磷酸改性柚子皮对水中Cr(Ⅵ)的吸附性能研究

比较改性前后柚子皮吸附Cr(Ⅵ)的能力差异,并对吸附原理进行分析。采用生物吸附法,研究其在不同条件下对Cr(Ⅵ)的吸附效果。结果表明,当含Cr(Ⅵ)废水中投加未经处理的柚子皮时,在pH为2,Cr(Ⅵ)的初始浓度在1.0 mg/L,吸附剂投加量为1.0 g,反应温度为25℃,吸附10 min基本达到平衡,该吸附过程符合二级动力学公式和Freundlich吸附等温线。当含Cr(Ⅵ)废水中投加经磷酸改性的柚子皮时,在pH为2,Cr(Ⅵ)的初始浓度在50.0 mg/L,吸附剂投加量为1.0 g,反应温度为25℃,吸附20 min基本达到平衡,该吸附过程符合二级动力学公式和Langmuir吸附等温线。磷酸改性的柚子皮吸附能力更强,可作为新型吸附材料加以开发和利用。     

热改性粉煤灰对水中Cr(Ⅵ)的吸附性能

将粉煤灰与助熔剂混合进行高温焙烧制得热改性粉煤灰(TFA),对其进行表征并考察其对水中Cr(Ⅵ)的吸附性能。与原粉煤灰相比,TFA疏松多孔,比表面积显著提高。20℃下的吸附实验结果表明:当初始废水p H为6.7、Cr(Ⅵ)质量浓度为10.00 mg/L、TFA加入量为4.0 g/L、吸附时间为90 min时,Cr(Ⅵ)去除率可达98.98%,吸附量为2.39 mg/g。用拟二级动力学模型可较准确地描述TFA对Cr(Ⅵ)的吸附过程;吸附实验数据与采用Freundlich等温吸附模型得出的计算值吻合很好;降低温度有利于吸附反应的发生。     

水热改性花生壳对水中Cr(Ⅵ)的吸附性能

为解决水体Cr(Ⅵ)污染,实现农业固废资源化利用,通过水热H_3PO_4改性制备了花生壳基吸附剂,并将其用于水中Cr(Ⅵ)的吸附。实验结果表明,在453 K下,与质量分数为15%的H_3PO_4水热反应10 h制备的改性花生壳性能最优;当吸附剂投加量为2 g/L,pH=2.0,Cr(Ⅵ)初始质量浓度为5 mg/L,吸附时间为120 min时,水中Cr(Ⅵ)去除率可达86.83%。改性花生壳对Cr(Ⅵ)的吸附过程符合伪二级动力学模型,属于Langmuir单分子层吸附。     

改性花生壳吸附去除水中Cr(Ⅵ)的性能研究

采用三乙烯四胺对花生壳颗粒进行改性制备吸附剂,以投加量、粒径、接触时间、Cr(Ⅵ)初始浓度、温度和溶液初始pH值为影响因素,通过静态实验,研究其对水中Cr(Ⅵ)的吸附性能。得到最佳吸附条件为吸附剂投加量1.0～1.6g/L,接触时间150min,初始浓度100mg/L,去除率可达99.36%,饱和吸附量达100.95mg/g。分析认为,主要的吸附机理可能是Cr2O27-与改性花生壳吸附点位上的功能基团之间的离子交换,伴随着静电吸附及氧化还原过程。     

玉米芯对水中Cr(Ⅵ)吸附性能研究

用玉米芯吸附水中的Cr(Ⅵ),研究了pH、投加量、振荡时间、初始浓度和温度对吸附效果的影响,并用动力学、热力学方程和吸附等温线对实验数据进行拟合。结果表明,pH=1时,玉米芯对Cr(Ⅵ)的吸附效果最佳;吸附过程符合准一级动力学模型,Freundlich与Langmuir等温吸附模型均能很好地描述吸附过程,高温时,Freundlich模型的拟合效果更好;对热力学参数ΔH,ΔG,ΔS的计算表明,该吸附过程是吸热、熵增的自发过程。     

改性糠醛渣对Cr(Ⅵ)的吸附性能

为了研究改性糠醛渣对水中Cr(Ⅵ)的吸附性能,利用红外光谱、扫描电镜、零电荷点对吸附剂进行了表征,考察了改性糠醛渣投加量、Cr(Ⅵ)初始浓度、pH、温度、吸附时间等因素对改性糠醛渣吸附Cr(Ⅵ)的影响,并研究了动力学机制。结果表明,当Cr(Ⅵ)初始浓度为20 mg/L,改性糠醛渣投加量为0. 07 g,溶液pH为1～3,在20℃条件下吸附50 min时,去除率可达96. 43%。吸附动力学过程符合准二级动力学方程。再生试验结果表明改性糠醛渣具有良好的重复使用性能。     

活性炭表面改性及其对Cr(Ⅵ)吸附性能的研究

分别用HNO3、H2SO4以及HNO3加乙酸铜溶液对活性炭进行了表面改性处理,测定了它们的表面化学性能,研究了改性活性炭对Cr(VI)吸附性能的影响。实验结果表明：通过上述改性,活性炭表面官能团数量发生了显著改变,特别是羧基增加较多;通过改性后的活性炭对Cr(Ⅵ)吸附性能有所提高。     

改性锯末对水中Cr(Ⅵ)和Cu(Ⅱ)的吸附性能实验研究

以甲醛或硝酸化学改性的锯末为吸附剂,研究了两种改性锯末对水中Cr(Ⅵ)和Cu(Ⅱ)的吸附性能,探讨了改性锯末的用量、重金属质量浓度、pH、吸附时间等因素对吸附效果的影响,得到了最佳吸附条件。实验结果表明:在废水中Cr(Ⅵ)的质量浓度80mg/L,pH为1.0~2.0,吸附时间2h,改性锯末用量60g/L的条件下,两种改性锯末对铬Cr(Ⅵ)的去除率均在95%以上;当Cu(Ⅱ)的质量浓度为100mg/L、pH5.0~6.0、吸附时间90min、锯末用量30g/L时,甲醛改性锯末对Cu(Ⅱ)的去除率高于90%,而硝酸改性锯末对Cu(Ⅱ)的去除率仅有72%。     

高锰酸钾改性活性炭去除水中Cr(Ⅵ)的试验研究

采用高锰酸钾对颗粒活性炭进行改性。在静态条件下,对改性活性炭处理Cr(Ⅵ)废水进行了研究,考察了pH、温度等因素的影响。结果表明,改性后的活性炭对Cr(Ⅵ)的吸附量有明显的提高,提高率为79.91%。酸性环境利于Cr(Ⅵ)的吸附,且pH应控制在6左右;低温对吸附有利;吸附能较好的满足Langmuir等温线和准二级动力学曲线,最佳拟合相关系数分别为0.9943和0.9983。     

磺化腐植酸处理模拟电镀废水中的六价铬

以0.1 g磺化腐植酸为吸附剂,在30℃恒温振荡下对水中Cr(VI)进行吸附,用可见分光光度法测定吸附前后水中Cr(VI)的含量.结果表明,Freundlich模型能够很好地用于描述磺化腐植酸对Cr(VI)的吸附,且当溶液pH在1.8左右,吸附时间为150 min时,磺化腐植酸对Cr(VI)的吸附率可达99%以上.     

Adsorption of hexavalent chromium on cationic starches with different degree of crosslinking

The influence of the degree of crosslinking in the association with the degree of cationization on the adsorption of Cr(VI) by crosslinked cationic starches (CCS) was examined. The amount of adsorbed Cr(VI) depends on the preparation of CCS before adsorption experiments (dry or preswollen CCS) and has a higher value when dry CCS are used. The amount of crosslinks in CCS needed to reach the maximum effectiveness of the cationic groups of CCS in the binding of Cr(VI) depends also on the form in which CCS are used. The adsorption capacity for Cr(VI) decreases both with dry and preswollen CCS when the adsorption temperature increases. The thermodynamic parameters are calculated. The negative values of ΔG° and ΔH° indicated that the adsorption process in both cases was spontaneous and exothermic. If preswollen CCS is used, the entropy change has a positive value and indicates that the randomness of the system increases, whereas the negative value of entropy change when Cr(VI) species are adsorbed by dry CCS shows that in this case the order of the system increases like in the classical adsorption process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Adsorption of hexavalent chromium by chitosan‐based polymeric surfactants

Chitosan‐based polymeric surfactants (CBPSs) were prepared by the partial N‐acylation of amine groups on chitosan with acid anhydrides. To apply the CBPSs for the removal of Cr(VI) commonly found in wastewater, a batch test was conducted to evaluate the adsorption capacity. The removal efficiency of Cr(VI) by the CBPS depended on several factors, including the solution pH, CBPS dose, and ionic strength. Our results show that the CBPSs exhibited a greater adsorption capacity for Cr(VI) than have other modified chitosans reported in the literature. The maximum adsorption capacity of Cr(VI) was 180 mg/g of CBPS at a final pH of 5.3. From the results of dynamic light scattering, we propose that the removal mechanism of Cr(VI) by the CBPSs was mainly through the adsorption of negatively charged chromium ions by positively charged amine groups on the CBPSs followed by colloidal precipitation because of its lower solubility. Conclusively, we found that the CBPS was significantly effective for the removal of Cr(VI). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 44–50, 2005     

Adsorption behavior of hexavalent chromium on synthesized ethylenediamine modified starch

The starch-based material, ethylenediamine modified cross-linked starch (CAS) was synthesized and employed to remove hexavalent chromium from aqueous solution. Maximum adsorption of total chromium was observed at reaction pH of 4.0 and adsorption equilibrium achieved within 4h. The adsorption process can be described by pseudo-second-order adsorption model and the best-fit isotherm is Freudlich equation. The mechanism is predominately based on electrostatic attraction. The FT-IR spectra indicate that the amino groups of CAS are protonated and the hexavalent chromium ions were effectively adsorbed. Furthermore, studies on chromium release by using inorganic electrolytes confirm the mechanism observed by sorption experiments, which HCrO₄ ⁻ ion plays an important role interacting with CAS. Chromium release increases with increasing negative charge of electrolyte following the sequence PO₄ ³⁻ > SO₄ ²⁻ > B₄O₇ ²⁻ > NO₃ ⁻.     

Adsorption study of hexavalent chromium using tamarind hull-based adsorbents

The adsorption characteristics of hexavalent chromium was studied with an adsorbent developed from waste tamarind hull. Experiments were conducted in batch mode to observe the influence of different parameters such as initial concentration of metal ions, adsorbent dosage, adsorbent particle size, stirrer speed, temperature and pH of the solution. Acidic pH strongly favored the adsorption. With decreasing the pH of the solution from 5.0 to 1.0, the removal of chromium was enhanced from 33% to 99%. The adsorption process was found to follow a pseudo-first-order rate mechanism and the rate constant was evaluated at 30 °C. The Freundlich, Redlich–Peterson and the Fritz–Schlunder isotherm fit the equilibrium data satisfactorily. Adsorption of chromium was found to increase with increase in the process temperature. Using an adsorbent dosage of 1.0 g/L and an acidic pH (2.0), the equilibrium adsorption capacity of the prepared adsorbent was found to be about 70 mg/g at 30 °C, which increased to about 81 mg/g at 50 °C. The entropy change, free energy change and heats of adsorption were determined for the process.     

Adsorption of hexavalent chromium from aqueous solutions by bio-chars obtained during biomass pyrolysis

In this study, bio-chars were evaluated as a potential adsorbent for the removal of Cr (VI) ions from aqueous solutions. The effects of some important parameters including initial pH (1.5–7), adsorbent dose (0.2–5 g/L), contact time (5–900 min) and initial Cr (VI) ion concentration (5–75 mg/L) were tested on the removal of Cr (VI) ions from aqueous solution in batch experiments. Maximum adsorption capacities of the tested bio-chars under the certain experimental conditions determined as optimal were 3.53 mg/g for NCBC, 3.97 mg/g for NZCBC and 6.08 mg/g for ACBC, respectively. Results of the kinetic and isotherm modeling studies revealed that the adsorption data fitted well with a pseudo-second order and Langmuir model. In among the tested bio-chars, the bio-char (ACBC) was largely equivalent to activated carbon: AC (9.97 mg/g) in terms of adsorption capacity. All results indicated that the bio-chars had higher adsorption capacity than some chars and activated carbons reported previously, and also that these bio-chars could be used successfully as low-cost adsorbents for the removal of chromium ions from aqueous solutions under the tested experimental conditions.     

Removal of hexavalent chromium by nanofiltration

Removal of chromate CrO₄²⁻ from water was investigated using nanofiltration as a possible alternative to the conventional methods of CrVI removal from aqueous solution. Retention measurements with single reference salt revealed that Donnan exclusion plays an important role. The phenomenological parameters σ and P were calculated using the Spiegler-Kedem equation. The rejection rate depends on the ionic strength and pH. The increasing of ionic strength decreases the retention. The effect of pH was clarified by using a stable diagram of the CrVI---H₂O system. Better retention was obtained at basic pH.     

Reduction of hexavalent chromium by copper

The galvanic reaction of metallic copper in Cr(VI)-laden aqueous solutions of varying pH was examined by in situ u.v.–visible spectrophotometry, rotating disc electrode chronopotentiometry and cyclic voltammetry. The galvanic reaction in 0.2 M H₂SO₄ solutions was pseudo first order in Cr(VI) concentration. Experiments with both magnetically stirred solutions and a copper mesh or a copper film in a rotating disc electrode configuration revealed the reaction to be diffusion-controlled with respect to Cr(VI) transport to the copper surface. Finally, cyclic voltammetry data in Cr(VI)-laden media of varying pH underline the important role of protons in the galvanic reaction.     

Electroreduction of hexavalent chromium by polyaniline

BACKGROUND: A plate‐gap model interpretation of enzymatic reaction kinetics and rotating disc voltammetry were applied for evaluation of the nature of the reaction of the electroreduction of Cr(VI) (as dichromate ions) on a polyaniline (PANI)‐modified glassy carbon (GC) electrode. RESULTS: The kinetic parameters (the maximal current (V_max) and Michaelis constant (K_M)) for electroreduction of Cr(VI) on the PANI‐modified GC electrode were determined as V_max = 0.34 × 10^?7 mol cm^?3 s^?1 and K_M = 0.47 × 10^?6 mol cm^?3. The reduction of dichromate is intensified by PANI film growth. CONCLUSION: To characterise the electroreduction of Cr(VI) on a PANI‐modified GC electrode, the kinetic parameters of the reaction were determined using a plate–gap model interpretation of enzymatic reaction kinetics and rotating disc voltammetry. The catalytic nature of Cr(VI) electroreduction on the PANI‐modified electrode has been shown. Copyright © 2009 Society of Chemical Industry