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%。     

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％。     

钢渣对水溶液中铬的吸附及其动力学研究

以钢渣为吸附剂去除溶液中的铬,考察了pH、钢渣投量及粒径、转速等因素对钢渣吸附效果的影响,并结合吸附动力学和扩散模型及钢渣的矿物组成变化探讨了钢渣对Cr(Ⅲ)的吸附去除机理.结果表明,钢渣对Cr(Ⅲ)具有明显的吸附去除效果,且不受溶液pH值的影响;当体系中存在还原剂Fe(Ⅱ)时,Cr(Ⅵ)可被还原为Cr(Ⅲ)而被钢渣吸附去除;在转速为180 r/min的条件下,钢渣对Cr(Ⅲ)的吸附过程遵循Lagergren一级吸附速率方程及Weber-Morris颗粒内扩散模型,此时钢渣内扩散是吸附过程的主要控制步骤.且Cr(Ⅲ)的初始浓度越高则吸附速率越低;X射线荧光(XRF)和X射线衍射(XRD)分析结果表明,铬在钢渣上的吸附去除主要是通过生成铬氧化物以及与钢渣中的Ca、Fe等元素生成难溶化合物来实现的.     

电动修复技术处理铬污染黏土试验研究

利用电动修复技术对红星化工厂铬渣污染黏土进行修复,试验电压分别为20,30,40,50,60V,以0.1mol/L KCl为两极电解液,阴极采用乙酸控制pH值在6左右,试验周期为5d.结果表明：电动修复能够去除土样中的铬,最高去除率可达58.26%;本试验50V即1.25V/cm电压梯度为经济有效的去除电压;Cr（Ⅵ）以含氧阴离子的形式向阳极迁移,Cr（Ⅲ）迁移较复杂,在沉淀态和游离态之间转换;阳极电解液中Cr（Ⅵ）的浓度易达到饱和,对Cr（Ⅵ）的去除产生抑制.     

钢铁冷轧线含铬废水处理及同步资源化利用

针对某钢铁厂冷轧机组排放的含铬废水中Cr（Ⅵ）浓度达标但总铬不能稳定达标、铬泥作为危废出厂等问题，采用纤维吸附技术从源头对Cr（Ⅵ）进行回收，确保出水水质达标，并通过基于离子交换技术的转化系统实现Cr（Ⅵ）的资源化利用。通过试验确定吸附系统的最优吸附周期与转化系统的最适pH值。系统优化后，出水Cr（Ⅵ）及总铬浓度分别保持在0.048、0.1 mg/L以下，满足《钢铁工业水污染物排放标准》（GB 13456—2012）；与原工艺相比，无需再外加药剂调节pH值，极大地节省了处理成本；铬泥产量减少90%以上；产生的重铬酸液可实现资源化利用，据统计产生的综合经济效益可达520.6万元/a。     

六钛酸钾晶须预富集FAAS法测定环境水样中Cr(Ⅲ)

研究了六钛酸钾对于Cr（Ⅲ）的吸附性能,提出了用六钛酸钾晶须作为富集剂,预富集、分离水中Cr（Ⅲ）的新方法。在pH值为6．0的条件下,吸附率可达到100％,吸附容量为12．3mg／g。以3mol／L的HNO3作为解脱剂,沸水浴加热40min,可将吸附在六钛酸钾上的Cr（Ⅲ）定量洗脱。火焰原子吸收光谱法（FAAS）的测定结果表明：Cr（Ⅲ）的浓度在0．20～4．0μg／mL范围内线性良好,检出限为3．5ng／mL,相对标准偏差为3．1％。在优化的试验条件下,实测了天然水中Cr（Ⅲ）的含量,加标回收率为94．0％-102．0％。     

高分子重金属絮凝剂PEX处理电镀废水研究

以电镀废水为处理对象，研究了高分子重金属絮凝剂PEX对废水中重金属离子、浊度及有机污染物的处理效果；同时考察了废水pH值对重金属离子去除效果的影响及重金属离子的回收率。结果表明，当废水pH≥6．0时，pH值的变化对重金属去除率的影响不大；在pH=6．5～7、PEX的投量为160mg／L时，对镍的去除率〉95％，对铜和铬的去除率〉99％，对有机物的去除率为64％；重金属离子的回收率随盐酸浓度的增大而提高，当盐酸浓度为15％时对镍离子的回收率为70％，对铜离子的回收率为24％左右。     

膨润土对重金属离子Pb~(2+),Zn~(2+),Cr(VI),Cd~(2+)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Pb2 ,Zn2 ,Cr(VI)和Cd2 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Pb2 ,Zn2 ,Cd2 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.     

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．     

粉末活性炭对邻苯二甲酸二乙酯的吸附性能研究

考察了投加粉末活性炭吸附去除水中邻苯二甲酸二乙酯的可行性,并采用Freundlich公式拟合纯水和原水条件下的等温吸附方程。试验结果表明,采用粉末活性炭可有效去除水中邻苯二甲酸二乙酯,活性炭投加量为30mg／L,吸附120min后,纯水和原水条件下邻苯二甲酸二乙酯去除率分别为93．3％和89．3％。根据吸附等温方程计算得出,以邻苯二甲酸二乙酯的标准限值（0．3mg／L）为平衡浓度,纯水、原水条件下最大投炭量（80mg／L）可应对的邻苯二甲酸二乙酯最高质量浓度分别为7．575和5．731mg／L。     

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.     

Biosorption of chromium(VI) from aqueous solutions by green algae Spirogyra species.

Biosorption of heavy metals is an effective technology for the treatment of industrial wastewaters. Results are presented showing the sorption of Cr(VI) from solutions by biomass of filamentous algae Spirogyra species. Batch experiments were conducted to determine the adsorption properties of the biomass and it was observed that the adsorption capacity of the biomass strongly depends on equilibrium pH. Equilibrium isotherms were also obtained and maximum removal of Cr(VI) was around 14.7 x 10(3) mg metal, kg of dry weight biomass at a pH of 2.0 in 120 min with 5 mg/l of initial concentration. The results indicated that the biomass of Spirogyra species is suitable for the development of efficient biosorbent for the removal and recovery of Cr(VI) from wastewater.     

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.     

Mechanism of hexavalent chromium removal by dead fungal biomass of Aspergillus niger

When synthetic wastewater containing Cr(VI) was placed in contact with the dead fungal biomass of Aspergillus niger, the Cr(VI) was completely removed from aqueous solution, whereas Cr(III), which was not initially present, appeared in aqueous solution. Desorption and X-ray photoelectron spectroscopy (XPS) studies showed that most of the Cr bound on the biomass was in trivalent form. These results indicated that the main mechanism of Cr(VI) removal was a redox reaction between Cr(VI) and the dead fungal biomass, which is quite different from previously reported mechanisms. The influences of contact time, pH, Cr(VI) concentration, biomass concentration and temperature on Cr(VI) removal were also evaluated. The Cr(VI) removal rate increased with a decrease in pH and with increases in Cr(VI) concentration, biomass concentration and temperature. Although removal kinetics was dependent on the experimental conditions, Cr(VI) was completely removed in the aqueous solution. In conclusion, a new mechanism of Cr(VI) removal by the dead fungal biomass has been proposed. From a practical viewpoint, this abundant and inexpensive dead fungal biomass has potential application in the conversion of toxic Cr(VI) into less toxic or nontoxic Cr(III).     

氢氧化铁对水中砷的吸附试验研究

就氢氧化铁对As(Ⅲ)的吸附动力学、吸附等温线以及pH和温度等影响因素进行了研究。结果表明:氢氧化铁对As(Ⅲ)的吸附动力学符合Lagergren二级吸附动力学模型,其吸附等温线可用Langmuir方程很好地描述,即属于单分子层吸附,试验得到的饱和吸附量为9.09mg/g;pH值在4.1~8.5内,氢氧化铁对As(Ⅲ)的去除率较高,保持在70%以上,超出这个范围,氢氧化铁对As(Ⅲ)的去除率逐渐降低,pH值为6.8左右时,氢氧化铁对As(Ⅲ)的去除率达到最高,约为94.8%;随着温度的升高,氢氧化铁对As(Ⅲ)的吸附率逐渐降低,在0~25℃时,氢氧化铁对As(Ⅲ)的去除率保持在80%以上。     

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.     

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.     

Hexavalent chromium removal from aqueous solution by adsorption on aluminum magnesium mixed hydroxide

A series of sols consisting of aluminum magnesium mixed hydroxide (AMH) nanoparticles with various Mg/Al molar ratios were prepared by coprecipitation. The use of AMH as adsorbent to remove Cr(VI) from aqueous solution was investigated. Adsorption experiments were carried out as a function of the Mg/Al molar ratio, pH, contact time, concentration of Cr(VI) and temperature. It was found that AMH with Mg/Al molar ratio 3 has the largest adsorption efficiency due to the smallest average particle diameter and the highest zeta potential; AMH was particularly effective for the Cr(VI) removal in a pH range from acid to slightly alkaline, even though the most effective pH range was between 2.5 and 5.0. The adsorption of Cr(VI) on AMH reached equilibrium within 150 min. The saturated adsorption capacities of AMH for Cr(VI) were 105.3-112.0 mg/g at 20-40 °C. The interaction between the surface sites of AMH and the Cr(VI) ions may be a combination of both anion exchange and surface complexation. The pseudo-second-order model best described the adsorption kinetics of Cr(VI) onto AMH. The results showed that AMH can be used as a new adsorbent for Cr(VI) removal which has higher adsorption capacity and faster adsorption rate at pH values close to that at which pollutants are usually found in the environment.