Showing papers on "Vermiculite published in 2017"

Improved thermal stability and flame resistance of flexible polyimide foams by vermiculite reinforcement

Abstract: In this work, a series of flexible polyimide composite foams with dianhydride and isocyanate as the starting materials were prepared by pre-dispersing vermiculite in isocyanate. The experimental results revealed that the cellular diameter of foams obviously decreased with the addition of vermiculite. The open cell content decreased with the increase of vermiculite, and foams containing vermiculite possessed higher apparent densities of about 10 kg/m3 when compared with the neat polyimide foams. The compressive strength was dramatically enhanced by vermiculite incorporation, and reached maximum when the filler content was 2%, indicating dramatically reinforcing effect of vermiculite. With the addition of vermiculite, the thermal stability and flame resistance of polyimide foams were improved. The limiting oxygen index of polyimide foams showed an increase from 31 to 33.5% with increase of vermiculite from 0 to 8% and the peak heat release rate decreased, indicating high flame retardant properties. Vermiculites possess excellent heat insulation and high temperature stability. When conditioned at high temperature, the filler would block the heat transfer during the bulk foam. Therefore, it is feasible to further increase the mechanical and thermal properties of polyimide foams by vermiculite filling. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44828.

Analysis of the Importance of Oxides and Clays in Cd, Cr, Cu, Ni, Pb and Zn Adsorption and Retention with Regression Trees.

Abstract: This study determines the influence of the different soil components and of the cation-exchange capacity on the adsorption and retention of different heavy metals: cadmium, chromium, copper, nickel, lead and zinc. In order to do so, regression models were created through decision trees and the importance of soil components was assessed. Used variables were: humified organic matter, specific cation-exchange capacity, percentages of sand and silt, proportions of Mn, Fe and Al oxides and hematite, and the proportion of quartz, plagioclase and mica, and the proportions of the different clays: kaolinite, vermiculite, gibbsite and chlorite. The most important components in the obtained models were vermiculite and gibbsite, especially for the adsorption of cadmium and zinc, while clays were less relevant. Oxides are less important than clays, especially for the adsorption of chromium and lead and the retention of chromium, copper and lead.

Crystal structure control of aluminized clay minerals on the mobility of caesium in contaminated soil environments.

Abstract: Radioactive caesium pollution resulting from Fukushima Dai-ichi and Chernobyl nuclear plant accidents involves strong interactions between Cs+ and clays, especially vermiculite-type minerals. In acidic soil environments, such as in Fukushima area, vermiculite is subjected to weathering processes, resulting in aluminization. The crystal structure of aluminized clays and its implications for Cs+ mobility in soils remain poorly understood due to the mixture of these minerals with other clays and organic matter. We performed acidic weathering of a vermiculite to mimic the aluminization process in soils. Combination of structure analysis and Cs+ extractability measurements show that the increase of aluminization is accompanied by an increase in Cs+ mobility. Crystal structure model for aluminized vermiculite is based on the interstratification of unaltered vermiculite layers and aluminized layers within the same particle. Cs+ in vermiculite layers is poorly mobile, while the extractability of Cs+ is greatly enhanced in aluminized layers. The overall reactivity of the weathered clay (cation exchange capacity, Cs+ mobility) is then governed by the relative abundance of the two types of layers. The proposed layer model for aluminized vermiculite with two coexisting populations of caesium is of prime importance for predicting the fate of caesium in contaminated soil environments.

Adsorption of ammonium from simulated wastewater by montmorillonite nanoclay and natural vermiculite: experimental study and simulation

Abstract: In this research, montmorillonite nanoclay (MNC) and vermiculite were used to adsorb ammonium (NH4+) from simulated wastewater. The effect of organic acids, cations, and anions on adsorption of NH4+ was also studied using batch experiments. The presence of organic acids significantly decreased the NH4+ adsorption using both adsorbents and the reduction followed the order of citric acid > malic acid > oxalic acid. The presence of cations in wastewater could decrease the adsorption of NH4+ and the ion exchange selectivity on the MNC and vermiculite followed the orders Mg > Ca ≥ K > Na and Mg > > Ca > Na > K, respectively. Adsorption of NH4+ by adsorbents in the presence of sulfate (SO4) was higher than those in the presence of phosphate (PO4) and chloride (Cl) anions. Results indicated that MNC and vermiculite had good potential for NH4+ removal depending on adsorbent dosage, pH, contact time, and initial NH4+ concentration. The effect of pH on removal of NH4+ indicated that MNC would be more appropriate as the adsorbent than vermiculite at low pH values. Kinetic analysis demonstrated that the rate-controlling step adsorption for NH4+ by MNC and vermiculite was heterogeneous chemisorption and followed the pseudo-second-order model. The desorption experiments indicated that the adsorption of NH4+ by adsorbents was not fully reversible, and the total recovery of adsorbed NH4+ for MNC and vermiculite varied in the range of 72 to 94.6% and 11.5 to 45.7%, respectively. Cation exchange model (CEM) in PHREEQC program was used to simulate NH4+ adsorption. Agreement between measured and simulated data suggested that CEM was favored in simulating adsorption of NH4+ by clay minerals. The results indicated that MNC and vermiculite have good performance as economic and nature-friendly adsorbents that can ameliorate the water and environment quality.

Environmental benign synthesis of lithium silicates and Mg-Al layered double hydroxide from vermiculite mineral for CO2 capture.

Abstract: This research introduces a completely new environmental benign synthesis route for obtaining two kinds of inter-mediate and high temperature CO2 sorbents, Mg-Al layered double hydroxide (LDH) and Li4SiO4, from vermiculite. The mineral vermiculite was leached with acid, from which the obtained SiO2 was used for the synthesis of Li4SiO4 and the leaching waste water was used for the synthesis of Mg-Al LDH. Therefore, no waste was produced during the whole process. Both Li4SiO4 and Mg-Al LDH sorbents were carefully characterized using XRD, SEM, and BET analyses. The CO2 capturing performance of these two sorbents was comprehensively evaluated. The influence of the Li/Si ratio, calcination temperature, calcination time, and sorption temperature on the CO2 sorption capacity of Li4SiO4, and the sorption temperature on the CO2 sorption capacity of LDH, were investigated. The optimal leaching acid concentration for vermiculite and the CO2 sorption/desorption cycling performance of both the Li4SiO4 and Mg-Al LDH sorbents were determined. In sum, this demonstrated a unique and environment-friendly scheme for obtaining two CO2 sorbents from cheap raw materials, and this idea is applicable to the efficient utilization of other minerals.

Soil-landscape relationship in a chronosequence of the middle Madeira River in southwestern Amazon, Brazil

Abstract: High temperatures and rainfall prevail in the Brazilian Amazon, but some areas have soils with high clay mineral contents of 2:1, and there is limited information concerning their properties. Therefore, it is important to study the soil formation and understand the environmental conditions in which they were formed. This study aimed to investigate the physical, chemical and mineralogical properties of the soil in relation to the environmental factors acting on a chronosequence in the Late Pleistocene sediments of the Middle Madeira River. Soil profiles were selected on three alluvial terraces. Morphological, physical, chemical, mineralogical, X-ray fluorescence, TEM and SEM characterizations were performed. The soils that exhibited a clayey texture, acidic reaction, low values of exchangeable bases and high values of aluminum had profiles containing a considerable presence of 2:1 clay minerals, especially illite, vermiculite, mica-vermiculite, hydroxyl-interlayered vermiculite and pyrophyllite. Soil mineralogy indicated that these soils were recently weathered, where the low values of sum of bases correspond to the low presence of these cations in the parent material. Meanwhile, high values of exchangeable aluminum were derived from the pyrophyllite alteration, different parent material and 2:1 clay minerals recent alteration. Therefore, the parent material, presence of amorphous silica, different climate conditions in the past and current drainage restriction contribute to the slow alteration rate of 2:1 clay minerals of the soils of the humid tropical Amazon environment.

Functionalization of Bentonite and Vermiculite after the Creation of Structural Defects through an Acid Leaching Process

Abstract: The synthesis and use of functionalized materials is growing every year. Thus, this work presents a methodology for the functionalization of bentonite and vermiculite after the acid leaching of the raw materials. Leaching was performed with sulfuric acid (H2SO4), and the functionalization was performed with (3-mercaptopropyl)trimethoxysilane (MPTS), which was oxidized after being anchored to the support. Compared to the results in the literature for directly functionalized raw bentonite, the materials had a greater number of anchored propyl sulfonic acid groups, and the greatest number of these groups led to an increase in the acidity of the raw materials. The raw and functionalized bentonite and vermiculite were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), thermogravimetric analysis (TGA), N2 adsorption and the surface acidity was determined by acid-base titration.

Effect of Nanozinc Oxide and Organic Expanded Vermiculite Compound on Antiaging Properties of SBR Modified Bitumen

Abstract: This work focuses on the effect of nanozinc oxide (nano-ZnO) and organic expanded vermiculite (OEVMT) compound on physical and aging properties of styrene butadiene rubber (SBR) modified bi...

Contemplating the feasibility of vermiculate blended chitosan for heavy metal removal from simulated industrial wastewater

Abstract: Wastewater contaminated by heavy metals pose great challenges as they are non biodegradable, toxic and carcinogenic to the soil and aquifers. Vermiculite blended with chitosan have been used to remove Cr(VI) and Cd(II) from the industrial wastewater. The results indicate that the vermiculite blended with chitosan adsorb Cr(VI) and Cd(II) from industrial waste water. Batch adsorption experiments were performed as a function of pH 5.0 and 5.5 respectively for chromium and cadmium. The adsorption rate was observed to be 72 and 71 % of chromium and cadmium respectively. The initial optimum contact time for Cr(VI) was 300 min with 59.2 % adsorption and 300 min for Cd(II) with 71.5 % adsorption. Whereas, at 4–6 there is saturation, increasing the solid to liquid ratio for chitosan biopolymers increases the number of active sites available for adsorption. The optimum pH required for maximum adsorption was found to be 5.0 and 5.5 for chromium and cadmium respectively. The experimental equilibrium adsorption data were fitted using Langmuir and Freundlich equations. It was observed that adsorption kinetics of both the metal ions on vermiculite blended chitosan is well be analyzed with pseudo-second-order model. The negative free energy change of adsorption indicates that the process was spontaneous and vermiculite blended chitosan was a favourable adsorbent for both the metals.

Complexity of clay mineral formation during 120,000 years of soil development along the Franz Josef chronosequence, New Zealand

Abstract: Weathering of primary silicates to secondary clay minerals over time affects multiple soil functions such as the accumulation of organic matter and nutrient cations. However, the extent of clay mineral (trans)formation as a function of soil development is poorly understood. In this study, the degree of weathering of sediments along a 120 kyr soil formation gradient was investigated using X‐ray diffraction, Fourier transform infrared spectroscopy and X‐ray fluorescence spectroscopy. Irrespective of site age, mica and chlorite were the dominant clay minerals. During weathering, a remarkable suite of transitional phases such as vermiculite and several interstratifications with vermiculitic, smectitic, chloritic and micaceous layers developed. The degree of weathering was correlated with soil pH and depletion of K, Ca, Na, Fe and Al, regarding both soil depth and site age. Kaolinite occurred especially at the 120 kyr site, indicating slow formation via transitional phases. The findings of this study r...

Parent Materials and Climate Control Secondary Mineral Distributions in Soils of Kalimantan, Indonesia

Abstract: Secondary mineral distributions in soils from Kalimantan, Indonesia, were investigated to examine the effects of the parent materials and climate at different elevations on the distributions. B horizon soils were sampled at 60 sites on gentle slopes at different elevations (20–1700 m altitude). Each major parent material (sedimentary, felsic, and intermediate to mafic) was represented at different elevations. The soil samples were classified from their total elemental compositions using cluster analysis. Secondary minerals were measured by X-ray diffraction and selective extractions. The samples were divided into ferric (high Fe contents), K&Mg (high K, Mg, and Si), and silicic (high Si) groups. The ferric soils were derived from mafic parent materials, whereas the others were derived from felsic or sedimentary parent materials. The K&Mg soils had higher total base contents (suggesting primary minerals) and were less weathered than the silicic soils. Secondary minerals in the ferric soils were characterized by high contents of Fe oxides and gibbsite. The K&Mg and silicic soils had similar secondary mineral (kaolinite and vermiculite) contents, but more mica was found in the former. Only the silicic group soils had secondary mineral contents that changed as the elevation changed (the kaolinite content increased and the vermiculite and poorly crystalline Al and Fe contents decreased as the elevation decreased). Higher temperatures at lower elevations may cause minerals to be altered more. Secondary mineral distributions were primarily controlled by the parent material (mafic or felsic/sedimentary) and, secondarily by the climate, which varied with elevation.

Removal of Cesium from Aqueous Solution by Adsorption onto Sivas- Yildizeli (Türkiye) Vermiculite: Equilibrium, Kinetic and Thermodynamic Studies

Abstract: In this study, cesium adsorption performance of raw vermiculite obtained from Sivas-Yildizeli region of Turkey was investigated using batch adsorption method. In order to obtain the optimum adsorption conditons; different adsorbent dosages, contact times, solution pH’s, initial cesium concentrations and temperature ranges were investigated. Amount of cesium ions and percentage of cesium adsorbed by vermiculite in solution media were calculated using ICP-OES technique and noted as mg/g and %adsorbed Cs. Kinetic studies demonstrated that adsorption process was in accordance with second order pseudo kinetic model and equilibrium isotherm modeling studies showed that the process was compatible with Langmuir, Freundlich and Temkin adsorption isotherm models meaning the Cs adsorption process had both phsyical and chemical character. Negative Gibbs energy values obtained from thermodynamic studies revealed that the adsorption process was spontaneous and had a high feasibility. Additionally, negative enthalpy value indicated that process was exothermic, meaning the amount of Cs ions decresead with increasing reaction temperatures and positive entrophy value showed that disorderliness between solid-liquid phase increased during adsorption. Results clearly indicate that vermiculite mineral has a promising potential in removing Cs + ions from aqueous media which leads mineral may also be used in decomposing and efficiently removing radioactive cesium from contaminated waters.

Vermiculite addition to soil decreases N water pollution by over 30

Abstract: The large amounts of nitrogen-containing mineral fertilisers in industrial agriculture are leading to water pollution with effects such as eutrophication and death of aquatic life. There is therefore a need for techniques to keep N in the soil to prevent leaching in waters. Here, we tested the effect of the addition of vermiculite, a phyllosilicate mineral, to the soil, on fertiliser NH4 +-N retention in laboratory experiments during 14–45 days. The added amount of vermiculite was twice the amount of the nitrogen fertilizer added. Our results show that addition of vermiculite increases NH4 +-N retention by over 30%, compared to a control. Adding vermiculite is thus a promising technique to control the eutrophication of water systems as well as reducing agriculture cost.

Formation of NH4-Illite-Like Phase at the Expense of Dioctahedral Vermiculite in Soil and Diagenetic Environments — An Experimental Approach

Abstract: Selective sorption and/or fixation of cations with low hydration energies (e.g. K+, NH 4 + , Rb+, Cs+) by vermiculites is a well known phenomenon in soil science and it has been described by many investigators since the 1950s. Because most of the available studies deal with trioctahedral vermiculites, cation fixation in dioctahedral vermiculites is not as well understood as fixation by trioctahedral structures. The objective of the present study was to investigate the influence of NH 4 + saturation on the structure of a natural dioctahedral vermiculite. Because no dioctahedral vermiculite standard reference material was available, two natural dioctahedral vermiculite-rich soil clay samples were used in the study. The clays were saturated with NH 4 + using different protocols to simulate natural processes that likely take place in soils. The degree of NH 4 + fixation by the dioctahedral vermiculite was evaluated using X-ray diffraction, elemental N analysis, and infrared spectroscopy. All the treatments that involved NH 4 + saturation caused NH 4 + fixation and irreversible collapse (i.e. contraction to ~10 A) of at least a portion of the previously hydrated (vermiculitic) interlayers. Air drying of the NH 4 + -saturated samples greatly enhanced the degree of the collapse. The results indicated that the collapse of dioctahedral vermiculite leads to the formation of a NH4-illite-like phase that is likely to occur in some soils and sediments that are rich in organic matter. The formation of a NH4-illite-like phase by NHNH 4 + fixation in vermiculitic interlayers needs to be taken into consideration in studies that deal with the clay mineralogy of sedimentary basins.