纳米零价铁颗粒去除As(III)和As(V)的动力学过程及性能研究

本研究系统分析了不同初始砷浓度和不同nZVI投加量等条件下,nZVI去除As（III）和As（V）的动力学过程和除砷性能.结果表明,nZVI可快速有效地去除As（III）和As（V）,除砷过程均符合准二级动力学模型,且As（III）的去除速率明显快于As（V）.在砷浓度为5 mg·L^-1时,As（III）去除速率常数达最大值0.30 g·mg^-1·min^-1,为As（V）去除速率（0.034 g·mg^-1·min^-1）的8.8倍.Weber-Morris粒子内扩散模型拟合结果表明,nZVI除砷速率是由外扩散和颗粒内扩散共同控制的.分析反应平衡时砷浓度测定结果,发现不同砷浓度条件下nZVI对As（III）的去除量为As（V）的1.5~2.6倍,nZVI对砷的去除量随初始砷浓度增加而降低,随nZVI投加量增加而增加.砷浓度为50.0 mg·L^-1时,As（III）和As（V）去除量达到最高,分别为152.14 mg·g^-1和62.02 mg·g^-1,均高于传统（羟基）氧化铁对As（III）和As（V）的去除量.因此,nZVI可高效去除水中As（III）和As（V）,且用于修复以As（III）污染为主的地下水更具有优势.     

Simultaneous oxidation of Mn(II) and As(III) on cupric oxide (CuO) promotes As(III) removal at circumneutral pH

Oxidation of Mn(II) or As(III) by molecular oxygen is slow at pH < 9, while they can be catalytically oxidized in the presence of oxide minerals and then removed from contaminated water. However, the reaction mechanisms on simultaneous oxidation of Mn(II) and As(III) on oxide mineral surface and their accompanied removal efficiency remain unclear. This study compared Mn(II) oxidation on four common metal oxides (γ-Al₂O₃, CuO, α-Fe₂O₃ and ZnO) and investigated the simultaneous oxidation and removal of Mn(II) and As(III) through batch experiments and spectroscopic analyses. Among the tested oxides, CuO and α-Fe₂O₃ possess greater catalytic activity toward Mn(II) oxidation. Oxidation and removal kinetics of Mn(II) and As(III) on CuO indicate that O₂ is the terminal electron acceptor for Mn(II) and As(III) oxidation on CuO, and Mn(II) acts as an electron shuttle to promote As(III) oxidation and removal. The main oxidized product of Mn(II) on CuO is high-valent MnO_x species. This newly formed Mn(III) or Mn(IV) phases promote As(III) oxidation on CuO at circumneutral pH 8 and is reduced to Mn(II), which may be then released into solution. This study provides new insights into metal oxide-catalyzed oxidation of pollutants Mn(II) and As(III) and suggests that CuO should be considered as an efficient material to remediate Mn(II) and As(III) contamination.     

Rapid removal of polyacrylamide from wastewater by plasma in the gas–liquid interface

Due to the severe restrictions imposed by legislative frameworks, the removal of polyacrylamide(PAM) rapidly and effectively from produced wastewater in offshore oilfields before discharge is becoming an urgent challenge. In this study, a novel advanced oxidation process based on plasma operated in the gas–liquid interface was used to rapidly decompose PAM, and multiple methods including viscometry, flow field-flow fractionation multi-angle light scattering, UV–visible spectroscopy, and attenuated total reflectanceFourier transform infrared spectroscopy were used to characterize the changes of PAM.Under a discharge voltage of 25 kV and pH 7.0, the PAM concentration decreased from 100 to 0 mg/L within 20 min and the total organic carbon(TOC) decreased from 49.57 to1.23 mg/L within 240 min, following zero-order reaction kinetics. Even in the presence of background TOC as high as 152.2 mg/L, complete removal of PAM(100 mg/L) was also achieved within 30 min. The biodegradability of PAM improved following plasma treatment for 120 min. Active species(such as O_3 and H_2O_2) were produced in the plasma. Hydroxyl radical was demonstrated to play an important role in the degradation of PAM due to the inhibitory effect observed after the addition of an ·OH scavenger, Na_2CO_3. Meanwhile, the release of ammonia and nitrate nitrogen confirmed the cleavage of the acylamino group.The results of this study demonstrated that plasma, with its high efficiency and chemicalfree features, is a promising technology for the rapid removal of PAM.     

不同状态MnO_2对废水中As(Ⅲ)的吸附研究

利用ＭｎＯ２对含Ａｓ（ＩＩ）废水进行了吸附实验，结果表明，ＭｎＯ２对Ａｓ（ＩＩ）有着较强的吸附能力，其饱和吸附量为４４．０６ｍｇ／ｇ（δ－ＭｎＯ２）和１７．９ｍｇ／ｇ（ε－ＭｎＯ２），阴离子的存在使ＭｎＯ２吸附量有所下降，一些阳离子（如Ｇａ３＋、Ｉｎ３＋）可增加其吸附量，吸附后的ＭｎＯ２经解吸后可重复使用。     

Shewanella oneidensis MR-1异化还原Fe(III)介导的As(III)氧化转化

在实验室模拟条件下,研究了Shewanella oneidensis MR-1作用下Fe(III)还原和As(III)氧化动力学及其影响因素.结果表明,Fe(III)被还原为Fe(II)的同时伴随着As(III)氧化为As(V);S. oneidensis MR-1 在含低浓度As(III)培养基上生长良好,在高浓度培养基上生长被抑制;As(III)通过制约菌体的生长与活性来抑制Fe(III)异化还原.同样,适量浓度的Fe(III)含量对As(III)氧化转化有很强的促进作用,但是过高浓度的Fe(III)浓度使得溶液中产生过多的Fe(II),从而对As(III)氧化转化有一定程度的抑制作用.此外,弱碱环境更有利于As(III)氧化转化.     

锰氧化物负载施氏矿物去除酸性矿山废水中As(III)的性能及机理

施氏矿物是天然的砷吸附剂,但其存在酸性条件下对As(III)吸附性能较弱且无法对As(III)氧化降毒的缺陷. 采用液相沉淀法成功制备出锰氧化物负载施氏矿物(MnO_x@Sch),研究锰负载量、初始pH值和共存离子对MnO_x@Sch去除As(III)的影响,并采用吸附动力学结合XPS、FTIR及TEM等表征探究该过程的机理. 结果表明:在初始pH=3、投加量为0.5 g·L^-1、As(III)初始浓度为1 mg·L^-1的条件下,As(III)与MnO_x@Sch反应后的剩余浓度仅为2.42~3.38 μg·L^-1.MnO_x@Sch去除As(III)受初始pH影响较小,H₂PO₄^-共存时As(III)去除存在明显的抑制作用. MnO_x@Sch 去除As(III)的过程符合准二级动力学方程和颗粒内扩散方程. 液相化学组分和固相产物表征分析显示MnO_x@Sch对As(III)的去除机理可概括为As(III)氧化、静电吸附和络合配位及配体交换. 研究结果可为施氏矿物及其改性材料应用于酸性矿山废水砷污染治理提供理论依据.     

Groundwater arsenic removal by coagulation using ferric(III) sulfate and polyferric sulfate: A comparative and mechanistic study

Elevated arsenic (As) in groundwater poses a great threat to human health. Coagulation using mono-and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric(III) sulfate (FS) and polyferric sulfate (PFS) performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca(ClO)₂. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water (<10 μg/L) was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure (XANES) and As k-edge extended X-ray absorption fine structure (EXAFS) analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As (0.9 μg/L-0.487 mg/L) than the US EPA regulatory limit (5 mg/L). Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.     

Groundwater arsenic removal by coagulation using ferric(III) sulfate and polyferric sulfate: A comparative and mechanistic study

Elevated arsenic (As) in groundwater poses a great threat to human health. Coagulation using mono- and poly-Fe salts is becoming one of the most cost-effective processes for groundwater As removal. However, a limitation comes from insufficient understanding of the As removal mechanism from groundwater matrices in the coagulation process, which is critical for groundwater treatment and residual solid disposal. Here, we overcame this hurdle by utilizing microscopic techniques to explore molecular As surface complexes on the freshly formed Fe flocs and compared ferric(III) sulfate (FS) and polyferric sulfate (PFS) performance, and finally provided a practical solution in As-geogenic areas. FS and PFS exhibited a similar As removal efficiency in coagulation and coagulation/filtration in a two-bucket system using 5 mg/L Ca(ClO)₂. By using the two-bucket system combining coagulation and sand filtration, 500 L of As-safe water (< 10 μg/L) was achieved during five treatment cycles by washing the sand layer after each cycle. Fe k-edge X-ray absorption near-edge structure (XANES) and As k-edge extended X-ray absorption fine structure (EXAFS) analysis of the solid residue indicated that As formed a bidentate binuclear complex on ferrihydrite, with no observation of scorodite or poorly-crystalline ferric arsenate. Such a stable surface complex is beneficial for As immobilization in the solid residue, as confirmed by the achievement of much lower leachate As (0.9 μg/L–0.487 mg/L) than the US EPA regulatory limit (5 mg/L). Finally, PFS is superior to FS because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water.     

利用天然磁黄铁矿去除水中As (V)的研究

考察了时间、pH、温度、吸附剂投加量、无机阴离子等因素对磁黄铁矿去除As(V)过程的影响.同时,对去除过程的动力学和等温线进行分析,并探究了动态去除的效果.结果显示:磁黄铁矿对As(V)的去除在24 h达到平衡;在pH值3~9范围内去除率都达到80%以上;温度升高和吸附剂用量增加都对As(V)去除具有促进作用;PO_4~(3-)、SiO_3~(2-)、CO_3~(2-)对吸附有较强的抑制作用;在As(V)初始浓度为2 mg·L~(-1)时动态吸附出水浓度在150个吸附床体积(BV)内能达到国家饮用水标准;吸附去除过程符合拟二级动力学方程和Langmuir等温方程.能谱仪和X射线电子能谱分析表明,去除过程是一个自发吸热的配位离子交换反应.本实验表明,天然磁黄铁矿是一种有潜力的除砷吸附剂.     

不同挂膜方式成熟滤料去除地下水中As(Ⅲ)研究

通过动力学和动态柱实验对比研究了不同挂膜方式成熟滤料去除地下水中As（Ⅲ）效能.并采用SEM-EDS?XRD及FTIR等表征手段对滤料形态和结构进行了分析.结果表明,两种滤料的形貌具有较大差异.采用化学挂膜的滤料去除As（Ⅲ）性能更优.二级动力学模型能较好地模拟两种滤料除As（Ⅲ）动力学过程,自然挂膜滤料和化学挂膜滤料拟合速率常数分别为8.568×10^-6和14.248×10^-6mg/（g·min）.Yan模型对动态柱实验穿透曲线的拟合系数R²>0.999.通过脱附再生实验,发现0.5mol/L的NaHCO₃作为脱附剂可使滤料有效再生.对比过滤前后滤料的XRD分析结果,滤料结构变化不大,除砷能力稳定.滤料表面铁锰氧化物含量直接影响滤料除As（Ⅲ）性能.两种滤料在除砷过程中均消耗了羟基.本研究为不同方法去除地下水中As（Ⅲ）提供了理论支撑,具有一定工程指导意义.     

阴离子对As(Ⅲ)在砖红壤与TiO2混合体系中的光催化氧化/吸附的影响

以磷酸根和硫酸根为例,采用一次平衡法研究了无机阴离子对As(Ⅲ)在砖红壤中光催化氧化和吸附的影响.实验结果表明,磷酸根和硫酸根的加入均降低了As(Ⅲ)在土壤中的氧化和吸附,磷酸根的影响程度大于硫酸根,而且两者的影响机理不同.磷酸根主要通过表面吸附机制即强烈地吸附在催化剂表面导致催化剂活性降低,以及与氧化产物As(V)竞争土壤颗粒表面吸附位来影响反应活性;而硫酸根则是在光催化氧化过程中通过捕获光生空穴(h+)和羟基自由基(OH.)生成光催化效率较低的SO4-.,从而影响As(Ⅲ)的光催化氧化效率.     

A laboratory scale study on arsenic（Ⅴ） removal from aqueous medium using calcined bauxite ore

The present work deals with the As（Ⅴ） removal from an aqueous medium by calcined refractory grade bauxite （CRB） as a function of solution pH, time, As（Ⅴ） concentration and temperature. The residual As（Ⅴ） was lowered from 2 mg/L to below 0.01 mg/L in the optimum pH range 4.0-7.0 using a 5 g/L CRB within 3 h contact time. The adsorption data fits well with Langmuir isotherm and yielded Langmuir monolayer capacity of 1.78 mg As（Ⅴ）/g of CRB at pH 7.0. Presence of anions such as silicate and phosphate decreased As（Ⅴ） adsorption efficiency. An increase temperature resulted a decrease in the amount of As（Ⅴ） adsorbed by 6%. The continuous fixed bed column study showed that at the adsorbent bed depth of 30 cm and residence time of 168 min, the CRB was capable of treating 340 bed volumes of As（V） spiked water （C0 = 2 mg/L） before breakthrough （Ce = 0.01 mg/L）. This solid adsorbent, although not reusable, can be considered for design of adsorption columns as an efficiency arsenic adsorption media.     

不同Fe(III)对活性污泥异化铁还原及除磷影响研究

以SBBR反应器活性污泥作为铁还原菌菌种来源,采用兼性厌氧/严格厌氧恒温培养试验,投加不同Fe(III)考察各条件下的异化铁还原能力,同时比较对磷的去除效果.结果表明:2种条件下Fe(III)还原能力具有较好的一致性,依次为:Fe(OH)3>氧化铁皮>青矿>红矿,其中严格厌氧条件下较好.同时,除磷效果与其呈正相关,富集培养至7d, Fe(OH)3及氧化铁皮体系出水磷浓度均达到2mg/L以下,之后继续降低,最终达到0.5mg/L以下.结合异化铁还原除磷机理,可以证明,不同Fe(III)表面吸附作用对TP的去除贡献较小,其主要作用为铁还原菌驱动下的化学沉淀去除.     

双表面活性剂修饰下纳米零价铁对水中Cr(Ⅵ)污染去除研究

为解决纳米级零价铁（nZVI）在环境中易团聚、易氧化的问题,强化其去除水中Cr（VI）的能力,选择非离子型表面活性剂聚乙烯吡咯烷酮（PVP）和阴离子表面活性剂油酸钠（NaOA）同时对nZVI进行修饰.同时,通过对比不同pH值、材料干湿状态、初始浓度及共存离子条件下的反应效果,结合材料的XRD和XPS表征、动力学实验和25℃等温线的拟合进行机理分析.结果表明：酸性条件有利于Cr（VI）的去除;材料的干湿状态对去除效率影响较大;材料去除水中Cr（VI）可在3 h内达到反应平衡,去除效率在90%以上,实验条件下最大去除量为183.1 mg·g^-1,反应过程符合准二级动力学模型及Langmuir模型;反应过程中Cr（VI）大部分转化为Cr（Ⅲ）.     

Adsorption of Co(Ⅱ) from aqueous solutions by water treatment residuals

A study on the removal of Co(Ⅱ) from aqueous solutions by water treatment residuals(WTR)was conducted in batch conditions. The sorption process of Co(Ⅱ) followed pseudosecondorder kinetics, with 30 hr required to reach equilibrium. Using the Langmuir adsorption isotherm model, a relatively high maximum sorption capacity of 17.31 mg/g Co(Ⅱ) was determined. The adsorption of Co(Ⅱ) was dependent on pH values and was affected by the ionic strength. Results show that Co(Ⅱ) adsorption was a spontaneous endothermic process and was favorable at high temperature. Most of the adsorbed Co(Ⅱ) stayed on the WTR permanently, whereas only small amounts of adsorbed Co(Ⅱ) were desorbed. The shifting of peaks in FT-IR spectra indicated that Co(Ⅱ) interacted with the WTR surface through strong covalent bond formation with Fe(Al)–O functional groups. It was concluded that WTR can be a suitable material from which to develop an efficient adsorbent for the removal of Co(Ⅱ) from wastewater.     

活性炭纤维对水中铁的吸附研究

以活性炭纤维(ACF)为溶液中铁离子的吸附剂,考察了吸附时间、吸附温度、ACF比表面积及表面酸碱性对Fe3 吸附行为的影响.通过平衡吸附实验获得的吸附等温线,并不符合Langmuir与Freundlich经验吸附方程.吸附温度升高与ACF比表面积增加,都有利于铁离子的吸附,说明吸附过程同时具备物理和化学吸附行为的双重特征.ACF表面碱性基团是影响铁离子吸附的主要因素.     

Enhanced removal of high-As(Ⅲ) from Cl(-Ⅰ)-diluted SO4(-Ⅱ)-rich wastewater at pH 2.3 via mixed tooeleite and(Cl(-Ⅰ)-free) ferric arsenite hydroxychloride formation

An advanced cost-saving method of removal of high-As(Ⅲ) from SO₄(-Ⅱ)-rich metallurgi cal wastewater has been developed by diluting the SO₄(-Ⅱ) content with As(Ⅲ)-Cl(-Ⅰ)-rich metallurgical wastewater and then by the direct precipitation of As(Ⅲ) with Fe(Ⅲ) at pH2.3.As(Ⅲ) removal at various SO₄(-Ⅱ)/Cl(-Ⅰ) molar ratios and temperatures was investigated The results showed that 65.2–98.2%of As(III) immobilization into solids occurred at the SO₄(Ⅱ)/Cl(-Ⅰ) mo...     

Al(III)对糖浆溶液中有机还原物质还原六价铬的影响

通过批实验研究了Al(III)对糖浆溶液化学还原六价铬反应的影响,揭示了不同条件下Al(III)对六价铬还原反应动力学的影响.结果表明:Al(III)能够促进糖浆溶液还原六价铬反应进行;其作用机制是Al(III)与糖浆溶液中有机还原物质及Cr(VI)反应形成三者的络合物,降低糖浆中多酚等有机还原物质还原Cr(VI)的反应活化能,提高六价铬还原反应速率.Al(III)存在时,该六价铬还原反应符合准一级动力学反应; pH 2.0,2.5,3.0,3.5时,添加Al(III)的实验组中六价铬反应速率常数比对应的空白对照组中反应速率常数分别增加了0.0251,0.0139,0.0058, 0.0048h-1.添加Al(III)前后反应体系中六价铬还原的反应活化能(Eа)分别为66.38,62.80kJ/mol.当糖浆浓度不足时,Al(III)能够提高糖浆溶液还原六价铬的反应去除率.     

Ethanol mediated As(III) adsorption onto Zn-loaded pinecone biochar: Experimental investigation, modeling, and optimization using hybrid artificial neural network-genetic algorithm approach

Organic matters (OMs) and their oxidization products often influence the fate and transport of heavy metals in the subsurface aqueous systems through interaction with the mineral surfaces. This study investigates the ethanol (EtOH)-mediated As(III) adsorption onto Zn-loaded pinecone (PC) biochar through batch experiments conducted under Box–Behnken design. The effect of EtOH on As(III) adsorption mechanism was quantitatively elucidated by fitting the experimental data using artificial neural network and quadratic modeling approaches. The quadratic model could describe the limiting nature of EtOH and pH on As(III) adsorption, whereas neural network revealed the stronger influence of EtOH (64.5%) followed by pH (20.75%) and As(III) concentration (14.75%) on the adsorption phenomena. Besides, the interaction among process variables indicated that EtOH enhances As(III) adsorption over a pH range of 2 to 7, possibly due to facilitation of ligand–metal(Zn) binding complexation mechanism. Eventually, hybrid response surface model–genetic algorithm (RSM–GA) approach predicted a better optimal solution than RSM, i.e., the adsorptive removal of As(III) (10.47 μg/g) is facilitated at 30.22 mg C/L of EtOH with initial As(III) concentration of 196.77 μg/L at pH 5.8. The implication of this investigation might help in understanding the application of biochar for removal of various As(III) species in the presence of OM.     

Enhanced removal of Cr(VI) by biochar with Fe as electron shuttles

Biochar is extensively used as an effective soil amendment for environmental remediation. In addition to its strong contaminant sorption capability, biochar also plays an important role in chemical transformation of contaminant due to its inherent redox-active moieties. However, the transformation efficiency of inorganic contaminants is generally very limited when the direct adsorption of contaminants on biochar is inefficient. The present study demonstrates the role of Fe ion as an electron shuttle to enhance Cr(VI) reduction by biochars. Batch experiments were conducted to examine the effects of Fe(III) levels, pyrolysis temperature of biochar, initial solution pH, and biochar dosage on the efficiency of Cr(VI) removal. Results showed a significant enhancement in Cr(VI) reduction with an increase in Fe(III) concentration and a decrease of initial pH. Biochar produced at higher pyrolysis temperatures (e.g., 700°C) favored Cr(VI) removal, especially in the presence of Fe(III), while a higher biochar dosage proved unfavorable likely due to the agglomeration or precipitation of biochar. Speciation analysis of Fe and Cr elements on the surface of biochar and in the solution further confirmed the role of Fe ion as an electron shuttle between biochar and Cr(VI). The present findings provide a potential strategy for the advanced treatment of Cr(VI) at low concentrations as well as an insight into the environmental fate of Cr(VI) and other micro-pollutants in soil or aqueous compartments containing Fe and natural or engineered carbonaceous materials.