The separator is an important component of the microbial fuel cells (MFCs), which separates anode and cathode entities and facilitates ion transfer between both. Despite the high research in ...separators in recent years, the need for cost-effective, waste-driven selective separators in MFCs persists. Present study discloses the strategic fabrication of functionalized-tea-waste-ash-clay (FTWA-C) composite separator by integrating functionalized tea waste ash (FTWA) with potter's clay. Clay was used as a base, while FTWA was used as cation exchanger. FTWA and clay were separately mixed in four different ratios, 00:100 (C1); 05:95 (C2); 10:90 (C3); 15:85 (C4). Mixtures were then crafted manually as consecutive four layers. C1-side faced anode while separator-cathode-assembly was developed at C4. The separator was characterized by evaluating proton and oxygen transfer coefficient, and water-uptake analysis. The separator was also analysed for elemental composition, microstructure, particle size, and surface area and porous structure. SEM analysis of FTWA showed the presence of 15-100 nm pores. EDS analysis of the FTWA-C showed the presence of hygroscopic oxides, mainly SO
4
2−
and SiO
2
. A slight peak observed at P/P
o
∼1, confirmed the presence of macropores. The FTWA-C separator showed proton transfer coefficient as high as 18.7 × 10
−5
cm/s, and oxygen mass transfer coefficient of 2.1 × 10
−4
cm/s. The FTWA-C displayed the highest operating voltage of 612.4.2 mV, the power density of 1.81 W/m
3
, and COD removal efficiency of 87.52%. The fabrication cost of this separator was estimated to be $9.8/m
2
. FTWA-C could be an affordable and high-efficiency alternative for expensive ion-exchange membranes in MFCs.
•Removal of heavy metals and dyes by clay-based adsorbents are summarized.•Natural clays and nano-clays with 1D nanotubes and 2D nanosheets as adsorbents.•Factors affecting adsorption, mechanisms and ...adsorbent regeneration are discussed.•Exfoliate clays to 2D or 1D and reassemble as multifunctional materials of future.
Natural and synthetic clays have been used as adsorbents for removal of heavy metals and dyes from aqueous solution for many decades. In the last decade, exfoliating the natural clays to low dimensional nanosheets or nanotubes for preparation of multifunctional clay-based adsorbents has attracted considerable attention. In this review, we have summarized the removal of heavy metals and dyes by clay-based adsorbents, from natural clays to 1D clay nanotubes and 2D clay nanosheets. Firstly, the structural and adsorption performance of various natural clays (montmorillonite/bentonite/smectite, kaolinite, illite, sepiolite, palygorskite/attapulgite, halloysite) are presented. Then the adsorption of dyes and heavy metals onto modified clays including thermally treated clays, acid-washed clays, inorganic pillared clays and organic modified clays are discussed. Next, we have introduced the novel nano-clay based adsorbents with low dimensional morphologies (2D nanosheets, 1D nanotubes, 1D nanorods and clay-supported nanoparticles). The clay adsorbents with exfoliated nanosheets or nanotubes show dramatically improved performance because of the fully exposed reactive sites and very high specific surface area. More importantly, the nanosheets and nanotubes can be readily composited with coupling agents or functional polymers to prepare multifunctional adsorbents. In addition, the adsorption behaviors of clay-based adsorbents along with factors affecting adsorption, adsorption mechanisms and regeneration of adsorbents have been discussed. Inspired by the natural and modified clays, future suggestions in designing novel adsorbents for various applications have also been suggested.
Water-based drilling fluids are increasingly being used for oil and gas exploration, and are generally considered to be more environmentally acceptable than oil-based or synthetic-based fluids. ...Unfortunately, their use facilitates clay hydration and swelling. Clay swelling, which occurs in exposed sedimentary rock formations, can have an adverse impact on drilling operations and may lead to significantly increased oil well construction costs. Minimizing clay swelling is therefore an important area attracting a large amount of interest from both academia and industry. To effectively reduce the extent of clay swelling the mechanism by which clay minerals swell needs to be understood so that efficient swelling inhibitors may be developed. Acceptable clay swelling inhibitors must not only significantly reduce clay hydration, but must also meet increasingly stringent environmental guidelines while remaining cost effective. The development of these inhibitors, which are generally based upon water soluble polymers, therefore represents a challenge to oilfield geochemistry. This review aims to provide a comprehensive understanding of the mechanism by which clay minerals swell and what steps have been taken in the development of effective and environmentally friendly clay swelling inhibitors.
In the current study, the influence of iron oxide nanoparticles and chitosan (CS) on the adsorption capacity of natural clay for chromium removal from aqueous media was explored. Clay-based ...adsorbents (clay, CS/Clay, Clay/Fe3O4, and CS/Clay/Fe3O4) were manufactured and their physicochemical properties were identified. The effects of operating factors on the adsorption efficiency were optimized. The results showed that the adsorption equilibrium data for the clay, CS/Clay, and Clay/Fe3O4 corresponds to the Langmuir model, while for the CS/Clay/Fe3O4 is consistent with the Freundlich model. The maximum adsorption capacity (qmax) of Cr(VI) using clay, CS/Clay, Clay/Fe3O4 and CS/Clay/Fe3O4 were 63.69 mg/g, 80.30 mg/g, 97.08 mg/g, and 117.64 mg/g, respectively. It was showed that the addition of chitosan and Fe3O4 magnetic nanoparticles to the clay increases its adsorption capacity. The values of ΔG° and ΔH° parameter for Cr adsorption using adsorbents were negative, indicating that the removal process is spontaneous and exothermic. The kinetic behavior obeyed the pseudo-second-order model. The chromium removal process using all the adsorbents had a two-step mechanism. The wastewater of a leather factory was effectively treated using clay based-adsorbents. Based on R2, MSE, SSE, and ARE values, good agreement was observed between the ANFIS model and experimental outcomes.
•Clay was composited with chitosan (CS) and Fe3O4 for Cr(VI) adsorption.•The maximum Cr-adsorption capacity onto CS/Clay/Fe3O4 was obtained 117.64 mg/g.•The adsorbent mass, Cr(VI) concentration, and pH affected the adsorption efficiency.•The adsorption process was followed pseudo second order kinetic model.•The ANFIS model was used to predict the Cr adsorption efficiency onto adsorbents.
A new series-parallel model for electrical conductivity of saturated clays that considers particles structure orientation is presented in this study. The new model introduces a simple approach to ...consider the effect of surface conductivity of clay particles on the electrical conductivity of saturated clays. The proposed approach considers the clay particle and its surrounding diffuse double layer, as a single unit called an effective clay particle, and assigns it an isotropic apparent electrical conductivity that can be determined using a simple experimental method. Therefore, the saturated clay can be considered as a two-phase material (binary mixture) namely, free pore water and effective clay particles. Considering the clay particles structure orientation, the proposed electrical conductivity model in this study geometrically configures the components of two-phase saturated clays in a series-parallel form to determine the electrical conductivity of clay. The proposed electrical conductivity model uses one parameter that can be determined experimentally and it reflects the anisotropic condition of the clay fabric. The validity of the proposed model is verified by comparing its results with the experimental results of three different clay types reconstituted at different dry density levels and particles structure orientations. The comparison shows the accuracy of the proposed model in predicting the electrical conductivity of saturated clays.
•Clay particles' orientation is essential to predict electrical conductivity.•Saturated clays can be considered as a two-phase material.•Two-phase saturated clays can be represented in a series-parallel configuration.•DDL water and inter-particle contacts provide a pathway for electrical flow.•The anisotropy of electrical conductivity can be expressed with a single parameter.
Natural clays have recently been proven to possess antibacterial properties. Effective natural antimicrobial agents are needed to combat bacterial contamination on food contact surfaces, which are ...increasingly more prevalent in the food chain. This study sought to determine the antibacterial activity of clays against the food-borne pathogens
ATCC 14028 and
ATCC 13565. Soils were processed to yield leachates and suspensions from untreated and treated clays. Soil particle size, pH, cation-exchange capacity, metal composition and mineralogy were characterized. Antibacterial screening was performed on six Malaysian soils via the disc diffusion method. In addition, a time-kill assay was conducted on selected antibacterial clays after 6 h of exposure. The screening revealed that Munchong and Carey clays significantly inhibit
(11.00 ± 0.71 mm) and
(7.63 ± 0.48 mm), respectively. Treated Carey clay leachate and suspension completely kill
, while
viability is reduced (2 to 3 log
). The untreated Carey and all Munchong clays proved ineffective as antibacterials. XRD analysis confirmed the presence of pyrite and magnetite. Treated Carey clays had a higher soluble metal content compared to Munchong; namely Al (92.63 ± 2.18 mg/L), Fe (65.69 ± 3.09 mg/L) and Mg (88.48 ± 2.29 mg/L). Our results suggest that metal ion toxicity is responsible for the antibacterial activity of these clays.
Previous studies on laterally loaded piles in clay have mainly focused on flexible and rigid piles. Little attention has been paid to semi-rigid piles (whose pile–soil stiffness lies somewhere ...between those of rigid and flexible piles), which may behave as either flexible piles or rigid piles, depending on the change in soil stiffness during cycling. This study aims to understand the cyclic lateral response of a repeatedly loaded semi-rigid pile in soft clay and the failure mechanisms of the soil around the pile, through a series of centrifuge model tests and three-dimensional finite element analyses using an advanced hypoplastic clay model. Numerical parametric studies were also performed to investigate the evolution of soil flow mechanisms with increasing pile rigidity. It is revealed that the semi-rigid pile behaved as if it were a flexible pile (i.e., flexural deformation dominated) during the first few cycles, but tended to behave like a rigid pile (i.e., rotational movement prevailed) during subsequent cycles, which progressively softened the surrounding soil. As a result, the mechanisms of soil flow around the semi-rigid pile exhibited an intermediate behaviour combining the mechanisms of both flexible and rigid piles. Three distinctive mechanisms were identified: a wedge-type mechanism near the surface, a full-flow mechanism (within the transverse sections) near the middle of the pile, and a rotational soil flow mechanism (in the vertical symmetrical plane of the pile) near the lower half of the pile. By ignoring the rotational soil flow mechanism, which has a much lower resistance than the full-flow mechanism, the American Petroleum Institute code (published in 2007) underestimated the cyclic bending moment and the lateral pile displacement by 10% and 69%, respectively. Application of jet grouting around the semi-rigid pile at shallow depth significantly altered the soil flow mechanism (i.e., it was a solely wedge-type mechanism around the grouted zone).
At first, a critical overview of current polycarboxylate (PCE) technology including the chemistry of different kinds of PCEs, characteristic molecular properties, their interaction with cement and ...application aspects are discussed. In the following, the classification and chemistry of clays and clay minerals is presented. In addition, the interaction of PCE superplasticizers with clay minerals and in particular the very harmful chemical sorption of PCE by montmorillonite (MMT) clay which causes a substantial reduction or even complete loss of PCE dispersing effectiveness are introduced. Possible mitigation strategies from the open literature to remedy the negative effects of clay are outlined. Over the last years, calcined clays have gained substantial attention as supplementary cementitious material (SCM). This paper also covers their chemistry and properties as well as their different interaction mode with PCE superplasticizers. Finally, future concepts in PCE technology regarding enhanced clay tolerance and enhancement of the fluidity of Limestone-Calcined Clay Cement (LC3) are proposed.
The paper presents an experimental investigation on the tensile strength of an unsaturated clay, both in remoulded and compacted states. To complete the experimental study, a new apparatus was ...designed with the purpose of determining direct tensile stress under controlled-displacement or controlled-force. The design exploits a direct shear test box, which was adapted to the scope of this investigation. Three different hydro-mechanical paths were followed before the tensile strength was determined: a) drying paths on remoulded samples; b) drying paths after compaction at different initial water contents; and c) dynamic compaction at different water contents, hence at different suctions and degrees of saturation. A microstructural investigation was also performed to better understand the experimental results and obtain the most relevant physical parameters. The preparation methods induced different initial fabrics, which dominated the water retention properties, as well as the tensile strength behaviour. A recent model for water retention, including the effects of multimodal fabric, was calibrated on available data and used to predict the suction of the samples along the drying paths, where direct information was not available. A simple model for tensile strength was proposed for its evolution, which included the role of multimodal fabric and their different water storage capabilities, the evolution of dry density and the initial water content (at the beginning of the tensile test path). For the compacted sample, typically showing a multimodal pore size distribution, the tensile strength was found to be a function of the state variables describing the macropore network. Dry density increases on drying appeared in all the cases to dominate the tensile response, Water exchange and suction increase were well correlated to the tensile response evolution.
•Investigation on the tensile strength of an unsaturated clay, both remoulded and compacted.•Three different hydro-mechanical paths were followed before the tensile strength was determined.•A microstructure investigation was performed to understand the experimental results.
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