Removal of Cr (VI) from aqueous solution by newspapers

The potential to remove Cr (VI) ions from aqueous solution using newspapers was investigated in the present study. The effects of relevant parameters such as solution pH, adsorbent concentration, and reaction temperature on Cr (VI) adsorption were examined. The adsorption of Cr (VI) ions onto newspapers was found to be highly pH-dependent and the highest uptake occurred at pH 1.0. The sorption equilibrium data were correlated to the Langmuir, Freundlich, Redlich-Peterson and Dubinin-Radushkevich equations. Five different non-linear error functions were examined and the result indicated that the Freundlich and Redlich-Peterson equations better fitted the equilibrium data than Langmuir isotherm. The maximum sorption capacity was found to be 55.06 mg/g at pH 1.0, adsorbent concentration 4 g/L and reaction temperature of 30 °C. Different thermodynamic parameters viz., changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) were also evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The kinetic experimental data were well fitted by the pseudo-second order, external film diffusion and diffusion models allowing the corresponding parameters to be evaluated. The sorption capacity increased with the decrease of adsorbent concentration.     

Removal of Cr(VI) from aqueous solution by surfactant-modified kaolinite

Removal of Cr(VI) from aqueous solution by hexadecyltrimethylammonium chloride (HDTMA) modified kaolinite (HMK) was investigated, where the maximum adsorptive capacity reached 27.8 mg/g Cr(VI) using HMK compared with only 0.7 mg/g using unmodified natural kaolinite (NK). The adsorption of Cr(VI) on HMK can be well described by the Langmuir isotherm, and the kinetic adsorption of Cr(VI) on both HMK and NK fitted a pseudo-second-order model. FTIR analysis showed that surface modified HDTMA was responsible for the high adsorptive capacity of Cr(VI). HMK was used to remove Cr(VI) from an electroplating wastewater.     

Removal of Cr(VI) from aqueous solution by London plane leaves

The effect of initial metal concentration, contact time and solution temperature on the removal of Cr(VI) from solution by waste London plane leaves, generated by the pruning of street trees, was investigated in batch mode conditions. The removal of Cr(VI) was highly concentration‐dependent and mainly governed by physico‐chemical adsorption under the weak acidic conditions studied. The equilibrium data fit well in the Langmuir isotherm model. The Langmuir constants were calculated at different temperatures and both the adsorption capacity and adsorption intensity increased with rising temperature. The endothermic nature of the Cr(VI) adsorption was confirmed by the thermodynamic parameters. The study has shown that the waste leaves can be used as an effective adsorbent for removal of Cr(VI) from wastewater. Copyright © 2003 Society of Chemical Industry     

Removal of glyphosate from aqueous solution by CuO coated MIL-101(Fe)

The composite of CuO coated MIL-101(Fe) (CuO@MIL-101(Fe)) was successfully prepared using a one-pot hydrothermal technology. X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer–Emmett–Teller (BET), and TG technologies were used to characterize its structural, morphological, and physicochemical properties. CuO@MIL-101(Fe) exhibited a better pH adaptivity, a faster removal ratio of 95.8% for glyphosate within 10 min at pH 7, and a higher selectivity of adsorption capacity, even reaching 231.6 and 233.5 mg g⁻¹ with coexisting Cl⁻ (10 mmol L⁻¹) and SO₄²⁻ (10 mmol L⁻¹). The enhanced adsorption performances of CuO@MIL-101(Fe) may be caused by Cu forming a coordination interaction with glyphosate. A possible mechanism of glyphosate removal was discussed on the basis of the FTIR and X-ray photoelectron spectroscopy (XPS) analysis. CuO@MIL-101(Fe) composite would be more favourable to capture glyphosate from wastewater.     

Removal of As(V) from aqueous solutions by waste crab shells

Waste crab shell, which has some functional groups like -NHCO or NO₂ groups, was used as an adsorbent to remove arsenate ions (As (V)). The functional groups in crab shells were confirmed by FT-IR analysis. Waste crab shell had a high uptake capacity of 35.92 mg/g-dry mass for arsenate ion at pH 4, and the regression curve using the Langmuir isotherm equation fit well with the experimental data. The effects of pH, loading of crab shells, and time on uptake capacity of arsenate ions were also investigated. The adsorption capacity of arsenate ions was increased as the pH value was increased because the amount of negative arsenic species increased as the pH value was increased. Waste crab shells could remove arsenate ions of about 45% with 0.5 g of loading amount, and adsorption of arsenate ions was almost completed in 30 min when initial concentration of arsenate ions was 100 and 9.3 mg/L, respectively. Considering recycling of crab shell, it could be an economical and promising adsorbent.     

Removal of Cr(VI) from aqueous solution using magnetite/non-oxidative graphene composites: Synergetic effect of Cr(VI) on dyes removal

Non-oxidative graphene (nOG) synthesized from natural graphite powder was modified with magnetite (Fe₃O₄) for removal of Cr(VI) and dyes in aqueous solution. The adsorption behavior of Cr(VI) on Fe₃O₄/nOG (M-nOG) was systematically investigated, and the simultaneous adsorption of Cr(VI) and dyes such as methylene blue (MB) and rhodamine B (RhB) was evaluated. Adsorption kinetic and isotherm of Cr(VI) were fitted well with pseudo-second-order model and Sips model, respectively. For the binary system, Cr(VI) removal was not affected with increasing the dye concentration, whereas the adsorption capacity of both MB and RhB was enhanced with increasing the concentrations of Cr(VI).     

Enhanced adsorptive removal of Cr(VI) in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine (PEI) modified palygorskite (Pal) was used for the adsorption of Cr(VI) in aqueous solution. The absorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Characterized results confirmed that the Pal has been successfully modified by PEI. The modification of PEI increased the Cr(VI) adsorption performance of the Pal by the adsorption combined reduction mechanism, and amino groups of the adsorbent play the main role in the enhanced Cr(VI) adsorption. The maximum adsorption capacity was 51.10 mg·g⁻¹ at pH 4.0 and 25 °C. The adsorption kinetics of Cr(VI) on the adsorbent conforms to the Langmuir isotherm model. The maximum adsorption occurs at pH 3, and then the adsorption capacity of PEI-Pal was decreased with the increase of pH values. The adsorption kinetics of Cr(VI) on PEI-Pal was modeled with pseudo-second-order model. The addition of Cl⁻, SO₄²⁻ and PO₄³⁻ reduced the Cr(VI) adsorption by competition with Cr(VI) for the active sites of PEI-Pal. The Cr(VI) saturated PEI-Pal can be regenerated in alkaline solution, and the adsorption capacity can still be maintained at 30.44 mg·g⁻¹ after 4 cycles. The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI) in aqueous solutions.     

Enhanced adsorptive removal of Cr(VI) in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine (PEI) modified palygorskite (Pal) was used for the adsorption of Cr(VI) in aqueous solution. The absorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Characterized results confirmed that the Pal has been successfully modified by PEI. The modification of PEI increased the Cr(VI) adsorption performance of the Pal by the adsorption combined reduction mechanism, and amino groups of the adsorbent play the main role in the enhanced Cr(VI) adsorption. The maximum adsorption capacity was 51.10 mg·g^-1 at pH 4.0 and 25 ℃. The adsorption kinetics of Cr(VI) on the adsorbent conforms to the Langmuir isotherm model. The maximum adsorption occurs at pH 3, and then the adsorption capacity of PEI-Pal was decreased with the increase of pH values. The adsorption kinetics of Cr(VI) on PEI-Pal was modeled with pseudo-second-order model. The addition of Cl^-, SO₄^2- and PO₄^3- reduced the Cr(VI) adsorption by competition with Cr(VI) for the active sites of PEI-Pal. The Cr(VI) saturated PEI-Pal can be regenerated in alkaline solution, and the adsorption capacity can still be maintained at 30.44 mg·g^-1 after 4 cycles. The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI) in aqueous solutions.     

石英砂负载氧化铁吸附去除溶液中亚甲蓝的研究

以石英砂为原料制得石英砂负载氧化铁(IOCS),考察了IOCS的性能、吸附条件对IOCS吸附亚甲蓝效果的影响及吸附柱的再生,并对吸附过程进行了动力学研究。结果表明,采用高温烧结法制备的IOCS吸附亚甲蓝效果较好;IOCS对溶液中亚甲蓝吸附的适宜条件:pH为13.5,亚甲蓝质量浓度约为6 mg/L,温度为293 K,上样液吸附流速为4 BV/h;IOCS对溶液中亚甲蓝的吸附动力学曲线可以用Weber-Morris曲线来拟合;Langmuir吸附等温方程和Freundlich方程都能较好地描述IOCS对溶液中亚甲蓝的吸附过程;0.01 mol/L的HCl对IOCS吸附柱的再生效果较好。     

活性炭负载Fe(III)吸附剂去除饮用水中的As(V)

利用活性炭负载水合铁氧化物制备了复合吸附剂,并用于饮用水中As(V)的去除. 研究了活性炭种类、粒度、溶液pH值、Fe(III)盐浓度和干扰离子等对As(V)去除的影响. 结果表明,煤质活性炭作为基质负载水合铁氧化物比椰壳炭和果壳炭具有更好的除砷效果. 随着炭粒度降低,除砷效率显著增加. 在pH 3~9范围内,活性炭负载水合铁氧化物可有效吸附As(V). F-, Cl-, SO42-的加入对As(V)的去除效率基本无影响,而SiO32-和PO43-则明显抑制As(V)的去除. Langmuir模型比Freundlich模型能更好地描述复合吸附剂对As(V)的吸附平衡. 动力学研究表明,As(V)吸附反应可用二级速率方程描述.     

Effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution by modified polyethyleneimine

A novel flocculant with the capacities of reduction and chelation was prepared in this paper. The flocculant, called polyethyleneimine–sodium xanthogenate (PEX), was synthesized by modifying polyethyleneimine with carbon disulfide and sodium hydroxide. The effect of pH on the removal of Cr(III) and Cr(VI) from aqueous solution with PEX was investigated by using flocculation experiments. The results showed that in the single-ion system (only including Cr(III) or Cr(VI) in the solution), the final Cr(III) decreased with the increase in pH from 2.0 to 10.0, while the final Cr(VI) increased at first and then decreased with the increase in this pH range studied. The removal of Cr(III) was not desirable at pH lower than 7.0, whereas the final Cr(VI) concentration reached the minimum value of 0.145 mg/L at pH 2.0. In the mixture system of Cr(III) and Cr(VI), the variation tendency for the removal of Cr(III) or Cr(VI) was very similar to that obtained in the single-ion system. The oxidation–reduction potential, zeta potential, and final pH in the supernatant were also measured to analyze the above results. Furthermore, FTIR spectra revealed that dithiocarboxylic acid groups on the macromolecular chains of PEX played a major role in the Cr(VI) reduction and Cr(III) chelation.     

Removal of Cr(VI) from water using Fe(II)-modified natural zeolite

In this study, natural zeolite aggregates with the particle size of 1.4–2.4 mm were modified by Fe(II). The unmodified zeolite and Fe(II)-modified zeolite (Fe-eZ) were subjected to batch and column tests to study the Cr(VI) sorption, transport, and retardation. Modification of the natural zeolite with Fe(II) resulted in an increase in Cr(VI) sorption to 6 mmol/kg. The Cr(VI) sorption followed a pseudo-second-order kinetics with a rate of 17 mmol/g h and a rate constant of 0.7 g/mmol h. Cr(VI) removal from solution increased with an increase in ionic strength, but decreased as the solution pH increased. At a Cr(VI) input concentration of 100 mg/L, unmodified zeolite did not show any Cr(VI) retardation at all. In contrast, the observed retardation factor of Fe-eZ for Cr(VI) increased by a factor of 6. The hydraulic conductivity of the zeolite showed little change before and after Fe(II) modification and before and after Cr(VI) sorption, suggesting its good mechanical stability to be used as packing materials for permeable reactive barriers in groundwater remediation.     

Removal of Cr(V1) from aqueous solutions by adsorption on fly ash-wollastonite

The ability of a homogeneous mixture of fly ash and wollastonite (1:1) to remove Cr(V1) from aqueous solutions by adsorption has been investigated. The extent of removal is dependent on concentration, pH and temperature of the solution. The applicability of the Langmuir isotherm for the present system has been tested and the surface mass transfer coefficient at 30°C and pH 2.0 determined. Maximum removal was observed at pH 2.0 and 30°C. The adsorption is first governed by diffusion followed by surface compound formation. The thermodynamic parameters, desorption results and infrared studies indicated that the surface compounds, formed by interaction of adsorbate ions and different constituents of mixed adsorbent, were stable in nature.     

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 555 nm. 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.     

Efficient removal of Cr(VI) and Pb(II) from aqueous solution by magnetic nitrogen-doped carbon

The magnetic nitrogen-doped carbon (MNC) was prepared from polypyrrole by a simple high temperature calcination process in this paper. The structure and properties of MNC were analyzed by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, Brunner-Emmet-Teller, vibrating sample magnetometer, and X-ray photoelectron spectroscopy. The capacity of MNC to adsorb Cr(VI) and Pb(II) was evaluated. The effects of the initial pH, dosage, concentration and temperature on the adsorption capacity of MNC were measured. MNC had a large specific surface area and a special porous structure. Its nitrogen and carbon sources were rich, and the ratio of carbon to nitrogen was fixed. The maximum Cr(VI)-adsorption capacity and maximum Pb(II) adsorption capacity of MNC could reach 456.63 and 507.13 mg∙g⁻¹ at 318 K, respectively. The pseudo-second-order model was used to describe the adsorption kinetics of MNC, and the Freundlich model was employed to discuss its isotherms. The adsorption process was affected by the electrostatic force, the reducing reaction, pores and chelation. The results of this study suggest that MNC is a material with superior performance, and is very easily regenerated, reused, and separated in the adsorption process.     

Functionalized chitosan with butylammonium ionic liquids for removal of Cr(VI) from aqueous solution

Environmental pollution by heavy metals is currently a problem of great concern for human health. In this context, this study aims to contribute with the synthesis and characterization of chitosan functionalized with three different ionic liquids (n-butylammonium acetate, sec-butylammonium acetate, and tert-butylammonium acetate) followed by its application in hexavalent chromium effluent treatment. The adsorbents synthesized (ChN, ChS, and ChT) were characterized by SEM, EDS, FTIR, BET, RDD, PSD, and XRD techniques. Afterward, the influences of temperature, contact time, and pH on the Cr(VI) adsorption process were evaluated. The solution with pH 3 displayed the highest adsorption capacities (107.31, 104.60, and 107.97 mg.g^-1 for ChN, ChS, and ChT, respectively). The kinetic data were better adjusted to the Weber-Morris kinetic model with an ideal time of 2 h. Furthermore, the influence of temperature was evaluated using the Freundlich and Langmuir isotherms, with maximum capacities of 142.05 (ChN), 131.58 (ChS), and 146.63 mg.g^-1 (ChT). The adsorbent displayed enhanced adsorption properties in comparison with raw chitosan by an intensification of the electrostatic interaction between amino groups and hexavalent chromium. Finally, the reusability was investigated, and significant results were observed (84.33 ± 4.87%) in the adsorption process after 4 cycles.     

硫酸盐还原剩余污泥-生物炭制备及对 Cr(VI)去除性能

以硫酸盐还原剩余污泥(sulfate reducing sludge, SRS)作为生物质原料，在500 ℃限氧条件下制备生物炭材料（SBC-500）。并以某污水处理厂污泥浓缩池中的厌氧污泥制备的生物炭（BC-500）作为对照，通过SEM、XRD、FTIR及BET对两种生物炭进行表征分析，并对比不同材料对Cr(Ⅵ)的去除能力。结果表明：相较于BC-500，SBC-500在产率、灰分及孔容方面具有优势，其BET比表面积为17.90 m2/g，明显大于BC-500（10.24 m2/g）。以SRS制备的SBC-500，其表面孔道结构明显，生物炭内部镶嵌有不规则边缘晶型结构，XRD观测到石墨烯碳、非晶型碳及FeS晶型结构存在，FTIR图谱出现O═S═O的反对称伸缩振动峰、S═O双键的特征吸收峰。在pH为3，投加量为0.2 g，Cr(Ⅵ)初始质量浓度为10 mg/L，吸附48 h后，SBC-500对Cr(Ⅵ)去除率达到100%，初始质量浓度增至200 mg/L时，SBC-500对Cr(Ⅵ)的吸附量为8.22 mg Cr(Ⅵ)/g，与BC-500相比，SBC-500对Cr(Ⅵ)具有更好的去除能力。该研究为剩余污泥实现资源化处置与受重金属污染水体修复提供新的理念与思路。     

Visible light photoreduction of Cr(VI) in aqueous solution using iron-containing zeolite tubes

In this study, a novel visible light photocatalyst consisting of iron-loaded zeolite tubes was designed to reduce Cr(VI) to Cr(III) in aqueous solution. Iron was incorporated into hollow, porous ZSM-5 tubes using two different methods. In the first method, the iron-encapsulated ZSM-5 tubes were prepared by introducing iron into the mesoporous silica template prior to the formation of the hollow ZSM-5 tubes resulting in an encapsulated iron species. In the second method, iron was ion-exchanged into the ZSM-5 shell during a post-synthesis treatment. The iron-loaded ZSM-5 structures were extensively characterized by powder X-ray diffraction (XRD), elemental analysis, solid-state ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR), electron paramagnetic resonance (EPR), electron microscopy with energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy (XPS). The iron in the iron-exchanged ZSM-5 tubes tended to aggregate compared to the iron in the iron-encapsulated ZSM-5 tubes. Both the iron encapsulated and iron-exchanged ZSM-5 hollow tubes were active for the visible light photoreduction of Cr(VI) to Cr(III) in aqueous solution. The iron-exchanged ZSM-5 tubes were very active initially but suffered from substantial iron leaching after the first use in aqueous Cr(VI) photoreduction relative to the iron-encapsulated ZSM-5 tubes which showed very little leaching of the iron.     

Removal of As(V) and Cr(VI) Ions from Aqueous Solution using a Continuous,Hybrid Field‐Gradient Magnetic Separation Device

Abstract

A continuous flow colloidal affinity magnetic separation device is used for the removal of As(V) and Cr(VI) from aqueous solutions. Langmuir isotherms fit the adsorption behavior of the individual ions on Orica MIEX^® ion exchange particles. In a mixture of equal weight percent As(V) and Cr(VI), the adsorption of As(V) begins only above a critical cut‐off concentration, implying preferential adsorption of the higher valence ion at the available sites. Cr(VI) is removed selectively from the mixture in the continuous flow device, consistent with the presence of a higher concentration of the higher valence ion in the proximity of a charged (anion‐exchange) surface.