Total Cr Removal Research Articles

Pd/Fe3O4 Nanocatalysts for Highly Effective and Simultaneous Removal of Humic Acids and Cr(VI) By Electro-Fenton with H2O2 in-Situ Electro-Generated on the Catalyst Surface

The widespread presence of humic acids (HAs) and chromium (Cr) in aquatic systems and drinking water sources is a serious threat to the environment and human being, which attracts great concerns from the protection of public health.1,2 However, no attempts on the potential interaction and simultaneous removal of these two types of contaminants have been made. Here, an electro-Fenton process was reported for the effective and simultaneous removal of HAs and Cr(VI), where H2O2 was in-situ produced from the electro-generated H2 and O2 by the presence of Pd/Fe3O4 nanocatalysts and Fe(II) was provided from the support. The effects of solution pH, applied current, Pd loading, and initial concentrations of HAs and Pd/Fe3O4 on the removal efficiency of HAs and Cr(VI) were carefully investigated. Under the optimized electrolysis conditions (pH 3.0, 40 mA, 5.0 wt % Pd, 100 mg•L-1 HAs and 5.0 g•L-1 Pd/Fe3O4), HAs were effectively mineralized, as revealed by a total organic carbon removal efficiency of 90%, and Cr(VI) was completely reduced accompanying with 90% total Cr removal. The HAs degradation driven by the contribution of anodic oxidation was found to be important but not dominant, whereas electro-Fenton process played a fundamental role for the mineralization of HAs. The reduction of Cr(VI) was primarily attributed to the contributions from Pd/Fe3O4 and atomic hydrogen on the Pd catalyst surface as well as the cathodic reduction. In a similar manner, a good recycle of Fe3+ to Fe2+ was accelerated. Moreover, most chromium was removed by the deposit of chromite from the solution, which is the most common and stable mineral of chromium in the environment. Importantly, the energy consumption of this electro-Fenton process for HAs degradation was almost 2 orders of magnitude lower than those of reported electrochemical oxidation. The Pd/Fe3O4 nanocatalysts showed excellent removal performances for HAs and Cr(VI) after eight times repeated treatment. This work reports a cost-effective methodology for simultaneous removal of HAs and Cr(VI) and provides a new insight for efficient elimination of complex contaminants. Figure 1

Scrap iron packed in a Ti mesh cage as a sacrificial anode for electrochemical Cr(VI) reduction to treat electroplating wastewater

Abstract A novel sacrificial anode comprised of scrap iron packed inside a cage made of titanium mesh was developed for Cr(VI) reduction. With electric currents applied, the surface passivation of scrap iron electrode could be avoided. Due to the large surface area with open structures provided, the applied current densities (1.18–3.54 mA/cm2) were low, resulting in low operating voltage and energy consumption. Complete Cr(VI) removal was achieved with electric currents applied, whereas only 20% of the Cr(VI) was removed without electricity. Direct Cr(VI) reduction on the iron surface was a dominant mechanism for the system operated at low (0.25 A) or no current. Acidic pH levels were more effective in Cr(VI) removal, due to more adsorption of Cr(VI) onto the precipitated Fe hydroxide. The trend in total Cr removal was almost the same as that of Cr(VI) removal, but time required to complete total Cr removal was extended. With intermittent electricity supply at a high electric current intensity, the energy consumption of the system was more efficient. Using scrap iron as a sacrificial anode under the intermittent current condition can save 72–77% of the total operational costs required by the conventional plate electrode.

Enhanced reactivity of nZVI embedded into supermacroporous cryogels for highly efficient Cr(VI) and total Cr removal from aqueous solution

Novel supermacroporous PSA-nZVI composites with nanoscale zero-valent iron particles (nZVI) embedded into poly (sodium acrylate) (PSA) cryogels were synthesized through ion exchange followed by in-situ reduction. The magnetic composites were evaluated for material characterizations and their efficiency for Cr(VI) and total Cr removal from aqueous medium in batch experiments. PSA-nZVI composites with high nZVI loading capacity up to 128.70 mg Fe/g PSA were obtained, and the interconnected macroporous structure of PSA cryogel remained unaltered with nZVI uniformly distributed on PSA cryogel as determined by TGA, SEM, TEM, XRD and XPS analyses. PSA-nZVI composites showed faster reaction rate than free nZVI both for Cr(VI) and total Cr removal, suggesting no mass transfer resistance and the enhanced reactivity of nZVI in PSA carrier. PSA-nZVI composites exhibited much more remarkable performance for Cr(VI) and total Cr removal than free nZVI particles in high removal capacity and broad pH application range (pH 4–10). The reaction mechanisms were also elucidated with XPS analyses before and after Cr(VI) reduction reactions. These results demonstrate that PSA cryogel acts as an excellent carrier and shows multiple functions in nZVI particle dispersion, pH buffering and oxidation resistance in addition to immobilizing nZVI particles from release.

On the critical use of zero valent iron nanoparticles and Fenton processes for the treatment of tannery wastewater

The use of iron nanoparticles in the heterogeneous Fenton oxidation treatment of tannery wastewater was investigated. A comparison with the conventional oxidation process, involving Fe(II) addition was performed. The main operating parameters influence, such as pH, temperature and reagents amount, on total phenolic species, total organic compounds, Cr(VI) content and chemical oxygen demand reduction was investigated.Heterogeneous Fenton oxidation resulted more efficient and fast with respect to the conventional process, but a higher amount of iron was required in the process. In this case, the optimal conditions were assessed at H2O2/COD (w/w) = 0.5, nZVI/H2O2 (w/w) = 0.75 and pH = 3, achieving a total Cr(VI) removal as well as a remarkable TOC, COD and phenols degradation efficiency (up to 70, 73 and 88%, respectively). The best results were obtained with the combination of the two processes, fixing the optimal conventional Fenton operating parameters (H2O2/COD (w/w) = 0.75, Fe(II)/H2O2 (w/w) = 0.15 and pH = 2.5), adopting a nZVI/H2O2 (w/w) ratio equal to 0.2. In such conditions, that also allowed to reduce the catalyst amount used with respect to the Heterogeneous Fenton process, a noticeable TOC, COD and phenols removal efficiency (81.15, 87.44 and 94.04%, respectively) was achieved. In addition, the iron sludge production of such combined process was close to that obtained in the conventional one.

Synergistic conversion and removal of total Cr from aqueous solution by photocatalysis and capacitive deionization

A novel system combining photocatalysis and capacitive deionization (CDI) was proposed and used to efficiently remove the total Cr from the aqueous solution for the first time. MIL-53(Fe) with wide visible-light absorption was successfully prepared by a simple solvothermal method, and applied as positive photoelectrode material of the photocatalysis-CDI system (PCS) to convert Cr(VI) to Cr(III). Active carbon was used as negative electrode material to absorb Cr(III). An enhanced removal of Cr(VI) can be obtained by applying visible light irradiation and 1.3 V direct current (DC) voltage simultaneously and the Cr(VI) removal can reach a maximum value of 81.6%, much higher than those under individual 1.3 V DC voltage (39.4%) or visible light irradiation (54.2%), demonstrating the synergistic effect from CDI and photocatalysis. More importantly, effective removal of the total Cr with high removal ratio (72.2%) can be achieved, which is difficult to be realized using current other technologies. The strategy in this work provides a promising method for the complete removal of high-valence heavy metal ions.

Electrochemical Cr(VI) reduction using a sacrificial Fe anode: Impacts of solution chemistry and stoichiometry

A systematic investigation of Cr(VI) reduction using electrochemical reduction revealed that the Cr(VI) reduction was extremely fast with reaction kinetics limited by the anodic generation of Fe(II). The Cr(VI) reduction rate increased with decreasing pH at the initial stage of reaction but the time to reach complete Cr(VI) reduction is pH independent. The amount of Fe(II) generated per mole of Cr(VI) reduced was calculated and compared with the stoichiometric value, i.e., 3 mole of Fe(II) needed per mole of Cr(VI) reduced. The values are 11.1% higher than the stoichiometric value for pH 7 and 9, but are 32.0% less for pH 3 and 5. The spontaneous reduction of Cr(VI) by Fe0 and adsorption of Cr(VI) to Fe(OH)3 precipitates might contribute the additional Cr(VI) removal. Effect of DO was investigated under various mixing schemes. Under N2 purging, Fe(II) generated for one mole of Cr(VI) reduced is 3.67% higher than the stoichiometric value, while mechanic mixing and aeration mixing show 15% and 19%, respectively, higher than stoichiometric value, indicating that DO does impact Cr(VI) reduction. The electrochemical Cr(VI) reduction process was also employed to treat electroplating wastewater with and without pH pre-adjustment, achieving 100% total Cr and Ni removal for both cases. ORP can be used as a controlling parameter when electrochemical reduction is implemented for Cr(VI) reduction.

Pd/Fe3O4 nanocatalysts for highly effective and simultaneous removal of humic acids and Cr(VI) by electro-Fenton with H2O2in situ electro-generated on the catalyst surface

The widespread presence of humic acids (HAs) and chromium (Cr) in aquatic systems and drinking water sources is a serious threat to the environment and human being. However, no studies on the potential interaction and simultaneous removal of these two types of contaminants have been conducted. Here, a novel electro-Fenton process was reported for the effective and simultaneous removal of HAs and Cr(VI), where H2O2 was in situ produced from the electro-generated H2 and O2 on the Pd/Fe3O4 nanocatalyst surface and Fe(II) was provided from the support. We show that HAs exhibit as reductants and sorbents as well as electron shuttles for the removal of Cr(VI); HAs were efficiently mineralized, as revealed by a total organic carbon removal efficiency of beyond 90%, and Cr(VI) was completely reduced with 90% of total Cr removal. The Pd/Fe3O4 nanocatalysts, as electron transfer and hydrogen atom transfer carriers, were found to play fundamental roles for the removal of HAs and Cr(VI). The HAs degradation was driven by the sequentially involved O2- and OH radicals during electro-Fenton process. The reduction of Cr(VI) was primarily attributed to the contributions from Pd/Fe3O4 nanoparticles and atomic hydrogen on the catalyst surface. In a similar manner, a good recycle of Fe3+ to Fe2+ was accelerated, which favored the Fenton reaction to generate reactive oxidizing species. Importantly, the energy consumption of this electro-Fenton process for HAs degradation was almost 2 orders of magnitude lower than those of reported electrochemical oxidation. The Pd/Fe3O4 nanocatalysts showed excellent removal performances for HAs and Cr(VI) after eight times repeated treatment. This work reports a cost-effective methodology for simultaneous removal of HAs and Cr(VI) and provides a new insight into efficient elimination of complex contaminants by heterogeneous catalysis.

Efficient removal of chromium from water by Mn3O4@ZnO/Mn3O4 composite under simulated sunlight irradiation: Synergy of photocatalytic reduction and adsorption

A novel Mn3O4@ZnO/Mn3O4 composite was designed to remove Cr (VI) and Cr (III) from water by concurrent photocatalysis and adsorption. The Mn3O4@ZnO photocatalyst with core-shell nano-sphere structure, was first fabricated by precisely controlled process using a mild hydrothermal method combined with atomic layer deposition (ALD). The wurtzite ZnO layer was uniformly deposited on hausmannite Mn3O4 surface, which formed a typical II-type heterojunction, separating the photo-generated electron-hole pairs effectively. Hence, rapid Cr (VI) reduction by Mn3O4@ZnO under simulated sunlight irradiation was achieved at 95.3% in 110min. The pure Mn3O4 as adsorbent could subsequently adsorb the reduced Cr (III) from aqueous solution. Noticeably, the total Cr removal efficiency was enhanced to 92.0% within 70min by concurrent photocatalysis and adsorption compared to 88.8% even within 120min in the separate two processes. Mechanism exploration proposed that more active sites on Mn3O4@ZnO surface would be released for continuous photocatalytic reduction of Cr (VI) after the transfer of reduced Cr (III) from Mn3O4@ZnO onto Mn3O4 surface. In addition, the synergy of photocatalysis and adsorption on Cr removal was the strongest at pH=6.0 and the highest removal efficiency of 96.0% was realized within 70min. The outstanding synergistic effect of photocatalytic reduction and adsorption makes the innovative Mn3O4@ZnO/Mn3O4 composite a promising candidate for Cr remediation in aquatic environment.

Isolation of indigenous Staphylococcus sciuri from chromium-contaminated paddy field and its application for reduction of Cr(VI) in rice plants cultivated in pots

ABSTRACTAccumulation of Cr(VI) in rice seeds cultivated in Cr-contaminated soil of the Sundarbans (India) is an environmental problem. Cr(VI) concentration in this soil was 6.2 ± 0.3 mg/kg, whereas total chromium was 32.04 ± 1.60 mg/kg. A Cr(VI)-removing bacterium isolated from Cr-contaminated paddy field soil of Sundarbans was identified as Staphylococcus sciuri. Enrichment culture of S. sciuri was applied to pot cultivation of rice in Cr-contaminated soil. After 8 weeks, 71 ± 3% Cr(VI) (final concentration 2.15 ± 0.01 mg/kg) and 65 ± 2% total Cr removal (end concentration 11.3 ± 0.5 mg/kg) were attained in bacterium-treated soils. Growth parameters indicated healthy development of plants cultivated in bacterium-treated soils that was not observed in control plants. Total Cr removal attained in rice seeds of plants cultivated in bacterium-treated soils compared with control rice seeds was 78 ± 4%. Total Cr concentration in test seeds was 0.72 ± 0.05 mg/kg (World Health Organization [WHO] permissible limit: 1.30 mg/kg), whereas the same in control seeds was 3.27 ± 0.16 mg/kg. Cr(VI) reduction achieved in rice seeds cultivated in bacterium-treated soil compared with control rice seeds was 95 ± 5%. Cr(VI) concentration in rice seeds cultivated in treated soil was 0.050 ± 0.003 mg/kg, whereas the same in untreated control was 0.93 ± 0.05 mg/kg. Successful paddy field soil bioremediation by any Staphylococcus species was demonstrated for the first time.

Removal and Recovery of Chromium from Aqueous Solutions by Reduction-Absorption Microreactor

A rutin-Cr(III) loaded alginate microspheres, which can act as reduction-adsorption microreactor, was designed to reduce Cr(VI) to Cr(III) and recover it. Different from the rutin-Cr(III) complex in alginate-chitosan microcapsule we previously reported, which can sustained release rutin-Cr(III) and reduce Cr(VI) to Cr(III), this microreactor can not only reduce Cr(VI) but also adsorb/recover Cr(III) in aqueous solution. This microreactor was prepared by loading metal complex of rutin into alginate microsphere. It was found that Cr(VI) was initially reduced to Cr(III) by rutin-Cr(III), and then the product Cr(III) was absorbed in the microspheres. Both Cr(VI) reduction rate and Cr(III) adsorption rate were pH-dependent. Cr(VI) can be completely reduced to Cr(III) at pH 1–4 with a reduction capability of 1.27 (±0.078) mmol/g (pH 1, 4 h). The highest blank alginate microsphere adsorption capacity was 1.82 (±0.042) mmol/g at pH 4. It was assumed that reduction-adsorption was the mechanism of total Cr removal by the reduction-absorption microreactor. Recovery experiment showed that 93% and 98% of Cr(III) can be recovered by EDTA and sodium citrate, respectively.

Continuous removal of Cr(VI) from wastewater by phytoextraction using Tradescantia pallida plant based vertical subsurface flow constructed wetland system

This study investigated the performance of Tradescantia pallida in continuous removal of Cr(VI) from contaminated water using a laboratory scale vertical subsurface flow (VSSF) constructed wetland system. The effect of different hydraulic residence time (HRT), i.e. 1, 2 and 3 day HRT, was first studied at an influent Cr(VI) concentration of 20 mg/L. Later experiments were carried out at different influent pH (7 and 4) and at different influent Cr(VI) concentration (20 and 30 mg/L), but with the same HRT of two days. Best results were achieved for 2 d HRT and for an influent pH of 7 with a maximum Cr(VI) removal efficiency of 97.2–98.3% and a maximum total Cr removal efficiency of 86–88.2%. Cr(VI) was found to be uniformly distributed in different segments of the wetland units. Compared with the control unit in which no plants were grown, the units with the plant biomass showed substantially high amount of Cr(VI) in its soil (63–68%). Bioconcentration factor and translocation factor values ranged from 16.45 to 23.21 and 0.37 to 0.90 respectively, which revealed the excellent Cr uptake potential of T. pallida. The highest accumulated Cr concentration (464.33 mg/kg) was found in plants grown in the system at pH 7.0, whereas the minimum accumulated Cr concentration (249.21 mg Cr/kg) was in plants grown in the system at pH 4.0. Furthermore, 3–4% of the total Cr input into the system was accumulated in the plants at the end of the operation. All these results revealed an excellent performance of the T. pallida plant based constructed wetland system for continuous removal of Cr(VI) from contaminated water.

Moisture content-affected electrokinetic remediation of Cr(VI)-contaminated clay by a hydrocalumite barrier.

An electrokinetic-permeable reaction barrier (EK-PRB) system was introduced in this study with hydrocalumite as the barrier material. The combined system effectively remediated the Cr(VI)-contaminated clay after a 72-h treatment, and the Cr(VI) removal efficiency increased with the initial soil moisture content. Further evidence was found that the changing soil pH value and current density were highly associated with the initial moisture content, showing its important roles in the Cr(VI) removal process. Additionally, the total Cr removal efficiency was much lower than that of Cr(VI) owing to the partial conversion of Cr(VI) to Cr(III) in the electrokinetic remediation process. Under high soil moisture conditions (40%), the removal efficiency of Cr(VI) and total Cr was 96.6 and 67.3%, respectively. Further analysis also revealed the new mineral phase, chromate hydrocalumite, for Cr fixation in the hydrocalumite barrier, which was significantly affected by the initial soil moisture content. Our results showed that the EK-PRB system with a hydrocalumite barrier is highly promising with great potential for the effective remediation of Cr(VI)-contaminated clay and engineering implementation.

Effects of reducing agent and approaching anodes on chromium removal in electrokinetic soil remediation

A soil remediation method combining in situ reduction of Cr(VI) with approaching anodes electrokinetic (AAs-EK) remediation is proposed. EK experiments were conducted to compare the effect of approaching anodes (AAs) and fixed electrodes (FEs) with and without sodium bisulfite (NaHSO3) as a reducing agent. When NaHSO3 was added to the soil before EK treatment, 90.3% of the Cr(VI) was reduced to Cr(III). EK experiments showed that the adverse effect of contrasting migration of Cr(III) and Cr(VI) species, which limits the practical application of this technique, was eliminated in the presence of the reducing agent. Furthermore, Tessier fractionation analysis indicated that the reducing agent changed the distribution of the chemical forms of Cr. The AAs-EK method was shown to acidize the soil as the anode moved toward the cathode and this acid front pushed the “focusing” region toward the cathode. After remediation, the pH of the soil was between 1.8 and 5.0 in AAs-EK experiments. The total Cr removal efficiency was 64.4% (except in the “focusing” region) when the reduction reaction was combined with AAs-EK method. We conclude that AAs-EK remediation in the presence of NaHSO3 is an appropriate method for Cr-contaminated soil.

Adsorption of heavy metals from industrial wastewater by using polyacrylic acid hydrogel

In this study, the removal of heavy metals (Cu(II), Ni(II), Zn(II), and total Cr) from real industrial wastewater (IWW), being taken from galvanotechnic industry, by means of polyacrylic acid (Aac) hydrogel was investigated. The effects of adsorbent dosage, contact time, and shaking speed on heavy metal removal from wastewater were monitored using real wastewater. In addition, adsorption isotherm and kinetics studies for adsorption of heavy metals were studied in this study. The adsorption capacities of Aac hydrogel for Cu(II), Ni(II), Zn(II), and total Cr were achieved as 2.74, 1.91, 6.83, and 6.61 mg/g, respectively. The removal of heavy metals using Aac hydrogel was fitted with Freundlich isotherm and pseudo-second-order kinetic models. Thermodynamic studies indicated that the process was exothermic and spontaneous. According to these results, Aac hydrogel is suitable adsorbents for removing heavy metals from IWW.

Comprehensive study on the removal of chromate from aqueous solution by synthesized kaolin supported nanoscale zero-valent iron

A removal mechanism of chromate (Cr) by synthesized kaolin supported nanoscale zero-valent iron (K-nZVI) from aqueous solution is demonstrated. Parameters which potentially influenced the functioning of K-nZVI have been investigated as well. Based on the scanning electron microscopy, Fourier transform infrared spectroscopes, X-ray crystal powder diffraction and X-ray photoelectron spectroscopy identifications, we confirm that amorphous Fe0 core/FexOy shell nZVI can be successfully loaded into the pores and cracks, and onto the surface of kaolin. Removal efficiency of Cr by K-nZVI decreased with increasing initial pH and Cr(VI) concentration, but increased while K-nZVI dosage increased. Humic acid and phosphate had similar dual impacts on chromium removal by K-nZVI, and the inhibitory effect was obvious at high concentrations in spite of their different reaction mechanisms. In contrast, high concentrations of sulfate and nitrate could advance the chromium removal. Adsorption isotherms indicate that the removal processes are endothermic. The data obtained can be better explained with Langmuir than Freundlich model. At the conditions of 318 K and optimized pH 4.0, the maximum adsorption capacity was 33.39 mg g−1 illustrating that K-nZVI was effective for the removal of total Cr. The removal mechanism is proposed to divide into four phases, including: (1) aqueous Cr(VI) ions are captured on the surface of K-nZVI; (2) the captured Cr(VI) are partly reduced to Cr(III) accompanied by Fe0 oxidizing to Fe2+; (3) part of oxidized Fe2+ continues to reduce Cr(VI); and (4) produced Cr(III), Fe2+, and Fe3+ are formed passivation layers on the K-nZVI surface which prevent further removal of chromium and result in redundant Fe0.

Potential application of inorganic sulfur reductants for Cr(VI) removal at sub-ppb level

In this study, the efficiency of inorganic sulfur reductants (ISRs) for the Cr(VI) removal from drinking water at sub-ppb level was evaluated. Particularly, NaHSO3, Na2S2O3, Na2S2O4, Na2S2O5, and Na2S were examined at doses up to 50 mg S/L, which is equivalent to an increase in sulfate concentration up to 150 mg/L in the treated water. Experimental results showed that the removal efficiency is strongly influenced by solution pH. The optimum pH lies at the range 2–4 for all ISRs tested, whereas their efficiency gradually decreases due to the competition with dissolved oxygen, as reaction pH value increases from 4 to 9. At the typical for natural water pH 7, only Na2S2O4 was found capable to reduce an initial Cr(VI) concentration of 100 μg/L down to the sub-ppb level. The reaction kinetics for this reagent showed that 85% of total Cr(VI) removal was achieved within 2 h. It is important to note that at the equilibrium, reached after 8 h, sulfate concentration was safely below the drinking water regulation limit. On the other side, the application of Na2S2O5, Na2S2O3, and NaHSO3 resulted in residual Cr(VI) concentrations not lower than 60 μg/L, while the addition of Na2S, which proved more efficient (residual Cr(VI) 18 μg/L), was responsible for an unpleasant odor indicating the sulfide’s presence.

Enhancement of Cr(VI) removal by modifying activated carbon developed from Zizania caduciflora with tartaric acid during phosphoric acid activation

Abstract Tartaric acid (TA) was employed to modify Zizania caduciflora (ZC)-based activated carbon during phosphoric acid activation for improving its Cr(VI) removal from aqueous solutions. The original activated carbon (AC) and TA-modified activated carbon (AC–TA) were characterized by N 2 adsorption/desorption, Boehm’s titration and X-ray photoelectron spectroscopy (XPS) analysis. The Cr(VI) removal abilities of AC and AC–TA were evaluated by batch sorption experiments. The residual Cr(VI) and total Cr concentration were determined to investigated the “Sorption-coupled reduction” mechanism. Equilibrium data for the Cr(VI) removal on AC and AC–TA were well described by the Freundlich model. The AC–TA exhibited much higher Cr(VI) and total Cr sorption capacities than AC. After blocking of carboxyl and hydroxyl functional groups, the carbons showed obviously higher Cr(VI) and total Cr removal than the original AC and AC–TA, indicating that electrostatic attraction played an important role on Cr(VI) removal. The higher Cr(VI) removal on AC–TA was attributed to its higher amount of oxygen-containing functional groups, which provided more electrons for Cr(VI) reduction and more positive sites for the produced Cr(III) sorption.

Visible light enhanced Cr(VI) removal from aqueous solution by nanoparticulated zerovalent iron

Cr(VI) removal using nanoparticulated zerovalent iron is enhanced under visible light in comparison with the dark process. Using an Fe:Cr(VI) molar ratio (MR) of 1, 77% removal was obtained after two hours under irradiation, compared with 60% in dark conditions; use of MR 2 allowed almost total Cr(VI) removal. Experiments with selected filters indicated that active wavelengths are above 555nm. The proposed mechanism involves a heterogeneous photocatalytic process promoted by the iron oxides present as an external layer of the nanoparticles acting as semiconductors after excitation with light, overcoming the passivation of the material taking place in the dark.

Comparative metal (Cu, Ni, Zn, total Cr, and Fe) removal from galvanic sludge by molasses hydrolysate

AbstractBACKGROUNDThe objective of this study was to evaluate the chemical extraction efficiency of five metals (Cu, Ni, Zn, total Cr, and Fe) from galvanic sludge using molasses hydrolysate produced from molasses, a by‐product of the sugar industry. The study was also aimed to compare the extraction efficiency of the molasses hydrolysate with those of nitric acid and EDTA.RESULTSThe experimental results showed that the metal removal (%) increased with extracting solution concentration, but decreased with increasing solid:liquid (S:L) ratio. The highest removal efficiencies using molasses hydrolysate were: Cu 90%; Ni 100%; Zn 90%; total Cr 100%, and Fe 81% at 10 min extracting time and S:L = 1:10 g mL−1.CONCLUSIONMolasses hydrolysate was found to be more effective than nitric acid and EDTA in the extraction of metals from the sludge. It was concluded that although using HNO3 was more economical than Na2EDTA and molasses hydrolysate, using molasses hydrolysate which is a novel, environmentally friendly, biodegradable extracting agent would be appropriate to prevent secondary pollution. © 2013 Society of Chemical Industry

Cr(VI) removal from aqueous solution using chemically reduced and functionalized graphene oxide

Chemically reduced and functionalized graphene oxide (GO) was prepared by refluxing of GO with ethylenediamine (ED) using dimethyl formamide (DMF) as solvent. It was confirmed that both ED and DMF contributed to the reduction and functionalization of GO. The resulting adsorbent (ED–DMF–RGO) with amine groups was highly efficient in removing Cr(VI) from its aqueous solution and could be easily separated by filtration. The optimum pH for total Cr removal was observed at pH 2.0 and the Cr(VI) removal capacity of ED–DMF–RGO at this pH was 92.15 mg g−1, which was about 27 times higher than that of activated carbon, even nearly 4–8 times higher than that of various modified activated carbons. The presence of other ions such as Na+, K+, Ca2+, Cl−, and Br− had little effect on the removal of Cr(VI). Interestingly, Cr(VI) was reduced to low-toxic Cr(III) during the adsorption process, which followed an indirect reduction mechanism. Both the Cr(VI) adsorption and subsequent reduction of adsorbed Cr(VI) to Cr(III) contributed to the Cr(VI) removal. The obtained ED–DMF–RGO may be applicable in Cr(VI) removal if they are produced on a large scale and at low price in near future.