不同氧化度碱性水钠锰矿氧化As(Ⅲ)和Cr(Ⅲ) 的动力学特性

用批量法研究了Mn平均氧化度分别为4.02、3.85和3.70的碱性水钠锰矿对As(Ⅲ)和Cr(Ⅲ)氧化的动力学特性。结果表明,碱性水钠锰矿氧化As(Ⅲ)和Cr(Ⅲ)先经历准一级动力学反应阶段,随后表观速率常数(k_obs)逐渐减小至趋近零,达到反应平衡,k_obs逐渐减小除了逆反应影响外,还与产物在矿物表面不断积累,钝化反应位点有关。初始反应阶段k_obs随氧化度增加而增大,氧化As(Ⅲ)的k_obs分别为: 0.095 1、0.039 6和0.007 1 min^-1;氧化Cr(Ⅲ)的k_obs分别为0.034 2、0.017 8和0.014 8 min^-1。氧化As(Ⅲ)的初始反应阶段生成的Mn(Ⅱ)基本保留在矿物表面,对反应位点钝化大,使k_obs减小速度快。而Cr(Ⅲ) 氧化初始阶段,Mn(Ⅱ)释放明显滞后于Cr(Ⅵ)释放,但随反应进行逐渐增加,与Cr(Ⅵ)释放量比值接近于反应计量比。故Cr(Ⅲ) 氧化生成Mn(Ⅱ)对位点的钝化远小于As(Ⅲ)氧化,其初始反应阶段后k_obs减小速度较慢,且氧化度越高,保持一级动力学的初始反应阶段越长,k_obs减小越慢。因此,水钠锰矿的Mn氧化度越高,氧化As(Ⅲ)和Cr(Ⅲ)的反应速率越快,As(Ⅲ)和Cr(Ⅲ)在碱性水钠锰矿表面氧化产物的释放行为是影响其反应动力学特性的重要因素。     

Fe-ZSM-5分子筛催化降解染料废水的研究

传统的Fenton均相亚铁盐催化剂处理染料废水,具有难以避免的二次污染和亚铁离子流失问题。分子筛催化剂相比传统催化剂具有高效环保的特点,在催化氧化染料废水领域有着良好的前景。本文通过液相离子交换法制备了Fe-ZSM-5非均相分子筛催化剂,替代传统的亚铁盐催化剂,应用X射线衍射对制备的Fe-ZSM-5分子筛催化剂进行表征,表明随离子交换次数的增加,Fe-ZSM-5催化剂负载的铁量上升,且较好地保持了分子筛结构,有利于提高亚铁离子的催化能力。通过实验确定了Fe-ZSM-5催化剂催化反应的最佳温度、pH值、Fe-ZSM-5的用量、反应时间等工艺参数,比较了Fe-ZSM-5催化剂和传统Fenton均相催化剂降解染料废水的脱色率和废水中铁离子的残留量,结果表明Fe-ZSM-5的脱色率达到98.5%,相比于Fenton均相催化剂的脱色率提升约3%;两种催化剂的铁离子残留量差别显著,Fe-ZSM-5催化剂处理的废水中只产生微量的Fe离子,可以认为Fe-ZSM-5非均相分子筛催化剂有效地解决了催化剂损耗和二次污染问题。     

表生环境下闪锌矿氧化反应模拟实验

采用混合流反应器装置,进行了表生环境条件下闪锌矿氧化动力学模拟实验研究,选择Fe³⁺和O₂为氧化剂,实验条件为:温度20～55℃,pH=1.0～7.8、氧化剂Fe³⁺浓度1.0×10^-5～1.0×10^-2 mol/L,氧气流量0.5 L/min。实验结果表明,在Fe³⁺为氧化剂时,闪锌矿氧化速率随着Fe³⁺浓度的增加、温度升高、pH值降低而增加,且氧化过程中Zn和Cd的释放速率大致相同,其反应的活化能分别为Ea(Zn) 41.75 kJ/mol或Ea(Cd) 42.51 kJ/mol,表明闪锌矿氧化速率主要受矿物表面反应控制;而以氧气作为氧化剂时,随着pH值的变化闪锌矿的氧化机理发生变化,在pH值小于5.95范围内,闪锌矿氧化速率随着pH值的增加而降低,进入碱性范围后,随着pH值增加,闪锌矿氧化速率反而增加。对实验数据进行双对数处理并建立了闪锌矿的氧化速率公式。     

铬天青S光度法及非线性拟合测定高纯硅中微量铝

铬天青S光度法是硅中铝含量的测定方法之一,该方法的标准曲线大多采用不过零点的线性拟合,导致低铝含量测定误差大。为提高方法准确度并降低方法检出限,研究了铝标准曲线低浓度部分的拟合问题,探讨了不同拟合模型对检测结果准确度的影响。实验结果表明,不同浓度铝标准液的吸光度在0~0.3 μg/mL范围内并不满足一次函数线性关系,采用三次函数关系y=-17.45230x³+10.42883x²+1.04047x (y为扣空白的吸光度,x为铝的质量浓度)拟合能获得良好结果,其相关系数R²为0.99975。利用已知铝含量的硅试液检验该公式,其相对标准偏差(RSD)为2.55%。样品中铝的测定值与电感耦合等离子体发射光谱法测定值吻合。该法可以显著提高低浓度的铝测定的准确性,可用于测定高纯硅中含量在0.55 μg/g以上的铝杂质。     

滇西北衙煌斑岩的岩石成因及动力学背景:年代学、地球化学及Sr-Nd-Pb-Hf同位素约束

北衙地区出露有多条煌斑岩脉,锆石LA-ICP-MS定年表明岩脉的侵位时间为34.96±0.66Ma,与滇西地区新生代岩浆活动的高峰期一致.岩石地球化学分析表明北衙煌斑岩具有高钾(K₂O/Na₂O为1.03~10.38)、富碱((K₂O+Na₂O)(平均7.55%)、高Mg^#(30~73),富集大离子亲石元素(LILE)(K、Rb、Ba)和轻稀土元素(LREE),亏损高场强元素(HFSE)和重稀土元素的特征.同位素以高(⁸⁷Sr/⁸⁶Sr)_i(0.70615~0.70825),低ε_Nd(t)(-5.3~-1.3),富集放射性Pb(²⁰⁸Pb/²⁰⁴Pb=38.542~38.856,²⁰⁷Pb/²⁰⁴Pb=15.553~15.617,²⁰⁶Pb/²⁰⁴Pb=18.482~18.612)为特征,¹⁷⁶Hf/¹⁷⁷Hf为0.282631~0.282882,ε_Hf(t)为-4.2~1.8.岩石地球化学和同位素特征表明该煌斑岩源自经俯冲板片交代富集了的岩石圈地幔,推测源区可能为含金云母的尖晶石相橄榄岩地幔与石榴石相橄榄岩地幔的过渡区,起源深度大致在75~85km,明显高于同区富碱斑岩的起源深度.构造和地球动力学背景分析表明,该煌斑岩以及滇西地区新生代岩浆作用都是对印度-欧亚大陆强烈碰撞的响应,都产在强烈伸展的动力学背景下,为岩石圈减薄的产物.     

湖南黄沙坪W-Mo-Bi-Pb-Zn多金属矿床硫铅同位素地球化学研究

湖南黄沙坪W-Mo-Bi-Pb-Zn多金属矿床规模大、矿种多、范围小、分带明显,是南岭有色金属成矿带的代表性矿床之一。成矿地质体为碱长花岗斑岩,与下石炭统灰岩接触带发生大规模矽卡岩化,形成大型钨、钼、铋、萤石以及铁的共生矿床。围绕矽卡岩向外,分布铜锌、铅锌、铅锌银的分带,对应的矿化组合分别为粗粒磁黄铁矿-闪锌矿-黄铜矿、中粗粒磁黄铁矿-闪锌矿-方铅矿、胶状黄铁矿-闪锌矿-方铅矿。围绕花岗斑岩,硫化物矿物的δ³⁴S值呈带状分布,其δ³⁴S总体变化为2.3‰~17.5‰,花岗斑岩中浸染状辉钼矿δ³⁴S为17.1‰,矽卡岩中硫化物δ³⁴S>15‰,矽卡岩附近及外侧的铅锌矿体10‰<δ³⁴S<15‰,外围的铅锌银矿体δ³⁴S<10‰。下石炭统中代表沉积特点的细粒浸染状黄铁矿δ³⁴S为-3.1‰~-22.6‰。铅同位素²⁰⁶Pb/²⁰⁴Pb为18.525~18.603,²⁰⁷Pb/²⁰⁴Pb为15.706~15.792,²⁰⁸Pb/²⁰⁴Pb为38.889~39.178。综合研究表明,黄沙坪矿床成矿物质硫和铅主要来自花岗斑岩。经硫同位素热力学平衡计算,引起δ³⁴S值围绕花岗斑岩体分带的主要原因是随温度下降以及物理化学条件变化导致的热力学分馏作用,其次是沉积岩围岩中低δ³⁴S值硫的加入。对南岭地区花岗岩、古生代地层等的δ³⁴S值对比研究发现,引起花岗斑岩岩浆高δ³⁴S值的主要原因是深部富含硫化物(δ³⁴S值高)地层对富含挥发份(Li-F)的碱长花岗岩岩浆的混染作用,其次是成矿作用过程中地层与岩浆的相互作用(包括同化混染)。围绕黄沙坪矿床,湘南地区矽卡岩型钨多金属矿存在一个较高的δ³⁴S值分布区。宝山矽卡岩型Cu-Mo-Pb-Zn矿床矿石硫化物δ³⁴S为-1‰~3.6‰,²⁰⁶Pb/²⁰⁴Pb为18.602~18.672,²⁰⁷Pb/²⁰⁴Pb为15.693~15.780,²⁰⁸Pb/²⁰⁴Pb为38.901~39.186。因此,宝山矿床与黄沙坪矿床的物质来源和成矿机制不同,宝山矿床硫、铅同位素组成集中,分布范围不同于黄沙坪,成矿物质来自岩浆岩。黄沙坪、宝山矿床代表了南岭地区燕山早期存在两类不同性质的岩浆活动与成矿组合。     

矿物类Fenton反应降解有机污染物的研究进展

作为高级氧化工艺之一,Fenton技术能高效地氧化降解有机污染物,矿物催化类Fenton体系的建立则是对Fenton技术的发展和提升。本文在简要介绍传统Fenton技术的基础上,重点阐述了负载型非均相催化类Fenton反应和天然含铁矿物催化类Fenton反应的产生及发展现状。最后结合笔者的科研工作结果展望了天然黑（铁）电气石在矿物催化类Fenton体系中的应用前景。     

缅甸抹谷紫方钠石光致变色效应脱色效率研究

光致变色效应是紫方钠石最显著且极具价值的光学特征。本文通过EDXRF、FTIR、UV-VIS-NIR、D65标准光源、照度计以及色度学方法,对缅甸抹谷紫方钠石光致变色效应脱色效率进行了定量研究。紫方钠石的主量元素为Na、Al、Si和O,此外含有少量Cl和S,微量元素可含Ca、K和Fe,UV-VIS-NIR光谱存在472、540和667 nm的3个吸收峰,其中以540 nm吸收强度最大,脱色过程中,其光谱吸收峰峰位不变,但强度随时间逐渐减小,540 nm吸收峰面积在0~80 s与时间呈线性负相关(R²=0.99);脱色过程中,当照度从5000 lx升高至30000 lx时,紫方钠石脱色效率明显升高,明度L^*升高,彩度C^*降低,色品a^*降低且色品b^*升高,色调由紫色向粉色调轻微变化,是电荷转移导致F中心被破坏的直接结果。     

川东北飞仙关组甲烷为主的TSR及其同位素分馏作用

川东北开江-梁平陆棚东北侧飞仙关组多孔鲕粒白云岩中发生了以甲烷为主的热化学硫酸盐还原作用(TSR),产生高达20%的H₂S;而西南侧鲕粒灰岩以低孔、低H₂S天然气为特征。东北侧白云岩主要发育白云石粒间溶孔或粒间扩大溶孔,这些溶孔可与方解石(δ¹³C=-10‰~-19‰)、储层沥青、元素硫、黄铁矿和石英紧密共生,可分布于片状储层沥青与白云石晶体之间,说明白云石溶解作用发生在沥青形成以后。白云石的溶解作用导致现今天然气以无机CO₂为主,δ¹³C_CO2主要介于-2‰~+2‰之间。这种溶解作用是在酸性条件下,硬石膏或天青石参与下发生的,可能先产生MgSO₄配对离子,而后MgSO₄又与甲烷反应产生H₂S,净增大了孔隙。研究还发现,普光气田及以东天然气的来源不同于河坝和元坝天然气;对普光气田及以东天然气分析显示,甲烷δ¹³C值与残余烃含量 之间存在对数相关关系。这表明TSR过程中,甲烷同位素分馏作用遵从封闭体系下瑞利分馏原理。据此计算显示,渡4井约有15%甲烷被氧化了。     

水中系列氢氧同位素标准物质的研制

我国氢氧同位素国家一级标准物质经过二十余年的使用,现已不能满足需求,急需研制代表当今分析技术水平的新的氢氧同位素国家标准物质。本文研制了系列(4个)水中氢氧同位素标准物质,其中三个采自天然水样,一个为人工配制的贫氘水,三种天然水样基本涵盖了我国境内天然水的氢氧同位素组成范围。每种标准物质随机抽取30瓶的均匀性子样,每份子样做双份分析,进行均匀性检验,四种标准物质的均匀性检验得到的F值都小于相应的自由度的临界值,显示四种标准物质的均匀性良好。标准物质的δ¹⁸O和δD值经过2年的稳定性检验,特征量值变化在不确定度范围,由此判定δD、δ¹⁸O值稳定性良好。采用国际间实验室采用不同原理的方法协同定值,11家国内外实验室分别采用Cr还原法、激光法、H₂-H₂O平衡法、高温热转换元素分析法进行水中氢同位素定值,采用CO₂-H₂O平衡法进行氧同位素定值;定值不确定度显著降低,δ¹⁸O的扩展不确定度小于0.08‰,δD的扩展不确定度小于0.9‰。该标准物质已被国家质检总局批准确为国家一级标准物质,批准号为GBW 04458~GBW 04461。     

Starch-assisted sol–gel synthesis of magnetic CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powder as photo-Fenton catalysts in the presence of oxalic acid

Magnetic photo-Fenton catalysts based on spinel CuFe₂O₄ were successfully prepared by the starch-assisted sol–gel method. Various synthetic conditions such as annealing temperatures (700, 800 and 900 °C) and molar ratios of Cu²⁺/Fe³⁺/C₆H₁₀O₅ in the precursor solution (from 1:2:2 to 1:2:4) were, respectively, used in order to study the influences of annealing temperatures and precursor starch contents on the magnetic and catalytic properties of CuFe₂O₄ powders. The photo-Fenton catalytic activity was evaluated via the degradation of methylene blue under ultraviolet and visible irradiation with H₂C₂O₄ as a new oxidizing agent. According to the results, when the annealing temperature increased to 800 °C, the spinel CuFe₂O₄ phase amount was increased, which strongly enhances the photo-Fenton catalytic performance. However, above 800 °C, the catalytic activity was reduced, due to the increase in particle size. The starch content also affected the surface Cu²⁺ content and the particle size of catalysts. The catalyst prepared at 800 °C with the molar Cu²⁺/Fe³⁺/C₆H₁₀O₅ ratio of 1:2:3 presented the best photo-Fenton performance, owing to its highest surface Cu²⁺ content. This catalyst also exhibits ferromagnetic properties (saturation magnetization of 25.836 emu/g and coercivity of 1010.23 Oe), which allows them to be easily separated from the solution by a magnet.     

Adsorption study on municipal solid waste leachate using <Emphasis Type="Italic">Moringa oleifera</Emphasis> seed

Effects of initial concentrations of Moringa oleifera seed coagulant for removing Chemical Oxygen Demand and Total Dissolved Solids from municipal solid waste leachate have been evaluated at an optimum pH of 7 and temperature of 318 K. The kinetic data obtained from the experiments were fitted to the pseudo first-order, pseudo second-order, Elovich and intraparticle diffusion models. Based on a regression coefficient (R ²), the equilibrium (kinetic) data were best fitted with the Elovich model (R ² = 0.993 for Chemical Oxygen Demand and R ² = 0.996 for Total Dissolved Solids) than that of other models. The results of the kinetic models study indicated that the adsorption capacity of M. oleifera seed as a coagulant for removing Chemical Oxygen Demand and Total Dissolved Solids in a leachate increased up to 100 mg L^?1, beyond which the adsorption capacity got reduced. Finally, the present study concluded that M. oleifera seed coagulant could be employed effectively for the removal of Chemical Oxygen Demand and Total Dissolved Solids in a municipal solid waste leachate.     

Optimization of ammonia removal by ion-exchange resin using response surface methodology

The ability of ion-exchange resin for ammonia removal from aqueous solution was studied. The results showed that Amberlite ion-exchange resin was effective in removing ammonia from aqueous solution. Factorial design and response surface methodology were applied to evaluate and optimize the effects of pH, resin dose, contact time, temperature and initial ammonia concentration. Low pH condition was preferred with the optimum pH found to be 6. High resin dose generated high removal rate and low exchange capacity. Results of factorial design and response surface methodology showed that temperature was not a significant parameter. The model prediction was in good agreement with observed data (R ² = 0.957). The optimum Q _e was 28.78 mg/g achieved at pH = 6 and initial TAN concentration of 3000 mg/L. The kinetics followed the pseudo-second-order kinetic model (R ² = 0.999). Equilibrium data were fitted to Langmuir and Freundlich isotherm models with Langmuir model providing a slightly better predication (R ² = 0.996). The resin was completely regenerated by 2 N H₂SO₄.     

Comparison of Fenton,ultraviolet–Fenton and ultrasonic–Fenton processes on organics and colour removal from pre-treated natural gas produced water

Produced water (PW) from natural gas field, characterized with high organic contents, has brought high environmental concerns world widely. Fenton and enhanced Fenton technologies were considered as the potential methods to degrade the organic contaminates in the PW, but with very limited data or reference. Here, we examined the optimum conditions of Fenton on organics and colour removal from natural gas PW after coagulation pre-treatment. Simultaneously, the optimal Fenton process integrated with ultraviolet (UV) and ultrasonic (US) irradiation were applied to enhance pollutants removal efficiencies. The optimal Fenton conditions were found at 60 min with molar ratios of 6:1 and 25:1 for H₂O₂/COD and H₂O₂/Fe²⁺, respectively and the initial pH of 3. Among these the three treatment processes, chemical oxygen demand (COD), total organic carbon, 5-day biological oxygen demand (BOD₅), and colour removal efficiencies were highest during UV–Fenton (82, 73, 68, and 95%,) followed by US–Fenton (79, 70, 66, and 95%) and Fenton treatment (70, 58, 51, and 92%), respectively. High biodegradability (BOD₅/COD) was also observed after UV–Fenton process (0.76) than the others (both 0.73). The current study showed a satisfactory carbon and colour removal efficiencies from PW using different Fenton processes; however, there still is a need for final polishing such as biological treatment or low cost constructed wetland before discharge. This study can be a good reference for engineering application PW treatment.     

Degradation of dimethyl sulfoxide through fluidized-bed Fenton process: kinetic analysis

In this study, fluidized-bed Fenton process (FBF) was used to degrade dimethyl sulfoxide (DMSO), one of the most widely used solvents. Oxidation by Fenton’s reagent, Fe⁺² and H₂O₂, is one of the cheapest advanced oxidation processes due to the high availability of the reagents. FBF is a modified approach that reduces the large amount of iron oxide sludge formed in conventional Fenton process. The optimal treatment efficiencies by FBF with 2 h of reaction were 95.22 % of DMSO degradation and 34.38 % of COD removal at the conditions of 5 mM DMSO, 68.97 g/L SiO₂ carrier, pH_initial 3.0, 5 mM Fe²⁺, and 32.5 mM H₂O₂. The kinetic study was also done to investigate the two stages involved in the oxidation. The first stage fitted the zero reaction order with overall initial rate’s apparent rate constant, k ₁, of ?0.099. The second stage fitted the first order of DMSO degradation, with rate constant, k ₂, of ?0.0005.     

Adsorption of methylene blue and crystal violet on low-cost adsorbent: waste fruits of <Emphasis Type="Italic">Rapanea ferruginea</Emphasis> (ethanol-treated and H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-treated)

This study assesses the ability of two low-cost adsorbents made from waste of Rapanea ferruginea treated with ethanol (WRf) and its H₂SO₄-treated analog (WRf/H₂SO₄) for the removal of two cationic dyes methylene blue (MB) and crystal violet (CV) from aqueous solutions. The adsorbent was characterized by scanning electron microscopy, Fourier transform infrared spectrometry, thermogravimetric analysis, point of zero charge (pH_pzc), specific surface, and functional groups. The adsorption of dye onto the adsorbents was studied as a function of pH solution (2–12), contact time (up to 120 min) and initial concentration (20–120 mg/L), and temperature (25, 35, and 55 °C). The influence of these parameters on adsorption capacity was studied using the batch process. The response surface methodology (RSM) was used in the experimental design, modeling of the process, and optimizing of the variables and was optimized by the response involving Box–Behnken factorial design (15 runs). The results show that the data correlated well with the Sips isotherm. The maximum adsorption capacities of MB and CV onto WRf were found to be 69 and 106 mg/g, and onto WRf/H₂SO₄, the adsorption capacities were 33 and 125 mg/g, respectively. The kinetic data revealed that adsorption of cationic dyes onto the adsorbents closely follows the pseudo-second-order kinetic model. Regression analysis showed good fit of the experimental data to the second-order polynomial model, with coefficient of determination (R²) values for MB (R²?=?0.9685) and MB (R²?=?0.9832) for WRf and CV (R²?=?0.9685) and CV (R²?=?0.9832) for WRf/H₂SO₄ indicated that regression analysis is able to give a good prediction of response for the adsorption process in the range studied. The results revealed that waste from R. ferruginea is potentially an efficient and low-cost adsorbent for adsorption of MB and CV.     

Removal of acetaminophen from hospital wastewater using electro-Fenton process

The current work deals with efficient removal of acetaminophen (AC) from hospital wastewater using electro-Fenton (EF) process. The degradation yield of 99.5% was obtained under optimal experimental conditions, namely 5.75 mg L^?1 initial AC concentration, 2.75 pH solution, 3-cm inter-electrode distance, 100 mg L^?1 KCl electrolyte, 122.5 µL L^?1 H₂O₂, 8 mA cm^?2 current density at equilibrium time of 8 min. Analysis of variance (ANOVA) suggested that the effect of mentioned operating parameters was statistically significant on the AC removal. The low probability amount of P value (P < 0.0001), the Fisher’s F-value of 65.91, and correlation coefficient of the model (R² = 0.9545) revealed a satisfactory correlation between the experimental and the predicted values of AC removal. The predicted removal efficiency of 99.4% was in satisfactory agreement with the obtained experimental removal efficiency of 98.7%. The AC degradation during the EF followed a first-order kinetic model with rate constants (K_app) of 0.6718 min^?1. Using the ordinary radical scavengers revealed that main mechanism of AC degradation controlled by the hydroxyl free radicals produced throughout the EF process. The excess amount of iron (II) scavenged the active radicals and diminished the concentration of ^·OH available to react with AC. The optimum molar ratio of H₂O₂ to Fe²⁺ was found to be 2.5. The developed EF process as a promising technique applied for treatment of real samples.     

Effect of Fenton process on treatment of simulated textile wastewater: optimization using response surface methodology

A large portion of water is consumed during various textile operations thereby discharging wastewaters with pollutants of huge environmental concern. The treatment of such wastewaters has promising impact in the field of environmental engineering. In this work, Fenton oxidation treatment was engaged to treat simulated textile wastewater. Box–Behnken design and response surface methodology were employed to optimize the efficiency of Fenton process. Iron dose, peroxide dose and pH were considered as input variables while the responses were taken as chemical oxygen demand and color removal. A total of 17 experiments were conducted and analyzed using second-order quadratic model. The quadratic models generated for chemical oxygen demand and color removal efficiencies were validated using analysis of variances, and it was found that the experimental data fitted the second-order model quite effectively. Analysis of variances demonstrated high values of coefficient of determination (R ²) for chemical oxygen demand and color removal efficiencies with values of 0.9904 and 0.9963 showing high conformation of predicted values to the experimental ones. Perturbation plots suggested that the iron dosage produced the maximum effect on both chemical oxygen demand and color removal efficiencies. The optimum parameters were determined as Fe²⁺ dose—550 mg/L, H₂O₂ dose—5538 mg/L, pH—3.3 with corresponding chemical oxygen demand and color removal efficiencies of 73.86 and 81.35%. Fenton process was found efficient in treatment of simulated textile wastewater, and optimization using response surface methodology was found satisfactory as well as relevant. From the present study, it can also be concluded that if this method is used as pretreatment integrated with biological treatment, it can lead to eco-friendly solution for treatment of textile wastewaters.     

Biosorption of fluoride by water lettuce (<Emphasis Type="Italic">Pistia stratiotes</Emphasis>) from contaminated water

Phytoremediation is a proven low-cost and sustainable method for the removal of toxic pollutants from water. This green technology has been practiced for the past several years all over the world. In the present study, the interaction of fluoride on the surface of the floating aquatic plant water lettuce (Pistia stratiotes) during fluoride removal was investigated. Batch kinetic studies were performed to examine the fluoride uptake capacity of the plant with different initial fluoride concentrations such as 3, 5, 10, and 20 mg/L. The effects of various process parameters on fluoride uptake dynamics such as pH, plant biomass, initial fluoride concentration, and time were examined. Freundlich’s isotherm model was found to (R ² = 0.957) fit well to the experimental data. The nature of reaction order followed pseudo-first-order kinetics, when the initial fluoride level in the solution was 5 mg/L. The experimental findings showed that the removal mechanism was driven by biosorption phenomenon. High fluoride concentration in the solution reduced the growth ratio of P. stratiotes. The lowest growth ratio of this aquatic macrophyte was found to be 76.80 ± 3.73% at 20 mg/L fluoride concentration. At lower fluoride concentrations such as 3 and 5 mg/L, the growth ratio of the plant was not reduced significantly.     

Using Goethite as a Heterogeneous Fenton Catalyst for The Removal of Tetracycline Hydrochloride: Effects of Its Adsorptive and Reductive Activities

The removal of the antibiotic compound tetracycline hydrochloride (TC) was investigated by using goethite/H2O2 as a heterogeneous Fenton reagent. Five principle operational parameters, especially solution pH value, were taken into account to investigate how the heterogeneous Fenton process factors mediated the TC removal. This process was effective but seriously impacted by the pH value and temperature, as well as the dosages of α-FeOOH, TC and H2O2. Very interestingly, the acidic and alkaline aqueous medium conditions were both very favorable due to the occurrence of transformation of Fe(III) to Fe(II) on goethite surfaces reduced by TC at pH 3.0⁴.0 even though with a low adsorption capacity of TC because its maximum adsorption of negatively charged form occurred at pH around 8.0[1], thereby greatly promoting the TC Fenton oxidative elimination. However, a rapid initial TC decay was observed at the first 5 min, followed by a much slower retardation stage, which was likely because the reductive transformation of Fe(III) to Fe(II) by TC in the solution was inhibited as the Fenton reaction proceeded. Moreover, the hydroxyl radical scavenger t-butanol addition can decrease the removal rate of TC in the goethite/H2O2 system to a certain extent. This further indicated that the main reactive species in this process were hydroxyl radicals[2]. All the goethite-catalysed heterogeneous Fenton reactions are responsible for the TC removal following the Langmuir-Hinshelwood model, were well fitted to pseudo-first order kinetics (R2>0.99), and their apparent activation energy (E) for this Fenton-like reaction was 31.86 kJ mol 1, a low value that is highly consistent with the ease of TC decay greatly enhanced by the temperature rise, indicated that the interfacial controlling interactions such as a proton induced solubilization and a reductive dissolution of goethite can clearly improve its Fenton catalytic activity[3], and these dissolution processes may not be effective in some cases, while the TC adsorption process may always play an important role to control the TC removal rate during the Fenton reaction.