Recovery of precious metals (PMs: AuIII and PtIV) from waste resources is of high importance due to the environmental concern and imbalance in the supply-demand ratio. A new approach has been ...explored for the recovery of PM using earlier developed bio-adsorbent, dithiocarbamate-modified cellulose (DMC). The adsorbent exhibits excellent adsorption efficiency (~99%) over a wide range of pH (< 1–6) and high selectivity towards AuIII and PtIV extraction from acidic solutions (H+: ≥ 0.2 mol L–1). The adsorption capacity (mmol g–1; AuIII: 5.07, PtIV: 2.41) and rate to reach equilibrium (≤ 30 min) were significantly higher than most of the reported bio-adsorbents. The AuIII or PtIV, after captured in DMC, was subsequently recovered as Au0 and Pt0 (yield > 99%) via incineration. The protocol was verified using real waste samples containing AuIII and PtIV in a mixed matrix of base metal ions, and a quantitative (~100%) and selective extraction of AuIII and PtIV were observed. The proposed technique is more effective and straightforward than the typical adsorption-desorption-reduction based method, because of the advantages like no-use of toxic eluents, and no-addition of any reductants to collect the PMs in elemental form.
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•New bio-adsorbent (DMC) for selective AuIII or PtIV extraction from acidic waste.•The high adsorption capacity of DMC assists rapid capture of AuIII or PtIV.•The adsorption of AuIII or PtIV onto DMC follows a complexation-reduction mechanism.•A straightforward pathway for the recovery of the metals as Au0 and Pt0 is proposed.•No toxic eluents or reductants were used in the proposed recovery technique.
Economic and ecological issues motivate the recovery of precious metals (PMs: Ag, Au, Pd, and Pt) from secondary sources. From the viewpoint of eco-friendliness and cost-effectiveness, biomass-based ...resins are superior to synthetic polymer-based resins for PM recovery. Herein, a detailed comparative study of bio-sorbent dithiocarbamate-modified cellulose (DMC) and synthetic polymer-based commercial resins (Q–10R, Lewatit MonoPlus TP 214, Diaion WA30, and Dowex 1X8) for PM recovery from waste resources was conducted. The performances and applicability of the selected resins were investigated in terms of sorption selectivity, effect of competing anions, sorption isotherms, impact of temperature, and PM extractability from industrial wastes. Although the sorption selectivity toward PMs in acidic solutions by DMC and other resins was comparable, the sorption efficiency of commercial resins was adversely affected by competing anions. The sorption of PMs fitted the Langmuir model for all the studied resins, except Q–10R, which followed the Freundlich model. The maximum sorption capacity of DMC was 2.2–42 times higher than those of the resins. Furthermore, the PM extraction performance of DMC from industrial wastes exceeded that of the commercial resins, with a sorption efficiency ≥99% and a DMC dosage of 5–40 times lower.
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•The suitability of DMC and other selected resins for PMs recovery was compared.•Competing anions have a greater adverse effect on ion exchange resins than on DMC.•The DMC sorption capacity was 2.2–42 times that of the commercial resins.•The PM sorption ability trend was DMC > Lewatit > Dowex ≈ Diaion > Q–10R.•DMC can be a better alternative for PM recovery than the studied commercial resins.
The biotransformation and detoxification mechanisms of arsenic (As) species have been active research topics because of their significance to environmental and human health. Biotransformation of As ...in phytoplankton has been extensively studied. However, how different growth phases of phytoplankton impact As biotransformation in them remains uncertain. This study investigated the biotransformation of As species in freshwater phytoplankton at different growth phases to ascertain at which growth phase different types of biotransformation occur. At the logarithmic growth phase, arsenate (As
) (>90%) and arsenite (As
) (>80%) predominated in culture media when phytoplankton were exposed to 20 nmol L
and 1.0 µmol L
of As
, respectively, and methylarsenic (methylAs) species were not detected in them at all. Intracellular As was mainly present in inorganic forms (iAs) at the logarithmic phase, while substantial amounts of organoarsenic (orgAs) species were detected at the stationary phase. At the stationary phase, As
comprised the majority of the total As in culture media, followed by As
and methylAs, although the methylation of As
occurred slowly at the stationary phase. Biotransformation of As
into As
and As methylation inside phytoplankton cells occurred mainly at the logarithmic phase, while the biotransformation of As into complex orgAs compounds occurred at the stationary phase. Phytoplankton rapidly released iAs and methylAs species out of their cells at the logarithmic phase, while orgAs mostly remained inside their cells.
Speciation of selenium (Se) is typically carried out using a sophisticated technique such as ICP-MS after preconcentration using an adsorbent; however, the separation and preconcentration of ...inorganic Se has not been realized in the solutions containing high concentrations of SO42–. A dithiocarbamate-modified cellulose (DMC) was used in this study for the selective extraction and preconcentration of inorganic Se in wastewater, with a portable liquid electrode plasma-optical emission spectrometry (LEP-OES) being employed for quantification. DMC was found to selectively and quantitatively adsorb selenite (SeIV) over a wide range of pH (1.0–8.0); however, less than 3.0% of selenate (SeVI) was adsorbed in a pH range of 3.0–11. Quantitative extraction of SeIV was achieved even in the presence of 3.5 mol L–1 SO42–. The maximum sample volume from which 10 mg of DMC could quantitatively extract SeIV was found to be 500 mL. KOH (0.60 mL, 1.5 mol L–1) was found to quantitatively desorb SeIV retained on the adsorbent and yielded an enrichment factor of 833. The recovery of Se species from synthetic flue-gas desulfurization wastewater containing SeIV and SeVI at concentrations of 5.0 µmol L–1 was 96.2 ± 1.8% and 105.8 ± 1.8%, respectively.
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•The adsorbent exhibited outstanding selectivity and capacity with respect to SeIV.•The selectivity of the adsorbent was higher than that of commercial resins.•A portable low-cost analyzer based on LEP-OES was used to quantify selenium.•The developed analytical method was applied to flue-gas desulfurization wastewater.•An accessible and simple method for the speciation of Se was established.
Organic complexation of Cu in estuarine waters in Japan was investigated using reverse titration competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV). We detected very ...strong Cu-binding organic ligands (L
1
) with conditional stability constants (
Kʹ
CuL1
) of more than 10
17
. These ligands were successfully determined throughout the water column in Otsuchi Bay as well as in three rivers flowing into the bay. Organic ligands in the rivers had a concentration range of 2.6 nM–5.0 nM and log
Kʹ
CuL1
values between 17.5 and 18.6. The use of reverse titration enabled the detection of high concentrations of a weaker ligand class (L
2
) in river waters that ranged from 339 to 354 nM with log
Kʹ
CuL2
values between 11.9 and 12.1. We estimated that L
1
was not derived from rivers or open ocean. Our incubation results indicated that the detected ligands did not increase with phytoplankton growth in Otsuchi Bay. Rather, coastal and benthic sediments may be major suppliers of L
1
due to the enrichment of these ligands close to the sediment source. In contrast, the possible sources of weak Cu-binding organic ligands in Otsuchi Bay were estimated to be humic substances.
Temperature and salinity effects on marine diatom species growth has been studied extensively; however, their effect on arsenic (As) biotransformation has been imprecise. This study reports the ...growth, and As biotransformation and speciation patterns at various temperatures and salinities of six marine diatom species: Asteroplanus karianus, Thalassionema nitzschioides, Nitzschia longissima, Skeletonema sp., Ditylum brightwellii, and Chaetoceros didymus. The growth rate and As biotransformation potentials of these species during three weeks of culture in f/2 based medium were significantly affected by wide temperature (0-35 °C) and salinity (0.3-50‰) ranges. Growth and As biotransformation were higher at optimum temperatures of 10-25 °C, and salinity of 10-35‰, whereas growth and arsenic biotransformation were lower at <5 °C and 5‰ and >25 °C and 35‰, respectively. The results showed that As(V) to As(III) biotransformation differed significantly (p < 0.05) between day 10 and 17. At optimum temperature and salinity levels, the cell size and As biotransformation were higher for all the species. A conceptual model on temperature and salinity effects on growth and As uptake and biotransformation mechanisms by these species has been proposed based on the findings of this study.
The reclamation of geogenic As-contaminated excavated soils as construction additives can reduce the post-disposal impact on the ecosystem and space. Although retaining soil characteristics while ...reducing contaminant load is a challenging task, washing remediation with biodegradable surfactants or chelators is a promising alternative to non-biodegradable counterparts. In this study, newly synthesized biodegradable surfactants (SDG: sodium N-dodecanoyl-glycinate, SDBA: sodium N-dodecanoyl-β-alaninate, SDGBH: sodium N-dodecanoyl-α,γ-glutamyl-bis-hydroxyprolinate, SDT: sodium N-dodecanoyl-taurinate, and DCPC: N-dodecyl-3-carbamoyl-pyridinium-chloride) and biodegradable chelators (EDDS: ethylenediamine N,N’-disuccinic acid, GLDA: L-glutamate-N, N’-diacetic acid, and HIDS: 3-hydroxy-2,2′-imino disuccinic acid) are evaluated for the remediation of As-contaminated soil. The operating variables, such as washing duration, solution pH, and surfactant or chelator concentration, are optimized for maximum As extraction. SDT shows the highest As-extraction efficiency irrespective of solution pH and surfactant variants, while HIDS is the superior chelator under acidic or alkaline conditions. A binary blend of SDT and HIDS is evaluated for As extraction under varying operating conditions. The SDT–HIDS binary blend demonstrates 6.9 and 1.6-times higher As-extraction rates than the SDT and HIDS-only washing, respectively, under acidic conditions. The proposed approach with a binary blend of a biodegradable surfactant and chelator is a green solution for recycling As-contaminated excavated soils for geotechnical applications.
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•Newly synthesized biodegradable surfactants are used to treat As-contaminated soil.•Biodegradable chelators are evaluated for the washing removal of soil-bound As.•Surfactant or chelator-induced As extraction correlated with washing variables.•Cationic surfactant was incompatible and displayed lowest As-extraction efficiency.•A binary blend of surfactant and chelator significantly enhanced As-removal rate.
Algae accumulate and metabolize arsenic (As) and facilitate cycling and speciation of As in seawater. The laboratory-controlled macroalgal cultures were exposed to different molar ratios of As(V) and ...phosphate (P) in seawater for evaluating the uptake and metabolism of As, as a function of As(V) detoxification through biotransformation. Chlorophyll fluorescence of algal species was not significantly affected by the culture conditions (p > 0.05). Addition of 10 μM P positively reduce As stress, but different As(V)/P ratios significantly affect the growth rate (p < 0.05). Algae readily accumulated As(V) after the inoculation, transformed intracellularly, and released gradually into the medium along the incubation period, depending on As(V)/P molar ratios. Reduction and methylation were the leading processes of As(V) metabolism by Pyropia yezoensis, whereas Sargassum patens showed only the reduction. Sargassum horneri reduced As(V) under low level (0.1 μM), but both reduction and methylation were observed under a high level (1 μM). At the end of incubation, 0.17, 0.15, 0.1 μM of reduced metabolite (AsIII) were recorded from 1 μM of As(V)/P containing cultures of Sargassum horneri, Sargassum patens, and Pyropia yezoensis, respectively. On the other hand, 0.024 and 0.28 μM of methylated metabolite (DMAAV) were detected under the same culture conditions from Sargassum horneri and Pyropia yezoensis, respectively. The results also indicated that P in medium inhibits the intracellular uptake of As(V) and subsequent extrusion of biotransformed metabolites into the medium. These findings can help to understand the metabolic diversity of macroalgae species on As biogeochemistry in the marine environment.
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•Chlorophyll fluorescence of algae unchanged up to 7 d under As(V) stress.•Sargassum horneri and Pyropia yezoensis reduce and methylate As(V).•Detoxification of As(V) by Sargassum patens coupled with only reduction.•Low levels of P enhance cellular uptake of As(V) and excretion process.•Fe-plaque leads to adsorb As and P on the surface of algae.
Numerous reports have described dithiocarbamate (DTC)-modified cellulose sorbents that can selectively separate metal ions from water. We have previously synthesized a novel sorbent modified with DTC ...containing N-heterocycles in the backbone for the selective removal of hazardous metal ions. The sorbent was found to partially dissolve and aggregate in solution, reducing its sorption capacity. In this study, to prepare the sorbent for use as a soli-phase extraction material for the removal of arsenite (AsIII) ions, we attempted to decrease the solubility of the sorbent. The sorbent was cross-linked with epoxy or complexed with iron, and the quantities of the modifiers were varied between 3.0 and 10 mol%. As a result, the iron-complexed sorbents were still partially soluble, and cross-linkage with 6.0 mol% of epoxy made the sorbent almost insoluble and dispersed in solution. This sorbent also exhibited the highest AsIII sorption performance among the sorbents synthesized in this study. Although DTC-modified polymers are reported to lose their sorption capability after storage at 40 °C, the sorbent was found to be thermally stable. The optimum contact time and pH for AsIII removal were 20 min and 3.0, respectively. The maximum sorption capacity of the epoxy-cross-linked sorbent, calculated from the Langmuir isotherm equation, was 600 μmol g−1 (45 mg g−1) at 25 °C. Additionally, the sorbent was highly selective toward AsIII compared with previously reported sorbents and capable of removing approximately 97% of AsIII from environmental water. In conclusion, cross-linking enhances the stability of the sorbents in solutions, which facilitates the removal of AsIII from environmental water.
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•Epoxy cross-linkage decreased solubility and enhanced dispersibility.•The epoxy-modified sorbent preserved its sorption ability after a storage at 40 °C.•The sorbent exhibited outstanding selectivity with respect to AsIII.•The sorbent removed about 97% of AsIII from contaminated environmental water.
Cadmium (Cd) contamination of farmland soils is a growing concern because of its highly toxic impact on ecosystems and human health. Chelator-assisted washing and chemical immobilization are ...effective remediation strategies for Cd-contaminated soils. Ethylenediaminetetraacetic acid (EDTA) has traditionally been used for soil washing, but its persistence in the environment and subsequent toxicity have raised significant ecological concerns. Consequently, biodegradable chelators have gained increasing attention as eco-friendly alternatives to the persistent chelator, EDTA. Therefore, this study evaluated the performance and efficacy of three biodegradable chelators: L-glutamate-N,N'-diacetic acid (GLDA), methylglycine-diacetic acid (MGDA), and 3-hydroxy-2,2'-iminodisuccinic acid (HIDS) in comparison to EDTA for remediating a real Cd-contaminated agricultural soil. The influence of treatment parameters, including chelator variants, washing time, chelator concentration, solution pH, and liquid-to-soil ratio (L/S) on Cd extraction was studied and optimized to attain the maximum removal rate. Following chelator-assisted washing, the efficacy of a stabilization preference combining FeCl3 and CaO in reducing the leaching potential of residual Cd in chelator-washed soil residues was also investigated. GLDA demonstrated comparable Cd extraction efficiency to EDTA, and the Cd extraction efficiency was found to be positively correlated with the soil washing parameters. However, under the optimized conditions (chelator concentration: 10 mmol L-1; washing time: 3 h; solution pH: 3; L/S ratio: 10:1), GLDA exhibited a higher Cd extraction rate than EDTA or the other chelators. Furthermore, a post-treatment process incorporating FeCl3 and CaO substantially diminished the water-leachable Cd content in the resultant soil residues. The proposed remediation strategy, which combines chemically assisted washing and stabilization, could be a practical option for extracting bulk Cd from soil and reducing the leaching potential of residual Cd.
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