Most read
This page lists the top ten most read articles for this journal based on the number of full text views and downloads recorded on Cambridge Core over the last 90 days. This list is updated on a daily basis.
Variation in the structural order of kaolinite in regolith as an effective indicator of REE mineralization
- Lianying Luo, Wei Tan, Xiaorong Qin, Shichao Ji, Xiaoliang Liang, Hongping He
-
- Published online by Cambridge University Press:
- 03 June 2024, e1
-
- Article
- Export citation
-
Regolith-hosted rare earth element (REE) deposits hosted by the granitic regolith in South China provide >90% of the world’s heavy REEs. Kaolinite is one of the major carriers of REE ions in regolith. The formation and transformation of kaolinite can be affected by chemical weathering and hydrodynamic conditions, but the contribution of each factor has not been evaluated. This study systematically investigated the variation in abundance of phyllosilicate minerals and structural order of kaolinite in the Renju regolith-hosted REE deposit. The total abundance of 1:1 phyllosilicate minerals increased upwards along the profile from Section I to Section III. However, semi-quantitative analyses indicated that Section III-1 (depth at 10–16 m) featured an evident decrease in both abundance and structural order of kaolinite upward along the profile. The morphological feature and abundance of kaolinite revealed intensive kaolinite-to-halloysite transformation and kaolinite dissolution in Section III-1. This suggests that the alternating wetting and drying zone in Section III-1 provided a favorable kinetic environment for the entry of water molecules into the kaolinite interlayer and the kaolinite-to-halloysite transformation, resulting in both lower structural order and abundance of kaolinite in Section III-1. Moreover, REE ions started to be enriched from the alternating wetting and drying zone and formed high-grade ores at the lower part of the water table, due to a significant increase in pore water and decrease in the seepage velocity. Therefore, the abundance and structural order of secondary kaolinite can serve as important indicators of hydrodynamic changes in regolith, as well as the mineralization of regolith-hosted REEs.
Review of secondary phases formed under natural alkaline conditions at low temperatures and implications for cement–bentonite interactions in radioactive waste repositories
- Misato Shimbashi, Shingo Yokoyama, Tsutomu Sato
-
- Published online by Cambridge University Press:
- 03 June 2024, e2
-
- Article
-
- You have access Access
- Open access
- HTML
- Export citation
-
The alteration of bentonite under alkaline conditions and the subsequent changes in properties such as permeability and self-sealing ability should be evaluated for the performance assessment of radioactive waste repositories. As the period of evaluation for alterations is extremely long, natural analog (NA) studies that can observe long-term phenomena similar to the system of radioactive waste repositories have significant advantages. However, locations that can be set up as NA study sites with significant similarity are limited and should be pursued by localizing analog systems. This literature review summarized studies reporting secondary phases formed at low temperatures (<100°C) under a broader range of natural sites which are chemically similar to the alkaline conditions expected at bentonite in radioactive waste repositories, including near pyrometamorphic rocks, near ophiolites, and in alkaline saline lakes. This review provides insights into the species, formation conditions, and stability of secondary phases that could be formed during cement–bentonite interactions and the timescale for mineralogical transitions from a metastable to a stable phase. The findings could be useful for selecting secondary phases to be considered in reactive transport modeling for predicting cement–bentonite interactions in radioactive waste repositories.
Role of clay cation exchange capacity, location of charge, and clay mineralogy on potassium availability in Indian Vertisols
- Priya P. Gurav, S.K. Ray, S.C. Datta, P.L. Choudhari, Christian Hartmann
-
- Published online by Cambridge University Press:
- 03 June 2024, e3
-
- Article
- Export citation
-
Precise information on the location of charge in clay minerals and their charge density in smectite-dominant soils is rare. The present study was undertaken with three benchmark Vertisols to establish the relationship between the clay cation exchange capacity (CEC), charge density, as well as the location of charge in smectitic soil clay minerals and their relationship with potassium (K) fixation and release. Potassium fractions and their threshold levels in the Vertisols were determined by standard methods. Soils were segregated into silt, total clay and fine clay fractions for X-ray diffraction analysis and fine clay fractions were used to determine the CEC using standard methods. The Hofmann-Klemen effect (HK) and modified Greene-Kelly test was done with the fine clay to determine the CEC of the tetrahedral sheet. Subsequently, the CEC of the octahedral sheet was calculated as the difference between total CEC and the tetrahedral CEC. The results showed that ~60–64% of the total CEC is attributed to the tetrahedral layers. The tetrahedral CEC that is proportional to the tetrahedral charge density was significant and negatively correlated with K release threshold values and all fractions of K. The tetrahedral CEC contributed more toward the K fixation and release than the octahedral CEC. The study shows that the dominant presence of high-charge smectites in the fine clay fractions of these Vertisols contributed to the tetrahedral CEC and consequently to the charge density of these soils, which implied a tendency to fix K easily and release it with greater difficulty compared to soils with low-charge smectites.
Adsorption-desorption of lead by polycarboxylate-coated bentonite
- Chuang Yu, Zhi-lei Zeng, Xiaoqing Cai, Zhi-hao Chen, Rao-ping Liao
-
- Published online by Cambridge University Press:
- 25 July 2024, e4
-
- Article
- Export citation
-
To develop more economical and efficient heavy metal adsorbents, natural bentonite was employed as a raw material, and triethoxyvinylsilane served as a grafting agent to achieve the grafting bonding of sodium polyacrylate and bentonite. Structural alterations in the modified bentonite were analyzed through thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The adsorption and desorption characteristics of SAPAS-Bentonite and raw bentonite were compared and tested under various conditions, including time, temperature, pH, and lead ion concentration. The adsorption and desorption properties of sodium polyacrylate-grafted bentonite (SAPAS-Bentonite) were compared under various conditions (time, temperature, pH, and lead ion concentration). The results revealed that the modified method successfully achieved nano-scale coating of bentonite particles with sodium polyacrylate, leading to an increase in the maximum adsorption capacity of lead ions by 47.5%, reaching 165.73 mg g. A greater adsorption affinity for lead ions was exhibited by the outer sodium polycarboxylate portion of SAPAS-Bentonite compared with the inner bentonite. The adsorption of internal bentonite was limited by blocking when the adsorption of sodium polyacrylate did not reach the upper limit. The adsorption isotherm shifted from the Langmuir monolayer characteristic of the original bentonite to the S-shaped isotherm, reflecting the sodium polycarboxylate properties of SAPAS-Bentonite. Both bentonites demonstrated strong retention capacity for lead, with SAPAS-Bentonite surpassing raw bentonite in performance. This study provides valuable insights into the potential of SAPAS-Bentonite in the treatment of heavy metal pollution.
Stability of Gaomiaozi bentonite: Interlayer hydration structure and aggregation morphology
- Zhaomin Tan, Chengyun Fu, Mark Julian Henderson, Xuezhi Dai, Jianfeng Cheng, Jingli Xie, Shan Zhu, Minhao Yan
-
- Published online by Cambridge University Press:
- 25 July 2024, e5
-
- Article
- Export citation
-
The sustainability of high-level radioactive waste repositories situated in fractured crystalline rocks depends on the stability of bentonite liners, and this can pose a problem in certain groundwater conditions that favor the formation of colloids from backfill materials that are prone to erosion. The influence of different environments on the structure of Gaomiaozi bentonite (GMZ) and GMZ colloids (GMZC) is presented here. Different hydrated interlayer structures of bulk and colloidal forms of this bentonite from small-angle X-ray scattering (SAXS) data are demonstrated. Analysis of the scattering data showed that GMZ had three interlayer water structures: dehydrated (0W), monohydrated (1W), and bi-hydrated (2W). The colloids readily agglomerated at acidic pH (pH <5) but showed resistance to agglomeration in an alkaline condition (pH >7). The effect of Na+, K+, Mg2+, and Ca2+ on the lamellar structure and agglomerate morphology of GMZC particles was investigated. In general, the tendency of colloids to agglomerate was greater in the presence of divalent metal cations compared with monovalent metal cations. High concentrations (10–5 to 10–3 mol L–1) of divalent ions imparted order into the stacked lamellar structure after the saturation of the interlayer. In contrast, monovalent ions reduced the tendency of the particles to aggregate, leading to an abundance of colloidal nanoparticles prone to erosion. This work helps to better understand the structural characteristics of GMZC in the groundwater environment, and provides a valuable reference for the evaluation of nuclide migration in the deep geological disposal of high-level radioactive wastes.
Highly efficient TiO2-pillared smectite clay with Ni and Co doping for Rhodamine B removal: kinetics of adsorption and photodegradation
- Adi Darmawan, Setyo Sulaksono, Muhamad Samsul Arifin, Hasan Muhtar, Sriyanti Sriyanti
-
- Published online by Cambridge University Press:
- 25 July 2024, e7
-
- Article
- Export citation
-
Clay exhibits the capability to adsorb dyes such as Rhodamine B (RhB); practical application reveals its susceptibility to desorption, however, compromising its efficacy for RhB removal. To address this concern, modification of Natural Boyolali Region Clay (NBR Clay) was conducted by introducing TiO2 pillars and incorporating Co and Ni as dopants. This modification aimed to augment the clay’s photodegradation capability and its RhB removal capacity. The principal objective of this study was to assess the characteristics of TiO2-pillared clay doped with Co and Ni and to evaluate its effectiveness in RhB removal. The prepared samples were analyzed using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis with differential scanning calorimetry (TGA-DSC), and gas sorption analysis (GSA). TGA results indicated stability for all samples up to 650°C, except for Co-Ti/NBR Clay. After 2.5 min, the adsorption capacity of both NBR Clay and NBR Clay+ethanol (EtOH) significantly surpassed that of Ti/NBR Clay, Ni-Ti/NBR Clay, and Co-Ti/NBR Clay. However, the adsorption energy of Ti/NBR Clay, Ni-Ti/NBR Clay, and Co-Ti/NBR Clay exceeded that of NBR Clay and NBR Clay+EtOH. Furthermore, all samples adhered to the Langmuir isotherm model, indicative of a physisorption mechanism. Notably, after 80 min, the percentage of photocatalytic degradation for plain clay reached 99.61%, and this value increased with the introduction of TiO2 and doping. The Co-Ti/NBR Clay sample exhibited the highest degradation rate at 99.97%. These findings underscore the favorable influence of TiO2 addition and doping on enhancing RhB removal efficiency.
Development and characterization of a slow-release dual-purpose N and Zn fertilizer based on diatomite and nano-diatomite
- Atena Mirbolook, Mirhassan Rasouli-Sadaghiani, Payman Keshavarz, Mina Alikhani Moghadam, Jalal Sadeghi
-
- Published online by Cambridge University Press:
- 31 July 2024, e6
-
- Article
- Export citation
-
Leaching and volatilization of N from urea, and precipitation and fixing of Zn by commercial fertilizers, has led to excessive costs for farmers and problems for the environment. Incorporating fertilizers in a porous material such as diatomite can prevent these losses by slowing the nutrient release. A new fertilizer formulation, based on the urea-zinc (UZn) complex in the eutectic solution of salt-urea was prepared. In the following, UZn was incorporated into diatomite and nano-diatomite by using hydroxypropyl methylcellulose (HPMC) as a binder. The treatments included the following: U: urea; UZn: urea-Zn; UZn-D: urea-Zn-diatomite; UZn-ND: urea-Zn-nano-diatomite; UZn-D-B: urea-Zn-diatomite-binder; and UZn-ND-B: urea-Zn-nano-diatomite-binder. The slow-release urea fertilizers (SRUFs) were characterized using FESEM/EDS, FTIR, CHN, XRD, DLS, and zeta potential techniques. Urea slow-release behavior, kinetics in water, and available Zn and N-forms leaching in the soil column were evaluated compared with conventional urea and zinc fertilizers. The pattern of release of urea in water was sigmoidal and after 12 h, only 20% of urea was released from fertilizers containing diatomite and HPMC. The NO3– release pattern in the soil started with a 12-day delay, and after that, the rate of NO3– leaching decreased by two to three times in the application of fertilizers containing HPMC compared with urea. The Zn concentration in the leachates of columns supplied with SRUFs was 35% less than for those supplied with ZnSO4. The results showed that the SRUFs make N and Zn available in the soil and but reduce the rate of their release.
Clay and Fe (oxyhydr)oxide mineralogy in the basalt weathering profile in Hainan (southern China): implications for pedogenesis process
- Hanlie Hong, Jiawei Wang, Chaowen Wang, Chen Liu, Thomas J. Algeo, Lulu Zhao, Lian Zhou, Daqian Zhang, Qian Fang
-
- Published online by Cambridge University Press:
- 26 July 2024, e8
-
- Article
- Export citation
-
In order to gain a better understanding of clay and Fe (oxyhydr)oxide minerals formed during pedogenesis of basalts in tropical monsoonal Hainan (southern China), a basalt-derived lateritic soil at Nanyang, Hainan, was investigated comprehensively. The results show that the lateritic regolith consists uniformly of kaolinite and Fe (oxyhydr)oxide minerals, with trace gibbsite only in the AE horizon. Abundant dioctahedral smectite in the basalt bedrock formed due to primary hydrothermal alteration, and transformed to kaolinite rapidly in the highly weathering saprolite horizon. The ‘crystallinity’ of kaolinite is notably low and its Hinckley index fluctuates along the soil profile, resulting from intense ferrolysis due to fluctuations between wet/dry climate conditions. From the base to the top of the profile, maghemite shows a decreasing trend, whereas magnetite, hematite, and goethite exhibit a slightly increasing trend, indicating that maghemite formed as an initial product of basalt weathering. Formation of Fe (oxyhydr)oxide species in basalt-derived soil is mainly controlled by local environmental conditions such as soil moisture, redox, and acidic conditions; thus, iron mineral-based paleoclimatic proxies could not be used for subtropical to tropical soils. The highly weathered saprolite has a similar δ56Fe value (+0.06‰) to that (+0.07‰) of the parent rock, while the AE to middle E horizons have greater δ56Fe values of +0.12‰ to +0.19‰. Fe isotopic signatures correlate positively with the Fe mass transfer coefficient (R2=0.77, n=6, ρ<0.05), indicating repetitive weathering and relative accumulation of isotopically heavier Fe in the upper soil horizons, which occurred by reductive dissolution of organic matter under oxic conditions, as reflected by the greater U/Th.
Evaluation of the antibacterial properties of commonly used clays from deposits in central and southern Asia
- Elshan Abdullayev, Joy R. Paterson, Eleanor P. Kuszynski, M. Daud Hamidi, Papreen Nahar, H. Chris Greenwell, Anke Neumann, Gary J. Sharples
-
- Published online by Cambridge University Press:
- 07 August 2024, e9
-
- Article
-
- You have access Access
- Open access
- HTML
- Export citation
-
One potential solution to the rising threat of antibacterial drug resistance is the application of therapeutic clays to treat wound infections. Clays with antibacterial activity have been identified from a range of sources with their antibacterial properties often attributed to the release of toxic metal ions such as Fe(II) and Al(III). Here, clays from Afghanistan, Azerbaijan and Bangladesh that are utilized for washing and healing purposes were examined. Their antibacterial activities were assessed in suspension and as aqueous leachates against representative Gram-negative, Escherichia coli, and Gram-positive, Bacillus subtilis, bacteria. The majority of the clays conferred no deleterious effect and, in fact, tended to promote bacterial growth, likely as a result of released organic and inorganic nutrients. However, one of the clays, obtained from the Dhaka region of Bangladesh, displayed significant bactericidal activity against E. coli and B. subtilis as a clay suspension but not as an aqueous leachate. Further experiments confirmed that contact between clay and the bacteria was necessary for most of the antibacterial effects. Detailed analysis of bulk and <2 μm clay fraction mineralogy and geochemistry revealed no single defining parameter or mineral component that could be used to easily distinguish natural clays with antibacterial properties from those without. Overall, the results suggest a mechanism of antibacterial action of the Dhaka clay that arises from acidic conditions, likely enabled by the absence of calcite in the bulk clay, metal release, the presence of interstratified chlorite-smectite, and direct clay–bacteria interactions.
Effects of occurrence form of soil organic matter on the Atterberg limits and thermal conductivity of clays
- Yue Gui, Qingkun Sang, Jie Yin
-
- Published online by Cambridge University Press:
- 10 September 2024, e10
-
- Article
- Export citation
-
Because of the interfacial interactions between mineral soil particles and soil organic matter (SOM), SOM occurs in various forms in the soil, and the mineral-associated and particulate forms are fundamental. Many recent studies have concentrated on the effects of SOM content and type on the geotechnical behavior of soil. However, the influence of SOM occurrence forms is not well understood, nor is there a scientific classification standard for SOM in geotechnical engineering. The main objectives of this study were to explore the effects of SOM occurrence forms on a few physical properties of clays to develop an engineering classification standard of SOM. First, this paper reviews the interfacial interaction mechanism, factors that influence the relation between mineral soil particles and SOM, and the classification method of SOM in soil science. Three predominant clays (montmorillonite, illite, and kaolinite) were then used as the matrix, and three groups of artificial soil samples with different SOM contents (wu ranging from 0 to 50% by weight) were prepared by adding peat. A chemical extraction method was used to determine the amount of different forms of SOM. Moreover, the Atterberg limits wL (wp) and thermal conductivity λ of artificial soil samples were tested. Based on the experimental results, the relationship between the form of SOM and these physical parameters was established. The experimental results show that the wL (wp) vs wu, and λ vs wu fitted curves were not monotonic but piecewise linear and could be divided into two straight lines with different slopes; wu corresponded to the inflection point of wL (wp) vs wu, and λ vs wu curves were closer to the threshold value wu,2. Finally, a simple engineering classification method of SOM is proposed.