Resin Impregnation Research Articles

Preparation of multiaxial glass fiber/epoxy prepreg and its mechanical properties in composites

AbstractThis study investigates the mechanical properties of composites made from biaxial warp‐knitted glass fiber/epoxy prepregs (BW‐GF/EP) in comparison to plain woven glass fiber/epoxy prepregs (PW‐GF/EP). The BW‐GF/EP composites demonstrated superior tensile strength, with an increase of 9.5%, and bending strength, with an increase of 12.2%, compared to the PW‐GF/EP composites. Despite having a lower tensile modulus, the BW‐GF/EP composites exhibited 8.7% higher interlaminar shear strength. Dynamic mechanical analysis showed that both materials had similar storage and loss moduli at lower temperatures, with PW‐GF/EP performing better at higher temperatures. Microscopy revealed that failure in PW‐GF/EP occurred at weave intersections, while BW‐GF/EP composites showed fiber rupture and delamination. The findings highlight the advantages of using biaxial warp‐knitted fabrics for improved composite performance.Highlights Developed biaxial warp‐knitted fabric prepregs to replace liquid molding techniques. Improved interlaminar shear strength, reducing delamination risks in composites. Achieved higher tensile and bending strength compared to plain weave composites. Enhanced resin impregnation and molding efficiency with biaxial warp‐knitted fabrics. Reduced environmental impact and costs by avoiding VOCs and minimizing waste.

Valorisation of acid mine drainage through effective recovery of selected rare earth elements using cationic resins

Acid mine drainage (AMD) presents a challenge to the environment if not well managed, but it also presents an opportunity for the recovery of economically valuable products, including rare earth elements (REEs), which are critical for the development of advanced, and green technologies. REE concentrations in AMD samples from coal and gold mines were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES) and their sorption by different cationic resins (CHT4083, CHP4502 and CHP00712) was evaluated. Optimum conditions for the sorption of the REEs by these resins were determined through batch experiments and desorption of the REEs from the resins using different concentrations of sulphuric acid (H2SO4) solutions. Coal mine drainage (CMD), with a low pH of 2.37, had higher amounts of REEs (ΣREE 226.3732 mg/L) than AMD from the gold mines (ΣREE 4.9705 mg/L), with a pH of 3.21. A REE sorption efficiency of up to 98% was obtained with CHP4502 and CHP00712 resins and further optimisation of CHP00712 revealed that a resin volume of 250 mL and a contact time of 10 min were required to successfully remove REEs from 500 mL AMD. The sorption capacities of the resin for the selected REEs were 3.88 mg/g, 0.88 mg/g, 1.37 mg/g, 3.18 mg/g, 0.67 mg/g, 0.01 mg/g and 0.27mg/g for Pr, Gd, Nd, Ce, Sm, Eu and Y, respectively. Elution of the resin with a 0.5 N solution of sulphuric acid desorbed the REEs. AMD from coal mines could be an alternate source of REEs and cationic resins can be used to recover these REEs from the CMD. Further investigations, including impregnation of resin to improve its sorption capacity, and temperature effects on the sorption process, are recommended.

Resin impregnation and interface property improvement of CFRP composite via modulating wettability of carbon fibers

In this work, the effects of different fiber wettability on resin impregnation during vacuum assisted resin transfer molding (VARTM) process and subsequent interface properties were comprehensively investigated. The fabrics with different surface morphology and wettability were successfully obtained via tuning the concentration of epoxy sizing agents. Results indicate that a low void content of less than 1% is achieved with the improvement of fiber wettability. Additionally, the interlayer property of composites is significantly improved by ∼12%. It is attributed to improved impregnation and capillary number, achieved by optimizing the dual-scale flow of resin in the preform via reducing the contact angle. Achieving equilibrium of dual-scale flow is an important factor in minimizing voids within the CFRP laminate. Furthermore, the introduction of epoxy functional groups significantly enhances interfacial bonding, contributing to an increase in the interlaminar shear strength of CFRP composites. This improvement effectively improves stress concentration by dispersing crack propagation. The findings in this work provide significant information for designing CFRP composites with superior mechanical properties via adjusting fiber wettability.

Selective separation of light and heavy rare earth elements from acidic mine waters by integration of chelating ion exchange and ligand impregnated resin

This study addresses the potential of sourcing Critical Raw Materials (CRMs) using Acidic Mine Waters (AMWs) as a secondary resource. AMWs, often viewed as waste, contain valuable metals like zinc and copper, as well as critical metals like magnesium and cobalt. Moreover, recent studies also reported the presence of Rare Earth Elements (REEs) at concentrations (mg/L) that make their extraction both technically and economically viable. The research focuses on a circular process to recover these metals from AMWs, specifically from the Aznalcóllar open-pit mine, which contains 216 mg/L of Al, 47 mg/L of Fe, 547 mg/L of Zn, and 18.56 mg/L of REEs. The proposed method involves pre-treating the AMW to remove Fe and Al, achieving removals of over 99.9 % and 90 %, respectively, at pH 4.5. Following this, transition metals like Zn, Cd, and Cu were removed as sulphides with a removal efficiency exceeding 99 %. This pre-treatment step reduced the concentration of competing metals in the ion-exchange process, thereby enhancing the recovery and purity of REEs. To separate heavy and light REEs, two types of resins in series were used: an impregnated resin (TP272) and a chelating resin (S930), which can be regenerated using sulphuric acid (H2SO4). The final recovery of REEs as oxalates was achieved using oxalic acid and ammonia at pH 1, with further optimization of the elution process to minimize ammonia consumption and undesired precipitation of other oxalates. Finally, REE oxalates with purities exceeding 90 % were obtained. This research demonstrates a sustainable method for efficiently recovering valuable REEs from AMWs, while also addressing environmental concerns related to hazardous sludge generation.

Comprehensive analysis of the effect of braiding angle on the wettability and mechanical properties of 3D braided carbon fiber fabric-reinforced composites

Fiber-reinforced composites are designed to enhance strength, stiffness, and lightweight properties. However, while the use of continuous fibers offer substantial performance benefits it presents challenges in achieving complex configurations. This study focused on evaluating the effects of different braiding angles on the mechanical properties of braided fabric-reinforced composites (B-CFRP). Continuous fiber tows were braided around a mandrel, with meticulous control over the key process parameters to ensure consistency. The composites were then processed using the Vacuum Assisted Resin Transfer Molding (VARTM) technique to achieve optimal impregnation of the resin. Mechanical properties, including tensile, flexural, compressive strength, interlaminar shear strength (ILSS), and impact strength, were performed to establish the relationship between resin impregnation and mechanical properties with different braid angles. Additionally, resin flow experiments and scanning electron microscopy (SEM) analysis were conducted to investigate how variations in braiding angle influence fiber arrangement, resin distribution, and fracture behavior. These insights aim to guide the design and manufacturing of high-performance composites.

Insulation Degradation of Epoxy Resin Impregnated Paper Bushing Under Discharge Arc Ablation

Insulation Degradation of Epoxy Resin Impregnated Paper Bushing Under Discharge Arc Ablation

Research on aliphatic resin-reinforced bamboo spun fiber bundles based on optimal twisting process

Bamboo, recognized as a sustainable material with remarkable properties, has found extensive application in the textile industry. This paper presents the findings of an investigation into the mechanical properties of twisted bamboo spun fiber bundles. The bundles were produced through the delignification and thinning of moso bamboo, followed by twisting in both the Z-direction and the S-direction, with varying twisting angles as experimental variables. The results indicated that the mechanical properties of the bamboo spun fiber bundle, produced under a single-strand Z-twist direction with a 20° twist angle, were optimal. These properties included the highest tensile strength of 154.25 MPa, a low modulus of elasticity, and a high elongation at break of 6.9 %, which represented superior preparation parameters. To enhance the bamboo spun fiber bundles during the preparation process—particularly because they tend to absorb moisture easily and disintegrate due to the removal of some lignin—a mixture of aliphatic epoxy resin and amine curing agents is employed. Following resin impregnation, both the expansion rate and orientation of the bamboo spun fiber bundles demonstrated a reduction compared to the unimpregnated one. The epoxy resin conferred dimensional stability and flexibility to the fiber bundles. Additionally, compared with those without impregnation, resin-impregnated bamboo spun fiber bundles resulted in a strength increase of 6.81 %, an enhancement in elongation at break of 9.79 %, a reduction in modulus of 2.67 %, a small plastic deformation of 13.96 % under cyclic loading, and a decrease in performance of only 3.5 % after high-temperature light ageing. This material demonstrated improved strength, toughness, and durability, aligning more closely with the requirements for textile fiber raw materials. The findings of this study refine processing parameters and broaden the application of bamboo spun fiber bundles in home furnishings and decorative contexts.

Polymer-Based Extracting Materials in the Green Recycling of Rare Earth Elements: A Review.

Rare earth elements (REEs) are becoming increasingly important in the development of modern and green energy technologies with the demand for REEs predicted to grow in the foreseeable future. The importance of REEs lies in their unique physiochemical properties, which cannot be reproduced using other elements. REEs are sourced through mining, with global exploration of additional commercially viable mining sites still ongoing. However, there is a growing need for recycling of REEs due to the current supply of REEs not matching the growing demand, the environmental impact of REE mining and processing (the so-called "balance problem"), and the generation of large volumes of harmful electronic waste (e-waste). Industrial REE processing is mainly carried out by hydrometallurgy processes, particularly solvent extraction (SX) and ion exchange (IX) technologies. However, these methods have a significant environmental impact due to their intensive use of harmful and nonsustainable reagents. This Review highlights the development of approaches involving polymer-based extracting materials for REE manufacturing as more sustainable alternatives to current industrial REE processing methods. These materials include supported liquid membranes (SLMs), solvent impregnated resins (SIRs), macro and micro capsules, polymer inclusion membranes (PIMs), and micro polymer inclusion beads (μPIBs). Polymer-based extracting materials have the advantage of more economical regent usage while applying the same extractants used in commercial SX, enabling applications analogous to the current industrial process. These materials can be fabricated by a variety of methods in a diverse range of physical formats, with the advantages and disadvantages of each material type described and discussed in this Review along with their applications to REE processing, including e-waste recycling and mineral processing.

Effect of Wood Species on Lignin-Retaining High-Transmittance Transparent Wood Biocomposites.

This study explores lignin-retaining transparent wood biocomposite production through a lignin-modification process coupled with epoxy resin. The wood's biopolymer structure, which includes cellulose, hemicellulose, and lignin, is reinforced with the resin through impregnation. This impregnation process involves filling the voids and pores within the wood structure with resin. Once the resin cures, it forms a strong bond with the wood fibers, effectively reinforcing the biopolymer matrix and enhancing the mechanical properties of the resulting biocomposite material. This synergy between the natural biopolymer structure of wood and the synthetic resin impregnation is crucial for achieving the desired optical transparency and mechanical performance in transparent wood. Investigating three distinct wood species allows a comprehensive understanding of the relationship between natural and transparent wood biocomposite properties. The findings unveil promising results, such as remarkable light transmittance (up to 95%) for Aspen transparent wood. Moreover, transparent wood sourced from White Spruce demonstrates excellent stiffness (E = 2450 MPa), surpassing the resin's Young's modulus. Also, the resin impregnation enhanced the thermal stability of natural wood. Conversely, transparent wood originating from Larch showcases superior impact resistance. These results reveal a clear correlation between wood characteristics such as density, anatomy, and mechanical properties, and the resulting properties of the transparent wood.

Self-healing carbon fiber/epoxy laminates with particulate interlayers of a low-melting-point alloy

In order to prolong the service life of fiber-reinforced polymer composites, the implementation of self-healing ability with the micro-encapsulated healing agent has been extensively studied. However, such microcapsule-based self-healing composites typically suffer from degraded mechanical properties due to the liquid-phase inclusions, thereby limiting their proliferation. Here, a low-melting-point alloy is utilized as the particulate inclusions of carbon fiber/epoxy laminated composites. Field's Metal particles (melting point: 62 °C) are distributed between woven carbon fiber preforms followed by the resin impregnation to realize laminated composites with a Field's Metal-enhanced interlayer(s). The resulting laminated composites demonstrate the autonomic repair of interlaminar failure with a 40 % of healing efficiency. Most of all, the mechanical properties of these self-healing laminated composites are comparable to the conventional laminated composites attributed to the rigid inclusions that can be compressed to increase the fiber volume. Since the Field's Metal particle inclusions can bestow polymer composites with self-healing ability and the potential increase in mechanical properties, Field's Metal-enhanced fiber-reinforced polymer composites are expected to unlock the practical utility of self-healing composites.

Simultaneous electrical and mechanical properties improvement for composite expanded graphite bipolar plate by incorporating surface-activated carbon black paving on the carbonized melamine foam skeleton

The bipolar plate is the critical component that directly impacts the output performance and lifespan of the fuel cell. Composite graphite-based bipolar plates, which can be tailored to exhibit desired properties, are promising candidates for high-performance fuel cells. However, the simultaneous optimization of their electrical and mechanical properties has been a major challenge in the field. This study introduces a foam skeleton made of carbonized melamine foam (CMF) into the graphite bipolar plate to create ample space for subsequent resin impregnation. Carbon black (CB) is added as a filler to form complete conductive paths, which is modified using low-temperature plasma to allow it to be more uniformly adsorbed in the skeleton. The microstructure design of the composite bipolar plate ensures excellent mechanical properties and significantly enhances its electrical conductivity. Moreover, it effectively eliminates the impact of carbon black on the surface roughness of the composite plate. This design also provides superior water management and reduces gas permeability. Practical application tests demonstrate that the developed composite plate exhibits better corrosion resistance and electrochemical stability than metal bipolar plates. Compared to carbonized bipolar plates, it displays better impact resistance and stability.

Compaction behaviour of flax-preforms during forming for composites

Flax reinforced composites are becoming popular in automotive and civil industries due to their green production and recycling, and for good specific strength. To manufacture composites, firstly a multi-layer of flax preforms undergo compressive pressure before resin impregnation that causes nesting, wherein, fibres of one layer fit into the adjacent layers. This debulking of the preforms under compression is an important feature that determines the fibre volume fraction of composites. In this study, four flax structures such as: nonwoven tapes, unidirectional fabric, hopsack fabric, and nonwoven tape with glass veils were investigated for compaction behaviour under pressures between 1 and 10 bars, in single and multi-layer states, in dry and wet states, under different loading cycles, and in different ply orientations (0°/0° and 0°/90°). Nesting has been calculated for single- and multi-layer stacks. It was observed that the nonwoven structures shown greater thickness reduction compared to woven structures. Nesting factor was found to be higher than 1 for the nonwoven structures under compaction, indicating lower nesting, compared to the woven structures. In terms of thickness under repeated compaction, the reduction was the highest during first compressions, compared to the 2nd and 3rd compressions, for all the structures. When wettability was examined, thickness reduction for wet plies was higher for all the structures, compared to the dry phase. Finally, a comparative study was shown to evaluate fibre volume fractions of the composites.

Synergistically improve the strength and porosity of carbon paper by using a novel phenol formaldehyde resin modified with cellulose nanofiber for proton exchange membrane fuel cells

To optimize the imbalance between the interfacial bonding and porosity properties of carbon paper (CP) caused by phenol formaldehyde resin (PF) impregnation, and therefore improve the performance of proton exchange membrane fuel cells (PEMFCs), a new approach through cellulose nanofibers grafted with methyl methacrylate (CNFM) as a modified reinforcement and pore-forming agent for PF is investigated. Through suppressing the methylene backbone fracture of CNFM-modified PF during its thermal depolymerization, the interfacial bonding between PF matrix carbon and carbon fibers is enhanced. Compared with unmodified CP, the in-plane resistivity of CNFM-modified CP is reduced by 35.78 %, while the connected porosity increases to 82.26 %, and more homogeneous pore size distribution (PSD) in the range of 20–40 μm is obtained for CNFM-modified CP. Besides, the tensile strength, flexural strength, and air permeability of CNFM-modified CP increase by 72.78 %, 298.4 %, and 103.97 %, respectively. In addition, CNFM-modified CP achieves the peak power density of PEMFCs to 701.81 mW·cm−2, exhibiting 10.98 % improvement compared with commercial CP (632.39 mW·cm−2), evidently achieving an integral promotion of CP and comprehensive performance.

Investigating the thermal cure behavior of sorbitol-derived biobased melamine–formaldehyde impregnation resins using DSC and FTIR analysis

Investigating the thermal cure behavior of sorbitol-derived biobased melamine–formaldehyde impregnation resins using DSC and FTIR analysis

Chemical changes in thermally modified, acetylated and melamine formaldehyde resin impregnated beech wood

Abstract Wood modification (by thermal or chemical treatment) helps to improve the dimensional stability of wood and enhance its resistance to biological agents. Beech wood is non-durable and exposure in exterior settings dramatically shortens its service life. To determine the full potential of beech wood for advanced applications, a better understanding of the chemical changes induced by modification is needed. Two chemical treatments (acetylation and melamine formaldehyde resin impregnation) and three thermal treatments (heating to 180, 200 and 220 °C) were performed on beech wood. The modification effect was examined based on (i) molecular changes in functional groups by Fourier-transform infrared spectroscopy (ATR-FTIR); (ii) extractive content; and (iii) pH changes. Moreover, the explanation of these changes was supported by the FTIR-analysis of isolated main wood components (cellulose, holocellulose and lignin) from the modified wood. The high temperatures applied to samples during thermal modification promoted the deacetylation and degradation of hemicelluloses. Hemicelluloses were targeted also by acetic anhydride and melamine resin, the bonding of which was confirmed by FTIR analysis. The formation of fewer methylene bridges affected the properties of the melamine network. This observation suggests the need to determine optimal curing conditions in future research, to reduce melamine-wood hydrophilicity.

Polybenzoxazine‐based PEMFC composite bipolar plates with three‐dimensional conductive skeleton

AbstractTo address the limitation of poor conductivity in composite bipolar plates (CBPs), a three‐dimensional (3D) conductive skeleton structure of graphite flakes (GF) is constructed using the sacrificial template method. This method prepares 3D polybenzoxazine/graphite flakes composite bipolar plates (3D‐PBA/GF CBPs) with high conductivity through vacuum impregnation of benzoxazine resin (BA). In this paper, the effect of the presence of a conductive network structure on the key properties of CBPs is analyzed, and the performance of GF randomly dispersed CBPs obtained through traditional solution dispersion is also compared. Thanks to the efficient conductive path within its 3D conductive skeleton structure, the 3D‐PBA/GF CBP achieves excellent conductivity meeting US Department of Energy (DOE) targets (in‐plane conductivity greater than 100 S/cm, area‐specific resistance less than 10 mΩ cm2) at a low filler content (50 wt%). In addition, CBPs with 3D conductive skeleton structures also exhibit qualified service performances to meet the requirements of proton exchange membrane fuel cells (PEMFCs). Compared with GF randomly dispersed CBPs, 3D‐PBA/GF CBPs exhibited higher power density in a single cell. This study demonstrates that constructing PBA/GF CBPs with a 3D conductive skeleton to achieve an accumulation distribution of conductive fillers is an efficient method for enhancing the conductivity of CBPs.

An exploratory study on bamboo permeability for evaluation of treatability with chemical solutions

The rapid and uniform impregnation of resins and preservative fluids is critical to improving the quality and durability of wood-based materials. Permeability coefficients obtained in laboratory experiments aid in the development of optimal conditions for uniform resin filling on an industrial scale. However, due to the shape and orientation of pores in the bulk structure of bamboo, simplified permeability equations may not be sufficient to provide realistic resin impregnation predictions. In this study, the permeability coefficients for Dendrocalamus asper bamboo were determined using air flow measurements and Forchheimer's equation in the x, y, and z directions, and they were correlated to the bamboo microstructure, providing a detailed perspective on how to further investigate this property for real-world applications, such as pressure treatments with chemical solutions. Porosity was measured using mercury intrusion porosimetry (MIP) and water immersion methods to aid in the permeability analysis. The results showed that the longitudinal direction had 1000 to 10,000 times higher permeability coefficients than the radial and tangential directions. This finding is consistent with the alignment of transport vessels as well as the limited pore network in the transversal bamboo section. The outer region of bamboo had higher radial permeability than the middle and inner layers, despite having lower porosity. It is hypothesized that the greater number of vessels, albeit smaller, provides a more direct path for air to flow. The Darcian permeability coefficients of bamboo were found to be comparable to those reported in the literature for wood. This exploratory study provided insights into a novel approach for assessing the treatability of bamboo species.

Mechanical Characterization and Production of Various Shapes Using Continuous Carbon Fiber-Reinforced Thermoset Resin-Based 3D Printing.

Continuous carbon fiber-reinforced (CCFR) thermoset composites have received significant attention due to their excellent mechanical and thermal properties. The implementation of 3D printing introduces cost-effectiveness and design flexibility into their manufacturing processes. The light-assisted 3D printing process shows promise for manufacturing CCFR composites using low-viscosity thermoset resin, which would otherwise be unprintable. Because of the lack of shape-retaining capability, 3D printing of various shapes is challenging with low-viscosity thermoset resin. This study demonstrated an overshoot-associated algorithm for 3D printing various shapes using low-viscosity thermoset resin and continuous carbon fiber. Additionally, 3D-printed unidirectional composites were mechanically characterized. The printed specimen exhibited tensile strength of 390 ± 22 MPa and an interlaminar strength of 38 ± 1.7 MPa, with a fiber volume fraction of 15.7 ± 0.43%. Void analysis revealed that the printed specimen contained 5.5% overall voids. Moreover, the analysis showed the presence of numerous irregular cylindrical-shaped intra-tow voids, which governed the tensile properties. However, the inter-tow voids were small and spherical-shaped, governing the interlaminar shear strength. Therefore, the printed specimens showed exceptional interlaminar shear strength, and the tensile strength had the potential to increase further by improving the impregnation of polymer resin within the fiber.

Comparative study on vanadium(V) adsorption performance of supported ionic liquid synthesized by physical impregnation and chemical grafting

This study loaded ionic liquids (ILs) onto chloromethylated polystyrene resins using physical impregnation and chemical grafting. The resulting ionic liquid-loaded resins were characterized using SEM-EDS, FTIR, and NMR spectral analyses, confirming the successful preparation of both the physical impregnation resin (PIR) and the chemical grafting resin (CGR). The study compared the influencing conditions, cyclicity, selectivity, and adsorption mechanism of PIR and CGR on adsorption vanadium(V). Under optimum adsorption conditions, CGR exhibited significantly higher adsorption capacity (261 mg/g) than PIR (27 mg/g). In terms of adsorption selectivity, the separation coefficients of CGR for Fe and Al (65.3 and 45.4) were much larger than those of PIR (6.3 and 10.6). Furthermore, the CGR exhibited a cycling capacity 1.5 times greater than the PIR, maintaining an adsorption capacity of over 98 % of the initial value within 12 cycles. Based on the adsorption mechanism, both loaded resins conform to the monolayer chemisorption described by Langmuir isothermal adsorption model and the pseudo-second-order kinetic model. The results showed that the adsorption performance, selectivity, and adsorption stability of CGR were considerably superior to those of PIR. A further comparison with numerous previous research results revealed that the adsorption capacity of CGR for vanadium was significantly increased, and the cycling performance was substantially enhanced, while the separation between it and the impurity ions was also improved.

Адсорбционное извлечение аминов из водных растворов

Aquatic biological resources are an important part of the ecosystems of our planet, since they are involved in economic turnover as a source of food. The composition of water, including waste water from enterprises, has a direct impact on the state of aquatic biological resources. To extract and concentrate metals from solutions, hydrometallurgical processes are used – extraction and sorption. Their implementation is possible with the use of special substances – extractants and in a number of processes – sorption materials (Solvent Impregnated Resins (SIR’s) and Levextrel’s) with a mobile phase of the extractant, combining the properties of sorbents and extractants. Despite the advantages of the latter, such as high kinetic parameters, lack of swelling and high values of mechanical strength, they are characterized by the disadvantages of extraction methods – the entrainment of the extractant into the aqueous phase in dissolved and emulsion forms. Under static conditions, the possibility of purification of aqueous solutions containing primary or tertiary amine by adsorption on carbon materials (activated carbon NWC, carbon NWC-T modified with carbon nanotubes, CS-PTFE modified with polytetrafluoroethylene), as well as on styrene-divinylbenzene nonionic copolymer Porolas-T and a natural shell rock adsorbent was studied. The kinetics of adsorption of аmines Primene-JMT and TOA from aqueous solutions by these adsorbents has been studied by the method of a limited volume of solution. Of the known pseudo-first order, pseudo-second order and Elovich models, the pseudo-second order model describes kinetic data more adequately (R2>0.99). The values of the distribution coefficients and the rate constants of adsorption of Primene-JMT and TOA are determined. A block diagram of adsorption purification of aqueous solutions from amines is proposed, the implementation of which will reduce the toxicity of waste solutions and return some of the expensive extractant to circulation.