Treatment of IGCC power station effluents by physico-chemical and advanced oxidation processes

The aim of this work was to improve the quality of aqueous effluents coming from the Gasification Unit in an Integrated Gasification Combined Cycle (IGCC) Thermoelectric Power Station, with the purpose of fulfilling the future more demanding normative. To this end, an integral wastewater treatment including coagulation, flocculation, neutralization, photocatalytic oxidation, and ion-exchange has been studied. A final scheme has been proposed to remove pollutants. All the parameters of the treated wastewater are below pouring specifications. In the first stage, the wastewater was treated with CaCl2 (optimal dose=11 g CaCl2/g F-) as coagulant and a commercial anionic polyelectrolyte (optimal dose=0.02 g/g F-) as flocculant to remove fluoride ions (99%) and suspended solids (92%). The water was then neutralized, improving the degree of transmission of ultraviolet light, allowing the faster photo-degradation of pollutants. The photochemical study included different systems (H2O2, UV/H2O2, Fenton, Fenton-like, UV/Fenton, UV/Fenton-like and UV/H2O2/O2). In the Fenton-like system, the influence of two parameters (initial concentration of H2O2 and amount of Cu(II)) on the degradation of cyanide and formate (taken as the reference of the process) was studied. Experimental results were fit using neural networks (NNs). Results showed that the photocatalytic process was effective for total cyanide destruction after 60 min, while 180 min was needed to remove 80% of formates. However, a more simple system with UV/H2O2/O2 yields similar results and is preferred for industrial application due to fewer complications. Finally, an ion-exchange process with Amberlite IRA-420 was proposed to remove the excess of chlorides added as a consequence of the initial coagulation process.     

转鼓式内电解装置处理水中酸性橙Ⅱ染料

设计制作了转鼓式内电解反应装置,将铁屑与活性炭按体积比为1:1混匀后装填在转鼓内,对偶氮染料酸性橙Ⅱ(AOⅡ)进行降解实验,考察了溶液pH、转鼓转速和溶液浓度对AOⅡ降解过程的影响.结果表明,AOⅡ降解过程符合准一级动力学方程,酸性条件有利于AOⅡ的降解,转鼓转速过快和溶液浓度过高则不利于AOⅡ的降解.解决了铁炭床长时间运行板结结块的问题.AOⅡ分子在转鼓式内电解的作用下,其可见光和紫外光区的特征吸收峰逐渐降低直至消失,并新生成更容易生物降解的对氨基苯磺酸盐.     

Evidence for coupled iron and nitrate reduction in the surface waters of Jiaozhou Bay

Iron and nitrate (NO₃^?) are dominant physiologically required nutrients for phytoplankton growth, and iron may also play a key role in the marine nitrogen cycle. In this study, we investigated the temporal and spatial distributions of dissolved iron (DFe) and Fe(II) in the surface waters of Jiaozhou Bay (JZB) from April 2 to July 26, 2017. High concentrations of DFe and Fe(II) predominantly occurred in nearshore and estuarine stations and concentrations were generally higher in April and May. The highest DFe concentration was observed along the coast of Hongdao (51.55 nmol/L) in May, while the lowest concentration was observed in the western coastal region (2.88 nmol/L) in April. The highest and lowest Fe(II) concentrations were observed in the Licun estuary (22.42 nmol/L) and outer bay (0.50 nmol/L) in May, respectively. We calculated the proportions of nitrate, nitrite, and ammonium in dissolved inorganic nitrogen (DIN) as well as the ratio of Fe(II) to DFe in all four months. The mean Fe(II)/DFe ratio was 0.48 in April, 0.43 in May, 0.69 in June, and 0.32 in July. The mean ratio of NO₃^? to DIN was 0.78 in April, 0.54 in May, 0.20 in June, and 0.62 in July. NO₃^?/DIN continuously decreased in the first three months, while Fe(II)/DFe remained high, which suggests that the reduction of iron and nitrate occurred simultaneously in the surface waters of JZB.     

Removal of Ni(II) from strongly acidic wastewater by chelating precipitation and recovery of NiO from the precipitates

Strongly acidic wastewater produced in nonferrous metal smelting industries often contains high concentrations of Ni(II), which is a valuable metal. In this study, the precipitation of Ni(II) from strongly acidic wastewater using sodium dimethyldithiocarbamate (DDTC) as the precipitant was evaluated. The effects of various factors on precipitation were investigated, and the precipitation mechanism was also identified. Finally, the nickel in the precipitates was recovered following a pyrometallurgical method. The results show that, under optimised conditions (DDTC:Ni(II) molar ratio = 4:1; temperature = 25 °C), the Ni(II) removal efficiency reached 99.3% after 10 min. In strongly acidic wastewater, the dithiocarbamate group of DDTC can react with Ni(II) to form DDTCNi precipitates. Further recovery experiments revealed that high-purity NiO can be obtained by the calcination of DDTCNi precipitates, with the nickel recovery efficiency reaching 98.2%. The gas released during the calcination process was composed of NO₂, CS₂, H₂O, CO₂, and SO₂. These results provide a basis for an effective Ni(II) recovery method from strongly acidic wastewater.     

海藻酸钠/蒙脱石联合负载型纳米Fe0对Cu(II)的去除研究

由于蒙脱石负载型纳米Fe~0(Mt-n ZVI)在使用中易随水迁移,造成出水水质混浊和Fe~0流失.因此,本研究制备了海藻酸钠(SA)和蒙脱石(Mt)联合负载型纳米零价铁(SA/Mt-n ZVI),探究其对水中Cu(Ⅱ)的去除效果,并考察了Cu(Ⅱ)初始浓度、pH值对去除率的影响.结果表明:以2%(质量分数)SA和6%(质量分数)Mt-n ZVI条件制备的SA/Mt-n ZVI小球对Cu(Ⅱ)处理效果好,反应24 h后,SA/Mt-n ZVI小球对初始浓度为40 mg·L-1Cu(Ⅱ)的去除率达到92.11%,与游离的Mt-n ZVI颗粒相比,其活性并未降低;Cu(Ⅱ)的去除率随其初始浓度升高而降低;在pH为2~6之间,Cu(Ⅱ)去除率随pH升高而升高.SA/Mt-n ZVI小球可有效净化污水中的Cu(Ⅱ),将其重复使用3次后,对Cu(Ⅱ)的去除率仍维持在59.52%.     

Mechanism of Cu(Ⅱ) adsorption inhibition on biochar by its aging process

Biochar exposed in the environment may experience a series of surface changes, which is called biochar aging. In order to study the effects of biochar aging on Cu（Ⅱ） adsorption, we analyzed the surface properties before and after biochar aging with scanning electron microscopy（SEM） coupled to an energy-dispersive X-ray spectrometer（EDX） and diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）, and then explored the influence of the aging process on Cu（Ⅱ） adsorption by batch experiments. After the aging process, the oxygen concentration, phenolic hydroxyl groups, aromatic ethers and other oxygen-containing functional groups on the biochar surface increased, while carboxyl groups slightly decreased. Thus, over a range of pH, the cation exchange capacity（CEC） and adsorption capacity of Cu（Ⅱ） on the aged biochar were smaller than those of new biochar,indicating that when biochar is incubated at constant temperature and water holding capacity in the dark, the aging process may inhibit Cu（Ⅱ） adsorption. Meanwhile, the dissociation characteristics of oxygen-containing functional groups changed through the aging process, which may be the mechanism by which the biochar aging process inhibits the Cu（Ⅱ） adsorption. Carboxyl groups became more easily dissociated at low pH（3.3–5.0）,and the variation of maximum adsorption capability（qm） of Cu（Ⅱ） on the old biochar was enlarged. Phenolic hydroxyl groups increased after the aging, making them and carboxyl groups more difficult to dissociate at high pH（5.0–6.8）, and the variation of qmof Cu（Ⅱ） on the aged biochar was reduced.     

Co-present Pb(II) accelerates the oxidation of organic contaminants by permanganate: Role of Pb(III)

• Simultaneous removal of organic contaminants and Pb(II) was achieved by Mn(VII). • Pb(II) enhanced Mn(VII) oxidation performance over a wide pH range. • Pb(II) did not alter the pH-rate profile for contaminants oxidation by Mn(VII). • Mn(VII) alone cannot oxidize Pb(II) effectively at pH below 5.0. • Pb(III) plays important roles on enhancing Mn(VII) decontamination process. The permanganate (Mn(VII)) oxidation has emerged as a promising technology for the remediation and treatment of the groundwater and surface water contaminated with the organic compounds. Nonetheless, only a few studies have been conducted to explore the role of the heavy metals (especially the redox-active ones) during the Mn(VII) oxidation process. In this study, taking Pb(II) as an example, its influence on the Mn(VII) decontamination performance has been extensively investigated. It was found that, with the presence of Pb(II), Mn(VII) could degrade diclofenac (DCF), 2,4-dichlorophenol, and aniline more effectively than without. For instance, over a wide pH range of 4.5–8.0, the dosing of 10 μmol/L Pb(II) accelerated the DCF removal rate from 0.006–0.25 min⁻¹ to 0.05–0.46 min⁻¹ with a promotion factor of 1.9–9.4. Although the UV-vis spectroscopic and high resolution transmission electron microscopy analyses suggested that Mn(VII) could react with Pb(II) to produce Mn(IV) and Pb(IV) at pH 6.0–8.0, further experiments revealed that Pb(II) did not exert its enhancing effect through promoting the generation of MnO₂, as the reactivity of MnO₂ was poor under the employed pH range. At pH below 5.0, it was interesting to find that, a negligible amount of MnO₂ was formed in the Mn(VII)/Pb(II) system in the absence of contaminants, while once MnO₂ was generated in the presence of contaminants, it could catalyze the Pb(II) oxidation to Pb(IV) by Mn(VII). Collectively, by highlighting the conversion process of Pb(II) to Pb(IV) by either Mn(VII) or MnO₂, the reactive Pb(III) intermediates were proposed to account for the Pb(II) enhancement effect.     

铁酸锌纳米晶的合成及其催化脱色性能研究

采用改进的共沉淀法与溶剂热法相结合制备了ZnFe2O4纳米晶,利用X射线衍射(XRD)、透射电镜(TEM)对ZnFe2O4的晶型和形貌进行了表征,讨论了其表面的光伏效应,以酸性橙Ⅱ的光催化脱色性能作为探针反应,详细地考察了催化剂的用量、底物浓度及溶液pH等因素对其脱色效果的影响.结果表明,制备的ZnFe2O4为正尖晶石型结构,平均粒径为7 nm左右,样品具有一定的捕获电子能力,在外加电场下光伏响应变化明显,在正电场下有最佳响应值,而当负电场达到一定值时,外电场的光伏响应占据主导地位.在酸性橙Ⅱ为20 mg/L、催化剂用量为1.0 g/L的中性条件下,其脱色效率达95%左右,而且经过4次重复使用后催化剂仍然具有一定的脱色性能.     

类Fenton反应对偶氮染料橙黄II的脱色研究

以橙黄II染料溶液为研究对象,通过正交实验确定了Fe-NTA/H2O2构成的类Fenton反应中各影响因子的最佳操作条件为:[H2O2]=20 mmol/L,[Fe-NTA]=2.5 mmol/L,pH=3。同时考察了反应时间、溶液pH值、H2O2浓度、Fe-NTA浓度对脱色效率的影响。实验表明脱色反应在30 m in内基本完成,类Fenton试剂能在较宽的pH范围内保持较好的脱色效果,而且在pH=6时,类Fenton试剂比传统Fenton试剂的脱色效率提高约75%。增加双氧水浓度可以提高橙黄II溶液脱色率,但超过20 mmol/L后效果提高不明显。在0.5~2.5 mmol/L的范围内,Fe-NTA浓度对脱色效果的影响不显著。     

苦杏仁酸、苹果酸、乳酸对Cr(VI)还原作用的比较

不同温度和pH条件下,通过批式试验研究了苦杏仁酸、苹果酸、乳酸还原Cr(Ⅵ)的反应速率.结果表明,这3种α-OH酸还原Cr(Ⅵ)的能力表现为:苦杏仁酸＞苹果酸＞乳酸.苦杏仁酸对Cr(Ⅵ)的还原作用受pH变化的影响较大,而乳酸受温度变化的影响较大.同时研究了Mn(Ⅱ)对3种α-OH酸还原Cr(Ⅵ)反应速率的影响.结果表明,Mn(Ⅱ)对3种α-OH酸还原Cr(Ⅵ)均有催化作用,其中对苦杏仁酸表现更为明显.