膨润土对重金属离子Pb2+,Zn2+, Cr(Ⅵ),Cd2+的吸附性能

试验研究了pH值、吸附时间和吸附剂用量对膨润土吸附重金属离子Pb^2＋，Zn^2＋，Cr（VI）和Cd^2＋的影响．结果表明，在本试验的pH值、吸附时间及吸附剂用量条件下，膨润土对Pb^2＋，Zn ^2＋，Cd ^2＋的吸附效果均优于其对Cr（Ⅵ）的吸附效果；pH值是影响上述吸附的重要因素，离子交换和表面络合是上述吸附的主要形式．     

改性沸石对Cr(VI)的吸附作用研究

研究了改性沸石对Cr(VI)吸附的影响因素,即研究了溶液酸度、吸附时间、吸附剂用量和Cr(VI)的初始浓度对吸附的影响.结果表明:溶液的pH值是影响吸附的主要因素;离子交换和表面络合反应是主要吸附形式;改性沸石对Cr(VI)的吸附符合Langmiur吸附等温式,属于单分子层吸附.     

改性膨润土吸附剂的制备及其吸附性能的研究

本文以钠基膨润土为主要原料,选用壳聚糖作为改性剂,通过微波辐射进行改性,制备出壳聚糖改性膨润土吸附剂,并研究了其对Cr（VI）的吸附陛能和吸附工艺条件。结果表明,吸附剂对Cr（VI）具有较好的吸附性能,吸附的适宜工艺条件是：pH值为5-6,吸附时间为30min,吸附剂用量为12．0g／L。与单一的膨润土或壳聚糖相比,该吸附剂对Cr（VI）离子的吸附速度快、吸附能力强,并且具有成本低、应用范围广的优点,Cr（VI）的去除率可达N85％。     

电气石超细粉吸附水体中Cu、Pb、Zn和Cd

研究了电气石对水中重金属离子Cu(Ⅱ)、Pb(Ⅱ)、Zn(Ⅱ)和Cd(Ⅱ)的吸附性能.电气石能有效去除水中重金属离子,其选择性吸附顺序是Pb(Ⅱ)＞Cu(Ⅱ)＞Cd(Ⅱ)＞Zn(Ⅱ).电气石对重金属离子的吸附量随着溶液中重金属浓度的增加而增加,60 min能达到吸附平衡.电气石能够提高金属溶液的pH值.电气石对Cu(Ⅱ)、Pb(Ⅱ)、Zn(Ⅱ)和Cd(Ⅱ)的饱和吸附量分别是78.86、154.08、67.25和66.67 mg/g.温度为25～55℃时对电气石吸附重金属的影响较小.四种重金属离子的吸附均符合Langmuir吸附等温线.电气石对混合溶液中的Cu(Ⅱ)、Pb(Ⅱ)、Zn(Ⅱ)和Cd(Ⅱ)具有竞争性吸附.试验结果表明,电气石可以作为一种有效的吸附剂去除水中的重金属.     

改性膨润土吸附处理含Cr（Ⅵ）废水的研究

用阳离子表面活性剂十六烷基三甲基溴化铵（CTMAB）对钙基膨润土进行活化改性,并用制备的改性膨润土对含Cr（VI）模拟废水进行吸附实验,研究了改性膨润土去除模拟水样中重金属Cr（VI）的适宜条件。结果表明,用质量分数为5%的CTMAB溶液改性后的膨润土去除Cr（VI）效果较好,当改性膨润土用量为10g/L、搅拌时间30min、pH值为3～5时、有机膨润土对含Cr（VI）废水的去除率超过85%。     

响应面法优化巴旦木壳对废水中Pb、Cu和Cd的吸附及同时测定

研究废弃巴旦木壳对模拟废水中Pb、Cu和Cd的去除率。在单因素实验的基础上,采用响应面法对吸附剂投加量、吸附时间和pH值3因素进行优化。实验结果表明,Pb、Cu和Cd分别在最佳吸附吸附剂投加量0.4 g,吸附时间49.38 min, pH值为9.96;吸附剂投加量0.4 g,吸附时间49.91 min, pH值为10.13;吸附剂投加量0.4 g、吸附时间49.83 min、pH值为10.42的条件下,去除率分别为87.42%、73.49%和85.11%。采用偏最小二乘法(PLS)对Pb、Cu和Cd模拟混合试样吸附后的溶液测定的曲线进行拟合回归,计算得出吸附剂对Pb、Cu和Cd的去除率分别为83.2%、66.0%和83.3%。用PLS对吸附后的模拟废水样品进行计算分析,并间接得出巴旦木壳对Pb、Cd和Cu的去除率和建立Pb、Cd、Cu三组分同时测定的多元校正分析方法。     

重金属Pb(II)在膨润土上去除特性研究

深入研究成本低廉的膨润土对水溶液中Pb(II)的吸附特性,采用Batch试验方法,分析了土水比、pH、离子强度、反应时间、温度及Pb(II)的初始浓度对Pb(II)在膨润土上吸附性能的影响,并对吸附动力学和吸附平衡试验进行了探讨。Pb(II)在膨润土上去除率与pH、离子强度有很强的依赖性。当pH<7时,膨润土对Pb(II)的吸附主要是离子交换,而当7相似文献   

TiO2复合吸附剂去除三氯甲烷的试验研究

采用TiO2复合吸附剂进行了消毒副产物三氯甲烷的去除试验,考察了吸附时间、吸附剂用量、溶液pH等因素对试验的影响,并与活性炭吸附法进行了对比.结果表明,当三氯甲烷的浓度为100μg/L时,经TiO2复合吸附剂在一定条件下处理后,去除率达98%,高于或相当于颗粒活性炭吸附法的处理效果.     

La(OH)_3改性膨润土制备及其对磷吸附性能研究

采用硝酸镧和氢氧化钠制备La(OH)_3改性膨润土,利用扫描电子显微镜(SEM)、能量色散X射线荧光光谱仪(EDX)和X射线衍射分析仪(XRD)对改性前后样品的组成、形貌进行表征,并分析了初始pH值、吸附剂添加量和吸附时间对其吸附磷性能的影响。结果表明,改性后膨润土形貌和成分均有明显变化;增加改性膨润土用量和吸附时间在一定范围内有助于提高对磷的吸附量,其吸附动力学可用拟二级动力学方程描述,等温吸附模型符合Langmuir方程。     

羟基磷灰石/蔗渣生物质炭对Pb~(2+)的动态吸附性能

针对工业废水中铅的处理,以羟基磷灰石/蔗渣生物质炭为吸附剂,对水中铅进行了吸附实验。根据动态吸附的客观规律,实验研究了pH值、Pb~(2+)质量浓度、吸附剂用量等对穿透曲线的影响。结果表明:穿透时间(tb)随pH值的变化规律为tb(pH=3.0)tb(d=0.4g)>tb(d=0.2g);穿透时间随着动态虑速的增加而减小。在不同的实验条件下,羟基磷灰石/蔗渣生物质炭对Pb~(2+)的动态吸附饱和时间为1 987min。采用Thomas模型和Adams-Bohart模型对数据进行处理,初步揭示了羟基磷灰石/蔗渣生物质炭吸附水中铅的规律。在处理某含铅采矿废水时,对铅的去除效果令人满意。     

Removal of chromium (VI) from wastewater using bentonite-supported nanoscale zero-valent iron

Bentonite-supported nanoscale zero-valent iron (B-nZVI) was synthesized using liquid-phase reduction. The orthogonal method was used to evaluate the factors impacting Cr(VI) removal and this showed that the initial concentration of Cr(VI), pH, temperature, and B-nZVI loading were all importance factors. Characterization with scanning electron microscopy (SEM) validated the hypothesis that the presence of bentonite led to a decrease in aggregation of iron nanoparticles and a corresponding increase in the specific surface area (SSA) of the iron particles. B-nZVI with a 50% bentonite mass fraction had a SSA of 39.94 m²/g, while the SSA of nZVI and bentonite was 54.04 and 6.03 m²/g, respectively. X-ray diffraction (XRD) confirmed the existence of Fe⁰ before the reaction and the presence of Fe(II), Fe(III) and Cr(III) after the reaction. Batch experiments revealed that the removal of Cr (VI) using B-nZVI was consistent with pseudo first-order reaction kinetics. Finally, B-nZVI was used to remediate electroplating wastewater with removal efficiencies for Cr, Pb and Cu > 90%. Reuse of B-nZVI after washing with ethylenediaminetetraacetic acid (EDTA) solution was possible but the capacity of B-nZVI for Cr(VI) removal decreased by approximately 70%.     

Sorption and detoxification of chromium(VI) by aerobic granules functionalized with polyethylenimine

This study describes the modification of aerobic granules by grafting polyethylenimine (PEI) for simultaneous sorption and detoxification of Cr(VI). After modification, the uptake capacity of modified aerobic granules (MAG) showed about 401.5 mg/g at pH 5.5 and increased by 274% compared to the control. Adsorption experiments were carried out as a function of contact time, pH and concentration of Cr(VI). It was found that the equilibrium sorption can be attained within 3 h and the process obeys the Redlich-Peterson isotherm model. The adsorption process is a function of pH of the solution, with the greater adsorption at pH 5.2. The interaction characteristics between the Cr and MAG were elucidated by applying FTIR and XPS analyses. FTIR results showed that the -NH₂ groups in the sorbent are involved in the adsorption process. XPS results verified the presence of Cr(III) on the MAG surface in the pH range 1.5-8.5, suggesting that some Cr(VI) anions were reduced to Cr(III) during the sorption.     

Removal and recovery of Cr(VI) from wastewater by maghemite nanoparticles

Hexavalent chromium existing in the effluent is a major concern for the metal-processing plant. In this study, a new method combining nanoparticle adsorption and magnetic separation was developed for the removal and recovery of Cr(VI) from wastewater. The nanoscale maghemite was synthesized, characterized, and evaluated as adsorbents of Cr(VI). Various factors influencing the adsorption of Cr(VI), e.g., pH, temperature, initial concentration, and coexisting common ions were studied. Adsorption reached equilibrium within 15 min and was independent of initial Cr concentration. The maximum adsorption occurred at pH 2.5. The adsorption data were analyzed and fitted well by Freundlich isotherm. Cr(VI) adsorption capacity of maghemite nanoparticles was compared favorably with other adsorbents like activated carbon and clay. Competition from common coexisting ions such as Na+, Ca2+, Mg2+, Cu2+, Ni2+, NO3-, and Cl- was ignorable, which illustrated the selective adsorption of Cr(VI) from wastewater. Regeneration studies verified that the maghemite nanoparticles, which underwent six successive adsorption-desorption processes, still retained the original metal removal capacity. In addition, the adsorption mechanisms were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopic techniques.     

Removal of trivalent and hexavalent chromium with aminated polyacrylonitrile fibers: performance and mechanisms

Aminated polyacrylonitrile fibers (APANFs) were prepared and used as an adsorbent in a series of batch adsorption experiments for the removal of Cr(III) and Cr(VI) species from aqueous solutions of different pH values. The results show that significant amounts of Cr(III) or Cr(VI) species can be adsorbed by the APANFs, although the adsorption performances was greatly dependent upon the solution pH values. In general, the amounts of adsorption for Cr(III) species increased whereas that for Cr(VI) decreased with the increase of the solution pH values, which suggests that different adsorption mechanisms dominated the removal of Cr(III) or Cr(VI) species on the APANFs. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy revealed that the adsorption of Cr(III) species on the APANFs was largely attributed to the formation of surface complexes between the nitrogen atoms on the APANFs and the Cr(III) species adsorbed, but the adsorption of Cr(VI) species on the APANFs was more likely effected through the formation of hydrogen bonds at high solution pH values or through both electrostatic attraction and surface complexation at low solution pH values. It was found that the Cr(VI)-adsorbed APANFs can be effectively regenerated in a basic solution and be reused almost without any loss of the adsorption capacity, while the Cr(III)-adsorbed APANFs needed to be regenerated in an acidic solution and the regeneration appeared to be less effective.     

Studies on removal and recovery of Cr(VI) from electroplating wastes

Phosphate treated sawdust shows remarkable increase in sorption capacity of Cr(VI) as compared to untreated sawdust. The adsorption process is pH dependent. 100% adsorption of Cr(VI) was observed in the pH range <2 for the initial Cr(VI) concentration of 8–50 mg 1⁻¹. The effect of various adsorbent doses at pH 2 confirms Langmuir adsorption isotherms. 100% removal of Cr(VI) from synthetic waste as well as from electroplating waste containing 50 mg 1⁻¹ Cr(VI) was achieved by batch as well as by column processes. The adsorbed Cr(VI) on phosphate treated sawdust was recovered (87%) using 0.01 M sodium hydroxide.     

Adsorption mechanism of hexavalent chromium by redox within condensed-tannin gel

We have proposed a new recovery system of hexavalent chromium Cr(VI) that is of great toxicity utilizing condensed-tannin gels derived from a natural polymer with many polyhydroxyphenyl groups. The adsorption mechanism of Cr(VI) to the tannin molecules was clarified. The adsorption mechanism consists of four reaction steps; the esterification of chromate with tannin molecules, the reduction of Cr(VI) to trivalent chromium Cr(III), the formation of carboxyl group by the oxidation of tannin molecules and the ion exchange of the reduced Cr(III) with the carboxyl and hydroxyl groups. It was found in this recovery system that a large amount of proton was consumed accompanied with the reduction of Cr(VI) so that the acidic solution containing Cr(VI) was transferred automatically to neutral one by choosing an appropriate initial pH. The carboxyl group which was created by the oxidation of tannin molecules parallel to the reduction of Cr(VI) to Cr(III) contributed to an increase in the ion-exchange sites of the reduced Cr(III). The maximum adsorption capacity of Cr(VI) reached 287 mg Cr/g dry tannin gel under the conditions of 0.77 water content of tannin gel and the initial pH = 2. This adsorption capacity was five to ten times higher than that obtained by the ion exchange between ordinary Cr(III) and tannin molecules for the tannin gels prepared under similar conditions. The system proposed here will provide an important information on a zero-emission-oriented process because it has such advantages as higher adsorption capacity of chromium and lower volume of secondary wastes compared with conventional process.     

Effects of pH and oxidation state of chromium on the behavior of chromium in the activated sludge process

The behavior of chromium (Cr) in the activated sludge process (ASP) was evaluated in laboratory-scale, fill-and-draw activated sludge experiments. Both pH and the oxidation state of chromium were confirmed as critical parameters in the ASP for evaluating the behavior of chromium. More than 55% of chromium was removed when trivalent chromium [Cr(III)] was introduced into the influent while less than 60% was removed when hexavalent chromium [Cr(VI)] was added over a pH range from 5 to 9. As pH was increased, the removal increased when Cr(III) was introduced but the reverse occurred with Cr(VI). Introduction of Cr(VI) into the influent resulted in less than 80% of chromium associated with solids; however, with Cr(III), more than 90% of chromium was bound with solids. These results suggest that the ASP is capable of controlling the transport of Cr(III) to the environment but such is not case for Cr(VI).Theoretical consideration based on thermodynamics predicted that no reduction of Cr(VI) into Cr(III) should occur and the only redox reaction should be the oxidation of Cr(III) into Cr(VI). However, no oxidation of Cr(III) into Cr(VI) was observed; some Cr(VI) was reduced into Cr(III). Kinetic constraints may have impeded the oxidation of Cr(III). Under the conditions of this study, Cr(III) may have been removed through adsorption rather than precipitation as Cr(OH)₃. Cr(VI) might be adsorbed on the bacterial surface through specific adsorption.     

Enhanced chitosan beads-supported Fe-nanoparticles for removal of heavy metals from electroplating wastewater in permeable reactive barriers

The removal of heavy metals from electroplating wastewater is a matter of paramount importance due to their high toxicity causing major environmental pollution problems. Nanoscale zero-valent iron (NZVI) became more effective to remove heavy metals from electroplating wastewater when enhanced chitosan (CS) beads were introduced as a support material in permeable reactive barriers (PRBs). The removal rate of Cr (VI) decreased with an increase of pH and initial Cr (VI) concentration. However, the removal rates of Cu (II), Cd (II) and Pb (II) increased with an increase of pH while decreased with an increase of their initial concentrations. The initial concentrations of heavy metals showed an effect on their removal sequence. Scanning electron microscope images showed that CS-NZVI beads enhanced by ethylene glycol diglycidyl ether (EGDE) had a loose and porous surface with a nucleus-shell structure. The pore size of the nucleus ranged from 19.2 to 138.6 μm with an average aperture size of around 58.6 μm. The shell showed a tube structure and electroplating wastewaters may reach NZVI through these tubes. X-ray photoelectron spectroscope (XPS) demonstrated that the reduction of Cr (VI) to Cr (III) was complete in less than 2 h. Cu (II) and Pb (II) were removed via predominant reduction and auxiliary adsorption. However, main adsorption and auxiliary reduction worked for the removal of Cd (II). The removal rate of total Cr, Cu (II), Cd (II) and Pb (II) from actual electroplating wastewater was 89.4%, 98.9%, 94.9% and 99.4%, respectively. The findings revealed that EGDE-CS-NZVI-beads PRBs had the capacity to remediate actual electroplating wastewater and may become an effective and promising technology for in situ remediation of heavy metals.