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Washing water containing poorly degradable heavy metal-EDTA complexes is produced by ethylenediaminetetraacetic acid (EDTA) washing of heavy metal-contaminated soil. A series of batch experiments were performed to explore the dechelation of heavy metal-EDTA complexes and the recovery of EDTA from simulated soil-washing solution using sulfide precipitation with Na2S. The results showed that the effect of Na2S dosage on the dechelation of Cd-EDTA solution was greater than that of other factors (reaction temperature, time, and pH) and excess EDTA suppressed cadmium removal. Additionally, the Cd removal efficiency reached 99.99 ± 0.001%, and the residual amount of Cd-EDTA was below the detection limit of ion chromatography (IC) measurements under the following optimal conditions: an initial Cd-EDTA solution pH of 6, a sodium sulfide-to-Cd-EDTA ratio of 2:1, a reaction temperature of 25 °C, and a contact time of 20 min. Furthermore, the results of analysis using inductively coupled plasma optical emission spectroscopy (ICP-OES), Fourier transform infrared (FT-IR) spectroscopy, and ion chromatography (IC) confirmed that the dechelation process could be completed in less than 20 min and that EDTA was completely recovered as trisodium EDTA (HNa3EDTA). The mechanism for the dechelation of Cd-EDTA and recovery of EDTA using sulfide precipitation with Na2S was also proposed. The recovered EDTA with acidification had the same ability to extract heavy metals from soil with fresh EDTA. This study may facilitate the recycling of soil-washing wastewater and reduce the cost of extracting heavy metals from soil using EDTA.

This study investigates the removal of selenium (IV) from water by reductive precipitation using sodium sulfide at neutral pH. Also, it examines the application of UV light as an activating method to enhance reductive precipitation. Furthermore, this work evaluates the effects of sulfide dose and solution pH on behavior of Se(IV) reduction. Selenium was effectively removed in sulfide solution at both neutral and acidic pH. UV irradiation did not enhance removal efficiency of Se(IV) at conditions tested, but it affected solids morphology and composition. SEM/EDS and XPS results showed that selenite was reduced to elemental Se or Se-S precipitates (e.g. SenS8-n) in sulfide solution. High resolution S 2p XPS spectra suggested the presence of sulfur-containing anions (e.g. S2O3(2-), HSO3(-), etc.) or elemental S (S(0)), monosulfide (S(2-)), and polysulfides (Sn(2-)), which could be produced from sulfide photolysis or reaction with Se. In addition, large aggregates of irregular shape, which suggest Se-S precipitates or elemental sulfur, were found more prominently at pH 4 than at pH 7, and they were more noticeable in the presence of UV with longer reaction times. In addition, XRD patterns showed that gray elemental Se solids were dominant in experiments without UV, whereas Se-S precipitates (Se3S5) with an orange color were found in those with UV.

In this research, mechanochemical reduction was carried out to remediate Cr(VI) contaminated soil, and the reduction effectiveness was evaluated by analyzing the corresponding leachable fraction obtained through the toxicity characteristic leaching procedure (TCLP) proposed by the EPA. The results indicated that mechanochemical reduction can efficiently reduce the Cr(VI) concentration in the leachate. Under a milling time of 2 h, milling speed of 500 rpm, ball-to-powder weight ratio of 14 and Na2S dosage of 5%, the Cr(VI) leaching concentration significantly decreased from 663.98 mg L−1 to 0.84 mg L−1, much lower than the regulatory limit of 5 mg L−1. In addition, the significant decrease in Cr(VI) was mainly due to the reduction of Cr(VI) to Cr(III), as supported by X-ray photoelectron spectroscopy (XPS). The mechanochemical reduction with mechanism proposed in this experiment may involve two major processes: solidification and reduction (stabilization).

Mine tailings often contain significant amounts of metals and sulfide, many traditional operations used to minerals was not as good as those currently available. This study investigated metals removal from lead-zinc mine tailings using bioleaching and followed by sulfide precipitation. Metals were dissolved from the tailings by the bacteria in a bioleaching reactor. During a 10% pulp density bioleaching experiment, approximately 0.82% Pb, 97.38% Zn, and 71.37% Fe were extracted after 50 days. With the pulp density of 10% and 20%, the dissolution of metals followed shrinking core kinetic model. Metals (Pb, Zn, and Fe) present in the pregnant bioleaching leachate. Metals were next precipitated as a sulfide phase using sodium sulfide (Na2S). Metal precipitations were selectively and quantitatively produced from the bioleaching leachate by adding Na2S. More than 99% of the zinc and 75% of the iron was precipitated using 25 g/L Na2S in the bioleaching leachate. The results in the study were to provide useful information for recovering or removing metals from lead-zinc mine tailings.

In the conventional dehairing process of leather manufacture, animal skins are subjected to a drastic chemical treatment using lime and sodium sulfide. Sulfide reduces disulfide bonds in keratin present in hair and epidermis and thereby detaches them from skin. Lime, being an alkali, contributes to opening up of collagen fiber structure by cleaving a major portion of the glycosaminoglycans from proteoglycans, the interfibrillar elements of skin connective tissue. Currently, as an alternative to chemical dehairing, enzyme based dehairing processes using proteases avoiding the use of lime and sulfide are being developed because of their environmental benefits. Though both chemical as well as enzymatic dehairing processes are aimed at removing noncollagenous proteins and proteoglycans in addition to fiber opening, the mechanism of enzymatic process is distinct from that of the chemical process. In this study, we attempt to study in detail the mechanism of hair saving enzymatic dehairing process for skins using a bacterial protease against the customary hair burn chemical dehairing process. Quantitative analysis shows that the collagen content remains unaffected in both treatments but there is a marked reduction of proteoglycan constituents from dehaired pelts in the enzymatic process when compared to lime-sulfide process. This is further substantiated by histochemical examination of the sections of dehaired pelts using different stains as well as immunohistochemical studies on the removal of decorin. HPLC profile shows that decorin is extensively degraded by the bacterial protease. This study conclusively demonstrates that proteolytic degradation of decorin and subsequent removal of proteoglycan aggregates play an important role in the opening up of the collagen fiber bundles during enzymatic dehairing.

The necessity of heavy metal removal from wastewater has led to increasing interest in absorbents. We have developed a new approach to obtain high metal adsorption capacity by precipitating metal sulfides with sodium sulfide on the surface of bentonite and adhere them to the absorbent. This method allowed to remove approximately 90% of cadmium as CdS from 10(-4)-10(-6) M CdCl2 solutions. Additional reactions are related to the removal of excess sodium sulfide by the release of hydrogen sulfide and oxidation to sulfur using carbogen gas (5% CO2, 95% O2) followed by aeration.

GSH-capped CdS nanocrystallites were synthesized by reacting Cd(II)-GSH with aqueous sodium sulfide using specific initial sulfide/Cd(II) ratios. Spectroscopic analyses of fractions obtained from a size exclusion column showed varying absorption spectra indicating a significant dispersion in size-distribution of nanocrystallites at lower sulfide/Cd(II) ratios. However, size distribution of the nanocrystallites was narrower at initial sulfide/Cd(II) ratios that exceeded 1.0. An ethanol precipitation procedure was used to remove free Cd(II)-GSH complexes and selectively isolate GSH-capped nanocrystallites in a very narrow size range. Size exclusion chromatography indicated similar chemical compositions and overlapping spectral profiles of ethanol-precipitated samples suggesting apparent uniformity in both the size and the cap content. All of the GSH-capped CdS nanocrystallites with varying cap contents degraded p-nitrophenol upon irradiation at 366 nm. However, photocatalytic degradation of p-nitrophenol was significantly higher in samples with higher sulfide/Cd ratio and less capping material. The addition of H2O2 enhanced levels of photo-oxidation of p-nitrophenol.

A series of microcosms were set up to verify the degradation pathway of CFC-113 in water under anaerobic conditions and to measure its half-life and that of its major degradation products HCFC-123a and chlorotrifluoroethene (CTFE). Anaerobic landfill leachate was used as a source of bacteria acclimated to chlorinated solvents. The rate of reaction in methanogenic leachate was also compared to that obtained in a buffer containing reduced hematin. In methanogenic landfill leachate, CFC-113 was transformed to HCFC-123a with a half-life of 5 days at 20°C. The same reaction occurred in sodium sulfide/cysteine buffers containing hematin, but at a much slower rate. The production of CTFE was independent of the presence of HCFC-123a and occurred abiotically. Under methanogenic conditions, HCFC-123a was found to be further dechlorinated to HCFC-133 and HCFC-133b. CTFE was found to be relatively stable in methanogenic landfill leachate but was decomposed rapidly in a buffer containing sulfide.

Electronic industrial wastewater sludge in Taiwan is normally passed through an acid-extraction process to reclaim most of the copper ions, the remaining residue may still need to be treated by various stabilization technologies using suitable additives. Cement solidification is used as the common method to stabilize the industrial wastewater sludge in Taiwan. However, this method has the disadvantage of an increase in waste volume. In the present study selective additives such as sodium sulfide, barium manganate and different phase of alumina were tested as a possible alternate additive to stabilize the heavy metal ion in the treated solid waste sludge via microwave heating treatment. The effects of additive amount, power of microwave irradiation and reaction time have been studied. Heavy metal leaching capacity is determined by using standard toxicity characteristic leaching procedure test and elemental content in the leachate is analyzed by inductively coupled plasma analysis. Sodium sulfide is effectively stabilizing the leaching copper ion with high selectivity in the presence of microwave irradiation and finally stabilized in the form of copper sulfide, which is a significant reaction to stabilize the copper ion leaching in the waste sludge. Complete stabilization of heavy metal ion and copper ion content (5mgL(-1)) in industrial sludge is achieved by heating the microwave treated barium manganate and alumina additives by adopting suitable reaction conditions. Hybrid microwave and conventional heating process with minor amount of additive providing the efficient heavy metal stabilization for treated electronic industry waste sludge.

This study tests an alternative method to the traditional unhairing method used during the process of tanning the hides. The new method is based on the substitution of sodium sulfide by hydrogen peroxide as an unhairing agent in both hair recovery and recirculation of the floats employed in the process. The properties of the hides obtained using the two methods have been compared and the results indicate that those hides have similar physical, chemical, and organoleptic properties. However, the differences existing from an environmental point of view are significant. These include reductions of water consumption (approx 70%), chemical oxygen demand (approx 35%), toxicity (98%) and total kjendhal nitrogen (50%). Also, the risk associated with the production of hydrogen sulfide is eliminated, which implies a great improvement in terms of safety for the workers. Given the large amounts of water and chemical pollution discharged in the process, the reductions in absolute values represent a significant improvement. A financial assessment was carried out to demonstrate that the proposed new system is 16% more economic than the traditional one. The contents of this paper are part of the “Savewatertan” CRAFT Project funded by the EU.

International audience; In biological gas treatment, like biofiltration of volatile organic compounds or odorous substances, the microbial nutritional needs could be a key factor of the process. The aim of this work is to propose a new packing material able to provide the lacking nutrients. In the first part of this study, two kinds of material composed of calcium carbonate, an organic binder and two different nitrogen sources, 3 ammonium phosphate and urea phosphate (UP), were compared. The new supports present bulk densities between 0.88 and 1.15 g cm(-3) moisture retention capacities close to 50% and 70%, and water cohesion capacities greater than six months for the material with 20% binder. In the second part, oxygen consumption measurements in liquid experiments show that these packing materials could enhance bacterial growth compared to pine bark or pozzolan and have no inhibitory effect. The biodegradation of different substrates (sodium sulfide and ammonia) and the support colonization by the biomass were evaluated. Finally, UP 20 was chosen and tested in a hydrogen sulfide or ammoniac biofiltration process. This showed that, for H2S concentrations greater than 100 mg m(-3), UP 20 has a real advantage over pine bark or pozzolan. (C) 2067 Elsevier Ltd. All rights reserved.

The present study focuses on the conversion of heavy metals involved in molten incineration fly ashes to metal sulfides which could be thereafter separated by flotation. The sulfidation treatment was carried out for five molten incineration fly ashes (Fly ash-A to Fly ash-E) by contacting each fly ash with Na 2 S solution for a period of 10 min to 6 h. The initial molar ratio of S 2− to Me 2+ was adjusted to 1.20. The conversion of heavy metals to metal sulfides was evaluated by measuring the S 2− residual concentrations using an ion selective electrode. The formation of metal sulfides was studied by XRD and SEM–EDS analyses. In the case of Fly ash-A to Fly ash-D, more than 79% of heavy metals of zinc, lead and copper was converted to metal sulfides within the contacting period of 0.5 h owing to a fast conversion of metal chlorides to metal sulfides. By contrast, the conversion of about 35% was achieved for Fly ash-E within the same contacting period, which was attributed to a high content of metal oxides. Further, the S 2− to Me 2+ molar ratio was reduced to 1.00 to minimize Na 2 S consumption and the conversions obtained within the contacting period of 0.5 h varied from 76% for Fly ash-D to 91% for Fly ash-C. Finally, soluble salts such as NaCl and KCl were removed during the sulfidation treatment, which brought about a significant enrichment in metals content by a factor varying from 1.5 for Fly ash-D to 4.9 for Fly ash-A.