ELECTROKINETIC SOIL PROCESSING COMPLICATING FEATURES OF ELECTROKINETIC REMEDIATION OF SOILS AND SLURRIES: SATURATION EFFECTS AND THE ROLE OF THE CATHODE ELECTROLYSIS.

Electrokinetic soil processing is an emerging technology for decontamination of certain radionuclides, heavy metals, or organic species from soils or slurries. Tests reveal that the process efficiencies in partially saturated kaolinite samples (without contaminants) are high, since water supplied at the anode eventually flushed across the specimens and saturated the deposits. Consolidation settlements are expected in the vicinity of anodes in fine-grained soils, even when both electrodes allow ingess or egress of the water. Uranyl ion at 1000 pCi/g could be effectively removed from kaolinite but the removal efficiency decreased close to the cathode due to the high pH in this region. A yellow uranium hydroxide precipitate was collected at the cathode. Thorium ion, even at 300 pCi/g, could not be efficiently removed throughout the cell because of its high adsorptive capacity, facile hydrolysis, and the precipitation of insoluble hydroxide. Methods are required to prevent hydroxide ion formation by the cathode reduction of water and thus enable extraction of these metal species in soluble forms.     

Enhanced electrokinetic remediation of polluted kaolinite with an azo dye

In this work, the feasibility of the combination of electrokinetic remediation and electrochemical oxidation for the remediation of polluted soil with organic compounds had been development and evaluated in kaolinite spiked with Reactive Black 5 (RB5) an azo dye. The process consists in the use of two combined phenomena to achieve a full remediation of RB5 spiked kaolinite and the degradation of the organic pollutant. Those phenomena were soil electrokinetic treatment combined to liquid electrochemical oxidation. Reactive Black 5 (0.39 g dye kg⁻¹) could be effectively removed from the kaolinite matrix by electrokinetics, however the removal results largely depended on the operating conditions. Complete removal of RB5 was achieved using K₂SO₄ as processing fluid (which enhanced the desorption of RB5 from the kaolinite matrix) and operating with pH control at 7 on the anode. This favoured the alkalinization of the system and, at high pH values, RB5 was ionized and migrated towards the anode chamber where it was collected and could be oxidized electrochemically. Also, it must be pointed out that in these optimized conditions the electric power consumption (56 kW/mg of removed dye) was ten times lower compared to the unenhanced electrokinetic process (with no pH-control in the electrode solutions). Separate electrochemical decolourization tests of RB5 showed the effectiveness of K₂SO₄ in the efficiency of the process. A linear relationship between K₂SO₄ concentration and the decolourization rate was found. Thus, nearly complete decolourization was achieved after 2 and 3 h of electrochemical treatment when the electrolyte concentration was 0.1 and 0.01 M of K₂SO₄, respectively.     

柠檬酸工业废水强化镉污染土壤的电化学法修复

通过批量解吸附实验和电化学修复实验,研究利用柠檬酸工业废水作为电化学修复的增效剂从高缓冲容量的天然土壤中去除镉的可行性。批量实验结果表明,当加入柠檬酸工业废水时,85%以上的镉能在土壤pH≤5.0的条件下从土壤中溶解到溶液中;在pH5.0～8.0范围内镉的解吸附率比用去离子水增加20%～45%。电化学修复实验结果表明,与相同pH值的HNO₃相比,该废水作为电极溶液可使镉在土壤中发生明显迁移;在距离阳极0～4 cm及8～10 cm处土壤镉含量由282 mg·kg^-1降低至167～200 mg·kg^-1,而在距阳极4～8 cm处土壤镉含量升高至约400 mg·kg^-1。经过514 h的电化学修复,约84.7%的镉可以从土壤中去除,其中约94.6%从土壤中去除的镉富集在阴极溶液中。可见柠檬酸工业废水是一种非常有前景的重金属污染土壤电化学修复增效剂。     

Effect of clay mineralogy on the feasibility of electrokinetic soil decontamination technology

To evaluate the effect of clay mineralogy on the feasibility of electrokinetic soil remediation technology, we contaminated six soils with Cu(II), Zn(II) and Pb(II) and performed electroremediation for 570 h. Cation exchange resin saturated with H⁺ was placed between soil and cathode to prevent soil alkalinization and trap the migrated heavy metal cations. After the treatment, the heavy metal cations were sequentially extracted with water, 1 M MgCl₂ and hot 6 M HCl. In soils dominated by crystalline clay minerals, Cu(II) and Zn(II) significantly migrated from anode end and accumulated at the cathode end forming sparingly soluble hydroxides. Removal rates of Cu(II) and Zn(II) were highest in a soil dominated with kaolinite and crystalline hematite. In humic–allophanic and allophanic soils, the high pH-buffering capacity of allophane kept the soil pH above 5, even at the anode end, and Cu(II) and Zn(II) did not migrate significantly. In all soils, the migration of Pb(II) was infinitesimal due to the formation of insoluble PbSO₄ and very strong surface complexation at the mineral surfaces. These results show that the reactivity of component clay minerals to H⁺ and heavy metal cations has a crucial effect on the efficiency of the electrokinetic remediation technology and it is not effective for remediation of allophanic soils. The results also indicate that allophanic soils may be useful as a barrier material in landfill sites.     

Influence of electroosmotic treatment on the hydro-mechanical behaviour of clayey silts: preliminary experimental results

Preliminary results of an investigation focused on the influence of electrokinetic treatment on the mechanical and hydraulic behaviour of clayey soils are presented. The experimental programme aims at providing a contribution to the sustainability of contaminant extraction or containment via electroosmosis. Changes in the hydraulic and mechanical properties of two illitic clayey soils, subjected to a DC electric field, were investigated. Samples of the two soils were subjected to electrokinetic filtration, for different periods of time, and under different constant loads. Afterwards, they were tested under one-dimensional compression to detect changes in stiffness and hydraulic conductivity due to the electrical treatment. After the application of a DC field for a few hours, a small reversible increment in the average soil stiffness was observed, with respect to the untreated soil, while the hydraulic conductivity was not affected substantially. Dramatic changes of the mechanical and hydraulic soil properties, correlated to changes of the soil pH, were observed following non-conditioned electrokinetic treatment with duration of the order of days.     

Role of stabilizers for treatment of clayey soil contaminated with phenanthrene through electrokinetic-Fenton process—Some experimental evidences

In electrokinetic-Fenton (EK-Fenton) process, the effects of the phosphate and SDS introduced from the anode chamber were investigated for the treatment of clay contaminated with phenanthrene. In tests with phosphate and SDS, the electrochemical phenomena were complicate trend compared to tests with HCl. These results resulted from complexation of phosphate with oxides and SDS, and then increase of dissolved SDS concentration with pH increase in regions near cathode. The electro-osmotic flow increased as zeta-potential on the soil surface decreased due to complexation of phosphate and SDS with oxides.In test with phosphate, the transportation of dissolved Fe ions toward the cathode was hindered significantly due to complexation with phosphate. However, in test with SDS, the dissolved Fe ions could be transported in the regions near cathode compared to test with phosphate. These results indicate that SDS dissolved the Fe ion from Fe oxide of soil structure and then the dissolved Fe ions with SDS as counter ion could be transported in regions near cathode. Furthermore, transition metal complexation with phosphate and SDS generated improvement of H₂O₂ stability. Particularly, in test with SDS, the improvement of H₂O₂ stability in high pH regions resulted from SDS transportation in regions near cathode. Consequently, in EK-Fenton process with longer reaction time, the increase of H₂O₂ stability resulted in increase of phenanthrene treatment efficiency.     

高盐度对突发重金属污染水源水应急处理的影响研究

针对沿海城市饮用水受咸潮影响的实际情况,探讨突发重金属污染的应急处理技术的可行性及高盐度对该技术的影响,试验结果表明,调节pH值-强化混凝可以有效控制突发的铅、镉、镍污染;亚铁还原(六价铬为三价铬)-铁盐混凝法可以有效控制突发的铬污染;NaClO氧化(三价砷为五价砷)-铁盐混凝法可以有效控制突发的砷污染;高盐度对突发重...     

A Laboratory-Scale Study of Applied Voltage on the Electrokinetic Separation of Lead from Soils

ABSTRACT

The application of electrokinetic (EK) soil-flushing technology to the separation of lead from a nonsynthetic, fine-grained, low permeability soil was examined. In these laboratory-scale experiments the effects of applied voltage (30 and 60 V DC) on cumulative electroosmotic (EO) flow, charge-input, and lead removal were investigated. To develop a more generalized cause-effect relationship, these parameters were studied using three anode/cathode reservoir conditioning schemes: NaNO₃/NaNO₃, NaNO₃/HAc (acetic acid), and HCl/HAc. Charge-input and cumulative EO flow generally increased when the applied voltage was raised. When reservoir pH controls were used, results were more consistent with theoretically predicted outcomes. Increasing the applied voltage increased the electrolysis of water, which increased the fluid conductivity and charge-input. Although cumulative EO flow increased in proportion to the voltage, the advantage of operating at a higher applied voltage diminished as the amount of lead remaining in the soil decreased. The highest lead removal rates for both the 30 and 60 V tests were achieved using the 0.1 M HCl/1.0 M HAc reservoir conditioning scheme. The addition of HCl to the anode reservoir solution enhanced the impact of the acid front, especially during the initial pore volumes of flow which occurred before the oxidation of water could produce significant amounts of H⁺ at the anode. Additionally, HAc in the cathode reservoir prevented the formation of a base front and the subsequent Pb readsorption/precipitation onto soil. The greater cumulative EO flow and charge-input in the experiments conducted with the HCl/HAc reservoir conditioning scheme resulted in faster Pb removal via advection and electrolytic migration. In contrast, the lowest remediation and removal values were obtained with the NaNO₃/NaNO₃ reservoir treatment scheme, which had a low cumulative EO flow, relative to the other tests, and lacked reservoir fluid pH control. To demonstrate the impact of soil pH on Pb removal, soil-bound Pb concentrations as a function of soil pH were also examined. The “critical pH” range necessary to ensure effective Pb removal was between 4 and 4.5.     

Simultaneous removal of metals and organic compounds from a heavily polluted soil

The paper describes the results of treatment of soil samples, deriving from a dismissed industrial site, contaminated with several metals: Hg, Ni, Co, Zn, Pb, Cu, Cr, As and organic substances. The soil was subjected to remediation based on a process in which an oxidising leaching agent was produced electrochemically in-line in an undivided electrochemical cell reactor equipped with a Ti/Pt-Ir anode and a stainless steel cathode. Leaching of the soil samples was performed under dynamic conditions using a leaching column. A subsequent regeneration of the leaching solution, which consisted in electrodeposition of metals and electro-oxidation of organic substances, was carried out in a packed-bed reactor equipped with a centrally positioned graphite rod, serving as an anode, and stainless steel three-dimensional filling as a cathode. The study was focused on how and to which extent the metals present in the soil, as organic complexes, can be solubilised and how the process rates are impacted by the solution pH and other process variables. Data obtained under non-oxidising conditions, typically adopted for leaching of metals, are compared with the performance of chlorine-enriched leaching solutions. The results obtained under various conditions are also discussed in terms of the total organic carbon (TOC) removal from the water phase.     

Electrokinetic remediation of lead‐, zinc‐ and cadmium‐contaminated soil

Electrokinetic remediation of lead‐, zinc‐ and cadmium‐contaminated sand and clayey soils has been investigated under laboratory‐scale conditions. Soil extracts of heavy metals (by 1 M HCl solution) were analysed by optical emission spectrometry. The efficiency of electrochemical remediation was partially dependent on the pH of the soil media. With pH increase, the migration of heavy metal ions toward the cathode was limited. When acetic acid was added to the sandy soil, almost complete remediation was achieved. A clay layer inserted in the cathode area did enhance the remediation rate. The most effective clean‐up was achieved for zinc and cadmium, with less effective clean‐up being achieved for lead. The effectiveness of the electrokinetic remediation of heavy metal‐contaminated clayey soil was low. The appropriate acidity was not achieved using acetic acid because of the high buffering capacity of clay, and metal ion migration was impeded by its sorption onto some clay components. The conclusion was made that clays could be used as immobilizing media for heavy metal ions by electrokinetic remediation of various soils. © 2001 Society of Chemical Industry     

粉煤灰硬化体中Cr(Ⅵ)的渗滤溶出行为

模拟雨水通过土壤的渗滤过程,进行了粉煤灰硬化体渗滤溶出试验.研究了外界水渗透通过粉煤灰硬化体时,其中可溶性Cr(Ⅵ)在硬化体、土壤、渗滤液中的迁移转换规律,评估了粉煤灰硬化体中Cr(Ⅵ)的溶出及其对土壤和地下水可能产生的影响.结果表明:水渗透通过粉煤灰硬化体时,会将其中部分的Cr(Ⅵ)带出,转移到土壤和渗滤液中;渗滤液中Cr(Ⅵ)的累计量与时间的对数呈线性增加关系,Cr(Ⅵ)的溶出过程主要受扩散控制;渗滤后体系中可溶性Cr(Ⅵ)总量显著减少,说明Cr(Ⅵ)在从硬化体向土壤和渗滤液中的迁移过程中还存在着形态的变化.灰色关联分析表明:溶出过程中,Cr(Ⅵ)的溶出与Ca2 和Na 的溶出有较密切的相关性.     

Mechanism for Soil Reinforcement by Electroosmosis in the Presence of Calcium Chloride

Electroosmosis has been extensively employed as an effective method for the dewatering treatment of soils and thus the reinforcement of weak soils. At the microscopic level, this treatment process is inherently complex due to in situ chemical and electrochemical reactions, migration of ions and particles, and the dependence of zeta potential of various particles on the local pH value in the soil. This complexity has hindered further understanding of mechanisms underlying the electroosmosis technology. Here, we design an external electric field in which alternating pulse wave potentials were partially used to adjust the pH value of the soil and manipulate the dynamics of in situ formed nanoparticles and their interconnectivity. The experimental results reveal that the in situ formation of Ca-rich particles, instead of water drainage, may serve as the main mechanism underlying the observed soil reinforcement when using calcium chloride as the treatment electrolyte. The interconnectivity of such particles may be the key for the shear strength improvement without significant settlement of the soil.     

Anodic oxidation of phenol for waste water treatment

The electrochemical oxidation of phenol for waste water treatment applications was investigated on lead dioxide packedbed anodes. Cells were operated in both batch and continuous modes with feed streams up to 1100 mg/l phenol dissolved in aqueous solutions of Na₂SO₄ and H₂SO₄ or NaOH. All the phenol in solution could be readily oxidized but complete total organic carbon (T.O.C.) removal was more difficult. The percent phenol oxidized increased with increasing current density, and decreased as initial phenol concentration, electrolyte flow rate, pH and anode particle size were increased. Results are compared to simple mathematical models.     

干湿循环下pH值对砂岩静态单轴力学特性的影响

为研究不同pH值溶液干湿循环作用对砂岩力学性能劣化的影响,采用pH值为3、5、6.5(蒸馏水)和7的 4种溶液对砂岩进行干湿循环作用,对经历0次(干燥状态)、1次、10次和20次干湿循环作用的砂岩进行纵波波速测定、吸水率试验、XRD试验和单轴抗压试验。试验结果表明:pH值相同时,随着干湿循环次数的增加,砂岩试件的单轴抗压强度逐渐降低;干湿循环次数相同时,随着溶液pH值的减小,砂岩试件的纵波波速呈下降趋势,吸水率逐渐增加,内部矿物成分发生变化,单轴抗压强度逐渐下降并趋于稳定。酸性溶液干湿循环作用下砂岩试件的劣化程度要比中性溶液更为严重,pH值越小劣化程度越大。     

Anodic oxidation of phenol for waste water treatment

The electrochemical oxidation of phenol for waste water treatment applications was investigated on lead dioxide packed-bed anodes. Cells were operated in both batch and continuous modes with feed streams up to 1100 nig/1 phenol dissolved in aqueous solutions of Na₂SO₄ and H₂SO₄ or NaOH. All the phenol in solution could be readily oxidized but complete total organic carbon (T.O.C.) removal was more difficult. The percent phenol oxidized increased with increasing current density, and decreased as initial phenol concentration, electrolyte flow rate, pH and anode particle size were increased. Results are compared to simple mathematical models.     

尕斯油田注水系统腐蚀原因和影响因素研究

针对尕斯油田注水系统的腐蚀特征,通过电化学测试、腐蚀挂片等方法研究了各因素对N80碳钢腐蚀的影响。研究结果表明,尕斯油田的污水对N80碳钢的腐蚀主要是析氢腐蚀;S2-浓度增加,污水腐蚀性增强;pH＜6时,析氢腐蚀加剧;矿化度增加,以及温度升高都能使腐蚀速率增加。     

Effect of solution pH on crack initiation and propagation in glass‐polyester pipes subjected to impact

The objective of this study was the determination of the influence of alkaline and acidic solutions on the impact properties of glass‐polyester composite pipes. First, the impact test was performed on virgin samples (without the influence of any liquid) to obtain knowledge about the original material properties. Subsequently, the specimens were soaked in water and in alkaline and acidic solutions: sodium hydroxide, ammonium hydroxide, phosphoric acid, and nitric acid. The specimens were left in each liquid for 3, 10, 30, and 60 days at room temperature. The impact toughness and the crack initiation and propagation energies were recorded for all samples. A comparison of the results was made based on the pH values of the aggressive media, as well as based on the original impact properties and number of days of treatment. This way, the service life of pipes for transport of theexamined solutions could be predicted. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Electrochemical oxidation of textile dye indigo

Electrochemical methods are being used increasingly as an alternative treatment process for the remediation of textile wastewaters. This study focused mainly on the colour removal and chemical oxygen demand (COD) reduction of vat textile dye (CI Vat Blue 1: indigo) from its aqueous solution by electrochemical oxidation. The process was carried out in a batch‐type divided electrolytic cell under constant potential using a Pt cage as anode and Pt foil as cathode. Operating variables such as supporting electrolyte, pH, ultrasonification and treatment time were investigated to probe their effects on the efficiency of the electrochemical treatment. Colour removal was estimated by monitoring the disappearance of the absorbance peak at 681.5 nm. It was found that in acidic conditions the electrolysis was more efficient. At pH 1, an NaCl concentration of 0.24 mol dm^?3, a dyeing solution concentration of 0.1% (w/v) and a period of 90 min of electrolysis, there was almost 100% colour removal and 60% reduction in COD. Voltammetric and IR investigations demonstrated that partial degradation of dye was achieved. The experimental results indicate that this electrochemical method could effectively be used as a pretreatment stage before conventional treatment. Copyright © 2005 Society of Chemical Industry     

利用休耕田处理水产养殖废水同步增强土壤肥力的试验

水产养殖废水一般在冬季排放,而冬季休耕田需引水灌溉调理土壤性质,因此,文中提出了水产养殖废水养分农田再利用技术。通过小试装置构建模拟休耕田对水产养殖废水进行处理,研究水量、植物类型对水质净化效果的影响,验证土壤、植物、微生物对水质具有综合净化效果。并进一步将小试试验成果用于中试应用试验,探究自然条件下水产养殖废水一次性大量排入休耕田,对地下水背景水质及土壤的影响。结果表明,当水量为300 L/m²时,水质净化效果最好,TN、TP、COD_Cr去除效率分别为87.6%、57.9%、60.4%;种植植物能显著提高水质净化效果,水芹(Oenanthe javanica)吸收氮、磷的占比分别为28.7%、16.2%,菖蒲(Acorus calamus)为32.6%、14.9%。中试应用试验结果表明：灌水后18 d左右,地下水的水质能够恢复至背景值水平,受纳废水能提高土壤肥力,增强土壤供氮、供磷能力。     

电化学氧化耦合絮凝技术深度处理焦化废水影响因素分析

采用了电化学氧化耦合絮凝技术处理焦化废水,研究了电流密度、pH值、水力停留时间(HRT)和絮凝剂投加量对CODCr去除效果的影响。研究结果表明,电化学氧化耦合絮凝技术处理焦化废水有较好的协同效应。当进水中CODCr的质量浓度为99 mg/L,在电流密度为30 mA/cm2,HRT为30 min,pH值为6.5,PAM投加量为600 mg/L时,CODCr去除率达到80%以上,出水水质指标稳定,并能达到GB 8978—1996《污水综合排放标准》一级排放标准。