膨润土负载纳米零价铁去除废水中Cr(Ⅵ)的动力学特性研究

利用液相还原法制备膨润土负载纳米零价铁(B-nZVI)并将其应用于含Cr(Ⅵ)废水的处理,研究了B-nZVI投加量、反应时间和溶液初始pH等3个因素对Cr(Ⅵ)处理效果的影响,探讨了B-nZVI对不同初始浓度的含Cr(Ⅵ)废水的降解动力学规律,通过扫描电镜和X射线衍射仪对反应前后的B-nZVI进行形貌分析。结果表明:膨润土能有效提高纳米零价铁(nZVI)的分散性并阻止其氧化。三因素对Cr(Ⅵ)去除率影响均达到显著水平(p0.05),其中投加量的影响达到极显著水平(p0.01);其显著性大小依次为:投加量溶液初始pH反应时间。在投加量为2.0g/L、反应40min、溶液初始pH=6的最佳工艺条件下,初始浓度为20mg/L的含Cr(Ⅵ)废水中Cr(Ⅵ)去除率可达99.15%。B-nZVI去除Cr(Ⅵ)的反应在不同Cr(Ⅵ)初始浓度下均能较好地符合准一级动力学模型,且可用L-H动力学模型描述;B-nZVI对Cr(Ⅵ)去除是吸附和还原共同作用的结果,且nZVI对Cr(Ⅵ)的还原作用是其去除的主要作用机制。     

纳米零价铁对钨离子的吸附相平衡和动力学

采用液相还原法制备纳米零价铁(nZVI),并用PXRD、TEM、BET和XPS等表征手段对材料进行表征。探讨了初始钨(Ⅵ)浓度、纳米零价铁用量和初始pH值对纳米零价铁吸附钨(Ⅵ)性能的影响,测定了纳米零价铁对钨(Ⅵ)的吸附等温线和吸附动力学曲线。研究结果表明,制备的纳米零价铁具有典型的核-壳结构,其粒径在10~30nm之间,BET比表面积为53m~2/g。纳米零价铁对钨(Ⅵ)的回收率随着初始钨(Ⅵ)浓度和初始pH值的增大而减小。在25℃条件下,纳米零价铁对钨(Ⅵ)的平衡吸附容量为172.82mg/g。Langmuir等温线方程可以很好地拟合纳米零价铁对钨(Ⅵ)的吸附等温线,且纳米零价铁对钨(Ⅵ)吸附动力学曲线符合准二级动力学模型。     

流变相法制备包裹型Starch/Fe~0及去除水中Cr(Ⅵ)的反应动力学研究

以水溶性淀粉(starch)为包裹剂,采用流变相反应法制备了包裹型纳米零价铁(Starch/Fe0)。并用XRD、SEM和TEM等手段对样品进行了表征。研究了样品投加量、pH值、初始Cr(Ⅵ)浓度及铜离子浓度对水溶液中Cr(Ⅵ)去除率的影响及反应动力学,探讨了包裹型Starch/Fe0去除Cr(Ⅵ)的反应机理。实验结果表明,包裹型Starch/Fe0投加量为0.6 g/L,pH值为5,初始Cr(Ⅵ)浓度为10 mg/L时,Cr(Ⅵ)的去除率可达100%。当反应体系中Cu2+和Cr(Ⅵ)共存时,Cu2+在反应中对Cr(Ⅵ)的去除有促进作用。包裹型Starch/Fe0对Cr(Ⅵ)的还原过程符合准一级反应动力学模型。     

壳聚糖负载纳米零价铁对Cr(Ⅵ)吸附性能的研究

采用液相还原法制备纳米零价铁,使用质量分数为1％的壳聚糖对纳米零价铁进行改性,制备壳聚糖负载纳米零价铁吸附剂.考察pH、温度、吸附剂用量、吸附时间对Cr(Ⅵ)吸附性能的影响.再进行正交试验,探究吸附剂对Cr(Ⅵ)的最佳吸附条件.使用X射线衍射仪、扫描电镜、红外光谱对吸附剂进行表征.结果 表明:吸附Cr(Ⅵ)的最佳条件是...     

薰衣草提取液绿色合成生物炭负载纳米零价铁去除水中亚甲基蓝的研究

以薰衣草提取液为还原剂，白酒废水污泥生物炭(WSB)为载体，采用绿色合成法制备了生物炭负载纳米零价铁复合材料(nZVI@WSB),并将其用于亚甲基蓝(MB)废水的处理，利用扫描电子显微镜-能谱(SEM-EDS)、透射电镜(TEM)、全自动比表面及孔隙度分析仪(BET)、傅立叶变换红外光谱(FT-IR)、X射线衍射图谱(XRD)和X射线光电子能谱(XPS)等手段对nZVI@WSB进行了表征，并考察了其对MB的吸附性能。结果表明：nZVI@WSB的比表面积和孔容增大、稳定性和反应活性增强。在投加量1.0g/L和不调节溶液初始pH的反应体系中，MB的去除率随着初始浓度的增加而升高，而升温也有利于MB的去除。nZVI@WSB对MB的吸附过程分别符合准二级动力学方程、Langmuir和Redlich-Peterson等温方程。热力学研究表明，nZVI@WSB吸附MB是自发、熵增的吸热过程。     

城市污泥改性物对电镀废水中Cr(Ⅵ)的吸附研究

在静态条件下,进行了以城市污泥改性物(MSMP)作吸附剂净化含Cr(Ⅵ)废水的试验.研究了含Cr(Ⅵ)废水的pH值、浓度、接触时间和吸附剂的投加量等因素对MSMP吸附Cr(Ⅵ)的影响,确定了MSMP净化含Cr(Ⅵ)废水的最佳条件为:吸附时间20 min,pH值为中性,Cr(Ⅵ)起始浓度不超过50 mg/L,温度为30℃.结合对实际含Cr(Ⅵ)废水的吸附净化处理,证实了MSMP可用于电镀废水中Cr(Ⅵ)的吸附处理.     

Box-Behnken响应曲面法优化草酸改性杨树叶对六价铬的吸附

采用草酸改性杨树叶(OPL)作为新型生物吸附剂对水溶液中六价铬[Cr(Ⅵ)]进行吸附,探讨了影响吸附效果的主要因素,并利用Box-Behnken响应曲面法对吸附条件进行优化。单一因素实验结果表明,溶液pH、吸附剂投加量和Cr(Ⅵ)离子初始质量浓度对Cr(Ⅵ)在生物吸附剂OPL表面的吸附产生较大影响。Box-Behnken响应曲面法对吸附条件的优化结果表明,当pH为1.66、投加量为0.29g、Cr(Ⅵ)初始质量浓度为50mg/L时,生物吸附剂OPL对Cr(Ⅵ)的吸附效果最好,预测去除率为99.98%,与实测去除率仅偏差4.8%。     

氨化烟末生物碳吸附剂的制备及其对Cr(Ⅵ)的吸附行为

以卷烟废弃烟末为原材料,对其进行碳化处理后再引入氨基功能团制备氨化烟末生物碳吸附剂(NH₂/TPB),研究p H、投加量、温度、吸附时间对NH₂/TPB吸附Cr(Ⅵ)的影响。通过扫描电镜(SEM)、傅里叶红外光谱(FTIR)、X射线光电子能谱(XPS)等技术进行机制分析。结果表明:初始浓度为210 mg/L、pH=4、投加量为0.8 g/L、温度为45℃、吸附时间为120 min时,NH₂/TPB对Cr(Ⅵ)的最大吸附量为103.627 mg/g。吸附过程符合准二级动力学模型和Langmuir吸附等温模型。Cr(Ⅵ)吸附去除机制主要包括静电相互作用、还原反应以及与-NH₂、-OH、-COOH的配位络合,与Si-O-Si的"π-π"相互作用。通过5次吸附-解吸试验发现,Cr(Ⅵ)去除率在82.88%以上。研究表明氨化烟末生物碳具备处理与修复酸性含Cr(Ⅵ)废水污染的潜力。     

仿生FeS复合材料的制备及其对Cr(Ⅵ)的吸附性能

纳米FeS比表面积大且还原性强,对Cr(Ⅵ)吸附性能优异,但不稳定、易团聚,为解决这一问题,本文以油菜花粉为生物模板,通过共沉淀-焙烧法制得仿生FeS复合材料(bioFeS)。通过SEM、XRD及XPS等方法对bioFeS复合材料的表面微观形态和结构进行了表征。以Cr(Ⅵ)为目标污染物,分别考察了吸附剂用量、反应时间、反应温度、初始Cr(Ⅵ)浓度和pH对bioFeS复合材料吸附Cr(Ⅵ)性能的影响,探究了反应机制。结果表明：油菜花粉生物模板成功分散了FeS,制得的bioFeS复合材料比表面积大,在反应时间为120 min、pH值为1、吸附剂投加量为0.2 g·L^-1、反应温度为25℃的条件下,bioFeS复合材料对Cr(Ⅵ)的吸附量可达88.95 mg·g^-1;该吸附过程符合准二级动力学和Langmuir等温吸附模型;共存离子NO₃^-和SO₄^2-会抑制Cr(Ⅵ)的去除。结合吸附动力学、热力学及XPS表面元素分析可知bioFeS复合材料除铬机制主要是吸附及化...     

碳热还原法制备的碳载零价铁对水中U(VI)的去除研究

随着核电的发展, 放射性污染物流入环境, 污染水土资源。纳米零价铁(nZVI)材料因还原性强、去除效率高等优势, 被广泛应用于水资源污染修复。本研究以海藻酸钠(SA)为碳源, 采用一步碳热还原法制备碳载零价铁(Fe-CB)材料, 并将其用于水溶液中放射性核素U(Ⅵ)的去除。采用微观光谱和宏观实验研究Fe-CB对U(Ⅵ)的吸附性能和作用机理。研究发现Fe-CB具有丰富的官能团(如-OH和-COOH)及较高的比表面积, 弥补了纳米零价铁(nZVI)分散性差和去除效果低的不足。在298 K时, Fe-CB对U(Ⅵ)的吸附去除在3 h内达到平衡, 最大吸附量为77.3 mg·g ^-1, 是能够自发进行的化学吸附。X射线光电子能谱分析仪(XPS)分析发现Fe-CB对U(Ⅵ)的去除主要是通过吸附和还原的协同作用来实现的, 吸附过程是U(Ⅵ)与Fe-CB发生表面络合, 还原过程是通过零价铁的还原性将U(Ⅵ)还原成U(Ⅳ)。研究结果表明Fe-CB材料可作为优良的吸附剂, 在环境污染治理领域具有良好的应用前景。     

Formation and mechanism of nanoscale zerovalent iron supported by phosphoric acid modified biochar for highly efficient removal of Cr(VI)

The effect of phosphoric acid modified biochar on activity of nanoscale zero valent iron particles is not clear until now. In this research, Egeria najas powder driven biochar-supported nanoscale zero valent iron was modified by phosphoric acid (P-BC/nZVI) for highly effective removal of Cr(VI) from wastewater. The TEM and XRD of P-BC/nZVI indicated that nZVI particles were successfully immobilized on the P-BC surface. The batch experiment results show that the Cr(VI) removal efficiency by P-BC/nZVI was higher than that of BC/nZVI, nZVI, P-BC and BC. Moreover, the optimal ratio of nZVI to P-BC lies at 3:1 with fixed P-BC/nZVI dosage of 0.75 g/L, initial Cr(VI) concentration of 20 mg/L, solution pH of 2, and reaction temperature of 333 K. Additionally, Cr(VI) removal capacities by nZVI, BC/nZVI and P-BC/nZVI aged for 15 days in water were 12.9 %, 28.55 % and 99.35 %, respectively. Furthermore, corresponding reaction kinetics fitted well with pseudo-second order model, and adsorption isotherm fitted to Sips isothermal model. The SEM-EDS and XPS confirm that Cr(VI) was participated in the reaction, and about 63.43 % of Cr(VI) was reduced to Cr(III), and the rest was adsorbed on the surface of P-BC/nZVI. The removal mechanism of Cr(VI) by P-BC/nZVI was complex, including adsorption, reduction and surface complex formation.     

Removal of heavy metal lead(II) using nanoscale zero-valent iron with different preservation methods

In this study, different nanoscale zero-valent irons (nZVI) were prepared in order to improve their stability and reactivity to heavy metal lead (Pb (II)). The composition, particle size and morphology of obtained nZVI were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscope (SEM). The effects of nZVI dosage, pH, initial Pb (II) concentration and reaction time on the removal efficacy of Pb (II) were investigated. The results show that undried nZVI has more active sites due to its weaker oxidation, and thus the removal efficiency of Pb(II) by undried nZVI was higher than that by dried nZVI. As a result, the same removal efficiency could be achieved with the use of less undried nZVI for the identical concentration of Pb(II). Furthermore, the experimental procedure could be apparently simplified, which eliminates the steps of washing, separation and dehydration compared with the traditional preparation method. The experimental data could be well fitted by the Langmuir adsorption isotherm model, and the maximum adsorption capacity of dried and undried nZVI is 671.14 and 807.23?mg·g^?1 at pH 6, respectively. The experimental data followed the pseudo second-order kinetic model with a kinetic constant of 7.65?×?10^?4 and 1.39?×?10^?3 for undried and dried nZVI, respectively. In conclusion, undried nZVI had high adsorption capacity and adsorption rate for Pb(II) in the solution.     

Characteristics and mechanisms of hexavalent chromium removal by biochar from sugar beet tailing

Removal of Cr(VI) from aqueous solutions using biochar from sugar beet tailing (SBT) was investigated as a function of pH, contact time, and biochar mass via batch experiments. The surface characteristics of SBT biochar before and after Cr(VI) sorption was investigated with scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. Desorption and X-ray photoelectron spectroscopy studies showed that most of the Cr bound to SBT biochar was Cr(III). These results indicated that the electrostatic attraction of Cr(VI) to positively charged biochar surface, reduction of Cr(VI) to Cr(III) ion, and complexation between Cr(III) ion and SBT's function groups were probably responsible for Cr(VI) removal by SBT biochar. An initial solution with a pH of 2.0 was most favorable for Cr(VI) removal. The sorption process can be described by the pseudo-second order equation and Langmuir isotherm. The maximum sorption capacity for Cr(VI) was 123 mg/g under an acidic medium, which was comparable to other low-cost sorbents.     

Carbonate effects and pH-dependence of uranium sorption onto bacteriogenic iron oxides: kinetic and equilibrium studies

The removal of U(VI) from groundwaters by adsorption onto bacteriogenic iron oxides (BIOS) has been investigated under batch mode. The adsorbent dosage, the uranium concentration, the concentration of carbonate and the use of a real groundwater spiked with uranium comprised the examined parameters. In addition, the effect of pH was examined in two different water matrixes, i.e., in distilled water and in real groundwater. Equilibrium studies were carried out to determine the maximum adsorption capacity of BIOS and the data correlated well with the Langmuir and Freundlich models. The presence of carbonate affected adversely the adsorption of U(VI) onto BIOS. The maximum adsorption capacity of BIOS was 9.25 mg g(-1) at 0.1mM carbonate concentration and decreased to 6.93 mg g(-1) at 0.5mM carbonate concentration, whereas at carbonate concentration of 2mM practically no adsorption occurred. The data were further analyzed using the pseudo-second order kinetic equation, which fitted best the experimental results. The initial adsorption rate (h) was found to increase with decreasing the concentration of carbonate in all cases. When experiments were accomplished in the absence of carbonate, the pH values did not have an effect on the adsorption of U(VI). However, the extent of U(VI) adsorption was strongly pH-dependent when the experiments were carried out in the real groundwater. The maximum adsorption capacity increased sharply as the pH decreased and optimum removal was obtained in the pH range 3.2-4.0, thus bacteriogenic iron oxides can found application in the removal of U(VI) by adsorption from low pH or low carbonate waters.     

Mesoporous magnetic biochar composite for enhanced adsorption of malachite green dye: Characterization,adsorption kinetics,thermodynamics and isotherms

This study aimed to prepare a corn straw-derived biochar supported nZVI magnetic composite (nZVI/BC) and evaluate its efficiency in adsorption of malachite green dye (MG). The prepared nZVI/BC composite was characterized by XRD, FTIR, TEM, TEM-EDS, VSM, XPS, TGA, zeta potential and BET surface area. The prepared mesoporous composite showed enhanced efficiency for the adsorption of MG dye. Adsorption models and kinetic results indicated that the adsorption of MG onto nZVI/BC composite was more fitted to Langmuir isotherm and follows second order kinetics. Intraparticle diffusion model indicated that the adsorption follows a three steps mechanism. The maximum adsorption capacity of nZVI/BC composite (515.77 mg MG/g composite) was much higher than most of reported biochar adsorbents. The removal process of MG onto nZVI/BC composite does not only proceed via adsorption mechanism, but also through an oxidative degradation mechanism. The Magnetic character of the biochar enables its easy separation and reuse for many cycles.     

Adsorption of Cr(VI) from synthetic solutions and electroplating wastewaters on amorphous aluminium oxide

The adsorption behaviour of amorphous aluminium oxide was studied with respect to Cr(VI) in order to consider its application to purify electroplating wastewaters. A batch method was employed using Cr(VI) concentrations ranged from 10 to 200mg/l. The Langmuir model was found to describe the adsorption process well, offering a maximum adsorption capacity of 78.1mg/g. The effect of ionic strength (0-0.1M KNO(3)), pH (3-9) and competitive solutes (molar ratio [Cr(VI)]/[SO(4)(2-)]=1 and 100) on the retention process was evaluated. Cr(VI) adsorption on amorphous aluminium oxide appeared to be dependent on ionic strength with a more pronounced effect in acid conditions. Conversely, adsorption was not affected by pH in acid medium, but decreased when pH sifted to alkaline values. The presence of SO(4)(2-) greatly reduced Cr(VI) removal across the entire pH range when both solutes were present in similar concentrations. Amorphous aluminium oxide also showed a high adsorption capacity when used in the purification of Cr(VI) electroplating wastewaters. The adsorbent doses required to attain more than 90% of Cr(VI) removal varied between 1 and 5 g/l depending on Cr(VI) concentration in wastewaters.     

Effects of pH and dissolved oxygen on Cr(VI) removal in Fe(0)/H2O systems

The effects of pH and dissolved oxygen (DO) on aqueous Cr(VI) removal by micro-scale zero-valent iron (Fe(0)/H(2)O system) were investigated. Batch experiments were conducted at pH 4.0, 5.0 and 6.0 under oxic and anoxic conditions. Column experiments were performed at pH 5.0 and 7.5 under oxic condition. Spectroscopic analyses were applied to explain the mechanism of Cr(VI) removal using X-ray absorption near-edge structure (XANES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results showed that the kinetics of Cr(VI) removal were fastest at pH 5 under both oxic and anoxic conditions. As a rule, Cr(VI) removal were faster under oxic conditions than under anoxic conditions. Column experiments showed that Cr(VI) removal was about 1.7-fold higher at pH 5 than at pH 7.5. XANES (X-ray absorption near edge structures) results showed that Fe(0) reduced Cr(VI) to Cr(III) under both oxic and anoxic conditions. X-ray diffraction patterns of the Cr(VI)-Fe(0) reaction products suggested partial formation of chromite (FeCr(2)O(4)) at pH 5 and 6 under oxic conditions. However, nano-sized clusters of Cr(III)/Fe(III) hydroxide/oxyhydroxide were formed on the surface of Fe(0) under anoxic conditions. These results indicate that the presence of oxygen in solution plays an important role in control of the kinetic of Cr(VI) removal and in development of various Cr(VI) reduction products.     

Nanoscale zero-valent iron modified with carboxymethyl cellulose in an impinging stream-rotating packed bed for the removal of lead(II)

A novel impinging stream-rotating packed bed (IS-RPB) was proposed to continuous, macro and industrialized prepare nanoscale zero-valent iron (nZVI) with simultaneously modified with carboxymethyl cellulose (CMC) for the removal of Pb²⁺. The obtained CMC-nZVI particles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The components on the surface of CMC-nZVI after react with Pb²⁺ were also analyzed by X-ray photoelectron spectroscopy (XPS). The IS-RPB makes it possible for the continuous, macro and industrialized preparing of CMC-nZVI particles, and CMC can significantly improve the dispersion and reduce aggregation of nZVI particles. The effects of solution pH, initial Pb²⁺ concentration and reaction time on the removal efficiency of Pb²⁺ by nZVI and CMC-nZVI particles were also investigated. The results show that CMC-nZVI particles outperform nZVI particles in removing Pb²⁺, and the removal efficacy reaches a maximum of 838.84 mg·g⁻¹ for nZVI particles and 1237.32 mg·g⁻¹ for CMC-nZVI particles at pH = 6.0. The adsorption of Pb²⁺ by nZVI and CMC-nZVI particles can be described by the Langmuir isotherm adsorption model with a R² of 0.999, and the calculated maximum adsorption capacity is 900.90 and 1376.07 mg·g⁻¹ for nZVI and CMC-nZVI particles. The adsorption of Pb²⁺ follows the pseudo second-order kinetics with a linear correlation coefficient R² of 0.999. In addition, the effect of co-existing cations such as Na⁺, Cu²⁺, Ni²⁺ and Cd²⁺ on Pb²⁺ removal efficiency was also investigated. The results showed that Na⁺ had no effect on Pb²⁺ removal efficiency and Cu²⁺ and Ni²⁺ had inhibited Pb²⁺ removal efficiency. Cd²⁺ had an inhibitory effect on Pb²⁺ removal efficiency when the concentration was 50 mg·L⁻¹ and 100 mg·L⁻¹, Cd²⁺ enhanced Pb²⁺ removal efficiency while the concentration of Cd²⁺ was 200 mg·L⁻¹.     

Enhanced removal of trace Cr(VI) ions from aqueous solution by titanium oxide-Ag composite adsorbents

Titanium oxide-Ag composite (TOAC) adsorbents were prepared by a facile solution route with Ag nanoparticles being homogeneously dispersed on layered titanium oxide materials. The as-synthesized TOAC exhibited a remarkable capability for trace Cr(VI) removal from an aqueous solution, where the concentration of Cr(VI) could be decreased to a level below 0.05 mg/L within 1h. We have systematically investigated the factors that influenced the adsorption of Cr(VI), for example, the pH value of the solution, and the contact time of TOAC with Cr(VI). We found that the adsorption of Cr(VI) was strongly pH-dependent. The adsorption behavior of Cr(VI) onto TOAC fitted well the Langmuir isotherm and a maximum adsorption capacity of Cr(VI) as 25.7 mg/g was achieved. The adsorption process followed the pseudo-second-order kinetic model, which implied that the adsorption was composed of two steps: the adsorption of Cr(VI) ions onto TOAC followed by the reduction of Cr(VI) to Cr(III) by Ag nanoparticles. Our results revealed that TOAC with high capacity of Cr(VI) removal had promising potential for wastewater treatment.