Metal Removal Rate Research Articles

Synthesis and Machining Characteristics Evaluation of Silicon Nitride Made Magnesium Alloy Composites

<div>The advantages of magnesium alloy composites over traditional engineering materials include their high strength and lightweight for automotive applications. The proposed work is to compose the AZ61 alloy composite configured with 0–12% silicon nitride (Si<sub>3</sub>N<sub>4</sub>) via semisolid-state stir processing assisted with a (sulfur hexafluoride—SF6) inert environment. The prepared AZ61 alloy and AZ61/4% Si<sub>3</sub>N<sub>4</sub>, AZ61/8% Si<sub>3</sub>N<sub>4</sub>, and AZ61/12% Si<sub>3</sub>N<sub>4</sub> are machined by electrical discharge machining (EDM) under varied source parameters such as pulse On/Off (T<sub>on</sub>/T<sub>off</sub> <sub> </sub>) time (100–115/30–45 μs), and composition of composite. The impact of EDM source parameters on metal removal rate (MRR) and surface roughness (Ra) is measured. For finding the optimum source for higher MRR and good surface quality of EDM surface, the ANOVA optimization tool with L16 design is executed and analyzed via a general linear model approach. With the influence of ANOVA, the T<sub>on</sub>/T<sub>off</sub> and composite composition found 95.42%/1.27% and 0.36% impact for MRR and 30.74%/21.01%/18.27% of T<sub>on</sub>, T<sub>off</sub>, and Ra. The optimum parameters for electrical discharge machining have been determined, and the composite material of AZ61/8% Si<sub>3</sub>N<sub>4</sub> has been identified as having a favorable MRR/Ra value compared to other materials.</div>

Improving the performance of HDPE plastic membranes for heavy metal removal by incorporating EVA/PDMS

Plastic waste poses a significant environmental threat. To address this issue and mitigate water pollution caused by heavy metals, this study repurposed HDPE plastic waste into functional membranes. To enhance the membrane's properties, HDPE was blended with EVA to improve hydrophilicity and flexibility, and then coated with PDMS to reduce pore size. These membranes were fabricated using a sustainable and cost-effective TIPS process with mineral oil as a solvent. Characterization techniques, including SEM, FTIR, EDX, contact angle measurement, AFM, and stress-strain analysis, were employed to investigate the morphological, chemical, and mechanical properties of the membranes. Zeta potential measurements were also conducted to assess the surface charge. The performance evaluation revealed that PDMS coating significantly increased the rejection of Ni(II) and Pb(II) ions (up to 63% and 78%, respectively), while EVA addition improved the pure water flux (from 16 to 44 L/m²h). The membranes exhibited good performance over a range of pH, contact time, and metal ion concentrations. Additionally, the membranes demonstrated excellent cleaning efficiency with NaOCl and citric acid, maintaining high flux recovery and metal removal rates after multiple cycles. The study's findings highlight the potential of repurposing plastic waste into functional membranes for water treatment applications, contributing to a more sustainable and circular economy.

Magnesium Alloy and Silicon Nitrides Composite Study: Synthesis and Abrasive Water Jet Machining Behavior and Optimization

<div>Related to traditional engineering materials, magnesium alloy-based composites have the potential for automobile applications and exhibit superior specific mechanical behavior. This study aims to synthesize the magnesium alloy (AZ61) composite configured with 0 wt%, 4 wt%, 8 wt%, and 12 wt% of silicon nitride micron particles, developed through a two-step stir-casting process under an argon environment. The synthesized cast AZ61 alloy matrix and its alloy embedded with 4 wt%, 8 wt%, and 12 wt% of Si<sub>3</sub>N<sub>4</sub> are subjected to an abrasive water jet drilling/machining (AJWM) process under varied input sources such as the diameter of the drill (D), transverse speed rate (v), and composition of AZ61 composite sample. Influences of AJWM input sources on metal removal rate (MRR) and surface roughness (Ra) are calculated for identifying the optimum input source factors to attain the best output responses like maximum MRR and minimum Ra via analysis of variant (ANOVA) Taguchi route with L16 design approach. The ANOVA analysis revealed that D, v and the composition of AZ61 alloy composite contribute 26.45%, 16.28%, and 20.84%, respectively, to the output response conditions for higher MRR. Additionally, design 7 exhibits a high MRR of 0.017 g/s and a surface roughness (Ra) of 0.84 μm. The optimum AWJM input source of design 7 is proposed for industries to mass production applications.</div>

Nickel-based alloy efficient milling with ceramic tool and experimental verification in closed impeller

Nickel-based alloys are a class of materials that possess exceptional properties, including superior corrosion, oxidation, and fatigue resistance. They are increasingly utilized in high-performance critical components, particularly in the fields of aerospace engines and gas turbines. Nickel-based alloys pose significant challenges during machining due to their high cutting forces and work hardening, leading to low machining efficiency, severe tool wear, and subpar surface quality of the machined parts. To address these challenges, an orthogonal cutting experiment was conducted on GH4061 alloy to evaluate the machining performance by using monolithic ceramic milling tools. The optimal cutting parameters combination for dry cutting of nickel-based alloys was determined. The surface quality was tested and analyzed, including surface micro structure, residual stress, and surface roughness. The machining experiment was conducted on GH4061 closed impeller. The results demonstrated that high-speed cutting was more effective than low-speed cutting in improving the surface quality of the machined part. In the rough processing, monolithic ceramic milling tools was used to quickly remove the excess material. The adhesive and diffusion effects mainly contributing to the wear of the monolithic ceramic tool in GH4061 milling. Average surface roughness 1.41 μm can be obtained through dry milling using a monolithic ceramic tool with cutting speed 602.88 m/min, cutting depth 0.3 mm, cutting width 6 mm and feed per tooth 0.03 mm/z, along with metal removal rate 5184 mm3/min. High cutting speed will resulting in relatively low residual stress in the surface layer as well as a lower thickness of the surface alternation layer. Finally, a physical GH4061 closed impeller was machined to verify the proposed milling method.

Mechanochemical Thioglycolate Modification of Microscale Zero‐Valent Iron for Superior Heavy Metal Removal

AbstractMicroscale zero‐valent iron (mZVI) is widely used for water pollutant control and environmental remediation, yet its reactivity is still constrained by the inert oxide shell. Herein, we demonstrate that mechanochemical thioglycolate (TG) modification can dramatically enhance heavy metal (NiII, CrVI, CdII, PbII, HgII, and SbIII) removal rates of mZVI by times of 16.7 to 88.0. Compared with conventional impregnation (wet chemical process), this dry mechanochemical process could construct more robust covalent bonding between TG and the inert oxide shell of mZVI through its electron‐withdrawing carboxylate group to accelerate the electron release from the iron core, and more effectively strengthen the surface heavy metal adsorption through metal(d)‐sulfur(p) orbital hybridization between its thiol group and heavy metal ions. Impressively, this mechanochemically TG‐modified mZVI exhibited an unprecedented NiII removal capacity of 580.4 mg Ni g−1 Fe, 17.1 and 9.5 times those of mZVI and wet chemically TG‐modified mZVI, respectively. Its application potential was further validated by more than 10 days of stable groundwater NiII removal in a column flow reactor. This study offers a promising strategy to enhance the reactivity of mZVI, and also emphasizes the importance of the modification strategy in optimizing its performance for environmental applications.

Mechanochemical Thioglycolate Modification of Microscale Zero-Valent Iron for Superior Heavy Metal Removal.

Microscale zero-valent iron (mZVI) is widely used for water pollutant control and environmental remediation, yet its reactivity is still constrained by the inert oxide shell. Herein, we demonstrate that mechanochemical thioglycolate (TG) modification can dramatically enhance heavy metal (NiII, CrVI, CdII, PbII, HgII, and SbIII) removal rates of mZVI by times of 16.7 to 88.0. Compared with conventional impregnation (wet chemical process), this dry mechanochemical process could construct more robust covalent bonding between TG and the inert oxide shell of mZVI through its electron-withdrawing carboxylate group to accelerate the electron release from the iron core, and more effectively strengthen the surface heavy metal adsorption through metal(d)-sulfur(p) orbital hybridization between its thiol group and heavy metal ions. Impressively, this mechanochemically TG-modified mZVI exhibited an unprecedented NiII removal capacity of 580.4 mg Ni g-1 Fe, 17.1 and 9.5 times those of mZVI and wet chemically TG-modified mZVI, respectively. Its application potential was further validated by more than 10 days of stable groundwater NiII removal in a column flow reactor. This study offers a promising strategy to enhance the reactivity of mZVI, and also emphasizes the importance of the modification strategy in optimizing its performance for environmental applications.

Effect of Electrode Positioning on Electrokinetic Remediation of Contaminated Soft Clay with Surface Electrolyte.

Soft clay contamination is an increasingly global issue with significant implications for land development and human health. Electrokinetic remediation (EKR) has demonstrated significant potential for cleaning contaminated soils. It is crucial to develop efficient processes that minimize environmental impact and reduce costs. A series of citric acid (CA)-enhanced EKR tests were conducted using a novel experimental setup, with the electrolyte positioned above the soil surface, to examine the impact of four different electrode arrangements on the effectiveness of EKR. The position of the electrode end had a significant impact on the migration of ions in the anolyte and catholyte, which in turn affected the volume reduction in the anolyte, the magnitude of the current, and the migration of heavy metals. The electrode arrangement mode c (electrodes suspended in the electrolytes) can enhance the migration of the anolyte and reduce the drainage of the soil, making it an effective measure for improving the removal rate of heavy metals. After the heavy metal remediation is complete, the bearing capacity of the soil should be increased. Changing the electrode arrangement to mode d (anode suspended in the anolyte, a very small part of the cathode inserted into the soil) is an effective measure for reducing the soil water content and improving soil strength.

Evaluating productivity characteristics of laser engineered net shaping titanium alloy

Advances in Additive Manufacturing (AM) technologies have made it possible to reduce the design and prototyping costs to a minimum especially for a low-productivity material like titanium. Titanium alloys are commonly and widely used alloys in the aerospace and biomedical sector due to their advantageous material properties. This paper is an evaluation study of factors affecting the productivity characteristics of Laser Engineered Net Shaping (LENS) titanium alloy (Ti-6Al-4 V) using face milling. Some of the productivity challenges associated with titanium such as rapid tool wear, poor surface finish, and high-power consumption are explored in this paper. All materials processed using AM face the same critical problem that the manufactured part requires a post machining since AM produces relatively poor surface finish. Machining trials are conducted using the combinations of machining parameters such as spindle speed of 800 and 1600 rev/min; feed rate of 50 and 100 mm/min; and a constant depth of cut of 1 mm, respectively. Titanium being a poor thermal conductivity material, the effect of coolant was investigated using wet/dry machining. Data related to the productivity factors and material behavior under a milling trial was recorded and analyzed. The obtained data from the trials include productivity factors such as Metal Removal Rate (MRR), power consumed, and the surface finish for each plate/trial. The power consumed in dry milling was observed to be lower than that in wet milling which is contrary to the observations from conventional wet milling. The paper concludes the trends observed for LENS titanium are opposed to the trends in conventional machining such as increasing cutting speed will result in lower cutting force and power consumed.

Experimental Investigation of Electro-Discharge-Machined EN-24 and EN-42 Alloys

<div>The EN24 and EN42 materials were machined by the electric discharge machine (EDM). The study aimed to optimize the input variables for the multiple outputs, such as metal removal rate (MRR), tool wear rate (TWR), and surface roughness. The machining of the metal is essential to analyze the surface quality and the production rate. The MRR is a prediction of the production rate and surface roughness resembling the quality of the surface. The input variables were current (A), pulse on time (t<sub>on</sub>), and pulse duty factor (T). The three levels of current were 3A, 6A, and 9A. The t<sub>on</sub> time was selected as 30 μs, 50 μs, and 70 μs. The pulse duty factors were selected as 4, 5, and 6. The Taguchi optimization techniques are used to optimize process parameters. The L9 orthogonal array was selected for the process. ANOVA analysis was employed to check the rank of the input parameters relative to the output. The maximum MRR were at 9A, 70 μs, and 4 duty factor for the EN24. The best MRR were at 9A, 70 μs, and 5 duty factor for the EN42. The contribution of t<sub>on</sub> was maximum compared in the tool wear analysis. The optimum value of tool wear was at 6A, 70 μs, and 4 duty factors for the machining of EN42 and EN24. The surface analysis for EN24 was yielding at 9A, 70 μs, and 4 duty factor, and 9A, 70 μs, and 5 duty factors for the EN42. The maximum contribution of pulse on time for surface finish for machining both the materials. The scanning electron microscopy (SEM) analysis also analyzed the surface quality.</div>

Wire EDM machining characteristics of squeeze cast Al-Zn-Mg-Cu/(SiC + Al2O3) hybrid composite by TOPSIS approach

This research focuses on the squeeze-cast Al-Zn-Mg-Cu metal matrix reinforced with 10% silicon carbide and 10% aluminium oxide particles machined by wire-cut electro-discharge machining (WEDM) to examine the consequences of input factors like pulse-on time, current, pulse-off time, and wire speed over the responses of metal removal rate (MRR) and surface roughness. The pulse-on time (7–11 µs), current (2–4 amps), pulse-off time (6–10 µs), and wire speed (1–3 m/min) used during WEDM machining are all variable. The TOPSIS approach was utilised to identify the optimal processing settings. According to the optimised findings, larger MRR of 3.95 mm3/min and reduced surface roughness of 3.295 µm were achieved by combining pulse-on time, current, pulse-off time and wire speed at 7 µs, 2 amp, 6 µs and 1 m/min, respectively. With a scanning electron microscope, the machined surfaces are examined. Based on the study of the machined surface, the micrograph of sample order no. 1, which has relatively less hills and gorges, has a ton of 7 µs, toff of 6 µs, current of 2 amps and wire speed of 1 m/min. Under a microscope, the amount and size of the craters and fractures created appear to be decreasing. The moderate current intensity and low pulse-off time result in a reduction in the intensity of the electrical discharge. This enhances the surface finish since there are fewer, smaller craters and fissures. The obtained findings may be used by the manufacturers to improve WEDM machining of Al 7075 reinforced with SiC and Al2O3 particles.

Evaluating the effectiveness of the TOPSIS approach for three-wire electrode machining of D2 steel using the wire EDM method

Due to the high demand for D2 steel as a tool material and the difficulty of the machine, optimization of process parameters in advanced manufacturing machines is needed. This study investigates three wire electrodes: brass, coated copper, and annealed copper, analyzing their impact on tool material. Employing 0.25 mm wires, 10 mm D2 steel cubes are cut for consistent comparison. An L27 orthogonal array tests six parameters at three levels, optimizing with analytic hierarchy process technique for order preference by similarity to the ideal solution (AHP-TOPSIS). The response parameters were the metal removal rate (MRR) and kerf width (KW). Pulse on/off time, wire tension, spark voltage, input current, and wire feed rate vary systematically for each wire. The tests validate the efficacy of the AHP-TOPSIS method in optimizing WEDM parameters and machining performance. ANOVA reveals pulse-on and pulse-off times as crucial factors for various wire electrodes. Under diverse conditions, pulse duration increases spark efficiency. Based on the AHP-TOPSIS method results, weights of outputs revealed that the annealed copper wire yields the highest MRR value (0.232 mm3/sec). The brass wire exhibited the lowest MRR value (0.127 mm3/sec) compared to the others.

Model test of in-situ remediation for heavy metal-contaminated clayey soil by artificial freezing and shaft washing

The low permeability of clayey soil and the pressure of liquid extraction and injection tend to form preferential flow paths in the soil, diminishing the remediation efficiency of shaft washing. Therefore, a new in-situ repair method combining artificial freezing and shaft washing is proposed. Using Pb and Cd contaminated clayey soil as the research object, in-situ model tests of different eluent types, concentrations, and suction modes were conducted to investigate the removal rate of heavy metals and the distribution of temperature and water field. The results demonstrated that the artificial freezing method can effectively induce the water (eluent) migration from the unfrozen zone to the freezing front. Besides, it effectively resolved the issue of poor washing efficiency caused by preferential flow between the extraction and injection wells during the extraction process. After five freeze-thaw cycles, the removal rate of Pb and Cd reached 46.16 % and 59.04 %, respectively. The combination of artificial freezing and plastic drainage plate technology merges artificial freezing and shaft washing methods to achieve the remediation of heavy metal-contaminated soil, providing a reference for the in-situ remediation of heavy metal-contaminated clayey soil.

Predictive modeling of MRR, TWR, and SR in spark-EDM of Al-4.5Cu–SiC using ANN and GEP

In this study, Al-4.5Cu alloy was reinforced with varying weight percentages of SiC particles (2%, 4%, 6%, and 8%) to create metal matrix composites via the stir casting method. The formation of intermetallic compounds was confirmed through energy dispersive spectroscopy and x-ray diffraction analysis. This article compares the performance of Artificial Neural Network (ANN) and Gene Expression Programming (GEP) models in predicting the Metal Removal Rate (MRR), tool wear rate, and surface roughness in the die-sinking electro-discharge machining (EDM) process of the ex-situ developed Al-4.5%Cu–SiC composites. The study considers three machine parameters—pulse on time (TON), pulse off time (TOFF), and current (I)—along with the weight fraction of SiC particles as input variables for the models. Both ANN and GEP models demonstrated high predictive accuracy for the EDM performance metrics, with correlation coefficients (R) ranging from 0.973 68 to 0.980 65 for the ANN model and 0.980 11 to 0.982 59 for the GEP model. Notably, the GEP model exhibited superior predictive capability, as evidenced by its higher correlation coefficients and lower root mean square error, indicating greater effectiveness in predicting the EDM process outcomes than the ANN model.

Cyclic biomachining of copper: Maximum metal removal rate with minimum depleted solution

Bacterially assisted leaching has been proposed for many innovative applications, such as urban mining or micromachining, but many technical challenges including substrate toxicity and downstream processing of the leach liquor must be solved before its industrial implementation. This study was conducted with the final goal of improving the average specific metal removal rate (SMRR) and reducing the amount of depleted solution generated in the leaching process of copper workpieces, with special attention paid to the detection of microbial activity inhibition.The copper leaching rate is almost entirely dependent upon the Fe3+ concentration with Fe3+/Fe2+ ratios higher than 0.3, after which A. ferrooxidans oxidation action becomes relevant. In both biotic and abiotic experiments, the SMRR peaked after the first hour of treatment, and it decreased sharply after three hours. A consecutive process alternating bioleaching and oxidant regeneration stages was proposed to improve performance, which considerably reduced both the time needed to dissolve a certain amount of metal and waste generation. The decrease in copper removal (25 %) and the increase in the time required for oxidant regeneration after five leaching cycles (longer than 90 h) were attributed to bacterial inhibition in the presence of 10.7 g Cu2+ L−1, which was established as the limiting metal concentration for reusing the biologically active solution.

Optimization of process parameters in micro electrochemical machining using TOPSIS technique with Analytical Hierarchy Process (AHP)

Electro-chemical machining (ECM) is one of the extensively used unconventional machining processes employed in industries to machine difficult-to-machine materials such as super alloys, titanium alloys, stainless steel, etc It does not impart any mechanical stresses on the workpiece. The primary requirement of the work material used in this process should be electrically conductive materials. In favour of these characteristics, Hastelloy C276 is used as a work material because it exhibits excellent physical properties over cast iron. Generally, the quality of machining mostly relies on the electrolyte (mmol L−1), feed rate (mm/rev), and duty ratio. These credential parameters are considered in this present work to enhance the machining quality, such as circularity, taper angle, and metal removal rate (MRR). The Taguchi L9 orthogonal array is used to learn machining behaviour under various circumstances. And this time, an Analytic Hierarchy Process (AHP) is used to allocate the weight for each response in the TOPSIS multi-criteria decision-making method. According to the findings, sodium nitrate (NaNo3) has a higher metal removal rate than sodium chloride (NaCl) and sodium bromide (NaBr). It will, however, result in a low-quality hole. The taper angle is inversely proportional to the feed rate.

Analysis and optimization of machining parameters of AZ91 alloy nanocomposite with the Influences of nano ZrO2 through vacuum diecast process

The magnesium alloy composite is a vital material for automotive applications due to its features like high stiffness, superior damping resistance, high strength, and lightweight. Here, the motto of research is to establish the AZ91 alloy nanocomposite with the exposures of 0, 1, 3, and 5 volume percentages (vol%) of nano zirconium dioxide (ZrO2) particles (50nm) through fluid stir metallurgy route associated with 1x105 Pa vacuum die cast process. Exposures on structural morphology, hardness, and impact toughness of composite are analyzed and identified as the nano AZ91 alloy composite enclosed with 5vol% is homogenous particle dispersion, enhanced hardness (97.6HV), and optimum toughness of 21.2J/mm2. However, composite faces machining difficulties due to the hard abrasive particles with higher hardness, resulting in tool wear. This experiment predicts the optimum mill parameters during the end mill operation of magnesium alloy nanocomposite (AZ91/5vol%) by using a tungsten carbide coated end mill cutter to attain the maximum metal removal rate with low surface roughness and tool wear analyzed via the general linear model (GLM) ANOVA approach. The input conditions for end milling operation vary, like feed rate (0.1 -0.4mm/rev), depth of cut (0.05 -0.2mm), and spindle speed (250-1000rpm). During the ANOVA GLM approach, the L16 design experiment is fixed for further interaction analysis. The results predicted by the depth to cut and feed rate were dominant and played a major role in deciding the tool wear, surface roughness, and MRR.

Examining amino acids as environmentally friendly corrosion inhibitors for Cu and Co chemical mechanical planarization

Aliphatic amino acids (AAs) were investigated as environmentally friendly alternatives to benzotriazole (BTA) in the chemical mechanical planarization (CMP) process for Cu interconnects. The study evaluated the corrosion resistance, galvanic corrosion, and polishing removal rates (RR) for Cu and Co in a silica-based slurry containing methionine, glutamic acid, and leucine. Corrosion characteristics were determined using linear sweep voltammetry, and the removal rate was assessed by polishing wafers under controlled CMP conditions. Metal surfaces were analyzed by X-ray photoelectron spectroscopy, and scanning electron microscopy. Results indicated that the distinctive functional groups in the amino acids influenced corrosion and polishing behaviors driven by different Cu species in the passivating film layer. Methionine with its sulfur-containing side chain, exhibited exceptional inhibition capabilities by stabilizing Cu(Ⅰ) species compared to Cu(Ⅱ), involving a combination of physisorption and chemisorption. It also effectively controlled Cu-Co galvanic corrosion with a low igc = 0.9 μA/cm². Leucine, with its branched hydrocarbon chain, mitigated Cu corrosion through physisorption (20.5 kJ/mol), but increased galvanic corrosion for Co (igc = 45 μA/cm²). Leucine formed a thin passive layer that easily broke down during the Cu(I) to Cu(II) transition. Glutamic acid, with its additional carboxylic acid group, was not effective as a corrosion inhibitor but showed a relatively low |∆Ecorr| = 5 mV. Metal removal rates of Cu and Co followed the same trend with corrosion results. The selectivity of Cu:Co:TEOS removal with methionine was more comparable than that achieved with other additives, beneficial for Cu barrier CMP.

Influence of Electrolyte Concentration on Metal Removal Rate and Surface Finish Quality in Electrochemical Machining Masking

Electrochemical machining (ECM) is a specialized and precise manufacturing technique involving selective metal removal to achieve the desired shape or form. This article’s primary focus is examining the technical facets associated with the procedure. The elements mentioned encompass the system’s design and optimization, the electrolyte solution’s careful selection, and the precise control of the etching parameters. When considering the overall framework, it is essential to consider important factors such as the concentration of electrolytes, the operational voltage, and the value of the current flowing through the system. The main objective of this study is to evaluate the influence of different concentrations of sodium chloride electrolyte on the metal removal rate (MRR). This will be achieved by utilizing a direct current power supply. The present investigation used aluminum, steel, and stainless steel materials as the substrate for experimentation. These materials were selected to have identical dimensions for the anode and cathode. The main objective of this study is to evaluate the influence of varying concentrations (0.5, 1, 1.5, and 2 mole/liter) of sodium chloride electrolyte on the material removal rate and surface roughness. The findings have been disclosed, revealing the utmost removal rate for aluminum, steel, and stainless-steel materials across all levels of electrolyte concentration. The experimental information is currently presented, related to the rates of metal removal at various electrolyte concentrations of 2 moles per liter. The rates of mass loss observed in aluminum are comparatively higher when compared to those surveyed in steel and stainless steel. The roughness of a machined surface is inversely proportional to the concentration of the electrolyte.

Heavy metals immobilization of LDH@biochar-containing cementitious materials: Effectiveness and mechanisms

The utilization of tailings for producing solid waste-based concrete can effectively mitigate the environmental consequences stemming from tailings accumulation. However, the presence of high concentrations of heavy metal ions in certain tailings can deleteriously affect the microstructure of the cement matrix. This study investigated the in-situ immobilization performance of Pb2+ and Mn2+ by calcium-aluminum layered double hydroxides (CaAl-LDH) and LDH@biochar blended in cement-based materials. The equilibrium adsorption capacity of CaAl-LDH/LDH@biochar for heavy metals in aqueous solution was assessed by adsorption kinetics, while the effect of pH value on the removal rate of heavy metals was also studied. The workability and mechanical properties of cement mortar are significantly improved with the addition of 4 % LDH@biochar. LDHs@biochar can effectively reduce the deteriorating effects of heavy metal ions on the fundamental properties of cement materials. Compared with CaAl-LDH, the leaching concentrations for Pb2+ and Mn2+ in LDH@biochar at 28 d is decreased by 59 % and 39 %, respectively. The stable adsorption of Pb2+ and Mn2+ by LDH@biochar is attributed to multiple mechanisms, including interlayer anion exchange effect, chemical adsorption of surface functional groups and electrostatic attraction. This study provide valuable insights for enhancing the efficiency of heavy metal immobilization in cement-based materials.

Effect of eco-friendly pervious concrete pavement with travertine waste and sand on the heavy metal removal and runoff reduction performance

To address the negative environmental and economic impact of the large amounts of solid waste generated during travertine mining and to reduce the dependence on natural aggregates and cement for pervious concrete pavement applications, travertine waste, as aggregate and powder, was used for the travertine powder pervious concrete (TPPC) to improve the utilization of solid waste and decrease CO2 emissions. The experimental results showed that using 25% travertine aggregate and 5% powder results in a compressive strength reduction of only 9.8% to 25.92 MPa but a significant improvement in water permeability of 57.1% from 3.89 to 6.11 mm/s. To improve the performance of TPPC, further research was done on the effect of sand addition rate (SAR) on TPPC's density, compressive strength, porosity, water permeability, freeze-thaw resistance and heavy metal removal capacity to obtain an optimal incorporation ratio. As SAR rises, the compressive strength of TPPC with sand (STPC) initially increases and then decreases, while permeability behaves inversely. At 3% SAR, the compressive strength reached a maximum of 26.51 MPa, primarily due to the sand added to fill in some of the pores and stabilize the gradation. After 25 cycles, the strength loss rate of STPC varies from 11.39 to 17.93% and the freeze-thaw resistance is most excellent when SAR is 3%. The removal rate of heavy metals using the immersion method was found to be significantly higher (83.4–100%) compared to the rapid method (11.7–28.1%). Therefore, the 3% SAR was recommended for the mixture design of STPC. A laboratory-scale version of the pavement was constructed to assess the efficacy of STPC pavement (STPCP) in reducing runoff and removing heavy metals. The results showed that STPCP could remove more than 94% of runoff with varying intensities after 1 h. The STPCP exhibited removal rates ranging from 42.0 to 99.4% for Cd2+ and 79.5–95.4% for Cu2+. STPCP also attained a removal rate above 98% for Pb2+ after 30 min, demonstrating its environmental friendliness.