失效锂离子电池材料真空热处理及氨性浸出

研究了失效锂离子电池中塑料、电极隔膜等有机物的真空脱除,并以电池级纯钴酸锂(LiCoO2)为原料,与活性炭粉混合,在真空中进行热还原,还原产物用含NH3和NH4HCO3的氨性水溶液浸出。实验结果表明,当加热温度大于450℃,真空压力<400 Pa时,失效锂离子电池中有机挥发物基本被脱除。在400℃真空温度下纯LiCoO2不被炭粉还原;当还原温度达到600℃,LiCoO2转变为CoO、Co和Li2CO3;在800℃时,还原产物主要为六方相、立方相金属钴及少量的CoO。还原产物中的钴易于被氨性水溶液浸出,浸出3 h后,钴基本进入溶液中,锂的浸出率也达到97%以上。     

A novel dismantling process of waste printed circuit boards using water-soluble ionic liquid

Recycling processes for waste printed circuit boards (WPCBs) have been well established in terms of scientific research and field pilots. However, current dismantling procedures for WPCBs have restricted the recycling process, due to their low efficiency and negative impacts on environmental and human health. This work aimed to seek an environmental-friendly dismantling process through heating with water-soluble ionic liquid to separate electronic components and tin solder from two main types of WPCBs—cathode ray tubes and computer mainframes. The work systematically investigates the influence factors, heating mechanism, and optimal parameters for opening solder connections on WPCBs during the dismantling process, and addresses its environmental performance and economic assessment. The results obtained demonstrate that the optimal temperature, retention time, and turbulence resulting from impeller rotation during the dismantling process, were 250 °C, 12 min, and 45 rpm, respectively. Nearly 90% of the electronic components were separated from the WPCBs under the optimal experimental conditions. This novel process offers the possibility of large industrial-scale operations for separating electronic components and recovering tin solder, and for a more efficient and environmentally sound process for WPCBs recycling.     

Removal of arsenic from contaminated groundwater by solar-driven membrane distillation

Experimental investigations were carried out on removal of arsenic from contaminated groundwater by employing a new flat-sheet cross flow membrane module fitted with a hydrophobic polyvinylidenefluoride (PVDF) microfiltration membrane. The new design of the solar-driven membrane module in direct contact membrane distillation (DCMD) configuration successfully produced almost 100 per cent arsenic-free water from contaminated groundwater in a largely fouling-free operation while permitting high fluxes under reduced temperature polarization. For a feed flow rate of 0.120 m³/h, the 0.13 μm PVDF membrane yielded a high flux of 74 kg/(m² h) at a feed water temperature of 40 °C and, 95 kg/m² h at a feed water temperature of 60 °C. The encouraging results show that the design could be effectively exploited in the vast arsenic-affected rural areas of South-East Asian countries blessed with abundant sunlight particularly during the critical dry season.     

Thermal removal of PCDD/Fs from medical waste incineration fly ash--effect of temperature and nitrogen flow rate

The fly ash used in this study was collected from a bag filter in a medical waste rotary kiln incineration system, using lime and activated carbon injection followed by their collection as mixed fly ash. Experiments were conducted on fly ash in a quartz tube, heated in a laboratory-scale horizontal tube furnace, in order to study the effect of temperature and nitrogen flow rate on the removal of PCDD/Fs. Results indicated that in this study PCDD/Fs in the fly ash mostly were removed and desorbed very little into the flue gas under thermal treatment especially when the heating temperature was higher than 350 °C, and dechlorination and destruction reactions took important part in the removal of PCDD/Fs. However, in terms of flow rate, when flow rate was higher than 4 cm s⁻¹, destruction efficiency of PCDD/Fs decreased dramatically and the main contributors were P₅CDF, H₆CDF and H₇CDF desorbed to flue gas, the PCDD/Fs in the fly ash decreased with enhanced flow rate.     

The study of operating variables in soil washing with EDTA

This study discusses the operating variables for removal of metals from soils using EDTA, including the type of EDTA, reaction time, solution pH, dose, temperature, agitation, ultrasound and number of extractions. For As, Cd, Cu, Pb and Zn, the removal efficiency order was: H₄-EDTA > Na₂EDTA > (NH₄)₂EDTA. At low EDTA concentrations the removal increased progressively with increasing dose while above 0.4 mmol/g only small increases in extraction efficiency were observed. EDTA induced a two-step process including a rapid desorption within the first hour, and a gradual release in the following hours. The extraction efficiency of metals decreased with increasing pH in the range of 2-10. Consecutive extractions using low concentrations were more effective than a single extraction with concentrated EDTA if the same dose of EDTA was used.     

Hydraulic performance of a proposed in situ photocatalytic reactor for degradation of MTBE in water

Methyl tert-butyl ether (MTBE) groundwater remediation projects often require a combination of technologies resulting in increasing the project costs. A cost-effective in situ photocatalytic reactor design, Honeycomb II, is proposed and tested for its efficiency in MTBE degradation at various flows. This study is an intermediate phase of the research in developing an in situ photocatalytic reactor for groundwater remediation. It examines the effect of the operating variables: air and water flow and double passages through Honeycomb II, on the MTBE removal. MTBE vaporisation is affected by not only temperature, Henry’s law constant and air flow to volume ratio but also reactor geometry. The column reactor achieved more than 84% MTBE removal after 8 h at flows equivalent to horizontal groundwater velocities slower than 21.2 cm d⁻¹. Despite the contrasting properties between a photocatalytic indicator methylene blue and MTBE, the reactor efficiency in degrading both compounds showed similar responses towards flow (equivalent groundwater velocity and hydraulic residence time (HRT)). The critical HRT for both compounds was approximately 1 d, which corresponded to a velocity of 21.2 cm d⁻¹. A double pass through both new and used catalysts achieved more than 95% MTBE removal after two passes in 48 h. It also verified that the removal efficiency can be estimated via the sequential order of the removal efficiency of one pass obtained in the laboratory. This study reinforces the potential of this reactor design for in situ groundwater remediation.     

Solvent extraction for heavy crude oil removal from contaminated soils

A new strategy of heavy crude oil removal from contaminated soils was studied. The hexane-acetone solvent mixture was used to investigate the ability of solvent extraction technique for cleaning up soils under various extraction conditions. The mixtures of hexane and acetone (25 vol%) were demonstrated to be the most effective in removing petroleum hydrocarbons from contaminated soils and approx 90% of saturates, naphthene aromatics, polar aromatics, and 60% of nC₇-asphaltenes were removed. Kinetic experiments demonstrated that the equilibrium was reached in 5 min and the majority of the oil pollutants were removed within 0.5 min. The effect of the ratio between solvent and soil on the extraction efficiency was also studied and results showed that the efficiency would increase following the higher solvent soil ratio. Then the multistage continuous extraction was considered to enhance the removal efficiency of oil pollutants. Three stages crosscurrent and countercurrent solvent extraction with the solvent soil ratio 6:1 removed 97% oil contaminants from soil. Clearly the results showed that the mixed-solvent of hexane and acetone (25 vol%) with character of low-toxic, acceptable cost and high efficiency was promising in solvent extraction to remove heavy oil fractions as well as petroleum hydrocarbons from contaminated soils.     

Reduction of dioxin emission by a multi-layer reactor with bead-shaped activated carbon in simulated gas stream and real flue gas of a sinter plant

A laboratory-scale multi-layer system was developed for the adsorption of PCDD/Fs from gas streams at various operating conditions, including gas flow rate, operating temperature and water vapor content. Excellent PCDD/F removal efficiency (>99.99%) was achieved with the multi-layer design with bead-shaped activated carbons (BACs). The PCDD/F removal efficiency achieved with the first layer adsorption bed decreased as the gas flow rate was increased due to the decrease of the gas retention time. The PCDD/F concentrations measured at the outlet of the third layer adsorption bed were all lower than 0.1 ng I-TEQ Nm⁻³. The PCDD/Fs desorbed from BAC were mainly lowly chlorinated congeners and the PCDD/F outlet concentrations increased as the operating temperature was increased. In addition, the results of pilot-scale experiment (real flue gases of an iron ore sintering plant) indicated that as the gas flow rate was controlled at 15 slpm, the removal efficiencies of PCDD/F congeners achieved with the multi-layer reactor with BAC were better than that in higher gas flow rate condition (20 slpm). Overall, the lab-scale and pilot-scale experiments indicated that PCDD/F removal achieved by multi-layer reactor with BAC strongly depended on the flow rate of the gas stream to be treated.     

废旧电路板与碳酸钙共热解脱卤的研究

采用热重分析仪和石英管式炉热解反应器，分别对以酚醛树脂为基板的废旧电路板和混合碳酸钙后的废旧电路板进行热解实验研究，着重考察了添加碳酸钙后的酚醛树脂基板废旧电路板热解特性及添加量不同对卤素脱除效果的影响。实验结果表明，碳酸钙的加入对废旧电路板的降解行为和热解油的基本组成没有明显的影响，但热解油的各组分含量有所差异；随着热解温度的提高或者CaCO₃含量的增多，卤素可以更多地由有机卤向无机卤转变并束缚在固体残渣中，由此得到较好的脱卤效果。当60%PR-WPCBs与40%CaCO₃共热解，热解油中的溴化物也减少了7.6% 。在600℃等量CaCO₃与PR-WPCBs共热解时生成75.6%无机卤，其中70.62%束缚于固体残渣中，可见达到较好的脱卤效果。     

Removal potential of anti-estrogenic activity in secondary effluents by coagulation

Anti-estrogenic activity in wastewater is gaining increased attention because of its endocrine-disrupting function. In this study, the level and removal efficiency by coagulation of anti-estrogenic activity in secondary effluents of domestic wastewater treatment plants were studied. Anti-estrogenic activity was detected in secondary effluent samples at a tamoxifen (TAM) equivalent concentration level of 0.38–0.94 mg-TAM L⁻¹. Dissolved organic matters (DOM) with the molecular weight (MW) less than 3000 Da in hydrophobic acids (HOA) and hydrophobic neutrals (HON) fractions of the secondary effluent were the key fractions related to anti-estrogenic activity. Coagulation with FeCl₃ and polyaluminium chloride (PAC) can remove the anti-estrogenic activity of the secondary effluents, but the removal efficiency was limited. The removal efficiency using FeCl₃ coagulant was higher than that induced by PAC. Dissolved organic carbon was continuously removed with increased coagulant dose (0–120 mg L⁻¹ FeCl₃ or 0–60 mg L⁻¹ PAC). However, the removal of anti-estrogenic activity was not enhanced further when the coagulant concentration was beyond a critical value (30 mg L⁻¹ FeCl₃ or 10 mg L⁻¹ PAC). The highest removal of anti-estrogenic activity was about 36% by FeCl₃ and 20% by PAC. Size exclusion chromatography results indicated difficulty in removing DOM with MW less than 3000 Da in the secondary effluent during coagulation even at a high coagulant concentration, which led to low removal efficiency of anti-estrogenic activity.     

Molecular and physiological approaches to understand the ecology of methanol degradation during the biofiltration of air streams

A 13.4 L biofilter treating an off-gas stream supplemented with methanol under two different situations was studied in terms of MeOH removal efficiency, microbial ecology and odor removal. During Period 1 (P1) the reactor was packed with wood bark chips with no pH control, treating an off-gas resulting from the aerobic chamber of a membrane biological reactor treating sewage and located outdoor, whereas during Period 2 (P2) a compressed air stream fed with MeOH was treated using PVC rings and maintaining pH at neutral values. Both systems operated at 96 g MeOH m⁻³ h⁻¹ achieving removal efficiencies of around 90% during P1 and 99.9% during P2. The relative activity of biomass developed in both systems was assessed using respirometric analysis with samples obtained from both biofilms. Higher biomass activity was obtained during P2 (0.25-0.35 kg MeOH kg⁻¹ VSS d⁻¹) whereas 1.1 kg MeOH kg⁻¹ VSS d⁻¹ was obtained in the case of P1. The application of molecular and microscopic techniques showed that the eukaryotes were predominant during P1, being the yeast Candida boidinii the most abundant microorganism. A specific Fluorescence in situ hybridization probe was designed for C. boidinii and tested successfully. As a result of the neutral pH, a clear predominance of prokaryotes was detected during P2. Interestingly, some anaerobic bacteria were detected such as Desulfovibrio, Desulfobacteraceae species and also some archaea such as Methanosarcina.     

Supercritical water oxidation of tannery sludge: Stabilization of chromium and destruction of organics

The supercritical water oxidation (SCWO) of industrial tannery sludge was investigated to understand the simultaneous destruction of organic pollutants and recovery of high content chromium. Experiments were performed in a batch reactor at temperatures of 350–500 °C, reaction time of 150–300 s and different oxygen ratios, to exhibit the effect of operation conditions. Results showed that removal efficiency of chemical oxygen demand (COD) increased with higher temperature, larger oxidant amount and reaction time; a maximum value of 96% was obtained. Meanwhile, destruction yield was much higher under supercritical conditions than that in subcritical water. In addition, removal efficiency of Cr from sludge reached more than 98% under all conditions; higher temperature played a positive role. Further, leaching toxicity tests of heavy metals in solid products were conducted based on toxicity characteristic leaching procedure. All heavy metals except nickel showed a greatly reduced leaching toxicity through their stabilization. The chromium oxide recovered in ash was amorphous below 550 °C, so that the structure of Cr could not be identified by X-ray diffraction pattern. Special attention should be paid on nickel as its leaching toxicity increased due to the corrosion of reactor surface under severe reaction conditions.     

Mechanochemical degradation of chlorinated contaminants in fly ash with a calcium-based degradation reagent

This report presents our results in a low-temperature mechanochemical hydrodechlorination process applied to fly ash coming from a municipal waste incinerator in order to efficiently remove all traces of PCDDs, PCDFs and PCBs. We found that the most suitable degradation agent is a mixture of metallic calcium and calcium oxide. A sample of fly ash presenting a TEQ of 5200 pg g⁻¹ was completely detoxified (no traces of PCDDs, PCDFs and PCBs detected) after ball-milling at 400 rpm over night.     

Method of removal of volatile organic compounds by using wet scrubber coupled with photo-Fenton reaction - Preventing emission of by-products

The photo-Fenton reaction was applied as a novel method for the removal of volatile organic compounds (VOCs) in the gas phase, and its effectiveness was experimentally examined. In conventional VOCs removal methods using a photocatalyst or ozone, VOCs are oxidized in the gas phase. Therefore, incompletely oxidized intermediates, which may have adverse effects on health, are likely to contaminate the treated air. On the other hand, in the VOCs removal method developed in this study, because the VOCs are oxidized in the liquid phase by the photo-Fenton reaction, any incompletely oxidized intermediates produced are confined to the liquid phase. As a result, the contamination of the treated air by these harmful intermediates can be prevented. Using a semi-batch process, it was found that the removal efficiency for toluene in a one-pass test (residence time of 17 s) was 61%, for an inlet toluene gas concentration of 930 ppbv, an initial iron ion concentration of 20 mg L⁻¹, and an initial hydrogen peroxide concentration of 630 mg L⁻¹. The removal efficiency was almost constant as long as H₂O₂ was present in the solution. Proton transfer reaction mass spectrometry analysis confirmed the absence of any incompletely oxidized intermediates in the treated air.     

Evaluation of PPCPs removal in a combined anaerobic digester-constructed wetland pilot plant treating urban wastewater

The removal efficiency of 16 pharmaceuticals and personal care products (PPCPs) from urban wastewater (dissolved and particulate phases) was evaluated for the first time in a hybrid pilot plant consisting of an upflow anaerobic sludge blanket reactor followed by two sequentially connected horizontal flow constructed wetlands: a surface flow wetland (SF CW) and a subsurface flow wetland (SSF CW). Whereas the PPCP removal associated with the dissolved phase exhibited a seasonal pattern, the fraction associated with the suspended solids showed less seasonality. In the dissolved phase, the overall removal efficiency in summer ranged from 70% to 85% for salicylic acid (SAL), methyl dihydrojasmonate, caffeine (CAF), ketoprofen and triclosan, whereas in winter it declined for most of the PPCPs to between 30% and 50%, except for CAF and SAL (>80%) and carbamazepine and butylated hydroxyl toluene (11-18%). In the suspended solids, the removal exceeded 80% for most of the target PPCPs. The efficiency of the different treatment steps was also compound-dependent, but the SF CW generally exhibited the highest removal efficiency for most of the contaminants analyzed. The characterization of the organic matter retained in the wetland gravel beds revealed the occurrence of hydrophobic contaminants such as phthalate esters and fragrances at moderate concentrations (i.e., up to 3.5 μg kg⁻¹), which declined strongly over the course of the different treatment steps. In the SF CW, the net mass accumulation rates of tonalide and galaxolide were 4 and 23 g y⁻¹ respectively, whereas in the SSF CW they were 0.3 and 1.8 g y⁻¹ respectively.     

Influences of thermal decontamination on mercury removal, soil properties, and repartitioning of coexisting heavy metals

Thermal treatment is a useful tool to remove Hg from contaminated soils. However, thermal treatment may greatly alter the soil properties and cause the coexisting contaminants, especially trace metals, to transform and repartition. The metal repartitioning may increase the difficulty in the subsequent process of a treatment train approach. In this study, three Hg-contaminated soils were thermally treated to evaluate the effects of treating temperature and duration on Hg removal. Thermogravimetric analysis was performed to project the suitable heating parameters for subsequent bench-scale fixed-bed operation. Results showed that thermal decontamination at temperature >400 °C successfully lowered the Hg content to <20 mg kg⁻¹. The organic carbon content decreased by 0.06-0.11% and the change in soil particle size was less significant, even when the soils were thermally treated to 550 °C. Soil clay minerals such as kaolinite were shown to be decomposed. Aggregates were observed on the surface of soil particles after the treatment. The heavy metals tended to transform into acid-extractable, organic-matter bound, and residual forms from the Fe/Mn oxide bound form. These results suggest that thermal treatment may markedly influence the effectiveness of subsequent decontamination methods, such as acid washing or solvent extraction.     

Photo-dissociation of dimethylamine by KrBr excilamp

A study of dimethylamine photo-dissociation in the gas phase has been conducted using UV radiation delivered from a KrBr^* excilamp, driven by a sinusoidal electronic control gear with maximum emission at wavelength of 207 nm. The electrical input power and radiant power of the lamp were measured to determine their effects on the degradation. The influence of flow velocity and initial concentration of dimethylamine were also examined. In order to evaluate the photo-dissociation process comprehensively, several parameters were investigated, including removal efficiency, energy yield, carbon balance and CO₂ selectivity. It is shown that the removal efficiency increases with enhanced input power and decreased gas flow rate. A high removal efficiency of 68% is achieved for lamp power 102 W and flow velocity 15 m³ h⁻¹. The optimum dimethylamine initial concentration is around 3520 mg m⁻³, for which the energy yield reaches up to 442 g kW h⁻¹ when the input power is 65 W. In addition, two chain compounds (1,3-bis-dimethylamino-2-propanol; 3-penten-2-one, 4-amino) and three ring organic matters (1-azetidinecarboxaldehyde, 2,2,4,4-tetramethyl; N-m-tolyl-succinamic acid; p-acetoacetanisidide), were identified by GC–MS as secondary products, in order to demonstrate the pathways of the dimethylamine degradation.     

Reducing phosphorus flux from organic soils in surface flow treatment wetlands

Treatment wetlands have a finite period of effective nutrient removal after which treatment efficiency declines. This is due to the accumulation of organic matter which decreases the capacity and hydraulic retention time of the wetland. We investigated four potential solutions to improve the soluble reactive P (SRP) removal of a municipal wastewater treatment wetland soil including; dry down, surface additions of alum or calcium carbonate and physical removal of the accreted organic soil under both aerobic and anaerobic water column conditions. The flux of SRP from the soil to the water column under aerobic conditions was higher for the continuously flooded controls (1.1 ± 0.4 mg P m⁻² d⁻¹), dry down (1.5 ± 0.9 mg P m⁻² d⁻¹) and CaCO₃ (0.8 ± 0.7 mg P m⁻² d⁻¹) treatments while the soil removal and alum treatments were significantly lower at 0.02 ± 0.10 and −0.07 ± 0.02 mg P m⁻² d⁻¹, respectively. These results demonstrate that the two most effective management strategies at sequestering SRP were organic soil removal and alum additions. There are difficulties and costs associated with removal and disposal of soils from a treatment wetland. Therefore our findings suggest that alum addition may be the most cost effective and efficient means of increasing the sequestering of P in aging treatment wetlands experiencing reduced P removal rates. However, more research is needed to determine the longer term effects of alum buildup in the organic soil on the wetland biota, in particular, on the macrophytes and invertebrates. Since alum effectiveness is time limited, a longer term solution to P flux may favor the organic soil removal.     

Developing slow-release persulfate candles to treat BTEX contaminated groundwater

The development of slow-release chemical oxidants for sub-surface remediation is a relatively new technology. Our objective was to develop slow-release persulfate-paraffin candles to treat BTEX-contaminated groundwater. Laboratory-scale candles were prepared by heating and mixing Na₂S₂O₈ with paraffin in a 2.25 to 1 ratio (w/w), and then pouring the heated mixture into circular molds that were 2.38 cm long and either 0.71 or 1.27 cm in diameter. Activator candles were prepared with FeSO₄ or zerovalent iron (ZVI) and wax. By treating benzoic acid and BTEX compounds with slow-release persulfate and ZVI candles, we observed rapid transformation of all contaminants. By using ¹⁴C-labeled benzoic acid and benzene, we also confirmed mineralization (conversion to CO2) upon exposure to the candles. As the candles aged and were repeatedly exposed to fresh solutions, contaminant transformation rates slowed and removal rates became more linear (zero-order); this change in transformation kinetics mimicked the observed dissolution rates of the candles. By stacking persulfate and ZVI candles on top of each other in a saturated sand tank (14 × 14 × 2.5 cm) and spatially sampling around the candles with time, the dissolution patterns of the candles and zone of influence were determined. Results showed that as the candles dissolved and persulfate and iron diffused out into the sand matrix, benzoic acid or benzene concentrations (C_o = 1 mM) decreased by >90% within 7 d. These results support the use of slow-release persulfate and ZVI candles as a means of treating BTEX compounds in contaminated groundwater.     

Industrial wastewater pre-treatment for heavy metal reduction by employing a sorbent-assisted ultrafiltration system

This work examined the adoption of a sorbent-assisted ultrafiltration (UF) system for the reduction of Pb(II), Cu(II), Zn(II) and Ni(II) from industrial wastewater. In such a system metals were removed via several processes which included precipitation through the formation of hydroxides, formation of precipitates/complexes among the metal ions and the wastewater compounds, adsorption of metals onto minerals (bentonite, zeolite, vermiculite) and retention of insoluble metal species by the UF membranes. At pH = 6 the metal removal sequence obtained by the UF system was Pb(II) > Cu(II) > Zn(II) > Ni(II) in mg g⁻¹ with significant amount of lead and copper being removed due to chemical precipitation and formation of precipitates/complexes with wastewater compounds. At this pH, zinc and nickel adsorption onto minerals was significant, particularly when bentonite and vermiculite were employed as adsorbents. Metal adsorption onto zeolite and bentonite followed the sequence Zn(II) > Ni(II) > Cu(II) > Pb(II), while for vermiculite the sequence was Ni(II) > Zn(II) > Cu(II) > Pb(II) in mg g⁻¹. The low amount of Pb(II) and Cu(II) adsorbed by minerals was attributed to the low available lead and copper concentration. At pH = 9 the adoption of UF could effectively reduce heavy metals to very low levels. The same was observed at pH = 8, provided that minerals were added. The prevailing metal removal process was the formation of precipitates/complexes with wastewater compounds.