Increasing Bed Depth Research Articles

Rosa damascena waste as biosorbent for co-existing pollutants removal: Fixed-bed column study and ANN modeling

The adsorption behavior of Cd(II) and Pb(II) ions in a coexisting environment, alongside with both dyes (Reactive Red198 and Blue29) was systematically investigated by using a continuous fixed-bed column completely packed with Rosa damascena waste biosorbent (RDWB). Artificial neural network (ANN) model was also utilized to predict the performance of RDWB for various inputs. Their column performance was assessed by optimizing parameters such as bed depth, influent flow rate, and biosorbents’ concentration. It was found that an increasing bed depth considerably extended the operational lifespan and decrease in flow rate delays the column adsorption. Its adsorption capacities were 24.9, 24.6, 24.0 and 24.3 mg/g for Pb(II), Cd(II), Red198, and Blue29, respectively. The RDWB also had a higher adsorption capacity, as compared to previously used biosorbents such as chitosan and biochars due to its good thermal stability and high surface area of 421.46 m2/g. The adsorption of target pollutants took place through ion exchange and electrostatic interactions with negatively charged functional groups on the adsorbent’s surface. The experimental data were fitted by various column adsorption models such as the Thomas, Yoon-Nelson, and Adams-Bohart. The findings showed that the Thomas model exhibited a strong correlation with the experimental data. In contrast, the Adams-Bohart model was applicable to the initial phase of the breakthrough curve (Ce/C0 ≤ 0.1). For industrial applications, a scale up model was also presented with the cost analysis of the biosorbent. The comparison of predicted values with experimental percentage (%) removal values of target pollutants by the RDWB indicated the excellent performance of the ANN model for this work.

Synthesis of Prussian blue-embedded magnetic micro hydrogel for scavenging of cesium from aqueous solutions; Batch and dynamic investigations

A magnetic micro porous structure composite based on alginate and Prussian blue (M-SA-PB) was simply prepared for cesium removal from the aqueous solutions. The gelation and formation of PB proceeded through the same step, which made the PB homogenously distributed and firmly attached to the alginate matrix. The homogenizer was applied to break down the bulky gel structure into micro-ones, and the lyophilizer will provide the porous structure. Batch cesium sorption experiments showed that the adsorption kinetics and isotherms were attributed to the pseudo-second-order model and Langmuir isotherm. Moreover, the Cs-ion is favorably adsorbed on the M-SA-PB composite surface as a monolayer towards Cs, with a maximum adsorption capacity reach of 191.0 mg/g. Furthermore, the M-SA-PB adsorbent showed excellent adsorption selectivity of Cs from multiple-ion solutions. Our work was extended to use the M-SA-PB composite in dynamic cesium sorption. The column studies showed that the removal efficiency of Cs+ increased with increasing bed depth as well as the initial cesium concentration. Finally, as previously mentioned, the M-SA-PB could be considered an excellent Cs+ scavenger employing both batch and dynamic approaches, which makes it a promising adsorbent for practical investigations.

Wastewater treatment by using fixed bed column biosorption process with bio-degradable waste modified Aloe.barbadensis miller leaves powder

Present study focused on abundantwaste of Aloe. barbadense miller leaves treated with sodium bicarbonate(MABL)for the removal of Cd (II) from aqueous solution and industrial effluent using fixed bed continuous process.The experimentation data obtainedfrom breakthrough curves for different conditions (flow rate = 10––30 mL/min, Cd (II) concentration from 20 to 60 mg/L, Different bed height (Bio-adsorbent doses = 10–30 g).Uptake capacity ofCd(II) increased with increased bed depth but remained constant at any flow rate.The optimum conditions obtained were a flow rate 10 mL/min, bed height of 10 cm, and initial concentration of 20 mg/L at the maximum total adsorption capacity is 54.05 mg/g and removal efficiency is 56.3 %. Characterization of the scanning electron microscopy analysis–energy dispersive X-ray spectroscopy (SEM-EDX) analysis confirms the adsorption of Cd (II) in the bio-adsorbent surface. Column behaviors was predicted by mathematical model with desirable accuracy. Thomas model was the best Kinetics model in the biosorption process on the Cd(II) with good correlation coefficient of the experimental data in comparison of Yoon Nelson model,Bohart- Adam model (R2 > 0.90).The efficiency of bio-adsorbent regeneration achieved by 0.1 M HCl was very high, that was 50–33 % for Cd (II)during first to third reused cycle. MABL is also used to removal of Cd (II) by applying a semi-simulated real wastewater in fixed bed column So that it can be concluded that MABL is a good bio-adsorbent for treating wastewater having low concentrations of Cd (II) contamination.

Research on the Quality Improvement and Consumption Reduction of Iron Ore Agglomeration Based on Optimization

In order to increase agglomeration production and improve its quality while reducing energy consumption, a new intelligent blending method has been established at Ansteel to optimize its sinter blends. The statistical model of the ore blending results shows that (1) a blending ratio of 47.2% Ore A and 52.8% Ore C corresponded to the best sinter yield of 72.44%. (2) From the viewpoint of sinter reducibility, sinter basicity should not be less than 1.98 when the proportion of Ore A in the blend is more than 35%. Due to the low mixing efficiency of disc pelletizers, Ansteel has therefore gone through a massive technical transformation at Sinter Plant 3 to replace its 16 existing disc pelletizers with one drum granulator. Since the installation of the drum granulator, the standard deviation has decreased from 1.517 to 0.7332 for total Fe (T.Fe) and from 0.146 to 0.0956 for basicity. In the case of the drum granulator, the standard deviation for sinter T.Fe and basicity were 0.6926 and 0.05449, respectively, as compared to 0.8902 and 0.2033 for the disc pelletizers. In addition, a single lattice method is proposed to optimize the particle-size distribution of the coke breeze to further improve sinter quality and reduce fuel consumption. The lattice method indicated that the optimum coke breeze to achieve maximum sinter tumble strength should consist of approximately 57.20%: −1 mm, 25.63%: 1–3 mm, 11.17%: 3–5 mm, and 6.00%: >5 mm particles. Given the international trend of increasing bed depth, Ansteel has successfully achieved a bed height of 1050 mm or more under its blend conditions, which typically contain 75% concentrates. Finally, some new iron ore agglomerations research is discussed.

A Combined CFD-Response Surface Methodology Approach for Simulation and Optimization of Arsenic Removal in a Fixed Bed Adsorption Column

An experimentally validated CFD model was developed for lab-scale arsenic (As) fixed-bed columns using COMSOL Multiphysics. The effects of key factors such as the adsorbent bed depth, the feed flow rate, and the initial As concentration (conc.) on the overall As removal performance were investigated. Subsequently, the CFD was combined with response surface methodology (RSM) to optimize process conditions and examine main and interaction effects of these factors on model responses, i.e., the As removal efficiency and the bed saturation time. The ANOVA results suggested that quadratic regression models were highly significant for both responses. The established regression model equations predicted the response values closer to CFD measurements. It was found that, compared with the initial As conc. and the feed flow rate, the effect of the bed depth was more significant. Moreover, both the As removal efficiency and the bed saturation time were increased reasonably with the increasing bed depth and decreased with the increasing feed flow rate and initial As conc. The optimum conditions for the As removal process were obtained as the bed height of 80 cm, the initial As concentration of 2.7 mmol/m3, and the feed flow rate of 1 L/min. The present combined CFD−RSM approach is a useful guideline in overall design and optimization of various lab-scale and industrial applications for removal of As from wastewater.

The Dynamic Behaviour of a Binary Adsorbent in a Fixed Bed Column for the Removal of Pb2+ Ions from Contaminated Water Bodies

In the search for a technically efficient and abundant adsorbent in water treatment processes, a bio-composite adsorbent derived from agricultural wastes has been identified as a potential candidate. In this study, eggshells and sugarcane bagasse were combined in varied proportions (1:0, 1:3, 1:1, 3:1 and 0:1) and applied as biosorbents in a lab-scale adsorption column. The effect of bed depth (4–12 cm) of the biosorbents was investigated which enabled the prediction of breakthrough curves for the removal of Pb (II) ions. The life span of the column was extended by increasing the bed depth of the column. The binary adsorbent of 1:3 weight ratio of <75 µm particle size showcased the highest removal efficiency of 91% at a bed depth of 12 cm. The mass transfer zone (MTZ) increased with increasing bed depth with a minor portion of the bed left unused, signifying that the process was highly efficient. The Thomas model constant, KTh, decreased with increasing bed depth with the maximum amount of Pb adsorbed being 28.27 mg/g. With the Yoon–Nelson model, KYN decreased with an increase in τ as the bed height increased. In this study, a novel approach was adopted where the proposed methodology enabled the use of a bio-composite adsorbent in heavy metal removal. The findings of this research will aid in the design and optimisation of the pilot-scale operation of environmentally friendly treatment options for metal laden effluent.

Microstructure of gamma-ray developed polymeric nanocomposite respecting cesium and cobalt removal from aqueous solutions

The nanoparticles of fly ash (FA) were obtained by high energy ball milling of their parent Class C kind for subsequent synthesis of poly(acrylamide-acrylic acid)/fly ash (poly(AM-AA)/FA) nanocomposite. The gamma-radiation induced polymerization was applied to achieve this concern. Different techniques were utilized to characterize such nanocomposite. The sorption abilities of the synthesized nanocomposite toward 60Co2+ and 134Cs + radionuclides were evaluated using batch and fixed-bed column approaches. Batches were designed at constants of solution pH (6.5–7.0 ± 0.02), nanocomposite particle size and dosage (106–250 μm and 0.1 L/g, respectively). The microstructure of such nanocomposite (<100 nm) was mainly amorphous with porous rough surfaces containing homogenous distribution of the incorporated nano-FA. About 56.46 and 47.9 mg/g of Co2+ and Cs+ were sorbed at equilibrium with an ion exchange reaction mechanism. Langmuir, Freundlich and Dubinin–Radushkevich D–R isotherm model parameters were calculated indicating the favorability of all sorption processes. The spontaneous and endothermic natures of sorption were observed by the calculated ΔG° and ΔH° thermodynamic parameters, respectively. Thomas, Yoon–Nelson and Adams Bohart models were fitted to the fixed-bed column data at varied conditions. The predicted sorption capacities of Thomas were very close to those obtained experimentally. Modeling of the fixed-bed column data dominates that the external mass transfer kinetics was predominant in the initial parts of the fixed-beds. Values required for retaining 50% of the initial sorbate concentration were extended from 89.05 to 68.55 to 177.2 and 149.3 min for 60Co2+ and 134Cs + radionuclides, respectively, by increasing bed depth from 1.5 to 3.0 cm. Modification of FA to its nano-scale form with the subsequent synthesis of a nanocomposite material having sorption capabilities made a duplicate beneficial environmental concern.

Experimental study on the alumina fine powder internal compression characteristics under gas pressurization

The compression characteristics at the different positions inside a powder bed under gas pressurization were experimentally studied by a visualization tank. It was found that the pressurization rate had an important effect on the powder compression which accelerates the arrival of high pressure. The compression characteristics of the beds at different positions differed significantly and the compression ratio increased with the increasing bed depth. The smaller the pressurization rate, the more significant the difference in compression ratio of different powder layers; conversely, the compression processes of different powder layers tend to be consistent at higher pressurization rates. The prediction model of relative compaction density variation was established with the error within ±5%. The paper provides an important reference for regulating the flow of the compressed powder bed.

Column dynamic studies for lanthanum(III) and neodymium(III) sorption from concentrated phosphoric acid by strongly acidic cation exchange resin (SQS-6)

ABSTRACT In this work, solid-liquid extraction of lanthanum and neodymium ions by column technique from concentrated phosphoric acid solutions using the strongly acidic cation exchange resin was experimentally investigated. Measurements of breakthrough curves were measured as a function of column bed depth, initial metal concentration in the feed solution and flow rate. It was found that the breakthrough and time increased with the increase in bed depth and the total mass adsorbed by La(III) and Nd(III) increased with increasing bed depth. At higher initial metal concentrations, the column is quickly saturated, resulting in shorter breakthrough and exhaustion time. It was observed that with increasing the initial metal concentration from 0.10 to 0.50 g/L, the equilibrium adsorption capacities increase from 9.68 to 27.45 mg/g for La(III) and from 4.57 to 19.43 mg/g for Nd(III). Breakthrough time reaching saturation was increased significantly with a decrease in the flow rate. As the flow rate increased from 1.0 to 4.0 ml/min, the exhaustion time of La(III) and Nd(III) decreased from 135.0 to 40.0 min and from 90.0 to 35.0 min, respectively. The capacity of La(III) and Nd(III) was found to be 33.55 and 17.30 mg/g, respectively. The experimental sorption capacity and the time required for 50% adsorbate breakthrough (τ) are close to those calculated resulting from the Thomas and Yoon-Nelson model. These results indicate that the experimental data obey the Thomas and Yoon-Nelson model.

Study of Parameters Affecting Thermal Drying Process. (Dept. M)

Parameters affecting drying process has been studied experimentally as it associated with heat and mass transfer between porous bed to be dried and air which flows through the porous bed. To perform this study, a test rig is designed and constructed as it consists of vertical circular duct packed with wet porous bed which is made from clay balls of 20 mm in diameter. Drying process occurs as a result of forcing hot air vertically to pass through the wet porous bed, evaporation of moisture is existed in the bed due to the simultaneous heat and mass transfer. The studied operating parameters are inlet air temperature, inlet air mass flux, porous bed depth and porosity of balls. The average heat and mass transfer coefficients are estimated for flow of hot air through the wet porous bed. The results indicated that, the drying rate is directly proportional to inlet air temperature, mass flux of air, dimensionless bed depth and ball porosity. So, Drying process can be achieved in lower time as increasing both air mass flux and or inlet air temperature and decreasing bed depth. Also, heat transfer coefficient and mass transfer coefficient increase with increasing inlet air temperature, inlet air mass flux, and ball porosity, but they decrease with increasing bed depth. Comparison between the obtained experimental results and the previous work gave the same trend.

Utilizing mining dam bottom sludge as a novel adsorbent for AuO removal from wastewaters: Batch and column studies

In this study, the adsorption of Auramine O (AuO) dye using bottom sludge (BS) was investigated in batch and continuous systems. The BS was characterized by EDX, BET, XRD, DLS, ζ-potential, SEM, FTIR, helium pycnometer, and mercury porosimetry. The kinetic and isotherm data were fitted to pseudo-second-order and Langmuir models. The maximum amount of adsorption calculated from the Langmuir isotherm model was 5.09 mg/g. Thermodynamic studies showed that adsorption was endothermic and occurred spontaneously. Thomas, Clark, and Yoon-Nelson models were suitable (R2 > 0.95 for all these models) to explain the dynamic behavior of AuO-BS in the column system. Increased bed depth increased breakthrough time, while the breakthrough time declined with increased initial AuO concentration and flow rate. Optimum conditions were determined for the batch system as 4 g of BS dose, 100 rpm agitation speed, and 90 min reaction time; optimum conditions for the column system were 3 cm bed depth, 0.14 mL/min flow rate, reaction time of 181 h; and optimum conditions for both systems were 100 mg/L AuO concentration, 20 °C reaction temperature and pH 6.18 (natural). Under these conditions, the amounts of AuO adsorbed in batch and column systems were calculated as 2.06 mg/g (89.75%) and 2.63 mg/g (47.13%), respectively. The studies showed that efficient remediation of AuO from aquatic environments is possible with BS.

Microwave treated activated carbon from industrial waste lignin for denitrification of surface water

Highly porous adsorbent materials were developed from industrial waste lignin for denitrification of surface and groundwater. The effect of microwave treatment and zinc ion impregnation on denitrification capacities of the material was investigated. The denitrification efficiencies of prepared materials were investigated by performing batch and continuous column adsorption experiments. The effect of different experimental parameters, including initial nitrate ion concentration, solution pH, and contact time, was also investigated. Adsorption kinetic follows the pseudo-second-order kinetic mechanism. Adsorption isotherm follows the monomolecular adsorption and experimental data best fitted into the Langmuir isotherm model. Continuous column denitrification experiments were performed with granulated adsorbent at different experimental conditions to understand its applicability in the household water treatment unit. Thomas model breakthrough time and the nitrate removal efficiency increase with increasing bed depth, whereas it declines with flow rate and nitrate concentration. The economic viability and environmental friendliness were understood by conducting adsorption–desorption experiments with loaded materials. The performance of adsorbent did not alter significantly even after four consecutive adsorption–desorption cycles.

Novel Sorbent of Sand Coated with Humic Acid-Iron Oxide Nanoparticles for Elimination of Copper and Cadmium Ions from Contaminated Water

Nanoparticles of humic acid and iron oxide were impregnated on the inert sand to produce sorbent for treating groundwater contained of cadmium and copper ions by technology of permeable reactive barrier (PRB). Sewage sludge was the source of the humic acid to prepare the coated sand by humic acid—iron oxide (CSHAIO) sorbent; so, this work is consistent with sustainable development. For 10 mg/L metal concentration, batch tests at speed of 200 rpm signified that the removal efficiencies are greater than 90% at sorbent dosage 0.25 g/ 50 mL, pH 6 and contact time 1 h. The kinetic data was well described by the Pseudo first-order model indicating that physicosorption is the predominant mechanism. The maximum adsorption capacities (qmax) were calculated by Langmuir model and their values of 25.273 and 114.142 mg/g for cadmium and copper ions respectively. Computer solution (COMSOL) Multiphysics program has utilized to simulate the metal ions transport in the column tests. Model predictions as well as experimental measurements signified that increasing bed depth with decreasing of flow rate and inlet concentration leads to delay in the propagation of metal front.

Dynamic modelling of Alginate - Cobalt ferrite nanocomposite for removal of binary dyes from textile effluent

The performance of Alginate - Cobalt ferrite (ACF) in a fixed bed column was assessed for the simultaneous removal of binary dyes from textile effluent. The binary dye effluent containing 32.5 mg/L of reactive red 195 (RR195) and 21 mg/L of reactive yellow 145 (RY145) was used for the study. The effect of various parameters like bed depth (3, 6, 9 and 12 cm) and flow rate of influent (5, 7.5 and 10 mL/min) for the binary adsorption using ACF was studied. The results revealed that ACF bed capacity and maximum adsorption capacity showed an increasing trend with an increased bed depth and decreased flow rate. Dynamic modeling such as Yoon - Nelson model, Thomas model and Bed Depth Service Time model (BDST) were evaluated with the experimental data. Comparatively, Yoon - Nelson and Thomas model presented better fitness for the elimination of RR195 and RY145 dye. The experimental data from dynamic studies revealed ACF's effectiveness for the sequestration of binary dyes from textile effluent.

Black box dynamic modeling of Co(II) ions removal from aqueous solution using modified maghemite nanoparticles by fixed-bed column based on deep neural networks

The removal of cobalt(II) ions from an aqueous solution using a fixed-bed glass column containing modified maghemite γ-Fe2O3@SiO2 nanoparticle was investigated. The influence of various parameters such as bed depth, concentration of influent cobalt, and feed flow rate on the breakthrough curves and the column performance was also discussed. The column study indicates that the removal of cobalt(II) ions increased with increasing bed depth, whereas it decreased with the increase of both influent cobalt concentration and the flow rate. By increasing the flow rate, column saturation takes a shorter time. This study also indicated that with increasing bed depth the sites available for sorption increased in the column, therefore the input volume of cobalt solution also increased. The kinetic models indicated that the column maximum capacity increased with the flow rate and cobalt concentration, while it decreases with bed depth. Long–short term memory (LSTM) and multilayer perceptron (MLP) are merged to compose deep LSTM neural networks to form and predict the cobalt (II) ions removal onto fixed-bed column system was also concluded in this work.

Effective defluoridation of industrial wastewater by using acid modified alumina in fixed-bed adsorption column: Experimental and breakthrough curves analysis

The defluoridation performance of a simple and efficient adsorbent (SAA), developed by H2SO4 treatment of alumina, was explored in fixed-bed adsorption column (FBAC). The SAA was characterized by SEM, EDX, FTIR, XRD and Raman spectroscopy. The influence of different process affecting parameters like bed depth (2.5–7.5 cm), influent flow rate (1.5–2.5 mL/min), and fluoride concentration (40–60 mg/L) were explored. The increased bed depth, and reduced flow rate and fluoride concentration were found to improve the column performance. The fitting of Thomas, Yoon-Nelson, Clark, BDST, and Yan models to breakthrough curves were attempted. The best fitting (R2 > 0.9) was exhibited by Clark model. The column exhibited the maximum performance at bed depth of 7.5 cm, influent flow rate of 1.5 mL/min, and fluoride concentration of 40 mg/L. The column performance of SAA was superior to unmodified alumina. The SAA (5 g) demonstrated the successful result (% R = 89.76%; tb = 350 min; te = 1037 min) for the treatment of industrial effluent (16.54 mg/L) in FBAC. Besides, the column loaded by SAA exhibited reusability up to four cycles. These results implied the suitability of SAA for the treatment of fluoride contaminated industrial wastewater or groundwater in continuous operating mode.

Alum sludge as an efficient sorbent for hydrogen sulfide removal: Experimental, mechanisms and modeling studies

This paper firstly reported a systematic study of using alum sludge (waterworks residue) for H2S adsorption. Various trials were performed at ambient temperature in a fixed bed column to study the effects of H2S flow rate, sorbent bed depth on the alum sludge adsorption efficiency of H2S. The Breakthrough Curves were simulated by the Thomas model, Bed Depth Service Time model and Yoon-Nelson models. The mechanisms of H2S adsorption onto alum sludge was examined by different physiochemical characterizations of exhausted and raw alum sludge. Moreover, the mass transfer coefficients were determined from mathematical descriptions of breakthrough curves. The alum sludge adsorption capacity was determined to be 374.2 mg of H2S/g, slightly decreasing with the increasing flow rate and increasing with the increasing bed depth. All the three models successfully predict breakthrough curves which could be used for scaling-up purposes. The microporous structure, alkaline pH and the inherent metal species of the alum sludge promoted the formation of metal sulphate species. This study demonstrated that alum sludge could be used as cost-effective, largely available, and efficient sorbent for H2S removal.

Effective fluoride adsorption using water hyacinth beads doped with hydrous oxides of aluminium and iron

In this study, the effectiveness of water hyacinth beads doped with hydrous aluminium oxide (WH-HAO), hydrous iron oxide (WH–HFO) and hydrous aluminium oxide-iron oxide mixture (WH-HAO-HFO) was investigated for the removal of fluoride from aqueous solution in batch and fixed bed column systems. The effect of solution pH, initial fluoride concentration, flow rate, bed depth, and competing ions were studied. The adsorption capacities of the adsorbents were 4.43, 4.25, and 4.18 mg/g F for WH-HAO, WH-HAO-HFO and WH-HFO, respectively. Increasing solution pH had the effect of reducing fluoride adsorption, with the effect less pronounced for adsorption using WH-HFO adsorbent. Equilibrium modelling showed that the data better fitted the Freundlich isotherm compared to the Langmuir isotherm, which was consistent with the heterogeneous, rough and porous physical surface indicated by scanning electron microscope (SEM) characterization. Column sorption studies revealed that the breakthrough point was reached earlier at higher inlet fluoride concentration, lower flow rate and lower adsorbent bed depth. The maximum fluoride adsorption capacity of the adsorbent decreased with increasing flow rate and increasing inlet fluoride concentrations while the volume of fluoride solution treated before saturation was found to increase with increasing bed depth and flow rate. Competition to fluoride adsorption followed the order HCO3->PO43->SO42-. Adsorbent regeneration studies showed that at least 80% F adsorption was achieved in 3 sorption-desorption cycles using WH-HAO beads, and NaOH was the most effective desorption agent, achieving >80% desorption of previously adsorbed fluoride in 3 h. Water hyacinth doped with hydrous metal oxides and immobilized in alginate showed great potential for further exploration as adsorbent for the removal of fluoride from water in continuous flow systems.

A Study on the Removal of Copper (II) from Aqueous Solution Using Lime Sand Bricks

Heavy metals such as Cu(II), if ubiquitous in the runoff, can have adverse effects on the environment and human health. Lime sand bricks, as low-cost adsorbents to be potentially applied in stormwater infiltration facilities, were systematically investigated for Cu(II) removal from water using batch and column experiments. In the batch experiment, the adsorption of Cu(II) to bricks reach an equilibrium within 7 h and the kinetic data fits well with the pseudo-second-order model. The sorption isotherm can be described by both the Freundlich and Langmuir model and the maximum adsorption capacity of the bricks is 7 ± 1 mg/g. In the column experiment, the best removal efficiency for Cu(II) was observed at a filler thickness of 20 cm, service time of 12 min with a Cu(II) concentration of 0.5 mg/L. The Cu(II) removal rate increases with the increasing bed depth and residence time. The inlet concentration and residence time had significant effects on the Cu(II) removal analyzed by the Box–Behnken design (BBD). The Adams-Bohart model was in good agreement with the experimental data in representing the breakthrough curve. Copper fractions in the bricks descend in the order of organic matter fraction &gt; Fe-Mn oxides fraction &gt; carbonates fraction &gt; residual fraction &gt; exchangeable fraction, indicating that the lime sand bricks after copper adsorption reduce the long-term ecotoxicity and bioavailability to the environment.

Experimental study of the effects of non-uniformly distributed fine soil on mechanical properties of Shenyang-Dandong Railway coarse-grained soil

The stress produced by repeated train loads decreases with increasing railway subgrade bed depth, and slightly weathered coarse particles of subgrade bed fillings can be broken at different levels under continuous load. Thus, the mass of fine soil, with a diameter of not more than 0.075 mm, is different at different depths. Fine soil is also sensitive to frost heave and thaw settlement. In order to study the effects of non-uniformly distributed fine soil on the mechanical properties of coarse-grained soil of the Shenyang-Dandong Railway, triaxial tests were conducted with three types of specimens, undergoing six freeze-thaw cycle numbers(0, 1, 3, 7, 9, 12) and three confining pressures(100, 200, 300 k Pa). The freezing temperature is-5 °C and the thawing temperature is +15 °C. The stress-strain behavior, static strength, resilient modulus, cohesive force and the angle of internal friction were measured for different tested specimens. As a result, the law of static strength and resilient modulus of different specimens following the increase of freeze-thaw cycles under three confining pressures is obtained. The changing law of cohesive force and friction angle of three specimens following the increase of freeze-thaw cycles is also calculated, and the different results of different specimens are also compared.