Chemical Softening Research Articles

Analysis of influence mechanism of CO2-water coupling fracturing sandstone

The existence of hard rock layers has a serious impact on coal seam mining, in order to explore the acidification and crushing mechanism of hard sandstone rock layers, this paper adopts the self-developed CO2-water-rock coupling test device to carry out the testing of mechanical properties and internal structural characteristics of rock samples before and after the coupling action of the three sandstones, and analyzes the influencing factors of sandstone CO2 coupling crushing. The study shows that: the lower the temperature of CO2-water-rock coupling, the higher the pore pressure, the higher the volume fraction of CO2 in the coupling fracturing fluid, and the longer the coupling time, the greater the decrease in the mechanical strength of the rock samples, and the more complicated the splitting damage pattern is, and the CO2-water-rock coupling makes the pore and fracture volume fraction and fractal dimension of three kinds of sandstone samples increase to varying degrees, whereas the volume fraction of minerals and the fractal dimension decrease, and the CO2-water-rock coupling results in a decrease in the volume fraction of minerals and fractal dimension, and a decrease in the volume fraction of minerals and fractal dimension. The pore volume fraction and fractal dimension of the three sandstone samples increased to different degrees, while the mineral volume fraction and fractal dimension decreased, and the pore volume fraction and fractal dimension of the three sandstone samples decreased. The damage pattern of sandstone samples after coupling is affected by both chemical and mechanical damages. When using coupling fracturing fluid with 8 % CO2, the degree of mineral dissolution and dissolution is the largest, and the dissolution effect is larger than the precipitation effect, which has the most significant effect on the morphology type and connectivity of microscopic pore cracks, and the study in this paper has certain theoretical and practical value for the chemical softening of sandstone.

Improvement in thermoelectric properties of Zn–Mn co-doped nanostructured SnTe through band engineering and chemical bond softening

In this work, we used solvothermal technique to synthesize thermoelectrically viable Zn–Mn co-doped SnTe materials. However, the thermoelectric (TE) performance of pure SnTe is subpar due to the significant energy gap between its valence bands, inherent Sn-vacancies, and high electrical thermal conductivity. Band structure engineering and carrier concentration optimization of SnTe following Zn–Mn co-doping have the potential to enhance the Seebeck coefficient. In turn, a boost in the Seebeck coefficient significantly improved the power factor in Sn0.89Mn0.09Zn0.02Te by about five times as compared to pure SnTe at 473 K. The minimum lattice thermal conductivity (κ L) in Sn0.89Mn0.09Zn0.02Te is 0.54 W m−1K−1 at 473 K, which is almost half that of pure SnTe. The lower lattice thermal conductivity of co-doped samples may be a result of (i) a decrease in phonon group velocity by chemical bond softening and (ii) phonon scattering caused by nanostructuring, point defects, and grain boundaries. Consequently, maximum zT = 0.11 has been achieved in Sn0.89Mn0.09Zn0.02Te at 473 K, which is about five times that of pristine SnTe. Material quality factor (B) of Sn0.89Mn0.09Zn0.02Te is almost triple that of pristine SnTe at 473 K, which implies that Zn–Mn co-doped SnTe is more suited to construct a TE device. An increase in electric transport properties (weighted mobility and electronic quality factor) and a decrease in κ L after Zn–Mn co-doping contribute to the enhancement of B. The findings of this investigation suggest that the addition of Zn and Mn to SnTe can improve its TE performance.

Quantum dynamics studies on reactive scattering of Cl with rotationally excited H[formula omitted

In this work, extensive multi-configurational time-dependent Hartree (MCTDH) calculations in conjugation with the neural-network (NN) fitted potential energy surface (Science, 347 (2015), 60) were launched to study dynamics of Cl reacting with rotationally excited H2. Due to its direct abstraction mechanism, Cl + H2→ HCl + H in the ground state has no clear reaction resonances, which is well reproduced Here. For the reaction of Cl with H2 in rotationally excited states, the reactive probabilities are enhanced due to a Polanyi-like rule for rotationally excited states. Such Polanyi-like rule can be interpreted through the similar way as for the cases of vibrationally excited states. Moreover, distinctive resonances peaks are investigated for these cases implying a model for generating a quasi-bound rotation state. Similar to the chemical bond softening model for the vibrationally excited cases, a probable model is proposed in this work.

Sustainable yarns and fabrics from tri-blends of banana, cotton and tencel fibres for textile applications

Millions of tons of banana pseudo-stem are readily available annually, making it a sustainable resource for banana fiber. Banana fibres possess inherent mechanical strength and anti-microbial properties, accompanied by stiffness and a harsh feel that undermine their full utilization in textiles. An effort was made in this study to create eco-friendly yarns and fabrics by combining banana fiber reclaimed from banana agro-waste with cotton and regenerated cellulosic (Tencel) fiber in varying blend ratios. The negative influence attached to banana fibre due to its chemical softening was overcome by boiling it in distilled water. The softened banana fibres were evaluated based on feel, strength, and weight loss. Three blend ratios, i.e., 10%, 20%, and 30% of banana fibre by weight, were selected to produce Banana: Cotton: Tencel blended yarns. Yarn characterizations revealed excellent mechanical properties as compared to the benchmark Cotton: Tencel 50:50 yarns. The yarn bundle strength and single yarn strength obtained in the case of 20% banana fibre blended yarn were approximately 11% and 8.62% higher than the Cotton: Tencel 50:50 blended yarns and 22.90% better in the yarn quality index analysis, respectively. Fabrics were formed using the said yarns on an industrial loom. Banana fibre blended fabrics exhibited a 6.61% higher tear strength, 18.8% more air permeability, 20% more elongation, and 12% higher tensile strength as compared to the Cotton: Tencel blended fabrics. The provided findings in this study propose that following this design approach during textile manufacturing will lead to more environmental and economic gains with high performance.

Physicochemical properties of flowable composites using isobornyl methacrylate as diluent monomer.

this study sought to evaluate the effect of isobornyl methacrylate (IBOMA) as a diluent monomer on the physicochemical properties of experimental flowable resin composites. the organic resin matrix of a modal flowable resin composite was formulated with 50 wt.% of bisphenol-A-glycidyl methacrylate (Bis-GMA) and 50 wt.% of a diluent monomer, in which IBOMA was used as a combining or substituent diluent monomer to triethylene glycol dimethacrylate (TEGDMA). The resin matrices were filled with 55 wt.% particles, of which 10 wt.% was 0.05-μm fumed silica, and 45 wt.% was 0.7-μm BaBSiO2 glass. Polymerization shrinkage stress (PSS; n=10), degree of conversion (DC; n=3), maximum rate of polymerization (Rpmax; n=3), film thickness (FT; n=10), sorption (Wsp; n=10), solubility (Wsl; n=10), flexural strength (FS; n=10), flexural modulus (FM; n=10), Knoop microhardness (KH; n=10), and microhardness reduction after chemical softening (HR; n=10) were evaluated. Data were analyzed using one-way ANOVA, followed by Tukey's test (α=0.05; β=0.2). the results showed that the substitution or addition of IBOMA reduced FT (p=0.001), PSS (p=0.013), Rpmax (p=0.001), DC (p=0.001), FM (p=0.006) Wsp (p=0.032), and Wsl (p=0.021). However, when used as a complete substituent, IBOMA demonstrated significantly lower FS (p=0.017) and KH (p=0.008), while TEGDMA demonstrated significantly lower HR (p=0.022). the flowable composite containing IBOMA combined with TEGDMA showed no effect in KH and FS and effectively reduced the PSS, RP, FT, Wsp, and Wsl. However, it showed a reduction in DC, FS, and an increase in HR.

Discovery of the Layered Thermoelectric Compound GeBi2Se4 and Accelerating Its Performance Optimization by Machine Learning

Searching for new materials with intrinsically low lattice thermal conductivity is crucial for the exploration of high‐performance thermoelectric materials. Herein, the layered compound GeBi2Se4 with intrinsically low lattice thermal conductivity is discovered, and its thermoelectric performance optimization is accelerated by machine learning. The ultralow lattice thermal conductivity of 0.53 W m−1 K−1 at room temperature for the GeBi2Se4 sample can be ascribed to the large anharmonicity and miscellaneous crystal defects. By alloying tellurium (Te) at the selenium (Se) site, the lattice thermal conductivity is further reduced due to the alloy scattering effect and chemical bond softening while the density‐of‐states effective mass of electrons is significantly increased. Finally, the best n‐type thermoelectric GeBi2Se1.9Te2.1 sample with a dimensionless figure of merit zT of 0.56 at 460 K is screened out by machine learning and verified by experiments, which increases by 140% in comparison with the pristine GeBi2Se4.

Development of bio lubricant from castor oil via chemical softening: An ease towards sustainable substitute

In the 21st century, Environment sustainability is considered to be the superficial,coherent vision in the development of a societal goal. At the moment, the prices of crude oil have been skyrocketing which results into the depletion of petroleum reservoirs contributing to environmental pollution cum hazards. This has inspired researchers globally in the development of non-toxic, renewable, and sustainable. ecologically sound alternative i.e., Bio-lubricant which will aim to replace conventional petroleum-based lubricants towards a green and clean society deliberately. The proposed work introduces the design and development of biodegradable bio-lubricant from commercially available, non-edible castor oil via chemical softening by the virtue of two successive transesterification stages. The presented study, explores the chemical modification process of vegetable oil to intensify the yield, grade, and physicochemical vis-a-vis tribological properties of the produced lubricant. The proposed method of production of castor oil-based bio-lubricant via chemical softening is made to achieve a high yield i.e., exceeding 97.4 % with a kinetic investigation for optimized parameters including catalyst concentration, alcohol/oil ratio, temperature, additives calibrated to be 1% w/w NaOH, 6:1, 65 °C and 15% SLS (Sodium lauryl sulfate) respectively for the maximum conversion with minimum costs associated with the production of ecologically viable castor oil-based bio-lubricant. The peaks observed at 1730 cm−1 and 3025 cm−1 are associated with the stretching vibration of the carbonyl group (C = O) in the ester bond and the stretching of the C–H bond vibration in the fatty acid chains, respectively. This has been confirmed through Fourier-transform infrared spectroscopy (FTIR) and evaluated through ASTM analyses.

Synergistic cotreatment of cooling tower blowdown and produced waters: Modeling strategies for a comprehensive wastewater treatment simulation

Cooling tower blowdown from thermoelectric power plants and produced water from hydraulic fracturing may soften when mixed due to the complimentary chemistry of the two wastewaters. The potential benefit of low effort softening warrants the investigation of a cotreatment process concerning these industrial wastewaters. The synergy is expected to lessen chemical demand for softening and further enable sustainable practices such as designing for a zero-liquid discharge (ZLD) process. The treatment process may then provide a treated effluent suitable for use as blowdown makeup. In this study, the feasibility and effectiveness of a cotreatment train is explored through simulation of chemical softening, filtration, reverse osmosis (RO), multi-effect distillation (MED), and electrolysis unit operations within a comprehensive process model. Innovative modeling strategies are necessary to result in a meaningful process model when considering the significant complexity of the water chemistry for this treatment train. Through the methodology described in this work, a feasible process design is presented as a base case for treatment of experimentally characterized blowdown and produced water samples obtained in the northern Appalachian region. Thereafter, the base case also establishes a platform for more detailed process analyses of different scenarios in future work. Detailed descriptions of modeling methodologies, process design decisions, and simulation results are provided as a perspective on comprehensive modeling of multi-technology treatment trains for complex feedwaters. With the results of the cotreatment simulation, it is determined that the total water recovery of the process may serve to completely makeup the blowdown rate and partially make up the evaporative losses of a theoretical thermoelectric plant's water demand. This complete recovery is evaluated to require 18,343.531 kW of a chemical energy equivalent, 1184.971 kW of electricity, and 68,126.291MJh−1 of power plant steam to result in 408.532m3h−1 of treated water effluent at a quality of approximately 0.135gL−1 total dissolved solids for the base case design.

Exceptional features of the embryonic ontogeny of a direct‐developing Robber frog

AbstractIn frogs, the loss of the free‐living tadpole stage implies deep transformations in morphology and development, and the result is a combination of traits exclusive to direct development with the reduction or absence of typically larval features. Two traits stand out in terraranans, a mostly Neotropical clade with ca. 1200 species known or suspected to have direct development: (1) the development of forelimbs, which unlike in tadpoles and in several unrelated direct‐developing lineages, in this clade is described to occur completely exposed during ontogeny, and (2) the reduction of gills and their physiological replacement by highly vascularized tails for gas exchange. In this contribution, we report unusual aspects of the embryonic ontogeny in the Confused Robber frog Oreobates berdemenos, which complicate the interpretation of morphological diversity in Terrarana and in direct‐developing frogs in general. First, forelimbs develop initially entirely concealed by a larval operculum. Second, tail fins develop dorsal and ventral to the tail muscular core but their arrangement changes to lateral during ontogeny. Third, the expansion of the tail fins appears to be a plastic character whose variation likely responds to individual conditions of humidity and/or oxygenation of each egg within the clutch. Finally, we report cells with the morphology of hatching gland cells in the rostral region of embryos at stages about to hatch. If not vestigial, these cells could assist the egg tooth, which is characteristic of terraranans, with chemical softening of the egg capsules during hatching.

A constitutive model of compacted bentonite under coupled chemo-hydro-mechanical conditions based on the framework of the BExM

A coupled chemo-hydro-mechanical model for compacted bentonite based on the Barcelona expansive model (BExM) that distinguishes between the microstructure and macrostructure was developed in this work. The effective stress principle was modified by introducing the osmotic stress pπ, which is considered to govern the elastic strain of the compacted bentonite. The yield functions were deduced, and the yield surface was depicted in the smatric-pπ-pnet space. Validation of the proposed model was conducted by simulating a series of wetting–drying tests on compacted bentonite under different net vertical stress and osmotic stress conditions and by salinization-desalinization tests on compacted bentonite at different vertical stresses. A comparison between the predicted and measured volumetric strains in different wetting–drying and salinization-desalinization cycles proves the potential of the model to capture the main features of the volume change behavior in response to coupled chemo-hydro-mechanical processes. The results also indicate that the micro–macro coupling functions are not only dependent on the net vertical stress but are also associated with chemical effects. A conceptual method to incorporate chemical hardening and chemical softening mechanisms into the micro–macro coupling functions was then developed.

Fouling characterization and treatment of water reuse concentrate with membrane distillation: Do organics really matter

Membrane distillation (MD) for the treatment of concentrated brines has been limited in part by membrane fouling, resulting in subsequent flux decline and membrane wetting. This study provides new insight into the identification of fouling and scaling mechanisms and pretreatment strategies for mitigating flux decline with MD treatment of water reuse reverse osmosis concentrate (ROC). Bench-scale direct contact MD experiments were performed with untreated and pretreated ROC. Biological activated carbon (BAC), chemical water softening, or fluidized bed crystallization reactor coupled with ion exchange (FBCR-IX) were selected as pretreatment strategies to isolate the effects of organic fouling and calcium scaling. Organic and inorganic compounds were analyzed by high-performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS). Calcium ions were found to be the major contributor to flux decline despite the high organic content in the ROC. Minimal organic fouling is likely because the organic matter in the ROC is hydrophilic, limiting hydrophobic-hydrophobic interactions between the organics and the membrane. Furthermore, the water flux declined by 63 % after removing organic compounds by BAC pretreatment, with 60 % of the calcium mass precipitating from the solution. Whereas, the water flux remained constant after removing multivalent ions with fluidized bed crystallization. Cleaning the membrane by acid washing and temperature reversal recovered 73 % and 12 % of the water flux, respectively. The analyses outlined in this study can assist in selecting appropriate fouling and scaling mitigation strategies for water reuse ROC and a wide range of feed solutions used in MD applications.

Treatment of Mine Water with Reverse Osmosis and Concentrate Processing to Recover Copper and Deposit Calcium Carbonate

Mine water usually contains heavy metals and other inorganic and organic pollutants that contaminate water bodies. Reverse osmosis (RO) techniques are capable of producing purified water that meets discharge regulations. However, the problem of RO concentrate disposal and utilization is still not solved. The well-known zero liquid discharge (ZLD) process provides total concentrate utilization at the power industries but seems unreasonably expensive for the treatment of large amounts of mine water due to required chemical softening and the evaporation of concentrate. In the present article, a new approach to increase the recovery of reverse osmosis and to avoid high operational costs is demonstrated and discussed. The new technique involves radical RO concentrate flow reduction and withdrawal, together with dewatered sludge. The idea to "hide" concentrate in dewatered sludge is proposed and demonstrated during experiments. The article demonstrates results of the conducted experimental program aimed at reduction of volumes of all liquid wastes produced during mine water treatment using a new approach to concentrate it with a cascade of nanofiltration membranes and to reach a TDS value of 110-120 g per liter. The obtained concentrate is mixed with the wet sludge, which is further dewatered and withdrawn together with the dewatered sludge. Experiments are conducted that demonstrate a reduction in calcium in the concentrate due to deposition of calcium carbonate on the "seed crystals" in the circulation mode. Another distinguishing feature of the new technique is the separation of concentrate into two streams containing high concentrations of monovalent ions (sodium and ammonium chlorides) and divalent ions (calcium, magnesium and copper sulphates). Flow diagrams of the processes are presented to demonstrate the water treatment technique used to produce deionized water and two types of sludges: sludge after clarification and sludge after calcium carbonate deposition.

Feshbach resonances in the F + CHD3 → HF + CD3 reaction.

The signature of dynamics resonances was observed in the benchmark polyatomic F + CH4/CHD3 reactions more than a decade ago; however, the dynamical origin of the resonances is still not clear due to the lack of reliable quantum dynamics studies on accurate potential energy surfaces. Here, we report a six-dimensional state-to-state quantum dynamics study on the F + CHD3 → HF + CD3 reaction on a highly accurate potential energy surface. Pronounced oscillatory structures are observed in the total and product rovibrational-state-resolved reaction probabilities. Detailed analysis reveals that these oscillating features originate from the Feshbach resonance states trapped in the peculiar well on the HF(v' = 3)-CD3 vibrationally adiabatic potential caused by HF chemical bond softening. Most of the resonance structures on the reaction probabilities are washed out in the well converged integral cross sections (ICS), leaving only one distinct peak at low collision energy. The calculated HF vibrational state-resolved ICS for CD3(v = 0) agrees quantitatively with the experimental results, especially the branching ratio, but the theoretical CD3 umbrella vibration state distribution is found to be much hotter than the experiment.

КОСТЯНЫЕ ИЗДЕЛИЯ НЕОЛИТА СРЕДНЕГО ЗАУРАЛЬЯ: ИСТОЧНИКИ, ТИПЫ, ТЕХНИКА ИЗГОТОВЛЕНИЯ

The main sources of Neolithic bone products are cave and peat sites. All Neolithic bone products can be divided into 4 groups: weapons (456 copies), domestic and household items (22 copies), works of art (2 copies) and jewelry (112 copies).The technique of making bone products in the early Neolithic is practically no different from the Mesolithic. The ancient craftsmen used techniques such as padding, scraping, planing, cutting and shearing with stone chopping tools, sawing, grinding, polishing, as well as cutting grooves. The widespread use of chemical softening of bone and the use of turning to produce biconical arrowheads can be considered a revolutionary innovation of the Neolithic era.

Overcoming barriers for nitrate electrochemical reduction: By-passing water hardness

Water matrix composition impacts water treatment performance. However, matrix composition impacts have rarely been studied for electrochemical water treatment processes, and the correlation between the composition and the treatment efficiency is lacking. This work evaluated the electrochemical reduction of nitrate (ERN) using different complex water matrices: groundwater, brackish water, and reverse osmosis (RO) concentrate/brine. The ERN was conducted using a tin (Sn) cathode because of the high selectivity towards nitrogen evolution reported for Sn electrocatalysts. The co-existence of calcium (Ca2+), magnesium (Mg2+), and carbonate (CO32−) ions in water caused a 4-fold decrease in the nitrate conversion into innocuous nitrogen gas due to inorganic scaling formation on the cathode surface. XRF and XRD analysis of fouled catalyst surfaces detected brucite (Mg(OH)2), calcite (CaCO3), and dolomite (CaMg(CO3)2) mineral scales formed on the cathode surface. Surface scaling created a physical barrier on the electrode that decreased the ERN efficiency. Identifying these main sources of ERN inhibition was key to devising potential fouling mitigation strategies. For this reason, the chemical softening pre-treatment of a real brackish water was conducted and this significantly increased nitrate conversion and faradaic efficiency during subsequent ERN treatment, leading to a lower electric energy consumption per order. Understanding the ionic foulant composition responsible for influencing electrochemically-driven technologies are the first steps that must be taken to move towards niche applications such as decentralized ERN. Thus, we propose either direct ERN implementation in regions facing high nitrate levels in soft waters, or a hybrid softening/nitrate removal system for those regions where high nitrate and high-water hardness appear simultaneously.

Layered Tin Chalcogenides SnS and SnSe: Lattice Thermal Conductivity Benchmarks and Thermoelectric Figure of Merit.

Tin sulfide (SnS) and tin selenide (SnSe) are attractive materials for thermoelectric conversion applications. Favorable small band gap, high carrier mobility, large Seebeck coefficient, and remarkably low lattice thermal conductivity are a consequence of their anisotropic crystal structure of symmetry Pnma, made of corrugated, black phosphorus-like layers. Their internal lattice dynamics combined with chemical bond softening in going from SnS to SnSe make for subtle effects on lattice thermal conductivity. Reliable prediction of phonon transport for these materials must therefore include many-body effects. Using first principles methods and a transferable tight-binding potential for frozen phonon calculations, here, we investigate the evolution of thermal lattice conductivity and thermoelectric figure of merit in Pnma-SnS and -SnSe, also including the high-temperature Cmcm-SnS phase. We show how thermal conductivity lowering in SnS at higher temperatures is largely due to dynamic phonon softening ahead of the Pnma–Cmcm structural phase transition. SnS becomes more similar to SnSe in its lifetime and mean free path profiles as it approaches its high-temperature Cmcm phase. The latter nonetheless intrinsically constraints phonon group velocity modules, preventing SnS to overtake SnSe. Our analysis provides important insights and computational benchmarks for optimization of thermoelectric materials via a more efficient computational strategy compared to previous ab initio attempts, one that can be easily transferred to larger systems for further thermoelectric materials nanoengineering. The good description of anharmonicity at higher temperatures inherent to the tight-binding potential yields calculated lattice conductivity values that are in very good agreement with experiments.

Experimental studies on the pore structure and mechanical properties of anhydrite rock under freeze-thaw cycles

To study the deterioration mechanisms of anhydrite rock under the freeze-thaw weathering process, the physico-mechanical characteristics and microstructure evolutions of anhydrite samples were determined by a series of laboratory tests. Then, a descriptive-behavioral model was used to measure the integrity loss in anhydrite samples caused by cyclic freeze-thaw. Finally, the freeze-thaw damage mechanisms of anhydrite rock were revealed from the macro and micro aspects. The results show that the pore size of the anhydrite rock is mainly concentrated in the range of 0.001–10 μm. As the number of freeze-thaw cycles increases, there is a growth in the proportion of macropores and mesopores. However, the proportion of micropores shows a declining trend. The relations of the uniaxial compressive strength, triaxial compressive strength, cohesion, and elastic modulus versus freeze-thaw cycles can be fitted by a decreasing exponential function, while the internal friction angle is basically unchanged with freeze-thaw cycles. With the increase of confining pressure, the disintegration rates of the compressive strength and the elastic modulus decrease, and the corresponding half-life values increase, which reveals that the increase of confining pressures could inhibit freeze-thaw damage to rocks. Moreover, it has been proven that the water chemical softening mechanism plays an essential role in the freeze-thaw damage to anhydrite rock. Furtherly, it is concluded that the freeze-thaw weathering process significantly influences the macroscopic and microscopic damages of anhydrite rock.

Study on engineering process and equipment operation of total treatment project of leachate and concentrated solution

The accumulation of a large amount of leachate and concentrated liquid caused by MSW is a serious potential safety hazard and environmental hazard. A full treatment project of leachate and concentrate were performed, with treatment capacity of leachate 1100 t/d and concentrate 550 t/d. The leachate treatment process adopts “pretreatment + second-stage A/O biochemistry + ultrafiltration + chemical softening + second-stage DTRO+HPRO+RO+ ion exchange”. The main processing equipment is jet aerator, submersible mixer, centrifugal pump, ultrafiltration membrane assembly, softening membrane assembly, DT membrane column, RO system, ion exchange tank, sludge mixer, sludge dehydrator, etc. The concentrated liquid treatment process adopts “pretreatment +MVR forced circulation evaporation + triple-effect evaporation +RO+ ion exchange”. The main processing equipment is filter press, feed pump, compressor, MVR heater, circulating pump, discharge pump, original liquid pump, triple-effect evaporator, RO system, ion exchange tank, etc. The treatment results show that each indicator of external drainage meets the standard requirements of GB16889-2008 and DB37/3416.4-2018. The engineering process and equipment of the project run stably, with high recovery rate, and can properly solve the problem of concentrated liquid. So, engineering process and equipment operation of total treatment project of leachate and concentrated solution were studied, which has important reference significance for the full treatment of leachate from the national waste treatment plant.

Characterization of scalants and strategies for scaling mitigation in membrane distillation of alkaline concentrated circulating cooling water

Treatment of circulating cooling water via reverse osmosis for water reuse is attractive. However, the discharge of the concentrated circulating cooling water (CCCW) is still an issue to environment. In this paper, direct contact membrane distillation (DCMD) was exploited to treat alkaline CCCW for water reclamation and volume reduction. Results suggested that the alkaline CCCW can be concentrated to achieve high volume concentration factor. DCMD performance decline was primarily due to calcium carbonate (CaCO3) scaling. The CaCO3 deposited on the membrane surface was identified as calcite. Various strategies were adopted to mitigate membrane scaling. Acidization of the CCCW can effectively improve system performance. Additionally, the main scalant transformed from CaCO3 to calcium sulfate (CaSO4) with initial pH decrease. Physical cleaning using deionized water can effectively remove CaSO4 and restore DCMD performance. Compared with commercial antiscalants (sodium polyaspartic acid and amino trimethylene phosphonic acid), EDTA showed excellent scale-inhibition performance. The calcium and magnesium in the CCCW were efficiently pre-removed by chemical softening and ion exchange methods, resulting in improvement of DCMD performance. Given scale inhibition and chemical agent costs, chemical softening was the best strategy to alleviate membrane scaling. Our work suggested that DCMD can be selected as a promising approach for treating the high alkaline CCCW combined with proper strategies to control membrane scaling.

Pilot-scale study on seeded precipitation assisted nanofiltration for flue-gas desulfurization wastewater softening.

In order to reduce the cost of chemical softening, the seeded precipitation assisted nanofiltration (NF) process was introduced into zero liquid discharge (ZLD) of flue-gas desulfurization (FGD) wastewater treatment. A pilot-scale system was developed and run for 168 h in a coal-fired power plant. The system mainly consists of lime softening, ambient temperature crystallizer (ATC) and NF, in which the raw water treatment capacity was 1 m3/h. The results indicated that the system operated stably, the softening cost was 13.30 RMB/m3, and the electricity cost was 3.39 RMB/m3 for the FGD wastewater in this pilot system. High quality gypsum was got from the ATC unit, of which the purity was 95.8%. Through this system, the hardness removal rate was higher than 98.9% and the water recovery rate reached 96%. In addition, the pressure and permeate flux kept stable in the ultrafiltration (UF) unit and NF unit, indicating no scaling occurred in the two units during 168 h test. Thus, a feasible and cost-effective process was provided by using the seeded precipitation assisted NF to deal with the FGD wastewater.