Effect Of Heavy Metal Ions Research Articles

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.

Extraction and detection of mercury in electronic waste using efficient modified MOF

The harmful effects of heavy metal ions on human health and the ecosystem have made the detection of these ions in environmental samples increasingly important in recent years. There has been significant attention on the development of sensors that are selective and sensitive in detecting heavy metal ions. Due to their wide presence in the environment and high toxicity, the detection of Hg2+ ions is of great interest. MIL-101(Al)-N = 2NAPHT (2NAPHT = 3-hydroxy-2-naphthaldehyde, N = imine nitrogen) is a novel chemosensor that was solvothermally synthesized and characterized. A limit of detection of 5.48 ppb (2.73 ×10−8 M) was found for the chemosensor, which is highly selective and sensitive to Hg2+ ion detection. The fluorescence emission properties of MIL-101(Al)-NH2 were improved and more binding sites for analytes were introduced after functionalization with 2-hydroxy naphthaldehyde. The formation of the novel chemosensor was confirmed by using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), TEM, SEM, thermogravimetric analysis (TGA), and X-ray diffraction (XRD). Moreover, this chemosensor showcased a regenerative emission feature, retaining its detection ability for six successive cycles. The study revealed that the sorbent had a considerable Hg2+ capacity, amounting to 133.2 mg per gram of MIL-101(Al)-N = 2NAPHT chemosensor. The chemosensor MIL-101(Al)-N = 2NAPHT was also assessed for its capability to identify Hg2+ ions in electronic waste samples (silver oxide button cells). According to the results mentioned above, the chemosensor exhibited a high degree of sensitivity and selectivity towards Hg2+ ions. The MIL-101(Al)-N = 2NAPHT chemosensor is an effective and promising technology for the detection and removal of mercury from electronic waste, in conclusion.

Effects of Mn2+ and flow speed on blood and physiological indexes of larvae GIFT tilapia (Oreochromis niloticus)

To assess the toxicological effects of heavy metal ions on fish at different flowing speeds within aquatic environments, we investigated the impact of Mn2+ and flow speed on the physiological parameters of juvenile GIFT tilapia (95.2±4.3g,15.1±0.21cm). The experiment design included four different levels of Mn2+ concentration: control group (0mg/L), 0.1mg/L, 0.5mg/L and 1mg/L, as well as three different flow speeds: control group (0 body length/second), low speed (1 body length/second), and high-speed group (2 body lengths/second). The main research findings were as follows: Mn2+ had varying effects on the hematological parameters of juvenile GIFT tilapia. As the levels of Mn2+ increased, there was a remarkable reduction in both the red blood cell (RBC) number and hemoglobin content of the fish(P<0.05). The activity of SOD, CAT, the level of MDA in the liver and white blood cell (WBC) number exhibited an initial increase followed by a subsequent decrease, with the highest levels observed mostly in the 0.5mg/L group. However, With the prolongation of Mn2+ exposure duration, a significant decline in levels of RBC, hemoglobin, CAT and SOD was observed. In most cases, the highest values of those, as mentioned earlier four physiological parameters were recorded at 24 hours, while the lowest values were recorded at 96 hours when exposed to the same Mn2+ level. However, MDA levels reached their peak at 48 hours. These findings suggested that lower levels of Mn2+ might enhance the immune capacity of tilapia, while higher levels could impede its immune and antioxidant functions. An increase in flow speed led to a significant elevation in both the RBC number and hemoglobin content of the GIFT tilapia at 30d(P<0.05), but flow speed had no significant impact on the WBC of the fish(P>0.05). Its effect on the fish antioxidant parameters also showed a certain induction, and there were significant correlations between the activity of SOD, CAT, the level of MDA, and flow speed (P<0.05). At the same flow speed, the prolonging water-flow-stimulus duration could not increase the levels of three antioxidant parameters(P>0.05). These findings could provide fundamental data for investigating the influence of heavy metal stress on fish ecotoxicology in aquatic environments and the artificial running water breeding of GIFT tilapia in Hebei province, China.

Effect of heavy metal ions on rice protein fibrillation: Structure, morphology, and functionality

Heavy metal ions, the common contaminants in grain growing environment and food processing, pose an important effect on the aggregation behavior of food proteins. In this work, the effects of heavy metal ions Zn2+, Cd2+ and Cu2+ on rice protein (RP) fibrillation were investigated, and the relationship between fibril structures, morphology and functional properties was also discussed. Specifically, Zn2+ and Cd2+ not only facilitated the formation of rice protein fibrils (RPFs) by promoting the generation of β-sheet structures (57.3% and 54.4%, respectively), but also transformed the fibrils into long and straight rigid structures. Cu2+ led to more disordered structures (23.1%), inhibited RP fibrillation and induced branching/tangling structure. The result of the intrinsic fluorescence showed that Cu2+ could obviously decrease the fluorescence intensity of RPFs, indicating that the microenvironment of RP was changed by Cu2+. Correspondingly, Zn2+ and Cd2+ improved the solubility, emulsifying and foaming properties of RPFs, while Cu2+ enhanced the rheological properties.

Transcriptome Analysis Reveals the Inhibitory Effect of Cu2+ on Polyferric Sulfate Floc Reduction by Shewanella putrefaciens CN32.

Polyferric sulfate (PFS), an economical coagulant widely used for removing heavy metal contaminants from water, is susceptible to reduction and transformation by iron-reducing bacteria prevalent in sediments. However, the effect of heavy metal ions adsorbed in PFS flocs on this biological process remains unclear. According to our results, compared with other heavy metal cations (e.g., Cu2+, Cd2+, Zn2+, Ni2+, Pb2+, and Co2+), Cu2+ had a stronger inhibitory effect on PFS floc reduction by Shewanella putrefaciens CN32, a typical dissimilatory iron-reducing bacterium. The presence of Cu2+ remarkably influenced the global transcription of CN32, resulting in 782 upregulated genes and 713 downregulated genes that are mainly annotated in energy production, amino acid metabolism, protein biosynthesis, and oxidation‒reduction processes. The anaerobic TCA cycle for energy (electron) production was significantly activated in the presence of Cu2+, while the transcription of many genes related to the extracellular electron transfer pathway was downregulated, which is responsible for the decreased Fe3+ reduction. Moreover, the pathways of assimilatory sulfate reduction and subsequent cysteine biosynthesis were significantly enriched, which is hypothesized to result in the consumption of abundant energy produced from the enhanced anaerobic TCA cycle, revealing a strategy to address the oxidative stress caused by Cu2+. This work elucidates the unusual suppressive effects of Cu2+ on the microbial reduction of PFS flocs, which reveals the high resistance of PFS flocs to microbial destruction when used to treat Cu2+ pollution in water, thus demonstrating their tremendous practical prospects.

To explore the remediation mechanism and effect of biochar and KH2PO4 on soils contaminated with heavy metal ions Hg2+, Cd2+ and Pb2+

In this study, wheat straw-derived biochar was prepared by setting a temperature of 400 °C under an oxygen-limited environment using the technique of “programmed temperature increase control”. The results showed that the biochar had a strong adsorption capacity for Hg2+, Cd2+ and Pb2+ ions, and the adsorption pattern was Hg2+>Cd2+>Pb2+. There was a competitive adsorption effect during the coexistence of the ions. The results of the soil remediation tests showed that the effects of biochar on soil physicochemical properties and heavy metal distribution was generally greater than those of KH2PO4 in single or combined contaminated soil. The adsorption effect of heavy metal ions in soil was the best in the case of mixed additions. The results can provide a scientific basis for the treatment of heavy metal contaminated soil with wheat straw biochar in the future.

Simultaneous removal of bisphenol A and Cr(Ⅵ) by Pd–TiO2: Significantly improve the photocatalytic activity through synergistic effect

The synergistic effect of heavy metal ions and organic pollutants can enhance the photocatalytic performance and provides a new idea for environmental governance, so it has important research value. In this work, we prepared Pd–TiO2 composites by ascorbic acid reduction method, and obtained the crystal structure, morphology and surface state information of the composites through a series of characterizations, which verified the successful preparation of the composites. It was used for simultaneous photocatalytic removal of bisphenol A (BPA) and Cr(Ⅵ), and it was found that the photocatalytic removal efficiency was significantly improved compared to their individual removal. This can be attributed to the synergistic effect between BPA and Cr(Ⅵ), where they enhance the separation efficiency of photogenerated electron-hole pairs and prolong the lifetime of photogenerated carriers. In addition, the effects of BPA concentration and Cr(Ⅵ) concentration on photocatalytic removal efficiency were also investigated. The mechanism of photocatalytic degradation of BPA by Cr(Ⅵ) coupling system was discussed by changing the experimental conditions, it is proved that the photocatalytic products of BPA can improve the removal efficiency of Cr(Ⅵ).

Purification and characterisation of glutathione reductase from scorpionfish (scorpaena porcus) and investigation of heavy metal ions inhibition

In the current study, glutathione reductase was purified from Scorpion fish (Scorpaena porcus) liver tissue and the effects of heavy metal ions on the enzyme activity were determined. The purification process consisted of three stages; preparation of the homogenate, ammonium sulphate precipitation and affinity chromatography purification. At the end of these steps, the enzyme was purified 25.9-fold with a specific activity of 10.479 EU/mg and a yield of 28.3%. The optimum pH was found to be 6.5, optimum substrate concentration was 2 mM NADPH and optimum buffer was 300 mM KH2PO4. After purification, inhibition effects of Mn+2, Cd+2, Ni+2, and Cr3+, as heavy metal ions were investigated. IC50 values of the heavy metals were calculated as 2.4 µM, 30 µM, 135 µM and 206 µM, respectively.

Structural and Biochemical Characterization of Silver/Copper Binding by Dendrorhynchus zhejiangensis Ferritin.

Ferritin with a highly symmetrical cage-like structure is not only key in the reversible storage of iron in efficient ferroxidase activity; it also provides unique coordination environments for the conjugation of heavy metal ions other than those associated with iron. However, research regarding the effect of these bound heavy metal ions on ferritin is scarce. In the present study, we prepared a marine invertebrate ferritin from Dendrorhynchus zhejiangensis (DzFer) and found that it could withstand extreme pH fluctuation. We then demonstrated its capacity to interact with Ag+ or Cu2+ ions using various biochemical and spectroscopic methods and X-ray crystallography. Structural and biochemical analyses revealed that both Ag+ and Cu2+ were able to bind to the DzFer cage via metal-coordination bonds and that their binding sites were mainly located inside the three-fold channel of DzFer. Furthermore, Ag+ was shown to have a higher selectivity for sulfur-containing amino acid residues and appeared to bind preferentially at the ferroxidase site of DzFer as compared with Cu2+. Thus, it is far more likely to inhibit the ferroxidase activity of DzFer. The results provide new insights into the effect of heavy metal ions on the iron-binding capacity of a marine invertebrate ferritin.

Amyloid-like aggregation influenced by lead(II) and cadmium(II) ions in hen egg white ovalbumin

The aggregation of proteins into fibrillar, amyloid-like aggregates generally results in an improved, positive effect on various techno-functional properties within food products, such as gelation, emulsification, and foam stabilization. These highly stable structures, characterized by their repetitive, β-sheet rich motifs, may develop as the result of the thermal treatment of protein-rich food products. Heavy metal ions can influence amyloid-like aggregation of food proteins. Lead(II) and cadmium(II) represent some of the most abundant and common environmental water and food pollutants.In this work, the influence of heavy metal ions, lead and cadmium on amyloid-like aggregation of ovalbumin at high temperatures (90 °C) and under acidic conditions (pH 2.0) was investigated. Ovalbumin is used as a general model for how heavy metals can affect amyloid-like aggregation of a food protein. Structural changes were monitored via Thioflavin T and 8-Anilino-1-naphthalenesulfonic acid fluorescence, Fourier-Transform infrared spectroscopy, atomic force microscopy, dynamic light scattering, as well as computational analyses. The obtained results indicate that the added heavy metal ions bind to different sites within ovalbumin prior to thermal treatment. Lead binding sites are closer to the hydrophobic regions of an protein, while cadmium ion binding sites are more exposed. This specific binding of metal ions affects the morphologies of amyloid-like aggregates, resulting in lead-induced branching of amyloid-like fibrils, or cadmium-induced tangling of fibrils into dense amyloid clusters. This additive effect of heavy metal ions is most evident in ovalbumin samples which contain a mixture of both heavy metal ions.

The Use of Diethoxydimethylsilane as the Basis of a Hybrid Organosilicon Material for the Production of Biosensitive Membranes for Sensory Devices.

Biomembranes based on an organosilica sol–gel matrix were used to immobilize bacteria Paracoccus yeei VKM B-3302 as part of a biochemical oxygen demand (BOD) biosensor. Diethoxydimethylsilane (DEDMS) and tetraethoxysilane (TEOS) were used as precursors to create the matrix in a 1:1 volume ratio. The use of scanning electron microscopy (SEM) and the low-temperature nitrogen adsorption method (BET) showed that the sol–gel matrix forms a capsule around microorganisms that does not prevent the exchange of substrates and waste products of bacteria to the cells. The use of DEDMS as part of the matrix made it possible to increase the sensitivity coefficient of the biosensor for determining BOD by two orders of magnitude compared to a biosensor based on methyltriethoxysilane (MTES). Additionally, the long-term stability of the bioreceptor increased to 68 days. The use of such a matrix neutralized the effect of heavy metal ions on the microorganisms’ catalytic activity in the biosensor. The developed biosensor was used to analyze water samples from water sources in the Tula region (Russia).

Adsorption Study of Continuous Heavy Metal Ions (Pb2+, Cd2+, Ni2+) Removal Using Cocoa (Theobroma cacao L.) Pod Husks.

The serious toxicological effects of heavy metal ions in aquatic ecosystems have motivated the search for alternatives to reduce contamination of water sources from industrial wastewater. In this work, continuous adsorption of nickel, cadmium, and lead was assessed using a packed bed column filled with Cocoa (Theobroma cacao L.) pod husks widely available in the northern region of Colombia. The physicochemical characterization of the agricultural biomass was performed to quantify its chemical composition by bromatological, FT-IR, and energy-dispersive X-ray spectroscopy (EDS). The breakthrough curves were constructed for all heavy metal ions with bed depth of 4 and 7.5 cm, taking aliquots at 10, 30, 60, 90, 120, 150, 180, 210, 240, and 270 min. Moreover, experimental data were fitted to adsorption models in continuous mode to predict adsorptive performance (Adams–Bohart, Thomas, and Yoon–Nelson). For the FT-IR analysis of biomass before and after adsorption, the most representative bands occur around 3200–3900 cm−1 attributed to the presence of hydroxyl groups, showing the destruction of the peaks of lignocellulosic materials. The breakthrough curves revealed that for a 7.5 cm bed, adsorption performance reported the following order of promising results: Pb2+ > Ni2+ > Cd2+; while for a 4 cm bed, Pb2+ > Ni2+. The mechanism of adsorption of the evaluated metals onto cocoa pod husk was attributed to cationic exchange and microprecipitation due to the presence of Ca, K, and Si in the structure of the bio-adsorbent. Finally, the continuous adsorption was modeled under the mathematical expressions of Adams–Bohart, Thomas, and Yoon–Nelson reporting good fitting with correlation coefficient above 0.95.

A facile synthesis of ibandronate modified hydroxyapatite renewable nanomaterials for simultaneous removal of Cu2+/Pb2+ and chlortetracycline: Experimental design and adsorption mechanism study

A simple co-precipitation method was used to synthesize ibandronate nano-functionalized hydroxyapatite (IB-HAP) and used for the removal of Pb2+/Cu2+ and chlortetracycline. The effects of the amount of modifier IB added, the initial concentration and the pH value of the solution on the adsorption effect of heavy metal ions were investigated. When the P atom in IB accounts for 5% of the total phosphorus, the adsorption capacity of IB-HAP was 1565.3 mg/g (Pb2+) and 246.71 mg/g (Cu2+), respectively. By adding heavy metal ions and chlortetracycline (CTC) in different addition sequences, the co-adsorption effect of various pollutants on IB-HAP was studied. According to microstructure analysis and simulation, the adsorption mechanism was studied from a microscopic point of view. It is the first time that modifiers and pollutants were used as central molecules to study the interaction sites and interaction strengths with surrounding molecules in a wholly covered state by Hirshfeld surface analysis. Finally, the desorption experiments showed that IB-HAP had strong regeneration and sustainability. These results showed that IB-HAP was a potential adsorbent, and this study also provided new guidelines and valuable methods for analyzing the mechanism of co-adsorption of heavy metal ions and antibiotics.

Development of Steel Slag-Based Solidification/Stabilization Materials for High Moisture Content Soil

To solve the problems of high moisture content, high viscosity, and poor engineering mechanical properties of soil, this paper using with steel slag (SS) and desulfurization ash (DS) as initial raw materials, realizing the cooperative treatment of solid waste and solidification of silt soil. The synergistic utilization of SS and DS can reduce the production cost of curing agent and promote its own consumption. According to blended cement of various SS contents and inspected compressive strength performances, the most suitable raw materials ratio was selected. The best formula for this curing agent is cement:steel slag = 3:7 with 5% DS, and its 28-day compressive strength can reach 30 MPa. The experiment shows that the effect of DS and Na2SO4 reagent with the same quality on early compressive strength improvement of cement and SS system is not much different. In this study, the mineral composition and microstructure of different gel system blocks were characterized by XRD, SEM and EDX, and a large number of webbed structures were found in the SEM test, which was not seen in previous studies. Besides, unconfined compressive strength (UCS), water resistance, and toxic characteristic leaching procedure (TCLP) were used to evaluate silt solidified soil properties. The results demonstrated that the solidified silt could meet not only the standard of general subgrade; but also has a partial stabilization effect of heavy metal ions.

A New Method for Exonuclease Activity Analysis of Apurinic/Apyrimidinic Endonuclease 1 and Application in Heavy-polluted Ramie

Apurinic/apyrimidinic endonuclease 1 (APE1) exonuclease plays a vital proofreading role in the base excision repair pathway by removing 3’end group, including oxidatively damaged DNA bases, chain terminating nucleotide analog drugs, terminal blocking groups and mismatched bases. Herein, a simple and real time fluorometric method was developed for detecting APE1 exonuclease activity using molecular beacon as substrate. Experimental results demonstrated that the detection limit of this method was 0.01 U/μL for APE1, and the K m value was (0.27 ± 0.10) μmol/L. Moreover, the method was used to screen antibiotics and the results showed that streptomycin sulfate and gentamycin sulfate had a significant inhibitory effect on APE1 exonuclease activity in a concentration-dependent manner. Meanwhile, the assay was used for investigating the inhibitory effects of heavy metal ions on APE1 exonuclease activity. Finally, the method was further used to monitor the effect of heavy metal ions treatment of the APE1 exonuclease activity of ramie, and the results indicated that APE1 exonuclease activity was inhibited in a concentration-dependent manner after treatment with Pb 2+ and Cd 2+ , which was consistent with heavy metal ions assay in vitro . In summary, this method provided an alternative tool for the biochemical analysis for APE1 exonuclease activity, which was hopeful for the assessment for heavy metal ions adsorption according to the enzymatic activity change in phytoremediation. A convenient and sensitive real-time fluorometric method was proposed for APE1 exonuclease activity detection. This method performed well when it was applied for monitoring the effect of Pb 2+ and Cd 2+ treatment on APE1 exonuclease activity of ramie plant. This study provides an alternative tool for the biochemical analysis for APE1 exonuclease activity, which is hopeful for the assessment for heavy metals adsorption according to the enzymatic activity change in phytoremediation.

Immobilization of nickel ions by the confinement of surface aluminate spinel at low temperature

The accumulation of heavy metal on catalysts during petrochemical process produces deactivated catalysts that cannot be directly disposed in nature, due to the high toxicity. The elimination of the detrimental effect of heavy metal ions can be achieved by immobilizing these ions in the form of spinel structure, yet this requires high-temperature calcination. Herein, Ni2+ ions are stabilized and confined within the surface NiAl2O4 on Al2O3 through hydrothermal process and subsequent low-temperature thermal treatment. The formation of nickel aluminum layered double hydroxide (NiAl-LDH) as intermediate favors the generation of surface aluminate spinel at the temperature as low as 450 ​°C. The formation of surface spinel is beneficial to restricting the mobility of Ni2+ ions. The growth and immobilization mechanisms of the surface spinel structure were proposed, which contributes to alternative and promising route for the low-temperature approach of the retention of the heavy metal ions mobility.

A Review on Current Development of Animal Bone-Based Sorbent for Heavy Metals Removal from Contaminated Water and Wastewater

This review article presents the usage of various animal bones such as chicken bone, fish bone, pig bone, camel bone, and cow bone as reliable biosorbent materials to remove heavy metals contained in contaminated water and wastewater. The sources and toxicity effects of heavy metal ions are also discussed properly. Then specific insights related to adsorption process and its influential factors along with the proven potentiality of selected biosorbents especially derived from animal bone are also explained. As the biosorbents are rich in particular organic and inorganic compounds and functional groups in nature, they play an important role in heavy metal removal from contaminated solutions. Overall, after conducting study reports on the literature, a brief conclusion can be drawn that animal bone waste has satisfactory efficacy as effective, efficient, and environmentally friendly sorbent material.

Quantum Dots Based Fluorescent Probe for the Selective Detection of Heavy Metal Ions.

Heavy metal ions are one of the primary causes of environmental pollution. A marshal effect of heavy metal ions is a paramount ultimatum to humans, aquatic animals and other organisms present in nature. Multitude arrays of materials have been proclaimed for sensing of heavy metal ions and also many methodologies are applied for heavy metal ion sensing. Due to their toxicity and non-biodegradability, it is required to be perceived immediately prior to its manifestation of harmful effects. Quantum Dots (QDs) are zero-dimensional nanomaterial particles and owing to their distinctive optical and electronic properties, they are utilized as nanosensors. QDs have enriched fluorescence properties which includes broad excitation spectrum, narrow emission spectrum and photostability. QDs offer eclectic and sensitive detection of heavy metal ions due to presence of discrete capping agents and different functional groups present on the surface of the QDs. These capping layers and functional groups attune the sensing capability of the QDs, which leverages the interactions of QDs with various analytes by different mechanisms. This review, comprising of papers from 2011 to 2020,focuses on heavy metal ions sensing potential of various quantum dots and its applicability as a nanosensor for on field heavy metal ions detection in water. Quantum Dots (QDs) based Heavy Metal Detection.

PRODUCTION OF Candida BIOMASSES FOR HEAVY METAL REMOVAL FROM WASTEWATERS

Yeasts can accumulate heavy metals and grow in acidic media. In the present study, it was shown that Candida yeasts in an aqueous solution accumulate single Cu(II) and Ni(II) cations. The effect of heavy metal ions on the specific growth rate of biomasses and the uptake of metal ions during the growth phase was investigated in a batch system. Bioaccumulation efficiency decreased with increasing metal ion concentrations at constant sucrose concentrations. Both the specific growth rate and the biomass concentration were more inhibited in the bioaccumulation media containing Ni(II) ions singly as compared with the bioaccumulation media containing Cu(II) ions singly. The maximum specific growth rate and the saturation constant of yeasts were examined with a double-reciprocal form of Monod equation. Metal uptake performance decreased from 81.68% to 46.28% with increasing Ni(II) concentration from 25 mg/L to 250 mg/L for Candida lipolytica. Candida biomasses may be an alternative way of removal of heavy metals from wastewaters and may constitute a sample to produce new biomass. The study showed that Candida yeasts can be used as economical biomass due to their metal resistance and efficient production.

Laboratory study of strength, leaching, and electrical resistivity characteristics of heavy-metal contaminated soil

In this work, geotechnical properties of heavy-metal contaminated soil consist of basic properties, strength, leaching, electrical resistivity and microstructural characteristics were investigated. The results showed that the clay content, specific surface area and cation exchange capacity of the soil decreased as heavy-metal concentrations increased. The decrease in basic properties was more significant in Zn-contaminated soil than that in Pb-contaminated soil. The unconfined compressive strength (UCS) decreased as heavy-metal concentrations increased. The effect of Zn2+ on UCS was confirmed to be greater than that of Pb2+. The leached heavy-metal concentration increased with higher initial heavy-metal concentrations. A greater leaching capacity was observed in Zn-contaminated soil compared to Pb-contaminated soil. With increasing pore fluid resistivity, UCS values gradually increased and leached ion concentrations dramatically decreased before becoming stable. Zn-contaminated soil was found to have a lower strength and higher leached-ion concentration than Pb-contaminated soil. A set of equations was proposed to successfully predict the engineering properties of contaminated soil using pore fluid resistivity. Microstructural analysis presented that, as heavy-metal concentrations increased, clay particles aggregated, the flocculation structure and the inter-aggregate pores became enlarged. Zn-contaminated soil had larger aggregate and inter-aggregate pores, compared to Pb-contaminated soil. In general, significant effects of heavy metal ions on geotechnical properties of the contaminated soil have been revealed and analyzed in the present work, which could be predicted using the pore fluid resistivity in a more effective way.