ABSTRACT
We previously reported that monoalkyl dithiocarbamate-modified cellulose (DMC) exhibited excellent adsorption performance for arsenite (AsIII), cadmium (CdII), lead (PbII), gold (AuIII), silver (AgI), platinum (PtIV), and palladium (PdII). However, its adsorption capability for AsIII decreased by 96.4% after two weeks of storage at 40 °C under an air atmosphere. This decrease in adsorption ability could occur for other metals that dithiocarbamates can extract. In this study, we investigated the adsorption performance of DMC for various metals before and after storage and proposed a possible mechanism for this decrease. We found significant decreases in the adsorption abilities of PbII (11.4%), AgI (39.5%), PtIV (65.5%), and PdII (69.6%), whereas AuIII and CdII adsorption was largely retained, with decreases of 1.1% and 4.0%, respectively. FTIR analysis of the stored DMC revealed the formation of S-S bonds and the retention of dithiocarbamate peaks, indicating the formation of dithiocarbamate dimers (thiuram disulfides). To further support thiuram disulfide formation, dialkyl thiuram disulfides were tested for the adsorption of the seven employed metals. The metal adsorption behavior of dialkyl thiuram disulfides was almost identical to that of the stored adsorbent, ensuring thiuram disulfide formation. In conclusion, the loss of adsorption capability can be mainly attributable to the formation of thiuram disulfide.
ABSTRACT
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.
Subject(s)
Arsenites , Water Pollutants, Chemical , Water Purification , Adsorption , Cellulose , Hydrogen-Ion Concentration , Ions , Iron , Polymers , WaterABSTRACT
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-ß-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.
Subject(s)
Arsenic , Environmental Restoration and Remediation , Isopoda , Metals, Heavy , Soil Pollutants , Animals , Chelating Agents , Ecosystem , Metals, Heavy/analysis , Sodium , Soil , Soil Pollutants/analysis , Surface-Active AgentsABSTRACT
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.
Subject(s)
Selenium , Cellulose , Electrodes , Spectrum Analysis , WastewaterABSTRACT
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.
Subject(s)
Metals , Water , Adsorption , Cellulose , Hydrogen-Ion Concentration , KineticsABSTRACT
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.
ABSTRACT
A series of cellulose derivatives bearing dialkyl dithiocarbamate (DTC) groups were synthesized. Their ability of sorption of arsenite (As(iii)) and heavy metals and their storage stability in the solid state were investigated. Among them, DTC-modified cellulose derived from l-proline showed the highest sorption capacity for As(iii) and heavy metals to selectively remove them from aqueous media. It also showed exellent storage stability in air at 40 °C.
ABSTRACT
We synthesized three new dithiocarbamate (DTC)-modified cellulose biomaterials (DMC-1, DMC-2, and DMC-4) to investigate their adsorption capabilities as mitigators of arsenite (AsIII) in aqueous media. The main novelty of the adsorbents was that, among two inorganic species of arsenic, arsenite and arsenate (AsV), DMCs were highly selective to AsIII in the pH range 2-7. The surface areas of the adsorbents were unified by supporting the DMCs on silica gel (designated SSDMC-1, SSDMC-2, and SSDMC-4, respectively) to investigate the effect of the length of the alkyl chains connecting cellulose and DTC groups on AsIII adsorption. The Langmuir model showed a good regression coefficient (R2â¯>â¯0.96), and the isotherm results revealed that longer chains might enhance the AsIII capture ability. The adsorbents were also capable of removing various heavy metals, and the coexisting ions, FeIII, MnII, PbII, and ZnII, had no significant impact on the removal of AsIII by the DMCs. Moreover, DMC-2 could remove 98.4⯱â¯0.1% of AsIII from artificially contaminated river water.