Cadmium—Towards a rational use of a toxic element

Because of its toxicity, cadmium creates an environmental problem as well as a health hazard for exposed workers. Most cadmium emissions arise from the intentional use of the element. It is therefore mandatory to reduce cadmium consumption to the lowest possible level. Cadmium pigments, mainly used in plastic processing, can be replaced in all applications where the processing temperature does not exceed 300°C. Newly developed polyvinyl chloride stabilizers promise to be an excellent substitute for cadmium stabilizers in even the most demanding applications. Cadmium plating, still extensively used in the United States and the West Germany, has been virtually abandoned in Japan. Improved lead acid batteries are replacing vented nickel cadmium batteries because of their cost effectiveness. While in these applications cadmium use is declining, more and more cadmium is needed for the manufacturing of sealed nickel cadmium batteries. These relatively small electrochemical cells are used mainly by individual consumers. Here cadmium can only be replaced in some marginal applications. The high cadmium content of these batteries (up to 22%) makes them a good candidate for recycling of the heavy metal.     

聚合硫酸铁絮凝剂中痕量镉测定的研究

研究了测定聚合硫酸铁絮凝剂中痕量镉的新方法。本法是利用离子选择性电极测定聚合硫酸铁絮凝剂中的镉。研究内容包括测定条件、干扰试验、干扰排除等。本法不需调整 p H值 ,设备简单 ,操作简便 ,测定快速。在测定条件下 ,本法的线性范围为 1 .0× 1 0 - 2 ～ 9.0× 1 0 - 7,回收率为 91 %～ 1 0 7% ,适宜的 p H值范围为 3- 6。本法用于了实际样品测定 ,结果满意。     

腐殖酸树脂处理含Pb^2＋、CU^2＋、Ni^2＋废水的研究

利用泥炭为原料制备腐殖酸树脂.在动态条件下,研究了腐殖酸树脂对重金属离子Pb^2＋、Cu^2＋和Ni^2＋的吸附效果及吸附条件.同时探讨了腐殖酸树脂对重金属离子Pb^2＋、Cu^2＋和Ni^2＋的吸附与解吸再生机理,吸附机理研究表明,腐殖酸树脂对重金属离子Pb^2＋、Cu^2＋和Ni^2＋的主要吸附形式为离子交换吸附和络合吸附.结果表明,在废水pH值为5.0～7.0,Pb^2＋、Cu^2＋和Ni^2＋浓度分别为50 mg/L,经腐殖酸树脂处理,Pb^2＋、Cu^2＋和Ni^2＋去除率可达98%以上,且处理后废水近中性.含Pb^2＋、Cu^2＋和Ni^2＋电镀废水经腐殖酸树脂处理后,废水中Pb^2＋、Cu^2＋和Ni^2＋含量显著低于国家排放标准.     

Estimation of heavy metal emission fluxes on the territory of the NIS

As the result of our research, the specific procedures to use emission factor methodology were developed and applied for trace metal emission evaluation into the atmosphere over the territory of the former Soviet Union. The existing data on heavy metal emissions were revised as background information from official sources and expert estimations. Source categories and different initial information as well as the concept of spatial emission distribution were defined and observed. The calculated atmospheric emissions of lead, cadmium and mercury were produced among the main source categories of 12 NIS countries for 1990, 1995 and 1997, using modified emission coefficients.Total cadmium emissions into the atmosphere from determined source categories were estimated as 388.4 tonnes in 1990 for the whole domain with reduction by up to 207.0 tonnes per year for 1997. Mercury emissions were estimated as equal to 303.2 tonnes in 1990 and 159.8 tonnes in 1997. Lead emission amounted to 24903.0 tonnes in 1990, and 9652.5 tonnes in 1997.The results of the evaluation demonstrated the general trends of atmospheric heavy metal emissions with a greater decrease during the first half of the 1990s followed later by the rather stable level to be explained by recession in industrial activity and fuel consumption in NIS in that period. The significant spatial variations of atmospheric emissions over vast territories are described based on the results of their distribution according to 1×1 degree grid with remarkably higher values in the location of industrial cities.     

Relating cadmium concentrations in three macrophyte-associated freshwater invertebrates to those in macrophytes,water and sediments

We found that Cd concentrations in three species of macrophyte-associated invertebrates (the gastropods Bithynia tentaculata and Physa gyrina, and the amphipod Gammarus fasciatus) collected at twenty sites along the St. Lawrence River were correlated with Cd concentrations in their main food source, i.e. macrophytes and associated periphyton. Cd in these invertebrates was not significantly correlated with Cd concentrations in the sediments (even when corrections for iron oxide or organic carbon content were applied) or to calculated free-cadmium concentrations in the water. Cd levels in juveniles of B. tentaculata were very tightly linked to Cd concentrations in macrophytes, which is consistent with the close relationship that these organisms have developed with macrophytes. Linear models predicting Cd levels in juveniles of B. tentaculata from Cd levels in different macrophyte species were strong (R2 = 0.69-0.90). Analysis of covariance on these models showed no statistical difference of slope or intercept for any of the macrophyte species, except Vallisneria americana. We suggest that the macrophyte-periphyton complex is a key link in the transfer of cadmium to some aquatic invertebrates in the littoral zone of the St. Lawrence River and that macrophytes and their associated epiphytes should also be used as biomonitors.     

成都市郊区域农田中土壤镉形态研究

农田土壤是镉生态循环的重要介质，所含镉对人体健康的危害不可忽视。镉在土壤中以多种形态存在．可划分为水溶态、离子交换态，碳酸盐结合态、Fe及Mn氧化物结合态，有机结合态、残留态。不同存在形态镉的生物有效性各不相同，因而对环境和人体健康造成的影响也存在差异。水溶态镉，离子交换态镉具有很高的生物有效性。碳酸盐结合态镉在弱酸性条件下生物有效性较高，Fe及Mn氧化物结合态镉、有机结合态镉、残留态镉生物有效性很低。本研究采用连续提取法和原子吸收法对成都市某郊区基本农田的35份土壤样品中各形态镉进行了提取和测定。结果表明。成都市某郊区农田土壤的镉污染状况较为严重，37．14％的土壤含高生物有效性的水溶态镉或离子交换态镉。土壤中水溶态镉、离子交换态镉的存在与环境污染有密切联系。Fe及Mn氧化物结合态镉，有机结合态镉、残留态镉的存在受耕作因素和成土母质影响较大。     

Observation of chemical components of PM2.5 and secondary inorganic aerosol formation during haze and sandy haze days in Zhengzhou, China

Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China.During this study, a haze episode(haze days) and a typical haze process mixed with sandstorm(sandy haze days)were observed in Zhengzhou with a series of high-time-resolution monitoring instruments from November 22 to December 8, 2018.Concentrations of PM_(10) and crustal elements clearly increased in the sandy haze days.Concentrations of gaseous pollutants, metallic elements emitted from anthropogenic sources, nitrate, and ammonium during sandy haze days were slightly lower than those during the haze days but still obviously higher than those during the non-haze days.The sulfate concentrations, the sulfate fractions in PM_(2.5),and the sulfur oxidation ratios significantly increased in the sandy haze days.Heterogeneous reactions dominated the conversion of SO_2 during the haze and sandy haze days.Enhanced SO_2 conversion during the sandy haze days may be attributed to the high concentrations of transition metal ions from the sandstorm when the values of relative humidity(RH) were in 30%–70%, and high O_3 at certain time points.Gas-phase NO_2 oxidation reactions were the main pathways for nitrate formation.In the sandy haze days,higher nitrogen oxidation ratio(NOR) at daytime may be associated with higher RH and lower temperature than those in the haze days, which facilitate the gas-to-particle partitioning of nitrate; higher NOR values at night may be attributed to the higher O_3 concentrations, which promoted the formation of N_2O_5.     

Preparation and characterization of a novel hybrid chelating material for effective adsorption of Cu(Ⅱ) and Pb(Ⅱ)

The discharge of heavy metal ions such as Cu~2+and Pb~2+poses a severe threat to public health and the environment owing to their extreme toxicity and bioaccumulation through food chains Herein, we report a novel organic–inorganic hybrid adsorbent, Al(OH)_3-poly(acrylamide dimethyldiallylammonium chloride)-graft-dithiocarbamate(APD), for rapid and effectiv removal of Cu~2+and Pb~2+. In this adsorbent, the "star-like" structure of Al(OH)3 poly(acrylamide-dimethyldiallylammonium chloride) served as the support of dithiocarbamat(DTC) functional groups for easy access of heavy metal ions and assisted development of larg and compact floccules. The synthesized adsorbent was characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FTIR), and thermogravimetric analysis(TGA). APD was demonstrated to hav rapid adsorption kinetics with an initial rate of 267.379 and 2569.373 mg/(g·min) as well a superior adsorption capacities of 317.777 and 586.699 mg/g for Cu~2+and Pb~2+respectively. Th adsorption process was spontaneous and endothermic, involving intraparticle diffusion and chemical interaction between heavy metal ions and the functional groups of APD. To assess it versatility and wide applicability, APD was also used in turbid heavy metal wastewater, and performed well in removing suspended particles and heavy metal ions simultaneously through flocculation and chelation. The rapid, convenient and effective adsorption of Cu~2+and Pb~2+give APD great potential for heavy metal decontamination in industrial applications.     

Relating Cd2 + binding by humic acids to molecular weight: A modeling and spectroscopic study

Molecular weight(Mw) is a fundamental property of humic acids(HAs), which considerably affect the mobility and speciation of heavy metals in the environment. In this study, soil humic acid(HA) extracted from Jinyun Mountain, Chongqing was ultra-filtered into four fractions according to the molecular weight, and their properties were characterized.Complexation of cadmium was investigated by titration experiments. For the first time,Langmuir and non-ideal competitive adsorption-Donna(NICA-Donnan) models combined with fluorescence excitation-emission matrix(EEM) quenching were employed to elucidate the binding characteristics of individual Mw fractions of HA. The results showed that the concentration of acidic functional groups decreased with increasing Mw, especially the phenolic groups. The humification degree and aliphaticity increased with increasing Mw as indicated by elemental composition analysis and FT-IR spectra. The binding capacity of Cd~(2+) to Mw fractions of HA followed the order UF1( 5 kDa) UF2(5–10 kDa) UF4( 30 kDa) UF3(10–30 kDa). Moreover, the distribution of cadmium speciation indicated that the phenolic groups were responsible for the variations in binding of Cd~(2+) among different Mw fractions. The results of fluorescence quenching illustrated that the binding capacity of Cd~(2+) to Mw fractions was controlled by the content of functional groups, while the binding affinity was largely influenced by structural factors. The results provide a better understanding of the roles that different HA Mw fractions play in heavy metal binding,which has important implications in the control of heavy metal migration and bio-toxicity.     

湿法烟气脱硫系统中氧化态汞的还原和影响机制综述

利用湿法脱硫系统协同脱除二价汞是当前燃煤烟气脱汞的重要方法。然而脱硫系统是一个还原系统,吸收进入脱硫浆液中的二价汞会发生再次还原,显著降低汞的脱除效率。就脱硫浆液中二价汞的还原问题,详细阐述了当前研究者在液相二价汞的还原机制、液相离子、气相条件和操作条件等对二价汞还原的影响方面的研究进展。