Recovery of rare-earth elements from neodymium magnets using molten salt electrolysis

Rare-earth elements are used in neodymium magnets, and these elements are critical to Japanese industry. In this study, we focused on the electrochemical behavior of neodymium magnets for the recovery of rare-earth elements using molten salt electrolysis. The influence of the rare-earth elemental composition of the neodymium magnets on their anodic polarization behavior and oxidation mechanism was studied. The use of potentiostatic electrolysis enabled selective leaching of rare-earth elements from neodymium magnets in the potential range from ?1.8 to ?0.8 V. The oxidation potential limits the oxidation stage, enabling rare-earth elements to be leached from mixed neodymium magnets simultaneously.     

Ammoniacal leaching and recovery of copper from alloyed low-grade e-waste

The paper concerns a hydrometallurgical method for selective recovery of copper from low-grade electric and electronic wastes. The following consecutive stages were proposed: smelting of the scraps to produce Cu–Zn–Ag alloy, leaching of the alloy in ammoniacal solution, and selective copper electrowinning. Cu–Zn–Ag alloy was a polymetallic and five-phase system. It was leached in chloride, carbonate, sulfate and thiosulfate solutions. This resulted in the separation of the metals, wherein metallic tin and silver as well as lead salts remained in the slimes, while copper and zinc were transferred to the electrolyte. Copper was selectively recovered from the ammoniacal solutions by the electrolysis, leaving zinc ions in the electrolyte. The best conditions of the alloy treatment were obtained in the ammonia–carbonate system, where the final product was copper of high purity (99.9 %) at the current efficiency of 60 %. Thiosulfate solution was not applicable for the leaching of the copper alloy due to secondary reactions of the formation of copper(I) thiosulfate complexes and precipitation of copper(I) sulfide, both inhibiting dissolution of the metallic material.     

新型三维电化学氧化体系处理压裂返排液

采用不锈钢作阴极、镀钌铱的钛板作阳极、铁碳材料作粒子电极,构建新型三维电化学氧化体系,处理压裂返排液,并通过响应曲面法考察COD去除率和除油率的影响因素。实验结果表明:回归方程的相关系数及校正相关系数均大于0.9,回归方程的线性关系显著;返排液COD去除率和除油率影响因素的大小顺序均为电流电解时间粒子填充比,其中关键因素是电流,电解时间和粒子填充比之间的交互作用具有较大影响;在电解时间为31.8 min、电流为4.4 A、粒子填充比为61.2%的条件下,COD从606.4 mg/L降至68.5 mg/L,含油量从153.7 mg/L降至9.1 mg/L,达到GB 8978—1996《污水综合排放标准》中的一级标准。     

Ti/RuO2-IrO2-TiO2电极电解产生活性氯

采用电解法产生活性氯,降解废水中的有机物。考察了活性氯产生量的影响因素,并对Ti/RuO₂-IrO₂-TiO₂电极电解实际含氯废水的处理效果进行了研究。实验结果表明:通过增加Cl^-浓度和电流密度、减少SO₄^2-浓度和极板间距、降低电解温度的方法能够提高活性氯产生量,从而提高电极降解有机物的效果;对于Cl^-浓度为0.005 mol/L、COD为49 mg/L的废水,使用Ti/RuO₂-IrO₂-TiO₂电极,在极板间距为0.5 cm、电解温度为20 ℃、电流密度为20 mA/cm²、初始pH为8.0的条件下电解处理60 min,废水BOD₅/COD值由0.04提高到0.25,COD降至24 mg/L,达到DB 11/307—2013《水污染综合排放标准》中排入地表水体污染物B类排放限值(COD≤30 mg/L)的要求。     

钯负载泡沫镍电极电化学还原水中三氯乙酸

采用非电沉积法制备了钯负载泡沫镍电极,运用SEM技术对其进行了表征,并以其阴极、铂丝为阳极进行了电化学还原三氯乙酸的研究,考察了工艺条件对三氯乙酸降解效果的影响,并对反应动力学和反应机理和进行了探讨。结果表明:钯负载泡沫镍电极具有较高的比表面积和良好的储氢性能;以20 mmol/L硫酸钠为电解质,在电解温度为20℃、钯负载量为4.5 mg/cm~2的条件下恒流(10 mA)电解240 min,三氯乙酸降解率达99.76%,氯原子脱除率达73.86%;三氯乙酸的电化学还原反应过程以及三氯乙酸上未脱除氯原子浓度的变化均符合拟一级反应动力学方程;三氯乙酸在电化学还原过程中逐个脱除氯原子。     

Electrocoagulation of some reactive dyes: a statistical investigation of some electrochemical variables

In this study, the decolorization of strong colored solutions containing the reactive textile dyes by electrocoagulation was investigated. The experiments were statistically designed and carried out according to a 2(4) full factorial design with two replicate and four center points. This design was extended with eight additional axial points. Then, the non-linear regression was applied on the data by using MINITAB software. The variables chosen for this work are mixing rate, cell voltage, electrolysis time and current density. Results showed that the effective variables on decolorization process are cell voltage, electrolysis time and current density. In addition, to determine the effect of dye and electrode type on decolorization, the additional experiments were carried out. It was determined the dye and electrode type are important on the decolorization process.     

A sustainable system for decontamination of cephalexin antibiotic using electrocoagulation technology and response surface methodology

The emergence of synthetic micropollutants in wastewater due to domestic and industrial use has presented new challenges for treatment processes. Among these pollutants, pharmaceutical and personal care products (PPCPs) are considered emerging contaminants due to their potential to enter drinking water sources. Antibiotics, in particular, are of significant concern due to their high consumption in veterinary and human applications. In this study, the electrocoagulation (EC) process is used as an efficient technique for the removal of cephalexin (CFX) from pharmaceutical wastewater. The study aims to explore the ability of the EC process to remove CFX and optimize its performance using the response surface method based on Central Composite Design (RSM-CCD). The effects of initial CFX concentration, electrolysis time, initial pH, and electrode type (non-insulated and insulated) were considered in the optimization process. This research is distinct as it examines the influence of key factors on the elimination of CFX. The results showed that electrolysis time had the most significant effect on CFX removal using the EC process. The analysis of variance (ANOVA) test was used to evaluate the importance of independent variables and their interaction. The optimal operating conditions for maximum removal efficiency (86.53%) were an initial CFX concentration, reaction time, and initial pH of 34 mg/L, 34.35 min, and 6.5, respectively, using an insulated electrode. Under these optimal conditions, predicted CFX removal was 93.54%. These findings demonstrate that RSM-CCD is a useful tool for optimizing electrochemical removal processes for micropollutants such as CFX from wastewater streams. The study highlights the importance of considering electrode type in optimizing EC processes for micropollutant removal from wastewater.     

Impact of the use of waste on trace element concentrations in cement and concrete.

The results of model calculations carried out to identify and quantify the input pathways of trace elements into cement and concrete and to estimate the extent to which trace element concentrations in cement may change due to waste utilization are presented. As expected, primary raw materials represented the most important input pathway for trace elements into cement, but the contribution from wastes was not negligible. The use of waste led to a slight increase of the concentrations of cadmium, antimony and zinc in cement. For cobalt, lead and vanadium, this increase was less distinct and for all other trace elements considered, the effect of the use of wastes on trace element concentrations in cement could not be demonstrated clearly. The trace element content of concrete was governed by the aggregates for most elements considered. However, for arsenic, cadmium, lead and zinc, both cement and the additive coal fly ash contributed noticeably to the total trace element concentration in the concrete.     

石墨毡电极预处理模拟邻甲酚废水

采用聚丙烯腈基石墨毡电极，以NaCl为电解质，在恒流电解的条件下，对质量浓度为1 000 mg/L、COD=3 672 mg/L的模拟邻甲酚废水进行预处理。研究了电解时间、初始废水pH、NaCl加入量、电流密度对邻甲酚去除率的影响，考察了废水的COD变化，并探讨了反应机理。实验结果表明：石墨毡电极具有较好的导电性、吸附性，对邻甲酚具有较好的电化学氧化性能;常温常压下，初始废水pH为6~7、电流密度为90 A/m2、向300 mL废水中加入0.5 g NaCl时，经4 h电解，邻甲酚的去除率达到97.1%，COD的去除率达到47.3%;处理后废水的BOD5/COD由0.04提高至0.33，可不经稀释直接进行生物处理。     

单极性三维电极电解处理含钴废水

采用并联式单极性三维电极电解处理低浓度含钴废水并回收金属钴，比较了二维电极与三维电极的钴离子去除效果，探讨了填充材料、电流、填充比（填充材料与废水的质量比）、废水pH对钴离子去除效果的影响，建立了反应动力学模型，并进行了经济性分析。实验结果表明：三维电极对钴离子的去除效果远优于二维电极;在以网状Ti/RuO₂为阳极、不锈钢板为阴极并作为主电极、空心钢球为第三极、极间距5 cm、电解时间60 min、电流为0.6 A、填充比为2.5、不调节废水pH的条件下处理钴离子质量浓度为112.3 mg/L的废水，钴离子去除率可达85.6%、电流效率为68.3%;去除钴离子的电化学反应符合一级反应动力学模型;该方法具有良好的环境与经济效益。     

三维电极法处理六硝基茋生产废水

以Ti板为阴极、Ti/IrO₂-Ta₂O₅电极为阳极，采用三维电极法处理六硝基茋生产废水。通过单因素实验和正交实验确定的最佳工艺条件为：电解电压8 V，电解时间4 h，极板间距5 mm，初始废水COD=3 120 mg/L，m（玻璃珠）∶m（活性炭）=1∶3（选定活性炭的质量为5.0 g），ρ（硫酸钠）=500 mg/L。在此最佳工艺条件下，废水COD去除率为36.5%。     

电絮凝-过硫酸盐氧化协同工艺处理页岩气压裂返排废水

采用电絮凝-过硫酸盐氧化协同工艺处理页岩气压裂返排废水,通过电解过程产生的Fe2+活化过硫酸盐产生强氧化性的硫酸根自由基氧化废水中的有机物,同时Fe2+被氧化成Fe3+进而水解起到絮凝作用。实验结果表明,在电解时间25 min、电流密度41.7 m A/cm~2、电极间距4 cm、搅拌转速100 r/min、废水pH 7.0、过硫酸盐添加量0.006 mol/L的条件下,COD去除率达94.5%,出水BOD_5/COD从0.13增至0.56,电导率从104 mS/m降至71 mS/m,矿化度从16 704 mg/L降至4 065 mg/L,不可滤残渣含量从554 mg/L降至59 mg/L。电絮凝-过硫酸盐氧化协同处理的效果明显优于单独电絮凝和硫酸亚铁活化过硫酸盐氧化工艺,循环伏安测试结果表明其原因是硫酸根自由基的产生,同时溶液的导电性增强,强化了絮凝效果。     

Online elemental analysis of process gases with ICP-OES: A case study on waste wood combustion

A mobile sampling and measurement system for the analysis of gaseous and liquid samples in the field was developed. An inductively coupled plasma optical emission spectrometer (ICP-OES), which is built into a van, was used as detector. The analytical system was calibrated with liquid and/or gaseous standards. It was shown that identical mass flows of either gaseous or liquid standards resulted in identical ICP-OES signal intensities. In a field measurement campaign trace and minor elements in the raw flue gas of a waste wood combustor were monitored. Sampling was performed with a highly transport efficient liquid quench system, which allowed to observe temporal variations in the elemental process gas composition. After a change in feedstock an immediate change of the element concentrations in the flue gas was detected. A comparison of the average element concentrations during the combustion of the two feedstocks showed a high reproducibility for matrix elements that are expected to be present in similar concentrations. On the other hand elements that showed strong differences in their concentration in the feedstock were also represented by a higher concentration in the flue gas. Following the temporal variations of different elements revealed strong correlations between a number of elements, such as chlorine with sodium, potassium and zinc, as well as arsenic with lead, and calcium with strontium.     

臭氧氧化-三维电极电解联用技术深度处理造纸废水

采用臭氧氧化-三维电极电解联用技术深度处理造纸废水,通过单因素及正交实验法确定了最优工艺条件,并探讨了反应的动力学和机理。实验结果表明:废水处理的最优工艺条件为电极间距1.5 cm、电流密度9mA/cm~2、臭氧曝气量15 mL/min、活性炭填充量22 g/L、反应时间60 min,该工艺条件下,废水的COD去除率达93.70%;臭氧氧化-三维电极电解联用技术对废水中COD的去除过程符合一级反应动力学方程;臭氧氧化和三维电极电解间存在协同效应。     

海上含聚污水电化学处理装置的优化

为解决传统电化学方法在含聚污水处理时电极板消耗严重、絮渣量大的问题,通过改进电极板材料、组合数及结构等,研究适度降解-除油一体化电化学技术,在降低渣泥量的同时保证处理效果。实验结果表明:最佳电极板组合为"网状惰性金属复合物极板(阳)-网状铝极板(阴)-网状铝极板(阴)-网状惰性金属复合物极板(阳)";在电解电流为4.0 A、极板间距为8.0 cm、面体比(电极板面积与处理污水量的比值)为2/17 cm~2/mL、电解时间为30 min的最佳处理条件下,几乎无絮渣产出,含聚污水的浊度去除率为93.3%、聚合物降解率为92.0%、除油率为95.0%,展现了优良的处理效果。     

Ti_5O_9-Ti_4O_7电极电化学处理2,4,6-三硝基苯酚废水

采用压片-烧结法制备了Ti5O9-Ti4O7电极,采用XRD和SEM技术对Ti5O9-Ti4O7电极进行了表征。以自制的Ti5O9-Ti4O7电极为阳极,电解处理含2,4,6-三硝基苯酚(TNP)的模拟废水,考察了电流密度、电解质质量浓度、废水p H、废水温度和反应时间等因素对废水COD去除率和TNP降解率的影响。表征结果显示:该电极的主要成分为Ti5O9,并含有部分Ti4O7;该电极的比表面积较大。Ti5O9-Ti4O7电极电解处理含TNP废水的最佳实验条件为:电流密度20 m A/cm2、电解质Na2SO4质量浓度6.0 g/L、废水p H为7、废水温度30℃。在此最佳条件下电解反应180 min后,COD去除率为90.6%,TNP降解率为93.9%,表明Ti5O9-Ti4O7电极具有较高的催化能力和电流效率。     

Recovery of high purity zinc from filter ash produced during the thermal treatment of waste and inerting of residual materials.

The method described below recovers zinc, a valuable metal that is present in high concentrations in filter ash from the thermal treatment of waste, and returns the filter ash stripped of heavy metals to the combustion process in order to destroy organic substances. On an industrial scale, the heavy metals in the filter ash were mobilized by means of hydrochloric acid in the acidic fluids produced in the flue-gas scrubbing process without the addition of further chemicals. A pilot plant for implementing the selective reactive extraction (SRE) method on the ash extracts, using a highly selective complexant, was operated over a period of several months in order to obtain a concentrated, high-purity zinc salt solution (mono metal solution). A zinc depletion rate of 99.8% in the aqueous extract was achieved using mixer-settler units. The residual zinc concentration in the waste water was then < 2 mg L(-1). By stripping the loaded organic phase, a concentrated, high-purity mono metal solution with 190 g L(-1) zinc was obtained. Zinc metal with a purity > 99.99% is then separated by means of electrolysis. To destroy organic substances present in the filter ash, particularly dioxins and furans, the extracted filter ash cake was returned to the combustion process together with household waste. Plant operation, raw and pure gas parameters, and quality of the bottom ash produced were not impacted by such recirculation. The profitability of the overall process is attributable both to the recovery of valuable zinc metal and to the cost savings made in waste water treatment and in the disposal of the waste combustion residues because the remaining mixture of filter ash and bottom ash can be reused in a combined form. This method therefore supports the sustainable and economically viable reuse of filter ash.     

Fe3O4-PTFE电极制备条件和双阴极电-Fenton反应条件的优化

制备了Fe₃O₄-聚四氟乙烯（PTFE）电极,优化了原料配比和焙烧温度。对比了Fe₃O₄-PTFE单阴极和Fe₃O₄-PTFE与乙炔碳黑-PTFE电极并联双阴极体系对模拟Rhb染料废水的处理效果。实验结果表明：在m（Fe₃O₄）∶m（PTFE）=3.0∶2.5、焙烧温度为300 ℃的条件下制备Fe₃O₄-PTFE电极,采用阴极电-Fenton法降解模拟Rhb废水的效果最佳,电解反应120 min时Rhb降解率达86.91%;Fe₃O₄-PTFE电极与乙炔碳黑-PTFE电极并联作为双阴极电解Rhb废水时,最佳电压为6 V,最佳初始废水pH为3,在此条件下电解反应120 min时Rhb降解率达91.65%。     

Recovery of manganese oxides from spent alkaline and zinc–carbon batteries. An application as catalysts for VOCs elimination

Manganese, in the form of oxide, was recovered from spent alkaline and zinc–carbon batteries employing a biohydrometallurgy process, using a pilot plant consisting in: an air-lift bioreactor (containing an acid-reducing medium produced by an Acidithiobacillus thiooxidans bacteria immobilized on elemental sulfur); a leaching reactor (were battery powder is mixed with the acid-reducing medium) and a recovery reactor. Two different manganese oxides were recovered from the leachate liquor: one of them by electrolysis (EMO) and the other by a chemical precipitation with KMnO₄ solution (CMO). The non-leached solid residue was also studied (RMO). The solids were compared with a MnO_x synthesized in our laboratory.The characterization by XRD, FTIR and XPS reveal the presence of Mn₂O₃ in the EMO and the CMO samples, together with some Mn⁴⁺ cations. In the solid not extracted by acidic leaching (RMO) the main phase detected was Mn₃O₄.The catalytic performance of the oxides was studied in the complete oxidation of ethanol and heptane. Complete conversion of ethanol occurs at 200 °C, while heptane requires more than 400 °C. The CMO has the highest oxide selectivity to CO₂.The results show that manganese oxides obtained using spent alkaline and zinc–carbon batteries as raw materials, have an interesting performance as catalysts for elimination of VOCs.