阳极溶出伏安法测定海洋沉积物中的铅和镉

海洋沉积物经硝酸-高氯酸-硝酸消解后,以高氯酸做支持电解质,采用阳极溶出伏安法的标准加入法,连续测定海洋沉积物中的铅和镉时,铅和镉的半波电位稳定,峰形对称。方法的重复性好、准确度高,可以作为一种测定海洋沉积物中铅和镉含量的使用方法。     

ICP-MS法测定保鲜薄膜中微量溶出铅镉的研究

采用电感耦合等离子体质谱(ICP-MS)法,用4％乙酸溶液萃取分离Pb,Cd,对保鲜薄膜表面微量溶出元素Pb和Cd进行了分析.对影响其测量的各种因素进行了较为详细的研究,确定了实验的最佳测定条件.结果表明,方法的检出限为:0.03(Pb)和0.02μg/L(Cd),回收率为94.4％～104.2％,RSD小于2.02％.该法准确、快速、简便,应用于保鲜薄膜中的微量溶出铅镉的测定,结果满意.     

保存条件对日用陶瓷萃取液中铅、镉测定的影响探讨

本文以日用陶瓷产品的萃取液为研究对象,对影响萃取液中铅、镉含量的保存条件:材料、温度、浓度等关键因素进行实验。采用了单因素多水平方差分析方法,讨论不同保存条件对萃取液中铅、镉的浓度影响。     

浸泡时间对陶瓷包装容器有害物溶出量的影响

制备了含有铅、镉、铬、镍、钴、锑、锌7种有害物质的单色釉陶瓷容器,选取4%(体积分数)的乙酸作为浸泡液,采用电感耦合等离子原子发射光谱仪测量了不同浸泡时间内7种重金属的溶出量,研究了浸泡时间与重金属迁移量的相关性。结果表明,陶瓷包装容器中有害重金属的溶出量随着浸泡时间的增长而逐渐增大,共存元素相互之间存在干扰,待测元素的溶出量受共存元素含量的影响较大。     

阳极溶出伏安法水体镉污染快速测定方法研究

建立一种快速测定水体中镉、铅、汞、砷的阳极溶出伏安法。对现场快速测定影响因素进行探讨,并主要对镉的检出限、精密度和准确度进行研究,将该方法运用到广西龙江镉污染事故应急监测中,并与多种其他方法进行比对。结果表明:该方法运用最优温度为5~40℃,水样最佳p H范围为4~9。便携式阳极溶出伏安法测定污染水样中的镉,检出限为0.1μg/L,加标回收率在80%~110%间;在实际样品质量浓度在2~110μg/L范围内准确度均满足要求,实际样品测定精密度2%~5%;与在线监测结果的相对偏差≤4%,与石墨炉原子吸收测定结果相对偏差≤1%。该方法稳定、快速,灵敏度高,准确度好,可广泛用于重金属污染事故应急监测。     

ICP-AES法测定氧化铁皮中铅、铬、镉

建立了电感耦合等离子体原子发射光谱法测定氧化铁皮中铅、铬、镉的新方法。样品采用盐酸分解,以高纯铁进行基体匹配。铅、铬、镉的检出限分别0.0008%、0.00012%、0.00008%,最大相对标准偏差为8.33%,方法回收率介于92.0%-110%之间。     

高温钛酸铅钡PTCR陶瓷制备中铅的挥发与抑制

通过理论分析，提出了在ＢａＴｉＯ３中掺入ＰｂＴｉＯ３而不是按传统掺入ＰｂＯ或Ｐｂ３Ｏ４采用敝开式烧结工艺便可有效地减少烧结过程中Ｐｂ成分的损失。实验结果表明效果极好，同时表明Ｐｂ元素对居里温度的移动效率随Ｐｂ总含量而明显变化，在铅含量较低时，可获得比通常文献报导的高得多的值。本文阐述了这些规律，并作出了理论解释。     

氟硅酸盐体系电沉积铅镉合金的研究

研究了氟硅酸酸盐体系中铅、镉和铅-镉混合镀液的阴极极化曲线。结果表明，镀液中加入添加剂间苯二酚能显著增加阴极极化及改善镀层性能；用脉冲电沉积代替常规的直流电沉积进行铅-镉合金的电沉积，表观状态比较表明，脉冲电沉积所得镀层质量较直流法有明显改善。原子吸收分光光度法测定表明，直流电沉积和脉冲电沉积所得镀层镉含量均随电流的增加而增加。     

Simultaneous flow injection preconcentration of lead and cadmium using cloud point extraction and determination by atomic absorption spectrometry

A flow injection (FI) micelle-mediated separation/preconcentration procedure for the determination of lead and cadmium by flame atomic absorption spectrometry (FAAS) has been proposed. The analytes reacted with 1-(2-thiazolylazo)-2-naphthol (TAN) to form hydrophobic chelates, which were extracted into the micelles of 0.05% (w/v) Triton X-114 in a solution buffered at pH 8.4. In the preconcentration stage, the micellar solution was continuously injected into a flow system with four mini-columns packed with cotton, glass wool, or TNT compresses for phase separation. The analytes-containing micelles were eluted from the mini-columns by a stream of 3molL(-1) HCl solution and the analytes were determined by FAAS. Chemical and flow variables affecting the preconcentration of the analytes were studied. For 15mL of preconcentrated solution, the enhancement factors varied between 15.1 and 20.3, the limits of detection were approximately 4.5 and 0.75microgL(-1) for lead and cadmium, respectively. For a solution containing 100 and 10microgL(-1) of lead and cadmium, respectively, the R.S.D. values varied from 1.6 to 3.2% (n=7). The accuracy of the preconcentration system was evaluated by recovery measurements on spiked water samples. The method was susceptible to matrix effects, but these interferences were minimized by adding barium ions as masking agent in the sample solutions, and recoveries from spiked sample varied in the range of 95.1-107.3%.     

Extraction behaviour of 2-octylaminopyridine towards lead(II) from succinate media and its separation from other toxic metals

Liquid-liquid extraction of lead(II) from succinate media was carried out with 2-octylaminopyridine (2-OAP) in chloroform. Lead(II) was quantitatively extracted with 0.036 M 2-OAP in chloroform from 0.005-0.007 M sodium succinate when equilibrated for 5 min. Lead(II) from the organic phase was stripped with three 10 mL portions of 0.4M acetic acid and determined titrimetrically with EDTA. The nature of extracted species was determined from the log-log plot. The optimum conditions have been evaluated based on a critical study of weak acid concentration, extractant concentration, period of equilibration and effect of diluents. The metal loading capacity of the reagent was found to be 8 mg of lead(II) with 10 mL 0.036 M of the extractant. The extraction of the lead(II) was carried out in presence of various ions to ascertain the tolerance limit of individual. Temperature dependence of the extraction equilibrium constants was examined to estimate the apparent thermodynamic functions (Delta H, DeltaS and Delta G) for extraction reaction. Lead(II) was successfully separated from commonly associated metal ions such as Bi(III), Hg(II), Cr(VI), Cd(II), Zn(II), Al(III), Ca(II), Ba(II) and from binary and ternary mixtures. The method was extended for determination of lead(II) in real samples.     

Biosorption of cadmium (II) and lead (II) from aqueous solutions using mushrooms: A comparative study

Sorption capacity of oyster mushroom (Pleurotus platypus), button mushroom (Agaricus bisporus) and milky mushroom (Calocybe indica) were evaluated on biosorption of heavy metals, viz. cadmium (II) and lead (II) from aqueous solutions. The optimum sorption conditions were studied for each metal separately. The desired pH of the aqueous solution was found to be 6.0 for the removal of cadmium (II) and 5.0 for removal of lead (II) for all the mushrooms. The percent removal of both the metals was found to increase with the increase in biosorbent dosage and contact time. The fitness of the biosorption data for Langmuir and Freundlich adsorption models was investigated. It was found that biosorption of cadmium (II) and lead (II) ions onto the biomass of the three mushrooms were better suitable to Langmuir than Freundlich adsorption model. P. platypus showed the highest metal uptake potential for cadmium (q_max 34.96 mg/g) whereas A. bisporus exhibited maximum potential for lead (q_max 33.78 mg/g). Milky mushroom showed the lowest metal uptake capacity for both the metals. The present data confirms that mushrooms may be used as efficient biosorbent for the removal of cadmium (II) and lead (II) ions from aqueous solution.     

Organization of the production of 100 tons of lead tungstate crystals for the CMS experiment at CERN

The CMS collaboration at CERN has undertaken at the end of 1994 an ambitious R&D program on Lead Tugstate scintillating crystals for its electromagnetic calorimeter. All the parameters of this crystal have been extensively studied in order to optimize its performances in the context of the Large Hadron Collider. Full size crystals (23 cm in length, up to 2.5 × 2.5 cm² in section) with the desired trapezoidal geometry can now be grown and mechanically processed with a yield in excess of 80%. A thorough investigation of the raw material preparation and of the growing conditions has led to a significant improvement in the optical transparency and in the light yield of the crystals. A detailed understanding of the light emission mechanism was 1995. A systematic analysis of the parameters influencing the structural quality of the crystals was at the origin of a considerable improvement of the radiation hardness of full size crystals. All these progress will be illustrated by results of measurements on a statistically representative number of crystals. The conditions of these improvements will be discussed in the context of the mass production of more than 80,000 crystals in a cost effective way.     

Copper and cadmium adsorption on pellets made from fired coal fly ash

Studies on the utilization of low cost adsorbents for removal of heavy metals from wastewaters are gaining attention. Fired coal fly ash, a solid by-product that is produced in power plants worldwide in million of tonnes, has attracted researchers' interest. In this work, fly ash was shaped into pellets that have diameter in-between 3-8mm, high relative porosity and very good mechanical strength. The pellets were used in adsorption experiments for the removal of copper and cadmium ions from aqueous solutions. The effect of agitation rate, equilibration time, pH of solution and initial metal concentration were studied. The adsorption of both cations follows pseudo-second order kinetics reaching equilibrium after an equilibration time of 72 h. The experimental results for copper and cadmium adsorption fit well to a Langmuirian type isotherm. The calculated adsorption capacities of pellets for copper and cadmium were 20.92 and 18.98 mg/g, respectively. Desorption experiments were performed in several extraction media. The results showed that both metals were desorbed substantially from pellets under acidic solutions. For this reason, metal saturated pellets were encapsulated in concrete blocks synthesized from cement and raw pulverized fly ash in order to avoid metal desorption. The heavy metals immobilization after encapsulation in concrete blocks was tested through desorption tests in several aqueous media. The results showed that after 2 months in acidic media with pH 2.88 and 4.98 neither copper nor cadmium were desorbed thus indicating excellent stabilization of heavy metals in the concrete matrix. As a conclusion, the results showed that fly ash shaped into pellets could be considered as a potential adsorbent for the removal of copper and cadmium from wastewaters. Moreover, the paper proposes an efficient and simple stabilization process of the utilized adsorbents thus guarantying their safe disposal in industrial landfills and eliminating the risk of pollution for groundwater and other natural water receivers.     

Removal of lead, cadmium, zinc, and copper from industrial wastewater by carbon developed from walnut, hazelnut, almond, pistachio shell, and apricot stone

In this work, adsorption of copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) that exist in industrial wastewater onto the carbon produced from nutshells of walnut, hazelnut, pistachio, almond, and apricot stone has been investigated. All the agricultural shell or stone used were ground, sieved to a defined size range, and carbonized in an oven. Time and temperature of heating were optimized at 15 min and 800 degrees C, respectively, to reach maximum removal efficiency. Removal efficiency was optimized regarding to the initial pH, flow rate, and dose of adsorbent. The maximum removal occurred at pH 6-10, flow rate of 3 mL/min, and 0.1g of the adsorbent. Capacity of carbon sources for removing cations will be considerably decreased in the following times of passing through them. Results showed that the cations studied significantly can be removed by the carbon sources. Efficiency of carbon to remove the cations from real wastewater produced by copper industries was also studied. Finding showed that not only these cations can be removed considerably by the carbon sources noted above, but also removing efficiency are much more in the real samples. These results were in adoption to those obtained by standard mixture synthetic wastewater.     

Effects of alternating and direct current in electrocoagulation process on the removal of cadmium from water

In practice, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of cadmium from water using aluminum alloy as anode and cathode. The results showed that the removal efficiency of 97.5 and 96.2% with the energy consumption of 0.454 and 1.002 kWh kl⁻¹ was achieved at a current density of 0.2 A/dm² and pH of 7.0 using aluminum alloy as electrodes using AC and DC, respectively. For both AC and DC, the adsorption of cadmium was preferably fitting Langmuir adsorption isotherm, the adsorption process follows second order kinetics and the temperature studies showed that adsorption was exothermic and spontaneous in nature.     

Parameter estimation from observations of first-passage times of the Ornstein–Uhlenbeck process and the Feller process

Renewal point processes show up in many different fields of science and engineering. In some cases the renewal points become the only observable parts of an anticipated hidden random variation of some physical quantity. The hypothesis might be that a hidden random process originating from zero or some other low value only becomes visible at the time of first crossing of some given value level, and that the process is restarted from scratch immediately after the level crossing. It might then be of interest to reveal the defining properties of this hidden process from a sample of observed first-passage times. In this paper the hidden process is first anticipated as a non-stationary Ornstein–Uhlenbeck (OU) process with unknown parameters that have to be estimated only by use of the information contained in a sample of first-passage times. The estimation method is a direct application of the Fortet integral equation of the OU process. A non-stationary Feller process is considered subsequently. As the OU process, the Feller process has a known transition probability distribution that allows the formulation of the integral equation. The described integral equation estimation method also provides a subjective graphical test of the applicability of the OU process or the Feller process when applied to a reasonably large sample of observed first-passage data.

These non-stationary processes have several applications in biomedical research, for example as idealized models of the neuron membrane potential. When the potential reaches a certain threshold the neuron fires, whereupon the potential drops to a fixed initial value, from where it continuously builds up again until the next firing. Also in civil engineering there are hidden random phenomena such as internal cracking or corrosion that after some random time break through to the material surface and become observable. However, the OU process has as a model of physical phenomena the defect of not being bounded to the negative side. This defect is not present for the Feller process, which therefore may provide a useful modeling alternative to the OU process.     

Simultaneous removal of copper and lead ions from a binary solution by sono-sorption process

The aim of this work is to compare the simultaneous sorption of copper and lead ions from a binary aqueous solution in the presence and in the absence of ultrasound. The experiments under sonication were carried out by 20-kHz apparatus. Results indicated that the removal of copper and lead ions from a binary aqueous solution was greater in the presence of ultrasound than in control method. The removal of these ions was examined by varying experimental conditions such as the amount of sorbent, contact time, and temperature. In addition, the competitive sorption of ions was considered with different concentrations of each ion under the constant total concentration. The Langmuir isotherm model fits adequately the experimental data. In point of kinetics, the second-order kinetic model describes the sorption process for both ions. It was found that more than 90% of the lead and 60% of the copper ions was removed in less than 2 min from the solution under sonication. The thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were determined for the sorption of Cu²⁺ and Pb²⁺ from the temperature dependence of the sorption process.     

On the subsidization of firms in the process of transition from a planned to a market economy

It will be shown that in the process of transition from a planned to a market economy subsidies for firms which otherwise would go bankrupt may be socially optimal if they remain below a certain level.