Concentrations Of Heavy Metal Ions Research Articles

A biomimetic porous fibre bundle adsorbent for the rapid and complete removal of multiple low-level heavy metal ions

Improving diffusion and mass transfer kinetics to enhance the synchronous removal efficiency of adsorbents for low concentrations of various heavy metal ions is of great significance for reducing heavy metal removal. Here, a biomimetic porous fibre bundle adsorbent with multiple adsorption sites was constructed by embedding and bonding porous coconut shell biochar on amino and sulfhydryl group-functionalized cellulose nanofibre bundles in the process of fibrogenesis, which was inspired by the principle of spider silk. The high porosity, specific surface area (212.17 m2/g) and swelling rate (184 %) of the porous fibre bundle could effectively improve the diffusion and mass transfer kinetics. Multiple adsorption sites of amino, carboxyl, and sulfhydryl groups endow the adsorbent with a synchronous removal rate for various heavy metal ions in water. Therefore, the porous fibre bundle could remove low concentrations of Pb(II), Cu(II), Cd(II) and Cr(VI) to safe drinking water level standard concentrations (US EPA) within 20 min. This study provided a simple method for designing an effective adsorbent for lowering heavy metal removal.

Comparative Study on the Adsorption Characteristics of Heavy Metal Ions by Activated Carbon and Selected Natural Adsorbents

In this study, adsorption of the heavy metal ions (Pb(II), Cu(II) and Cd(II)) from water by peanut shells (PS), sawdust (S) and commercial activated carbon (AC) were comparatively studied. Thus, the relationship between different adsorption parameters and different heavy metal ion removal rates was investigated. The adsorption capacity of the three adsorbents for heavy metal ions increased with an increase in temperature, pH value, contact time, adsorbent dosage, and heavy metal ion concentration, however, it decreased with an increase of adsorbent particle size. All the adsorption processes are better described by Langmuir isotherm or Freundlich isotherm. Thus, the results show good agreement with pseudo-second-order kinetics and the adsorption processes are spontaneous heat absorption processes. Herein, all adsorbents have higher affinity for Pb(II) ions, and hence possess higher removal rates. In addition, heavy metal ions were desorbed significantly at acidic conditions in the desorption experiments. The results demonstrate that PS can be used as a green adsorbent instead of AC for the adsorption of heavy metal ions from the water.

Effect of antibiotic exposure on the characteristics of activated sludge in a landfill leachate biological treatment system

ABSTRACT Changes in the activated sludge performance in an anaerobic/aerobic biological treatment system for leachate was discussed under the condition of tetracycline (TC) exposure. The results show that a low concentration of TC did not have an obvious effect on the removal of chemical oxygen demand (COD) while a high concentration of TC had a certain promoting effect. Under the stimulation of TC, the particle size distribution of anaerobic/aerobic sludge tended to be more uniform, the particle size of anaerobic sludge decreased while the settleability increased; however, the particle size of aerobic sludge increased due to bulking. With the addition of TC, the concentration of most heavy metal ions in sludge samples increased.TC exposure results in the release of a large amount of extracellular polymeric substances (EPS), thus leading to a smoother surface of anaerobic sludge and a rougher surface of aerobic sludge. The high removal efficiency of COD under the high concentration of TC was also presumed to be due to EPS promoting the microbial absorption of anaerobic substances in the leachate. The results clearly showed that TC had a bacteriostatic effect. After antibiotic exposure, the abundance and diversity index of bacteria in each reactor decreased obviously, the microbial community evolved, and the dominant species at the genus and phylum levels of anaerobic/aerobic reactors changed. This study provides a better understanding the effect of TC on activated sludge and has reference value for the management of antibiotic exposure in leachate treatment facilities.

Durability of fly-ash geopolymer binder in deep-mixed expansive soils

This study investigates the durability and leachate behaviour of an alkali-activated fly ash (FA) as a binder to stabilise expansive soils in deep-mixing applications. To activate FA, a liquid alkali activator (LAA) to binder ratio (LAA–FA) was introduced and varied from 1.0 to 1.5. The effects on swelling–shrinkage, consolidation and unconfined compressive strength (UCS) characteristics under wetting–drying cycles (durability) were studied on deep-mixed expansive soils. Leachate studies were conducted to determine the environmental impact of alkali-activated FA. Heavy metal and sodium ion concentrations were measured in each leachate cycle. To examine the permanent microstructural and phase changes in the mixes, scanning electron microscopy (SEM) and x-ray diffraction (XRD) studies were conducted. The swelling–shrinkage behaviour of soil could be marginally controlled for LAA/FA = 1.0 and 1.25 due to heavy weight loss during the wetting–drying cycles. However, even after 12 durability cycles, the UCS of soil with LAA/FA = 1.5 retained 1.0 MPa and showed non-critical swelling–shrinkage behaviour. The heavy metals and sodium ion concentrations were in acceptable range for LAA/FA = 1.25 and 1.5. XRD and SEM studies revealed that soil treated with a binder ratio of LAA/FA = 1.5, showed high crystalline peaks and aggregated structures.

Bioaccumulation of Heavy Metals by Suaeda salsa in the Tidal Flat of the Liaohe Estuary

In order to explore the bioaccumulation of heavy metals by Suaeda salsa and its ecological restoration capacity in the tidal flat of the Liaohe estuary, the absorption and reduction effect of Suaeda salsa on heavy metals was determined via a combination of on-site monitoring and experimental tests. The results showed that, under a high-salt environment, Suaeda salsa had a decreasing effect on heavy metals zinc, copper and lead, and the bioaccumulation coefficient BCFSs–Zn > BCFSs–Cu > BCFSs–Pb. When the concentration of heavy metal ions was high, Suaeda salsa could still survive, but the absorptivity was low, reducing its ability to repair heavy metal pollution. By correlating the research data with the population density of Suaeda salsa, the total removal of heavy metals was obtained, about 2008.6 kg Zn2+, 347.5 kg Cu2+, 376.1 kg Pb2+. This paper could provide a theoretical basis and technical support for the promotion and application of ecological restoration via Suaeda salsa.

Chitosan—the miracle biomaterial as detection and diminishing mediating agent for heavy metal ions: A mini review

Proliferation of heavy metal ions as aquatic pollutants has been a matter of growing concern now a days. Several anthropogenic activities have fueled higher concentration of heavy metal ions in aquatic bodies above threshold values, as set by World Health Organization. Of late, chitosan for its exquisite properties has been widely used in tackling this burning problem of aquatic pollution caused by heavy metal ions. Accordingly, this mini review appraises the detection as well as diminution activities where chitosan plays the major contributing part. Starting from the intrinsic properties of chitosan, the detection strategy via chitosan composites is comprehensively delineated. Likewise, the removal activities via chitosan mediating agents are also overviewed, followed by future recommendations. It is believed that this mini review will give researchers a brief appraisal of two prominent activities related to controlling of heavy metal ion pollution.

A graphene-based porous composite hydrogel for efficient heavy metal ions removal from wastewater

A graphene-enhanced supramolecular hydrogel containing poly(acrylic acid)(PAA) and poly(4-vinylpyridine) (P4VP) was fabricated for the wastewater remediation. In this work, P4VP brushes were grown from functionalized graphene oxide (GO) through surface-initiated atom transfer radical polymerization. Then, the P4VP-grafted GO (i.e., GO-g-P4VP) was integrated into PAA matrix to form GO-g-P4VP@PAA hydrogel as a highly efficient adsorbent for extraction of toxic metal ions from wastewater. Due to the introduction of GO-g-P4VP, the GO-g-P4VP@PAA composite hydrogel exhibited good compressive strength, and a special interconnected 3D porous network was formed in the hydrogel. The effect of pH, initial heavy metal ion concentration, contact time, and adsorbent dosage regarding the adsorption capacity and removal efficiency of Pb2+ and Cd2+ on the hydrogel was examined. Under appropriate conditions, the GO-g-P4VP@PAA hydrogel can achieve maximum adsorption capacities of 257.28 mg/g for Pb2+, 175.79 mg/g for Cd2+. The adsorption kinetics of Pb2+ and Cd2+ on the GO-g-P4VP@PAA hydrogel followed a pseudo-second order model and the adsorption isotherms were more consistent with the Langmuir isotherm model. In addition, the GO-g-P4VP@PAA hydrogel exhibited good reusability. After five cycles, the removal efficiency of both Pb2+ and Cd2+ still remained above 80 %. These results demonstrate the GO-g-P4VP@PAA hydrogel serves as a desirable adsorbent in removal of heavy metal cations from wastewater.

Effect of Different Activators on Properties of Slag-Gold Tailings-Red Mud Ternary Composite

Red mud is a kind of solid waste produced in the process of aluminum extraction. Traditional methods of red mud treatment, such as open-pit accumulation and chemical recovery, are costly and environmentally hazardous. Gold tailings are industrial by-products produced in the process of gold mining and refining. In this study, NaOH, KOH, and Na2SiO3 were used as activators, and their effects on the properties of ternary cementitious composite containing blast furnace’s slag, gold tailings, and red mud were studied with the intention of preparing a new cementitious material that is an efficient recovery and utilization of solid waste. The macroscopic mechanical properties and hydration of the ternary cementation material were studied by means of compressive strength, XRD, FT-IR, and TG/DTG. The compressive strength testing showed that the maximum strength at 28 d was 43.5 MPa. The hydration products in the ternary cementitious system were studied by SEM and EDS, and it has been demonstrated that the strength of this cement was due to the formation of Aft (AFt, also known as Ettringite, has the chemical formula 3CaO·Al2O3·3CaSO4·32H2O. It is one of the important hydration products of cement-based cementitious materials, which can not only provide early strength for cement, but also compensate for early shrinkage of concrete.) and C-A-S-H gels. Samples activated by Na2SiO3 presented a most compact microstructure and the best macroscopic mechanical properties than the samples free of activator. The toxicity tests results showed that the content of heavy metal ions liberated by the cement’s leaching met the standard requirements, proving that the slag-gold tailings-red mud ternary composite was environmentally friendly.

Differential Response of Phaeodactylum tricornutum and Cylindrotheca fusiformis to High Concentrations of Cu2+ and Zn2+

Diatoms can be used as biosensors to assess aquatic environment quality, because they are widely distributed in almost all aquatic environments and show varied sensitivities toward heavy metal ions. The marine planktonic diatoms Phaeodactylum tricornutum (P. tricornutum) and Cylindrotheca fusiformis (C. fusiformis) are typical representatives of planktonic diatoms and benthic diatoms, respectively. C. fusiformis is very sensitive to changes in the concentration of heavy metal ions, and can be used as an indicator of the quality of the sedimental environment, while P. tricornutum can tolerate higher concentrations of heavy metal ions. To explore the potential difference in responses to heavy metal ions between planktonic and benthic diatoms, we compared the transcriptome of P. tricornutum and C. fusiformis under Cu2+ and Zn2+ treatment. The results indicated that P. tricornutum has several genes involved in ion transmembrane transport and ion homeostasis, which are significantly downregulated under Cu2+ and Zn2+ treatment. However, this enrichment of ion transmembrane transport- and ion homeostasis-related genes was not observed in C. fusiformis under Cu2+ and Zn2+ treatment. Additionally, genes related to heavy metal ion stress response such as peroxiredoxin, peroxidase, catalase, glutathione metabolism, phytochelatin, oxidative stress and disulfide reductase, were upregulated in P. tricornutum under Cu2+ and Zn2+ treatment, whereas most of them were downregulated in C. fusiformis under Cu2+ and Zn2+ treatment. This difference in gene expression may be responsible for the difference in sensitivity to heavy metals between P. tricornutum and C. fusiformis.

Analysis of the Mechanism of Acid Mine Drainage Neutralization Using Fly Ash as an Alternative Material: A Case Study of the Extremely Acidic Lake Robule in Eastern Serbia

Acid mine drainage (AMD) is a waste from mining sites, usually acidic, with high concentrations of sulfates and heavy metal ions. This study investigates the AMD neutralization process using fly ash (FA) as an alternative material. Samples of FA from coal-fired power plants in Serbia (“Nikola Tesla” (EF) and “Kostolac” (KOST)) were analyzed and used. The results were compared with the treatment efficiency of commercial neutralization agent (NaOH). The alkaline nature of FA was the basis for use in the treatment process of the extremely acid Lake Robule (pH 2.46), located in the mining areas of eastern Serbia. The optimal S/L ratio for the AMD neutralization process determined for EF was 25 wt.%, and for KOST it was 20 wt.%. The mechanism of the neutralization process was analyzed using the ANC test and PHREEQC program. The element concentrations and pH values in solutions indicated that FA samples could neutralize Lake Robule with more than 99% of Al, Fe, Cu, Zn, and more than 89% of Pb precipitated. Formation of insoluble (oxy)hydroxide forms (Fe3+ and Al3+ ions) creates favorable conditions for co-precipitation of other trace metals (Cu, Zn, Ni, Pb, and Cd) from AMD, which is further enhanced by cation adsorption on FA particles. FA proved to be a more effective neutralization agent than NaOH due to its adsorption effect, while among the FA samples, KOST was more effective due to the aging process through the carbonization reaction. Using FA as an alternative material is a promising and sustainable method for treating AMD, with economic and environmental benefits.

Effects of heavy metal ions Cu2+/Pb2+/Zn2+ on kinetic rate constants of struvite crystallization

Struvite (MAP) crystallization technology is widely used to treat ammonia nitrogen in waste effluents of its simple operation and good removal efficiency. However, the presence of heavy metal ions in the waste effluents causes problems such as slow crystallization rate and small crystal size, limiting the recovery rate and economic value of the MAP. The present study was conducted to investigate the effects of concentrations of three heavy metal ions (Cu2+, Zn2+, and Pb2+) on the crystal morphology, crystal size, average growth rate, and crystallization kinetics of MAP. A relationship was established between the kinetic rate constant Kt calculated by the chemical gradient model and the concentrations of heavy metal ions. The results showed that low concentrations of heavy metal ions in the solution created pits on the MAP surface, and high level of heavy metal ions generated flocs on the MAP surface, which were composed of metal hydroxides, thus inhibiting crystal growth. The crystal size, average growth rate, MAP crystallization rate, and kinetic rate constant Kt decreased with the increase in heavy metal ion concentration. Moreover, the Kt demonstrated a linear relationship with the heavy metal concentration ln(C/C*), which provided a reference for the optimization of the MAP crystallization process in the presence of heavy metal ions.

A novel route for sensing heavy metal ions in aqueous solution

Heavy metal ions are some of the major aquatic pollutants which are held responsible for many ailments as well as undesired effects on flora and fauna. The World Health Organization has prescribed some permissible levels for each of the heavy metal ions. The presence of ions above permissible limits results in toxicity in the aquatic bodies as well as for other water-dependent living organisms. Therefore, it is necessary to make monitoring schemes to keep a check on the concentration of heavy metal ions. Considering this, here we report a unique route to detect heavy metal ions. Through chemical exfoliation, tungsten disulphide (WS2) nanosheets were prepared and drop casted on finger-like Cu electrodes to build the sensing unit. When the sensing unit was treated with heavy metal ions like Cu2+, Co2+, Pb2+, Hg2+, Sn2+ ions, rise in the current across the unit was observed. The concentrations of all the heavy metal ions were the same, i.e., 1 ppm. The maximum current gain was calculated for Cu2+ ions. It was found that the current gain for different ions is different in the voltage range 4–6 V and remains constant except for Cu2+ and Co2+ ions. It is believed that this novel route will pave the way for rapid and simultaneous sensing of different pervasive heavy metal ions in aqueous solutions.

Ecological Monitoring of the Content of Heavy Metal Ions in the Aquatic Environment

Ecological Monitoring of the Content of Heavy Metal Ions in the Aquatic Environment

Recycled PET/metal oxides nanocomposite membrane for treatment of real industrial effluents: Membrane fabrication, stability, antifouling behavior, and process modeling and optimization

An environmentally friendly nanofiltration membrane from recycled PET (Polyethylene terephthalate) was fabricated for rejection of Pb (II) and Cr (VI) from synthetic and real industrial effluents. Various ZnO/y-FeOOH NPs concentrations from 0.5 to 1 wt% were investigated as a hydrophilic agent. The membranes were characterized by FE-SEM, XRD, WCA, AFM, and FTIR analysis. Membrane stability in acid/alkaline/boiling water was also studied. The Box–Behnken design (BBD) was used for the optimization of the metals rejection. The influence of the pH, transmembrane pressure (TMP), and heavy metal ion concentrations on the rejection were investigated. The optimal conditions were achieved as; 3.59, 0.5 bar, and 11 mg/L for Pb (II) and 3.9, 0.5 bar, and 10 mg/L for Cr (VI) rejection. The pure water flux (PWF) was 169.39 kg/m2·h, and the rejection rate of Pb (II) and Cr (VI) were 94.7 %, and 63.4 %, respectively. The antifouling behavior of the membranes was also studied by the filtration of milk solution. The rPET/ZnO/y-FeOOH membrane with 0.5 wt% of NPs had a high antifouling capability (FRR 96.2 %, Rr 90.21 %, and Rir 3.001 %). This study confirmed that the fabricated rPET/ZnO/y-FeOOH membrane is a promising filter for the removal of heavy metals from industrial effluents.

Effects of Heavy Metal Ions on Microbial Reductive Dechlorination of 1, 2-Dichloroethane and Tetrachloroethene

Microbial reductive dechlorination has been considered an effective process for the clean-up of organohalide-contaminated sites. Heavy metal ions are commonly present as co-contaminants in various organohalide-contaminated sites. To understand the impacts of heavy metal ions on the environmental fate of organohalides, we investigated the effects of Zn2+, Cu2+ and Cd2+ on reductive dechlorination of tetrachloroethene (PCE) and 1,2-dichloroethane (1,2-DCA) in sediment microcosms and transferred enrichment cultures. PCE and 1,2-DCA-dechlorinating enrichment cultures could be consecutively transferred in the presence of up to 10 mg/L Cu2+ or 10 mg/L Zn2+; by comparison, up to 50 mg/L Cd2+ had minor impacts on the microbial reductive dechlorination of PCE and 1,2-DCA. The inhibitory effects of tested heavy metal ions on microbial reductive dechlorination ranked in descending order are Zn2+, Cu2+, and Cd2+. Community profiling and principal component analysis indicate that the concentration and type of contaminants (e.g., heavy metal ions, organohalides) shaped the microbial community structure, an observation similar to a prior report. The enrichment of certain organohalide-respring bacteria (e.g., Dehalococcoides, Dehalogenimonas) during continuous transfers exposed to heavy metal ions suggests that they are capable of tolerating high concentrations of heavy metal ions. Our findings provide insights into the impacts of heavy metal ions on microbial reductive dechlorination and may be helpful for in situ bioremediation at sites contaminated with organohalides and heavy metals.

Efficient solar-driven interfacial water evaporation enabled wastewater remediation by carbonized sugarcane

Solar-driven interfacial water evaporation has great potential in wastewater remediation. Carbonized biomass materials emerged as attractive solar evaporators due to their excellent solar harvesting, solar-thermal converting, and water delivering capabilities. In this study, antimony doped tin oxide (ATO) was loaded to sugarcane that was then carbonized to obtain composite solar evaporator CS@ATO which delivered a solar absorption of 99 %, a solar evaporation rate of 1.43 kg m−2 h−1 and an efficiency of 95.3 %. Treated with CS@ATO, the concentrations of heavy metal ions in wastewater were reduced by 3–4 orders, and dyes in wastewater were removed almost completely. For seawater desalination with CS@ATO, the contents of the main cations in the collected fresh water were lower than the levels in drinking water defined by WHO. CS@ATO also exhibited long-term service capability in both wastewater remediation and seawater desalination. These results suggested great potential of CS@ATO in the aforementioned environment related applications.

Fuzzy comprehensive evaluation strategy for operating state of electrocoagulation purification process based on sliding window

In the process of electrocoagulation purification, there is a problem of passivation of the reactor electrode plates, and the process operating state is constantly changing, which badly affects the efficiency of electrocoagulation purification and the removal of heavy metal ion. However, in order to ensure that the concentration of heavy metal ion at the electrocoagulation outlet reaches the standard, the operators often replace the plates in advance or turn up the voltage to the maximum, resulting in increased power consumption and plates consumption. In order to solve this problem, this paper proposes a fuzzy comprehensive evaluation strategy for operating state of electrocoagulation purification process based on sliding window. Firstly, based on the combination of the Long and Short-Term Memory (LSTM) network and Autoregressive Integrated Moving Average Model (ARIMA), the predicted value of the removal rate of heavy metal ion in the electrocoagulation purification process is obtained. The predicted value and other important factors influencing the purification effect are used as the operating state evaluation indicators of the electrocoagulation purification process, and the operating state evaluation grade is divided according to the fuzzy rules. Secondly, the boxplot method is used to determine the threshold of each evaluation indicator, and the average value of the data of each indicator in each time window is calculated in real-time based on the sliding window. The current deterioration degree of each evaluation indicator is determined by the average value and the indicator threshold. Then, the basic weight of each evaluation indicator is calculated based on the grey relational analysis method, and the final weight of each indicator is determined according to the variable weight theory combined with the deterioration degree of each indicator. Finally, according to the fuzzy theory, the fuzzy comprehensive evaluation matrix is constructed by establishing the membership function, so as to evaluate the operating state of the electrocoagulation purification process. The effectiveness of the proposed evaluation strategy is verified by the industrial data collected from a wastewater treatment plant.

Meeting a threat of the Anthropocene: Taste avoidance of metal ions by Drosophila

The Anthropocene Epoch poses a critical challenge for organisms: they must cope with new threats at a rapid rate. These threats include toxic chemical compounds released into the environment by human activities. Here, we examine elevated concentrations of heavy metal ions as an example of anthropogenic stressors. We find that the fruit fly Drosophila avoids nine metal ions when present at elevated concentrations that the flies experienced rarely, if ever, until the Anthropocene. We characterize the avoidance of feeding and egg laying on metal ions, and we identify receptors, neurons, and taste organs that contribute to this avoidance. Different subsets of taste receptors, including members of both Ir (Ionotropic receptor) and Gr (Gustatory receptor) families contribute to the avoidance of different metal ions. We find that metal ions activate certain bitter-sensing neurons and inhibit sugar-sensing neurons. Some behavioral responses are mediated largely through neurons of the pharynx. Feeding avoidance remains stable over 10 generations of exposure to copper and zinc ions. Some responses to metal ions are conserved across diverse dipteran species, including the mosquito Aedes albopictus. Our results suggest mechanisms that may be essential to insects as they face challenges from environmental changes in the Anthropocene.

Study of influence of initial concentration of heavy metal ions on the quality of fertization processing of electroplating sludge

Influence of the key parameter for the ferritization process - initial total concentration of heavy metal ions (СƩ) on the quality of galvanic sludge processing has been experimentally studied. It was determined, that at СƩ = 5.33 g/dm3 and electromagnetic pulse activation of the ferritization process, the lowest values ​​of residual concentrations of heavy metal ions in the purified solution were obtained: for iron – 0,10; nickel – 0,19; copper – 0,12; zinc – 0,10 mg/dm3. The obtained values ​​correspond to the average degree of extraction of these ions of 99,97%. The purified solution is suitable for reuse in electroplating facilities. As a result of structural studies of sediment samples, it was found that at total heavy metal concentration of 5,33 g/dm3 in the ferritization reaction mixture, regardless of the method of activating the process, phases containing crystalline ferromagnetic phases of ferrites (Ni, Cu, Zn) Fe2O4 exceeds 92%. The efficiency of resource-saving electromagnetic pulse activation of the reaction mixture in the ferritization process is confirmed. Using this method of activation, energy consumption is reduced by 1,5 times compared to thermal one. The proposed resource-saving ferritization technology prevents environmental pollution, ensures the rational use of raw materials and energy, as well as allows to obtain marketable products from industrial waste.

Multi-layered g-C3N4 as a Fluorescent Probe for Hg2+ Detection.

Hg2+ is one of the most toxic heavy metal ions that exist in the environment and it forms large numbers of toxic binary compounds. Accurate and rapid detection of the concentration of heavy metal ions is a prerequisite technology to achieve pollution control and prevention. Fluorescent probes have attracted extensive attention because of their high sensitivity, prominent precision, convenient and fast visualization of heavy metals. Herein, we report multi-layered graphitic carbon nitride via a simple thermopolymerization treatment as a very effectual fluorescent probe for sensitive and selective detection of Hg2+ with a limit of detection as low as 1.14nM.