Removal of hexavalent chromium in aquatic solutions by pomelo peel

This study investigated the removal of hexavalent chromium(Cr(VI)) in aqueous solutions using pomelo peel(PP) and FeCl_3-modified pomelo peel(FPP) as novel biomass adsorbents.Batch adsorption experiments were performed to evaluate the effects of pH,time,temperature,initial concentration,and adsorbent dose on Cr(VI) removal by PP and FPP.The results show that the maximum adsorption capacity of Cr(VI)was 21.55 mg/g for FPP and 0.57 mg/g for PP at a pH of 2.0 and a temperature of 40℃.The surface shape,microstructure,and chemical composition of FPP were analyzed with scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and energy dispersive spectroscopy(EDS),and compared with those of PP.The results show that the adsorption performance of FPP was much better than that of PP,indicating that FPP can be an alternative high-efficiency adsorbent for Cr(VI) removal.     

壳聚糖基印迹水凝微球对Cr (VI)的选择性吸附研究

目前水环境污染物成分复杂,常用的化学沉淀法已很难将重金属污染物分类去除并资源化利用,由此产生了大范围的危废污染环境,需要进行二次处理。利用离子印迹技术对壳聚糖基水凝微球进行改性,制备具有对Cr (VI)特异识别性能的吸附材料(CTS-IGB）,对其在单一Cr (VI)溶液和模拟电镀废水中的吸附行为特征进行研究。研究结果表明:在20 ℃、pH值为3时,CTS-IGB在单一Cr (VI)溶液和模拟电镀废水中Cr (VI)的吸附量在180 min内分别达到37.4 和44.3 mg/g,半饱和吸附时间仅分别为5.8和23.5 min;吸附行为符合准二级动力学。吸附等温线拟合表明吸附过程符合Freundlich模型;热力学参数表明吸附过程是放热反应,且吸附后无序度减小;相比于未改性壳聚糖水凝微球,CTS-IGB在共存离子（模拟电镀废液及其他双组份溶液）工况下对Cr (VI)的选择性提高32%~74%。该材料可作为潜在的吸附材料用于污染水环境中Cr (VI)的分离及回收。     

Selective separation of Cr(III) and Fe(III) from liquid effluents using a chelating resin

This study aimed to assess the selective separation of Cr(III) from Fe(III) from liquid solutions by using a chelating ion exchange resin, Diaion CR 11, from Mitsubishi Chemical Corporation, in the H(+) form. Equilibrium experiments with synthetic solutions of iron and chromium were carried out in batch mode. For both metals favorable adsorption isotherms were obtained, and the experimental data were well described by the Langmuir model. However, the resin exhibited higher affinity for iron than for chromium. The regeneration experiments revealed that, for both metals, HCl provided higher removal efficiencies than H(2)SO(4) and HNO(3). Moreover, precipitation with NaOH allows selectively separate chromium and iron to be stripped from the resin. Experiments in fixed bed operation were carried out to assess the dynamic behavior of the sorption of Cr(III) and Fe(III) into the tested resin by using synthetic and industrial solutions. The experiments with industrial effluent showed that the resin can remove low levels of contaminant transition metal ions, and thus the effluent can be purified for reuse of chromium during periods of 20-25 min. The resin regeneration was achieved with a sequential treatment with HCl and NaOH/H(2)O(2). High efficiencies were observed for both monocomponent and multicomponent systems. A global strategy for separating and recovering Cr(III) from an effluent that also contains Fe(III) is presented, involving the integration of ion exchange (saturation and regeneration phases) and precipitation processes. In conclusion, our approach demonstrates that efficient separation of chromium and iron is possible if ion exchange operation in a fixed bed configuration is optimized and combined with conventional processes such as precipitation.     

Efficient removal of Cr(VI) by polydopamine-modified lignin from aqueous solution: Batch and XAFS studies

Lignocellulose has the potential to become a bio-based adsorbent due to its biodegradability and renewability. In this study, a novel polydopamine-functionalized-lignin (lignin@PDA), prepared via self-polymerization of dopamine (PDA) on lignin, was used as a bio-based adsorbent for rapid scavenging of hexavalent chromium (Cr(VI)). The morphology, functional groups, crystalline structure, and chemical composition of lignin@PDA were characterized with a scanning electron microscope–energy dispersive spectrometer, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The Cr(VI) adsorption process of lignin@PDA was studied using batch experiments as a function of pH, ionic strength, adsorbent dose, and contact time at room temperature. The adsorption rate of lignin@PDA was five times greater than that of the unmodified lignin, with a maximum adsorption capacity of 102.6 mg/g in an acidic medium. The adsorption of Cr(VI) on lignin@PDA fit the pseudo-second-order equation and the Freundlich model, indicating that the adsorption process was mainly dominated by chemisorption and surface complexation. The thermodynamic parameters showed that adsorption of Cr(VI) on lignin@PDA was an endothermic and spontaneous process. The X-ray absorption fine structure results showed that sorption and reduction of Cr(VI) into Cr(III) occurred simultaneously on lignin. Moreover, PDA coating not only improved the reactivity of lignin but also promoted the complete reduction of Cr(VI) by lignin. According to these results, polydopamine-functionalized-lignin is a promising bio-based adsorbent for immobilization of Cr(VI) from wastewater.

     

Removal of hexavalent chromium from wastewater by Fe0-nanoparticles-chitosan composite beads: characterization, kinetics and thermodynamics

Fe0-nanoparticles-chitosan composite beads (CS-NZVI beads) were prepared and used to remove hexavalent chromium (Cr (VI)) from wastewater. Characterization with a scanning electron microscopy (SEM) demonstrated that with the increase of the concentration of CS from 5.0 to 20.0 g/L and NaOH from 0.5 to 2.0 mol/L, the average aperture size of the CS-NZVI beads decreased from 26.8 to 10.6 μm and 42.6 to 0.8 μm, respectively. Batch experiments revealed that the removal of Cr (VI) using CS-NZVI beads was consistent with pseudo first-order reaction kinetics. The rate constant increased with increasing NZVI dosage but decreased with the increase in pH values. The Freundlich isotherm described the adsorption process better, suggesting that the CS-NZVI beads were heterogeneous in the surface properties. At equilibrium qmax was 35.97 mg/g. The thermodynamics study suggested that Cr (VI) removal by CS-NZVI beads was an endothermic and spontaneous process, reflecting good affinity of the sorbent for Cr (VI) ions and increasing randomness at the solid-solution interface during the adsorption process. This result will be very useful to understand the effects of NZVI on heavy metal Cr (VI) removal from wastewater in the successful application.     

Removal of Cr(VI) by magnetite nanoparticle.

Magnetite nanoparticles were synthesized by sol-gel method. The highly crystalline nature of the magnetite structure with diameter of around 10 nm was characterized with transmission electron microscopy and X-ray diffractometry. The surface area was determined to be 198 m2/g. Batch experiments were carried out to determine the adsorption kinetics and mechanism of Cr(VI) by these magnetite nanoparticles. The Cr(VI) uptake was mainly governed by physico-chemical adsorption. The adsorption process was found to be pH and temperature dependent. The adsorption data fit well with the Freundlich isotherm equation. The Freundlich constants were calculated at different temperatures. The adsorption capacity increased with rising temperature. Preliminary results indicate that magnetite nanoparticles may be used as an adsorbent for removal of Cr(VI) from wastewater.     

Adsorption of Cr(VI) in wastewater using magnetic multi-wall carbon nanotubes

Magnetic multi-wall carbon nanotubes were prepared with wet chemical treatments and characterized by a transmission electron microscope (TEM) and X-ray diffraction (XRD). They were used as adsorbents for the removal of Cr(VI) in aqueous solutions. The effects of adsorbent dosage, the concentration of Cr(VI) in aqueous solution, temperature, and pH value on the removal efficiency were studied. Results showed that the adsorption capacity of the magnetic multi-wall carbon nanotubes increased with the initial Cr(VI) concentration, but decreased with the increase of adsorbent dosage. The adsorption amount increased with contact time. The adsorption kinetics were best represented by the pseudo second-order kinetic model, and the adsorption isotherms indicated that the Langmuir model better reflected the adsorption process. The obtained calculation results for the Gibbs free energy revealed that the adsorption was a spontaneous and endothermic process. The enthalpy deviation was 3.835 kJ·mol⁻¹. The magnetic multi-wall carbon nanotubes showed significant potential for application in adsorption of heavy metal ions.     

Biosorption of chromium(VI), nickel(II) and Remazol blue by Rhodotorula muciloginosa biomass

The passive removal of commonly used reactive dye and two heavy metals, from aqueous solutions by inexpensive biomaterial, yeast Rhodotorula muciloginosa biomass, termed biosorption, was studied with respect to pH, initial dye concentration and initial metal ion concentration. The biomass exhibited maximum dye and chromium(VI) uptake at pH 5 and pH 6 for nickel(II) in media containing 50 mg/L heavy metal and 50 mg/L remazol blue. It was found that the highest chromium(VI) removal yields measured were 31.3% for 49.0 mg/l initial chromium(VI) concentrations. The nickel(II) removal yield was 32.5% for 22.3 mg/L. Higher R. Blue removal yields were obtained, such as 77.1% for 117.5 mg/L. The maximum dye biosorption yield was investigated in medium with a constant dye (approximately 50 mg/L) and increasing heavy metal concentration. In the medium with 48.8, 103.8 and 151.8 mg/L chromium(VI) and constant dye concentration, the maximum chromium(VI) biosorption was 7.4, 9.3 and 17.1%, whereas the maximum dye biosorption was 61.6, 56.6 and 55.9%. The maximum nickel(II) biosorptions in the medium with dye were 38.1, 22.1 and 8.8% at 23.7, 37.7 and 60.1 mg/L nickel(II) concentrations. In these media, dye biosorptions were 93.9, 86.4 and 93.3%, respectively.     

复合制剂修复铬污染土的条件优化及微观特性

针对单一还原法和固化/稳定化技术处理铬污染土效果不佳的问题,提出还原-固化/稳定化联用方法,通过单掺试验和L9(34)正交试验,确定了还原剂、吸附剂、固化剂所组成的复合制剂的最佳配比,并采用扫描电镜对固化/稳定化铬污染土进行了微观表征.研究结果表明,复合制剂最佳配比为:CaS5用量是污染土中Cr(Ⅵ)还原为Cr(Ⅲ)所...     

Removal of hexavalent chromium in soil and groundwater by supported nano zero-valent iron on silica fume

Silica fume supported-Fe(0) nanoparticles (SF-Fe(0)) were prepared using commercial silica fume as a support. The feasibility of using this SF-Fe(0) for reductive immobilization of Cr(VI) was investigated through batch tests. Compared with unsupported Fe(0), SF-Fe(0) was significantly more active in Cr(VI) removal especially in 84 wt% silica fume loading. Silica fume had also been found to inhibit the formation of Fe(III)/Cr(III) precipitation on Fe nanoparticles' surface, which was increasing the deactivation resistance of iron. Cr(VI) was removed through physical adsorption of Cr(VI) onto the SF-Fe(0) surface and subsequent reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) could be expressed by pseudo first-order reaction kinetics. The rate constant increased with the increase in iron loading but decreased with the increase in initial Cr(VI) concentration. Furthermore, column tests showed that the SF-Fe(0) could be readily transported in model soil.     

煤质活性炭对Cr(Ⅵ)和As(Ⅲ)的吸附及其影响因素

以煤质活性炭(CAC)为吸附剂,吸附水溶液中Cr(Ⅵ)和As(Ⅲ)。研究了pH值、温度、吸附时间和活性炭投加量等因素对活性炭去除Cr(Ⅵ)和As(Ⅲ)效果的影响。结果表明,Cr(Ⅵ)和As(Ⅲ)最佳吸附的pH值分别为2和5,且pH值对吸附率的影响较大。Cr(Ⅵ)的吸附受温度影响较大,当温度从20℃增加到40℃,吸附率由70%提高到了95%;As(Ⅲ)的吸附随温度的升高先增加后减少,其最佳吸附温度为30℃。Langmuir吸附等温式能够很好地拟合Cr(Ⅵ)和As(Ⅲ)的实验数据,而Pseudo second order模型则较好描述了Cr(Ⅵ)和As(Ⅲ)的吸附动力学。Cr(Ⅵ)和As(Ⅲ)吸附的热力学研究表明,该吸附是一个自发进行的自然吸热过程。     

铬污染土壤动态浸出特征及对地下水影响的模拟

以原长沙铬盐厂污染土壤为研究对象,利用动态淋溶试验,研究不同淋溶模式下土壤六价铬[Cr(VI)]淋出特征及其对地下水的影响。结果显示,淋溶流速会影响土柱中Cr(VI)达到解吸稳定所需要的时间,即在连续淋溶模式的高、中、低3种流速条件下,达到平衡的时间分别为1 、4 、15 d,而间歇淋溶模式的Cr(VI)浸出效率略低于连续淋溶模式,这主要是受到土壤中孔隙水更新效率的控制。利用COMSOL Multiphysics?5.6构建试验中Cr(VI)迁移的模型,计算连续、间歇2种淋溶模式下6种不同情景中Cr(VI)的质量浓度变化及累积浸出质量,结合模型计算与柱实验结果分析发现,当土壤中Cr(VI)质量分数达到二类用地筛选值（5.7 mg/kg）后,淋出液中Cr(VI)质量浓度仍为地下水V类水标准（0.1 mg/L）,此时淋出液中Cr(VI)质量浓度仍对地下水环境造成威胁;同一时间段内,间歇淋溶柱高流速情景下有最小淋出率（33.67 %）,连续淋溶柱高流速情景有最大浸出率（83.99 %）。研究表明,在场地地下水污染治理过程中,需要考虑土壤修复标准对地下水的影响,即水土共治。研究成果可为重金属污染场地修复工程提供参考。     

Mechanistic evidence and efficiency of the Cr(VI) reduction in water by different sources of zerovalent irons.

The objective of this research was to assess the mechanism and effectiveness of the zerovalent iron (ZVI) to remediate the Cr(VI) contaminated water. The mechanism of Cr(VI) reduction by ZVI was evaluated by characterising surface properties and chemical compositions of Fe and Cr products using SEM-EDS, XRD and XPS analyses. The effectiveness of ZVI in Cr(VI) reduction was assessed by the luminescent bacteria (Photobacterium Phosphoreum). The Cr(VI) was reduced to Cr(III), when the reactive Fe(o) was oxidised to Fe(II, III), showing the presence of Fe2O3, (Fe-Cr)2O3 and FeOOH. The SEM-EDS analysis showed that ZVI with a higher reducing capacity was more subject to changes of surface and morphological properties due to ionisation of ZVI. The Cr and Fe in precipitates subsisted exclusively in the Cr(III) or Fe(III) states with the respective forms of Cr(OH)3 or Cr2O3 and FeOOH or Fe2O3. Electrons produced from ZVI oxidation reduced Cr(VI) to Cr(III), thus resultantly Cr(III) precipitated or co-precipitated with Fe(III) to form Fe(III)-Cr(III) hydroxide or Fe(III)-Cr(III) oxyhydroxide. Toxicity of water reacted with ZVI was significantly lower than that of the untreated water.     

Chromate sorption and reduction kinetics onto an aminated biosorbent.

A novel biosorbent was prepared by chemically grafting of polyethylenimine (PEI) onto the fungal biomass of Penicillium chrysogenum through a two-step reaction. The modified biosorbent is favorable for the removal of anionic Cr(VI) species from aqueous solution due to the protonation of amine groups on the biomass surface. The sorption capacity for Cr(VI) increased by 7.2-fold after surface modification. Sorption kinetics results show that the pseudo-second-order kinetic model described the experimental data well. During the sorption process, X-ray photoelectron spectroscopy (XPS) was used to analyze the chromium species on the biosorbent surface and the results indicate that part of the Cr(VI) ions were reduced to Cr(III) ions which can be chelated with the amine groups on the biomass surface. The reduced Cr(III) ions formed some aggregates on the surface at higher solution pHs.     

改性活性炭对饮用水中铬酸盐的去除特性研究

研究了阳离子聚合物十六烷基三甲基氯化铵(CTAC)、癸基三甲基溴化铵(MTAB)以及三甲基正十四烷溴化铵(DTAB)对颗粒活性炭的改性特点以及改性后活性炭对饮用水中六价铬的去除效果。目的在于开发一种能有效去除饮用水中铬盐离子的吸附材料。研究中首先利用吸附平衡实验比较了未改性活性炭以及三种阳离子聚合物改性后活性炭对铬的吸附能力。结果表明:阳离子聚合物改性能有效提高活性炭对铬的吸附,同时CTAC改性后活性炭对铬盐的吸附效果要好于MTAB和DTAB。另外,活性炭对六价铬的吸附过程符合Langm iur吸附平衡模型以及二级动力学模型。阳离子聚合物在活性炭上的稳定性也是个重要的问题。对其检测的结果表明聚合物和活性炭的结合非常稳定,改性活性炭吸附六价铬的过程中阳离子聚合物的脱附量少于3%。     

Spatial and seasonal variations and ecotoxicological significance of sediment trace metal concentrations in Kebir-Rhumel basin (Northeast of Algeria)

This study sought to assess sediment contamination by trace metals (cadmium, chromium, cobalt, copper, manganese, nickel, lead and zinc), to localize contaminated sites and to identify environmental risk for aquatic organisms in Wadis of Kebir Rhumel basin in the Northeast of Algeria. Water and surficial sediments (0-5 cm) were sampled in winter, spring, summer and autumn from 37 sites along permanent Wadis of the Kebir Rhumel basin. Sediment trace metal contents were measured by Flame Atomic Absorption Spectroscopy. Trace metals median concentrations in sediments followed a decreasing order: Mn > Zn > Pb > Cr > Cu > Ni > Co > Cd. Extreme values (dry weights) of the trace metals are as follows: 0.6-3.4 microg/g for Cd, 10-216 microg/g for Cr, 9-446 microg/g for Cu, 3-20 microg/g for Co, 105-576 microg/g for Mn, 10-46 microg/g for Ni, 11-167 microg/g for Pb, and 38-641 microg/g for Zn. According to world natural concentrations, all sediments collected were considered as contaminated by one or more elements. Comparing measured concentrations with American guidelines (Threshold Effect Level: TEL and Probable Effect Level: PEL) showed that biological effects could be occasionally observed for cadmium, chromium, lead and nickel levels but frequently observed for copper and zinc levels. Sediment quality was shown to be excellent for cobalt and manganese but medium to bad for cadmium, chromium, copper, lead, nickel and zinc regardless of sites.     

Biosorption and bioreduction of Cr(VI) by locally isolated Cr-resistant bacteria.

Cr(VI) biosorption and bioreduction ability of locally isolated Cr-resistant bacteria was investigated using the shake-flask technique. A mixture of S. epidermidis and B. cereus showed the highest minimum inhibitory concentration (MIC) level at 750 mg/L Cr(VI) followed by S. aureus and Bacillus sp. of 250 mg/L, and A. haemolyticus of 70 mg/L. From the Langmuir adsorption isotherm, the treatment of cells with heat-acid resulted in the highest amount of Cr(VI) adsorped (78.25 mg/g dry wt. for S. epidermidis) compared to heat-acetone (67.93 mg/g dry wt. Bacillus sp.), heat only (36.05 mg/g dry wt. S. epidermidis) or untreated cells (45.40 mg/g dry wt. S. epidermidis and B. cereus). FTIR analysis showed the involvement of amine groups in Cr(VI) adsorption. In the bioreduction study, A. haemolyticus was able to completely reduce Cr(VI) up to 50 mg/L.     

利用工业酒精处理铬渣

利用工业酒精处理铬渣,使毒性大的Cr6+还原为毒性小的Cr3+,再用氨水中和,将Cr3+以Cr(OH)3的沉淀形式进行回收,从而达到铬渣的安全堆放。对Cr6+的解毒效果进行了单因素试验,得到最佳工艺条件:每10 g铬渣用酒精3 mL,酸度为0.5 mol/L,反应温度为40℃,反应时间为1 h。     

Efficient removal of Cr(VI) by tannic acid-modified FeS nanoparticles: Performance and mechanisms

Ferrous sulfide (FeS) nanoparticles constitute an effective hexavalent chromium (Cr(VI)) treatment reagent. However, FeS nanoparticles aggregate easily, significantly limiting their engineering applicability. To overcome this shortcoming and further improve Cr(VI) removal efficiency, this study used tannic acid (TA) to modify FeS nanoparticles. The results demonstrated that TA-modified FeS nanoparticles, TA-nano-FeS, had a significantly reduced tendency to agglomerate, and maintained particle diameters of 10–100 nm, which were much shorter than diameters of FeS nanoparticles. In addition, TA-nano-FeS could combine the surface-active functional groups of TA. The maximum removal capacity of TA-nano-FeS was 381.04 mg/g, which was 2.92 and 1.83 times higher than those of TA and nano-FeS, respectively. Furthermore, the acidic condition was more beneficial for Cr(VI) removal, and the coexisting cations (Ca²⁺ and Mg²⁺) slightly decreased the removal efficiency of Cr(VI). Adsorption, reduction, and co-precipitation were the removal mechanisms, and the reaction products included FeCr₂O₄, Cr₂O₃, Fe₂O₃, Cr(OH)₃, and S₈. The results provided valuable information for the practical application of TA-nano-FeS in Cr(VI) removal.     

Co-precipitation of Ni, Cr, Mn, Pb and Zn in industrial wastewater and sediment samples with copper(II) cyclo-hexylmethyldithiocarbamate for their flame atomic absorption spectrometric determination

A co-precipitation technique for nickel(II), chromium(II), manganese(II), lead(II) and zinc(II) with the aid of copper(II) cyclo-hexylmethyldithiocarbamate was established. The influences of some analytical parameters such as pH, sample volume, amounts of cyclo-hexylmethyldithiocarbamate and copper(II) on the recovery of metal ions were investigated. The heavy metals in the precipitate were determined by flame atomic absorption spectrophotometry. The range of detection limits for the heavy metals was 0.003-0.005 mg/L. The atomic spectrometric technique with co-precipitation procedure was successfully applied for the determination of Ni, Cr, Mn, Pb and Zn in industrial wastewater and sediment samples from Ladipo stream in Lagos, Nigeria. The mean concentrations for these metals using co-precipitation procedure were not significantly different from corresponding concentrations obtained using spectrometric techniques without co-precipitation procedure.