite surface, could greatly improve the chemisorption capacity of Cs+ after chitosan coating. The maximum removal rate for radioactive 137Cs+ was 97.91%, and 89.89% of 137Cs+ could be effectively removed in 0.5 h. Even in the presence of competing ions such as K+, the adsorbent material still has a good adsorption effect. The maximum desorption rate of 98.43% was achieved after elution by CaCl2.

Are Clay Minerals a Significant Source of Si for Crops? A Comparison of Amorphous Silica and the Roles of the Mineral Type and pH

Abstract: Identifying the source(s) of silicon (Si) for plant is a key issue in understanding the terrestrial cycle of Si and for deciphering the reservoir of bioavailable Si to Si accumulating crops. In soils, amorphous Si, one of the most bioavailable source, is mostly present as phytoliths and has been suggested for use as a Si fertilizer by diatomite application. Although clay minerals are known to contribute to plant nutrition, their role as a major source of silica for plants has not been fully addressed. We aim at evaluating the efficiency of clay minerals as a source of Si for crops. We conducted two pot experiments: one wheat-growing experiment to compare a clay (vermiculitic) mineral and amorphous silica particles (diatomite, which is used as a phytolith substitute), and one rice-growing experiment to compare two types of clay (kaolinite vs montmorillonite) common in rice cultivation. We confirmed that the amorphous silica was more efficient than vermiculite for Si uptake by wheat. However, the Si uptake was not significantly different between the 5% diatomite substrate and the 25% vermiculite substrate indicating that clays may challenge amorphous silica, as a source of Si for crops. The kaolinite probably delivered less Si to the rice than the montmorillonite because of the lower specific surface area and lower pH of kaolinite substrates. Because clays are generally much more abundant in soils than amorphous silica, we concluded that clays may be a substantial Si source for plants, depending on the clay mineralogy.

Effects of Clinoptilolite Zeolite and Vermiculite on Nitrification and Nitrogen and Phosphorus Acquiring Enzymes in a Nitrogen Applied Agricultural Soil

Abstract: The purpose of the study was to investigate the effect of clinoptilolite zeolite and vermiculite on (i) nitrogen (N) and phosphorous (P) acquiring enzymes’ activity, (ii) potential nitrification rate (PNR), and on (iii) availabilities of the inorganic N forms. These parameters are critical to description of N mineralization and nitrification processes regulating the fate of N in agricultural ecosystems. A time-course (60-days) microcosm study was conducted on a circumneutral agricultural soil, where clinoptilolite zeolite and vermiculite were added as a mixture with N substrate (i.e., urea or manure). Zeolite inhibited urease activity regardless of the N supply (manure or urea). On the contrary, the activities of acid phosphatase, alkaline phosphatase, N-acetylglucosaminidase (NAG), asparaginase, glutaminase, and arylamidase remained unaffected. Moreover, zeolite and vermiculite affected the NH4+ availability and retarded the NO3− accumulation in the soil, by 22 and 25%, respectively. Zeolite and vermiculite amendments showed lower potential nitrification rate (PNR) than single urea ones, by 58 and 45%, respectively, at day 15. Clinoptilolite zeolite and vermiculite affected nitrification activity and potentials of soil under organic and inorganic N amendment, whereas zeolite inhibited urease activity, suggesting an influence on the overall biochemical cycle of N. Further work is needed to elucidate as follows: (i) the responsible mechanism(s) behind the inhibited urease activity, (ii) the response of decomposing and nitrifying microorganisms, and (iii) the implications on N transformation rates.

Clay-Based Nanofluidic Membrane Derived from Vermiculite Nanoflakes for Pressure-Responsive Power Generation

Abstract: The intrinsic thermal and chemical stability of vermiculite clay is exploited here to fabricate a robust and responsive energy device that consumes atmospheric water molecules as the cathode reagen...

Clay mineralogical composition and chemical properties of Haplic Luvisol developed on loess in the protected landscape area Litovelské Pomoraví

Abstract: The character of parent material, organic matter and climatic conditions are the crucial factors of pedogenesis. They directly influence the intensity of weathering, transformation processes, elements release and geochemical cycles. The mineral transformation in a profile of the recent soil developed on loess (Haplic Luvisols, Siltic, Epidystric, Ochric) was studied. The land area Litovelske Pomoravi was chosen because of the stability of soil‐forming factors such as topography, relief, vegetation and climate. X‐ray diffraction (XRD) quantitative analysis of the fine earth (<2 mm) and XRD analysis of clay (<2 μm) and the fine clay fraction (<0.2 μm) were applied. The obtained results showed the most significant differences between the argic horizons (Bt1 and Bt2) and other soil horizons. The lower content of quartz and feldspars and higher content of dioctahedral micas and phyllosilicates in both Bt horizons was observed. It was assumed the clay illuviation/lessivage process was preceded by long‐term leaching of carbonate in humid continental conditions during almost the whole Holocene. The distribution of the clay fraction correlates with the distribution of phyllosilicates through the profile. Major clay minerals in the clay fraction (<2 μm) were illite and kaolinite, smectite, chlorite, vermiculite and several types of mixed‐layered phases. The analysis of the finer clay fraction (<0.2 μm) identified the new phase hydroxy‐interlayered minerals as the product of illite (vermiculite) weathering in humid continental conditions. HIGHLIGHTS: Clay mineralogy of Haplic Luvisols on loess was studied. XRD analysis identified the new phase of hydroxy‐interlayered minerals. Increasing of smectites, dioctahedral micas, and goethite as a result of clay illuviation/lessivage process was observed.