Solubility Of Heavy Metals Research Articles

Influence of soil inorganic amendments on heavy metal accumulation by leafy vegetables.

The present study aims to assess the effect of four inorganic soil amendments, such as lime (CaCO3), red mud consisting of 75% hematite (Fe2O3), gypsum (CaSO4·2H2O), and Al oxide (Al2O3), of an alkaline heavy metal-contaminated soil. For this purpose, a pot experiment was conducted by physically mixing individual six subsamples of a soil sample collected from Thessaly area with four inorganic soil amendments along with two leafy plants, spinach and lettuce. Al oxide causes the maximum reduction of the water-soluble Cu concentration, as its concentrations is no longer detectable. The Cu availability index decreases when aluminum oxide was used. The use of gypsum and red mud caused almost equal reduction while the smallest decrease was caused by the use of lime. The Zn availability index decreased equally when aluminum oxide and gypsum were mixed with the soil sample. The highest reduction of Cu and Zn transfer coefficient (TC) was observed when the Al2O3 was used. In spinach, Zn TC reduction was 39.8% and Cu TC reduction was 41.0%. In lettuce, the addition of Al2O3 led to Cu TC reduction of over 37.3% and Zn TC reduction of up to 38.7%. Generally, Al2O3 nanoparticles may function as suitable sorbents for the removal of Zn and Cu from soil samples, with an increasing effectiveness in spinach rather than lettuce. Liming materials seem to increase the soil alkalinity and promote the complexation of soluble heavy metals with hydroxide ions leading to immobilization of heavy metals in soil and reduce their amount in leafy vegetables. Remediation of contaminated soils is considered necessary to reduce environmental risks and to achieve the means available to increase agricultural production of safe and quality food.

Iron amended gravity-driven membrane (IGDM) system for heavy-metal-containing groundwater treatment

Gravity-driven membrane (GDM) system is a low-maintenance ultrafiltration system for decentralized drinking water treatment. GDM shows a high removal of pathogens, but a low removal of soluble heavy metal ions. In this study, to overcome this limitation, iron nails were introduced into a GDM system (IGDM) for the purification of heavy-metal-containing groundwater. The corrosion of iron nails continuously occurred in the influent, and rust particles were produced to remove heavy metal ions. The results suggested that the removal of As(V), Pb(Ⅱ), and Cd(Ⅱ) were all higher than 90% in the IGDM system; these removal efficiencies could be maintained because of the abundance of iron nails and the continuous formation of fresh rust. During the filtration, rust particles were partly deposited on the membrane surface, and the thickness of the cake layer in the IGDM correspondingly increased by 143% compared with that in the control GDM. The deposited rust had an inhibitory effect on the microorganisms in the cake layer, and the content of adenosine triphosphate (ATP) was reduced by 75% accordingly. However, the rust particles could adsorb organic membrane foulants, thereby alleviating organic fouling. Moreover, the bird’s-nest-like structure of the rust particles facilitated the formation of a porous cake layer, and no synergistic fouling effect of rust particles and organic foulants was observed. These positive effects offset the inhibitory effect of rusts on microorganisms and the thickness increase of the cake layer. Consequently, a stable flux of 3.5 L m-2 h-1 could still be achieved during the 105-day operation in IGDM system, although the value was 30% lower than that in the control GDM. All these results indicated that IGDM could be an economical and low-maintenance method for heavy metal removal in undeveloped areas. In addition, a house-hold scale (∼50 L d-1) IGDM was successfully operated, demonstrating the practical potential of this technology.

Abundance and fractional solubility of phosphorus and trace metals in combustion ash and desert dust: Implications for bioavailability and reactivity

Aerosol phosphorus (P) and trace metals derived from natural processes and anthropogenic emissions have considerable impacts on ocean ecosystems, human health, and atmospheric processes. However, the abundance and fractional solubility of P and trace metals in combustion ash and desert dust, which are two of the largest emission sources of aerosols, are still not well understood. In this study, the abundance and fractional solubility of P and trace metals in seven coal fly ash samples, two municipal waste fly ash samples, and three desert dust samples were experimentally examined. It was found that the abundance of aluminum (Al) in combustion ash was comparable or even higher than that in desert dust, and, therefore, care should be taken when using Al as a tracer of desert dust. The abundance and fractional solubility of P were higher in combustion ash, with a soluble P content ~4–6 times higher than that of the desert dust, indicating that combustion ash could be an important source of bioavailable P in the atmosphere. Except for Mn, the abundance and fractional solubility of other heavy metals were higher in the combustion ash compared to the desert dust, indicating the potential importance of combustion ash in ocean ecosystems, human health, and atmospheric processes. In contrast, both the abundance and solubility of Mn were highest in the desert dust, indicating a potentially important source of soluble Mn in the atmosphere. The fractional solubilities of P and trace metals are significantly affected by acidity and ions in the extraction solutions, and it is suggested that a buffer solution can better represent the acidity of the aqueous system in the true atmospheric environment. The results of this study improve our understanding of the sources of bioavailable and reactive P and trace metals in ambient aerosols.

Comparison of limestone calcined clay cement and ordinary Portland cement for stabilization/solidification of Pb-Zn smelter residue.

Decreasing carbon emissions by replacing Portland cement (PC) with supplementary cementitious materials (SCMs), such as low-grade limestone (LS) and calcined clays (CC), has tremendous potential for stabilization/solidification (S/S) of industrial hazardous waste primarily with heavy metals. Recently, a low-carbon-based cementitious binder, namely, limestone calcined clay cement (LC), has emerged as an alternative for S/S treatment of wastes. However, comprehensive comparison between LC and PC application in solidifying/stabilizing wastes has not been conducted. This study aims to investigate the S/S efficiency of Pb-Zn smelter residue (LZSR) comprising heavy metals lead (Pb), zinc (Zn), and cadmium (Cd) at higher concentrations. LZSR is treated with LC and PC for capturing strength and leaching toxicity. The test results indicate that low-grade CC and LS in the LC binder can promote the alkaline environment, and act as fillers in solidifying heavy metals. The toxicity characteristic leaching procedure leaching concentrations of untreated (UT) LZSR were 503 mg/kg, 1266 mg/kg, and 251 mg/kg for Pb, Zn, and Cd, respectively. After a 28-day curing, the leaching concentrations in LC-treated LZSR reduced to 4.33 mg/kg, 189.68 mg/kg, and 0.46 mg/kg, while the leaching concentrations of PC-treated LZSR reduced to 29 mg/kg, 338 mg/kg, and 6 mg/kg for Pb, Zn, and Cd, respectively. The maximum immobilization efficiencies for Pb, Zn, and Cd reached 85%, 99%, and 99%, respectively. Moreover, the insoluble phases for Pb, Zn, and Cd obtained from the sequential extraction test results were 63.5%, 72.1%, and 42.4% for LC-treated LZSR and 35.7%, 38%, and 43% for PC-treated LZSR with binder content of 8% binder and curing time of 28 days. Increasing curing time and binder content reduced leaching concentrations, and the underneath mechanisms were interpreted by XRD, SEM-EDS, and FTIR analyses. Overall, the results indicate that Pb, Zn, and Cd can be successfully immobilized using 8% LC binder by transforming soluble heavy metals to insoluble hydroxides and their complexes.

Spatial and Temporal Distribution and Pollution Evaluation of Soluble Heavy Metals in Liujiang River Basin

In the Liujiang River, soluble heavy metals Zn, Al, Co, As, Ni, Cr, Cu, Mn, Pb, Hg, and Cd were monitored day and night to determine their temporal and spatial distribution as well as the sources of this pollution. The Nemerow comprehensive pollution index method was then used to evaluate the environmental quality of the Liujiang River water body. The results showed that: ① For each river section (Lutang and Luowei), the amounts of soluble Al, Co, As, Ni, Cr, Mn, Pb, and Cd all met the Class Ⅲ water quality standard limit, as defined in the National Surface Water Quality Class Ⅲ Standard. The concentration of Zn and Cu was far below the standard limit, while the Hg content slightly exceeded the standard; the concentration of heavy metals in Liujiang River basin was highest in the normal season and lowest in the wet season. In terms of spatial distribution, the Luowei section had a higher heavy metal concentration. ② The single factor pollution indexes for elemental Hg, Cd, and As were higher in the Liujiang River basin. The Nemerow comprehensive pollution index evaluation shows that the risk of heavy metal pollution in the water body exhibits certain seasonal variations (March > November > June), indicating that rainfall in different seasons may result in reduced drinking water safety in the study area. The water of the Lutang and Luowei sections generally exhibited a moderate level of heavy metal pollution. The comprehensive pollution index of the Luowei section was higher than that of the Lutang section, and the pollution level was relatively severe. Therefore, the Luowei section should be listed as a priority control section of the Liujiang River basin by the water environment management department; ③ After assessing the difference in heavy metal pollution between annual and monthly rainfall periods, it was found that the selection of rainy season or conventional season has no significant impact on the assessment of heavy metal pollution in rivers, when the mass concentration of Cu in the river is used. However, the presence of As, Mn, Pb, Al, Cr, and Ni elements in the river will cause significant differences in the evaluation of heavy metal pollution on an interannual scale; ④ Multivariate statistical analysis results show that Cd, Cr, Ni, Co, and Pb in the Liujiang River are mainly derived from industrial production activities; As and Zn are mainly derived from rainwater leaching of domestic pollution waste; Mn, Al, and Cu are mainly derived from the application of pesticides and fertilizers.

Characterization of MSWI fly ashes along the flue gas cooling path and implications on heavy metal recovery through acid leaching

This study reports on detailed chemical and mineralogical characterization of the different municipal solid waste incineration ashes forming along the flue gas path of plants with separate dust removal and neutralization. In pursuit of optimizing heavy metal recovery through acid leaching, the metal extractability from empty pass ashes (EA), boiler ashes (BOA) and the electrostatic precipitator ashes (ESPA) was evaluated and compared. The focus was laid on matrix phases affecting leachability (e.g. alkalinity, oxidation–reduction potential), as well as on distribution and concentration of recoverable heavy metals and their binding forms. The data showed, that EA and BOA are geochemically similar and are essentially composed of two different materials: the heavy metal poor airborne ash particles and the Zn- and Pb-rich sulfate deposits that condensate on heat exchanger surfaces. Variation in relative amount and chemical composition of the deposits is responsible for fluctuations in bulk composition of EA and BOA. The ESPA shows different chemical and mineralogical characteristics than EA and BOA. The ESPA is enriched in the volatile heavy metals Zn, Pb, Cu, Cd and Sn, which are mainly incorporated in chlorides and sulfates. The high content of salt-bound and thus easily soluble heavy metals together with the lower alkalinity and lower oxidation–reduction potential indicates, that ESPA has a better leachability compared to EA and BOA. The EA and BOA, on the other hand, do not show any significant differences in leachability. The data may contribute to a basis for re-evaluating disposal routes of ash fractions with poor extraction properties.

Removal behavior and chemical speciation distributions of heavy metals in sewage sludge during bioleaching and combined bioleaching/Fenton-like processes

The removal and chemical speciation changes of heavy metals in the sewage sludge during the single bioleaching and combined bioleaching/Fenton-like processes were compared in this study. The improvement in the dewaterability of the treated sludge was also investigated. The single bioleaching led to a removal of Zn, Cu, Cd, Cr, Mn, Ni, As and Pb of 67.28%, 50.78%, 64.86%, 6.32%, 56.15%, 49.83%, 20.78% and 10.52% in 10 days, respectively. The chemical speciation analysis showed that the solubilization of heavy metals in mobile forms (exchangeable/acid soluble and reducible forms) and oxidizable form was the main reason for their removal. Subsequent Fenton-like treatment was carried out at different bioleaching stages when the bioleached sludge dropped to certain pH values (4.5, 4.0 and 3.0), by adding H2O2 at different dosages. The highest removal ratio of Zn, Cu, Cd, Cr, Mn and Ni could reach 75.53%, 52.17%, 71.91%, 11.63%, 66.29% and 65.19% after combined bioleaching/Fenton-like process, respectively, with appropriate pH and H2O2 dosages in less than 6 days. The solubilization efficiencies of these heavy metals in mobile forms were further improved by Fenton-like treatment. The removal efficiencies of As and Pb decreased due to their transformation into insoluble forms (mostly residual fraction) after Fenton treatment. The capillary suction times (CST) of the raw sludge (98.7 s) decreased by 79.43% after bioleaching and 87.44% after combined process, respectively.

Selection of organic materials potentially used to enhance bioremediation of acid mine drainage

Acid mine drainage (AMD), produced when sulfide minerals are subjected to oxygen and water, is one of the major issues in mining industries. Without proper management, AMD's release to the environment would cause seriously prolonged environmental and health issues, such as increases soil acidity and reduces water quality due to extremely low pH, high sulphate concentration, and heavy metal solubility. AMD treatments are divided into two categories, i.e., active treatment, conducted by applying a chemical to the AMD to neutralize pH and precipitate heavy metals; and passive treatment, which relies on biological and biochemical processes. The active treatment may provide an immediate effect, but costly and yet sustainable; meanwhile, passive treatment takes time to establish and to generate an effect, but it is more economical, sustainable, and environmentally friendly. The wetland system is an example of passive treatment. Therefore, this review focuses on passive treatments, especially the selection of organic materials used in constructed AMD wetland treatment. Organic materials play a central role in the wetland system, i.e., to chelate metal ions, remove sulphate from the solution, increase pH, and growth media for microbes, especially sulphate reducing bacteria (SRB) and plants are grown in the system. Overall, organic materials determine the effectiveness of the wetland system to neutralize AMD passively and sustainably.

Heavy metal removal from aqueous solutions by chitosan-based magnetic composite flocculants

In this study, three magnetic flocculants with different chelating groups, namely, carboxymethyl chitosan-modified Fe3O4 flocculant (MC), acrylamide-grafted magnetic carboxymethyl chitosan flocculant (MCM), and 2-acrylamide-2-methylpropanesulfonic acid copolyacrylamide-grafted magnetic carboxymethyl chitosan flocculant (MCAA) were prepared, synthesized, and characterized by photopolymerization technology. They were applied to the flocculation removal of Cr(III), Co(II), and Pb(II). The effect of flocculation condition on the removal performance of Cr(III), Co(II), and Pb(II) was studied. Characterization results show that the three magnetic carboxymethyl chitosan-based flocculants have been successfully prepared with good magnetic induction properties. Flocculation results show that the removal rates of MC, MCM, and MCAA on Cr(III) are 51.79%, 82.33%, and 91.42%, respectively, under the conditions of 80 mg/L flocculant, pH value of 6, reaction time of 1.5 hr, G value of 200 s−1, and precipitation magnetic field strength of 120 mT. The removal rates of Co(II) by MC, MCM, and MCAA are 54.33%, 84.99%, and 90.49%, respectively. The removal rates of Pb(II) by MC, MCM, and MCAA are 61.54%, 91.32%, and 95.74%, respectively. MCAA shows good flocculation performance in composite heavy metal-simulated wastewater. The magnetic carboxymethyl chitosan-based flocculant shows excellent flocculation performance in removing soluble heavy metals. This research provides guidance and ideas for the development of efficient and low-cost flocculation technology to remove heavy metals in wastewater.

Heavy metal solubilisation during the hydrothermal treatment of sludge

The present study analyses the combined effects of temperature (from 160 to 200 °C), and, for the first time ever, type of atmosphere (oxidising or inert) and pressure (from 60 to 100 bar) on the solubilisation of heavy metals during the hydrothermal treatment of wet no-diluted sewage sludge. Results revealed that Cd, Pb, Al and Fe were hardly affected by neither the atmosphere nor temperature, remained almost completely in the solid phase during all the hydrothermal treatments tested; while Cr, Ni, Cu and Zn were partially solubilised, being this solubilisation favoured by the presence of an oxidising atmosphere. In contrast, initial dissolved Hg was partially precipitated under both types of atmosphere, although it was re-dissolved after 30 min under an inert atmosphere. Regarding the working conditions, the highest temperature (200 °C) caused the greatest metal immobilisation, whereas the range of pressures tested barely had any effect on it. Concerning the reaction time, the lowest concentration of metals in the liquid fraction of the hydrolysed sludge was obtained during the initial 30 min of treatment.

Versatile 3D reduced graphene oxide/poly(amino-phosphonic acid) aerogel derived from waste acrylic fibers as an efficient adsorbent for water purification.

The fabrication of multifunctional materials to remove soluble heavy metal ions and dyes, as well as insoluble oils from waste water is urgently required, yet remains a daunting challenge because of difficulty in controlling their structure and property to satisfy various demands. Herein, for the first time, novel 3D reduced graphene oxide/poly(amino-phosphonic acid) (PAPA) aerogels (rGO/PAPAs) with different PAPA content were developed by solvothermal reduction of the graphene oxide and cross-linking with PAPA chain, and subsequently employed as versatile adsorbent for the removal of complex pollutants such as Cr(III) ion, methylene blue (MB) dye and various kinds of organic solvents from water. Benefiting from the synergistic effect of the reduced graphene oxide (rGO) sheet and PAPA component, as well as its unique 3D structure, the resultant aerogel (rGO/PAPA-2) gained amphiphilic, ultralight, and multifunctional properties. Thus, it showed a fast adsorption rate (within 15min) and high adsorption capacity (up to 327.1mg/g) for Cr(III) ion at an optimal pH of 5.5 due to its unique 3D network structure with abundant amino-phosphonic acid functional groups. The uptake of Cr(III) by rGO/PAPA-2 was fitted well with the Langmuir isotherm and pseudo-second-order kinetic model. The adsorption mechanism of Cr(III) onto rGO/PAPA-2 can be attributed to electrostatic attraction and surface complexation with APA groups. In addition, the rGO/PAPA-2 displayed an excellent adsorption performance for MB (694.5mg/g) and several organic solvents (83.2 to 254.3g/g). Moreover, the rGO/PAPA-2 exhibited a good regeneration (around 99%) and satisfactory recovery abilities for the tested adsorbates. Notably, PAPA chains can be easily prepared from waste acrylic fibers, making it become a cost effective but versatile candidate to prepare new material. Therefore, this work provides a new design strategy to fabricate the rGO/PAPA-2 aerogel with great prospect for sophisticated industrial wastewater cleanup.

Cadmium uptake and transfer by Sedum plumbizincicola using EDTA, tea saponin, and citric acid as activators

Sedum plumbizincicola (S. plumbizincicola) is known as a sufficient plant for phytoremediation of cadmium (Cd) polluted soils. This study aimed to investigate the effects of ethylene diamine tetraacetic acid (EDTA), tea saponin (TS), and citric acid (CA) on Cd uptake and translocation by S. plumbizincicola. To do so, using a pot experiment, we set four concentration levels of activators (1, 3, 5, and 10 mmol L−1) and a control (CK). Results showed that none of the applied activators had significant impact on soil pH. Except for CA-10, the concentration of available Cd in Cd polluted soils increased by 65.8–72.9% compared with CK. The EDTA-1, CA-1, and TS-5 treatments caused significant increases of 52.3, 67.2, and 38.4%, respectively, in the biomass of aerial parts of S. plumbizincicola (p < 0.05) compared with CK. Except for CA-3, activators increased Cd accumulation in the aerial parts of plants by 47–124% compared with CK. Of all activators, EDTA-3 caused the highest Cd accumulation of 6.64 g pot−1 in the aerial plant tissues followed by CA-10 (6.25 g pot−1) and TS-1 (5.48 g pot−1). Finally, our results suggested that the application of S. plumbizincicola together with different activators sufficiently reduced soil total Cd by 4.64–48.4% compared with CK. These findings suggest that appropriate application of EDTA, TS, and CA can promote phytoremediation of Cd contaminated soils by hyper-accumulators. In particular, the combined use of EDTA and S. plumbizincicola is an affordable and promising strategy for remediation of Cd contaminated soil. Novelty statement: Sedum plumbizincicola (S. plumbizincicola) is a well-known hyper-accumulator plant for remediation of cadmium (Cd) and zinc (Zn) contaminated soils. In addition, low molecular rganic acids and macromolecular chelating agents can improve the solubility and leaching of soil heavy metals. In the present work, we examined the combined effects of three activators (EDTA, tea saponin, and citric acid) with S. plumbizincicola to remediate a Cd contaminated soil in Anhui Province, East China. Our results indicated the effectiveness of these activators to increase soil available Cd, as well as improving the biomass of S. plumbizincicola and its Cd uptake. We believe that this study provides an efficient approach to increase the uptake of Cd by S. plumbizincicola, restoring Cd contaminated soils. Nevertheless, excessive activators may have adverse effects on soil aggregates and soil microorganisms. Therefore, it is necessary to control the amount of chelating agents and subsequently the deterioration of soil quality.

Assessing maximum soluble combined heavy metals not causing inhibition to brewery sludge in anaerobic wastewater treatment

Assessing maximum soluble combined heavy metals not causing inhibition to brewery sludge in anaerobic wastewater treatment

Bioavailability and Solubility of Heavy Metals and Trace Elements during Composting of Cow Manure and Tree Litter

Objectives. To characterize the total content of heavy metals (Cd, Cr, Cu, Hg, Mo, Ni, Pb, and Zn) and trace elements (As and Se) of interest, their bioavailability and solubility during the composting of cow manure and tree litter in piles inoculated with beneficial microorganism (IBM), or not inoculated (NBM), on the university campus of the Universidad Nacional Agraria La Molina (UNALM). Methods. The investigation evaluated composting in six piles, three IBM piles and three NBM piles, for 120 days. Every 30 days, a composite sample was taken from each pile. The raw materials used were cattle manure and tree litter. The variables analyzed were the total concentrations (content) of metals and trace elements of interest, extracted with diethylenetriaminepentaacetic acid/pentatetic acid (DTPA) (for the bioavailability study) and extracted with deionized water (for the solubility study). Results. The average values (n = 3) of the total content (mg·kg−1) on day 120 in IBM were in the following order: Zn (404.33) &gt; Cu (86.33) &gt; Pb (71.2) &gt; Cr (34.33) &gt; As (28.0) &gt; Ni (13.83) &gt; Mo (2.86) &gt; Se (1.38) &gt; Cd (1.32) &gt; Hg (0.39) and in NBM: Zn (466.0) &gt; Cu (112.23) &gt; Pb (73.23) &gt; Cr (35.33) &gt; As (29.67) &gt; Ni (14.37) &gt; Mo (3.23) &gt; Se (1.55) &gt; Cd (1.38) &gt; Hg (0.38). The values complied with the Austrian Compost Standard for Landscaping and Land Rehabilitation and the Peruvian Standard for Nonorganic Agriculture. Significant differences were observed in some elements ( p &lt; 0.05) between 0 and 120 days in both types of pile (IBM and NBM). Conclusions. For nonorganic agriculture in Peru, urban compost is recommended, whereby raw organic materials are inoculated with beneficial microorganisms during the composting process to reduce the bioavailability of Cu and Zn, as these elements showed less bioavailability than noninoculated piles. The composting process for both piles (IBM and NBM) reduced the solubility in Cu, Pb, and Zn.

Solubilization of Heavy Metals during Anaerobic Digestion of Sewage Sludge Using Acidogenesis

Sewage sludge produced by many municipal wastewater treatment plants contains various heavy metals that limit its use on agricultural land. The existing treatment processes for removing heavy metals are not cost-effective or eco-friendly due to the requirement of aeration or the use of various harmful leaching agents. This paper explores the solubilization of heavy metals present in the sewage sludge using the acidogenesis phase of the anaerobic digestion process without using any harmful compounds. To achieve this objective, an anaerobic batch reactor was used, in which sewage sludge was added with different solid concentrations and carbon source (glucose) concentrations. During this process, volatile fatty acids were produced, which decreased the pH of the system. The maximum decrease in the pH was observed in the reactor that had the maximum glucose concentration and the minimum total solid concentration. In this reactor, the pH dropped below 4.5. The solubilization of heavy metals was observed as Zn: 41% (333 mg/kg), Ni: 31% (8.5 mg/kg), Cr: 30% (13 mg/kg), Pb: 29% (11 mg/kg), Co: 28% (1.4 mg/kg), and Cd: 27% (0.5 mg/kg).

Heavy metal removal by biopolymers-based formulations with native potato starch/nopal mucilage

The contamination of water bodies by heavy metals is a critical problem for human health and ecosystems, and it can bioaccumulate in organisms to toxic levels and even lead to the living being’s death. This research aimed to synthesize and characterize a biopolymer with the capacity to remove heavy metals in wastewater, elaborated from potato starch, glycerin, and nopal mucilage. Native potato starch of the Allcca sipas variety was extracted by conventional methods; the mucilage was extracted with ethanol. Four formulations of biopolymers were synthesized at 60 and 70 °C. The solubility, structural characteristics, and adsorption capacity of heavy metals were evaluated. Starch, mucilage, and biopolymers presented predominant functional groups as -OH, -C-O-, -NH-, -C-H-, -C-OH determined by FTIR, allowing to remove up to 50.18% of Al, 56.81% of As, 35.95% of Cr, 37.43% of Hg and 73.22% of Pb determined through an ICPE-OES, for a contact time of 100 minutes at pH 5.0, heavy metal removal and solubility were significantly influenced (p-value &lt; 0.05) by the addition of starch and mucilage. The synthesized biopolymers present a high capacity for heavy metal removal in wastewater.

Recovery of Heavy Metals from Liquid Effluent by Galvanic Cementation

Copper was recovered from copper sulfate solution in a batch-recycled galvanic reactor operated under forced convection with the generation of electrical energy during the cementation process. The divided galvanic cell consisted of parallel copper and zinc plates. The mass transfer rate and the amount of electrical energy generated were found to be directly proportional to the solution flow rate and the initial concentration of metallic ions and inversely proportional to the distance between electrodes. The experimental results were expressed in terms of a dimensionless correlation including all parameters. The wastewater treatment presented herein cell can be utilized to recover many soluble heavy metal ions from solution with high efficiency.

Influence of selected mineral material on the water solubility and leachability of heavy metals from contaminated soil

Heavy metal pollution in soils is currently a critical environmental issue. Soil amendments can reduce the availability of contaminants and retard their offsite movement by water. A study was conducted to reduce the water solubility and leachability of heavy metals (HM) (cadmium (Cd), lead (Pb), nickel (Ni), chromium (Cr), and copper (Cu)) from polluted soil using various ground natural materials, namely slate, gypsum, lime, shale, and clay. Polluted soil samples were collected from Hattar Industrial areas of Haripur, Pakistan, noted for metal contamination. Mineral amendments were applied to those soil samples at the rate of 2.5 and 5% along with the control (no amendment). Results showed that the amendment material apparently reduced the solubilization of heavy metals (p Cr > Ni > Cd > Cu. After 10 days of incubation, the Cd concentration was reduced on average by the mineral amendment, but the reduction varied in the order slate > clay > lime > shale > gypsum. These materials were also differed for Pb (at p lime > clay > slate > gypsum, and for Ni as the order was slate > clay > gypsum > shale > lime. Chromium and Cu were reduced similarly. Reduction in the metal solubility was highly related to the application rate of material. The leachability of trace elements from soil was also a function of amendment and the material differed for heavy metals during the leaching process. This research indicates that mineral material may act as an adsorbent for the metal contaminant and thus reduces their leachability from soils. Moreover, the availability of heavy metals in contaminated soils can be reduced by using mineral amendment.

Kinetic and equilibrium study of (poly amido amine) PAMAM dendrimers for the removal of chromium from tannery wastewater

Abstract Water gets polluted by industrial effluents, mainly composed of heavy metals and organic materials. Water soluble heavy metals can be taken up by living organisms. Chromium mainly occurs in the form of chromate and cationic hydroxo complexes in water. Apart from conventional methods of heavy metal removal, there are some novel approaches such as using dendrimers for removal of heavy metal. Dendrimers are extremely branched nano sized polymers with a three-dimensional symmetry around a core that imparts poly functionality. PAMAM (poly amido amine) dendrimers having ethylene diamine as core and methyl acrylate as repeating unit was divergently synthesized. Characterization of PAMAM dendrimers was evaluated by UV–Vis spectroscopy, zeta sizer, scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) spectroscopy. Zero generation dendrimers have amine terminal groups, showed intense amide group peak at 1596.76 cm−1. The λ max value was 278 nm. SEM exhibited spherical shape for full generation while needle like structure for −0.5 generation. Evaluation of chromium removal from wastewater has been done by atomic absorption spectroscopy (AAS). The data revealed that optimal removal of Cr occurs at dendrimer concentration of 5 mL, Cr concentration of 300 ppm, contact time of 2 min and pH 7. The synthesized dendrimers have effectively removed Cr from tannery wastewater.

Characterization of dissolved organic matter in the rhizosphere of phytostabilizer Athyrium wardii (Hook.) involved in enhanced metal accumulation when exposed to Cd and Pb co-contamination

The characterization of DOM and its effect on heavy metal solubility in soils have been widely concerned, while few concerns on the phytostabilization of multi-metal contaminated soils. A pot experiment was performed to characterize dissolved organic matter (DOM) in the rhizosphere of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii (Hook.) when exposed to Cd and Pb simultaneously, and investigate its effect on Cd and Pb solubility in soils. The ME presented more DOM in the rhizosphere when exposed to Cd and Pb simultaneously than that exposed to single Cd or Pb, and also than the NME. The acid fractions (hydrophilic acid, hydrophobic acid) and hydrophilic fractions (hydrophilic acid, hydrophilic neutral, and hydrophilic base) were the dominant parts of DOM in the ME rhizosphere. The ME presented more acid and hydrophilic fractions in the rhizosphere when exposed to Cd and Pb simultaneously. Meanwhile, there were more O–H, C–O, N–H and C–H, assigned to carboxylic groups, phenolic groups, hydroxyl groups, and/or amino groups, present in DOM from the rhizosphere of ME when exposed to Cd and Pb simultaneously. These results highlighted the acid characteristics of DOM in the rhizosphere of ME when exposed to Cd and Pb simultaneously. DOM in the rhizosphere of ME thereby showed greater complexation degree for Cd (68%) and Pb (77%), thus showing greater ability to enhance Cd and Pb solubility in soils when exposed to Cd and Pb simultaneously. This is thereby considered to be one of the key processes for enhancing Cd and Pb uptake by the ME when exposed to Cd and Pb simultaneously.