Chemical speciation of particulate uranium in seawater

Uranium shows relatively conservative behaviour in seawater because of the formation of stable carbonato complexes, whereas particulate uranium, involved in suspended particles with the particle size of more than 0.45 m, is a minor constituent. It was found that particulate uranium, with a range from 0.24 to 39 Bq·1^–1, varies spatially and temporally. Its highest concentration occurs in the tropical region of the western North Pacific during the winter of 1983, corresponding to the 1983 El Nifio event. A leaching experiment revealed that major species of particulate uranium are labile organic complexes. Mass balance considerations suggest that particulate uranium in open ocean waters correlates with the presence of particulate organic matter (POM). A high peak of particulate uranium in 1983 may indicate that POM, i.e., primary productivity, increased in the western tropical Pacific during the El Niño event.     

Redox speciation of plutonium

Knowledge of the oxidation state distribution of plutonium in natural waters is necessary in modeling its behavior in environmental systems. The redox speciation of plutonium is complicated by such effects as hydrolysis, complexation, disproportionation, solubility, and redox interchange reactions. The insolubility of Pu(OH)₄ is often the limiting factor of the net solubility of plutonium in oxic natural waters where Pu(V)O ₂ ⁺ is the most stable oxidation state. Perturbations to the oxidation state speciation due to the complexation chemistry of the different oxidation states of plutonium and to the insolubility of plutonium(IV) in neutral aquatic systems are discussed. The merits and limitations of some chemical separation techniques used to study redox speciation of plutonium are presented, and recommendations made for obtaining reliable oxidation state distribution data.     

Chemical speciation of trace metals in seawater: a review.

The recent development of the chemical speciation of trace metals in seawater is described. The speciation studies reveal that metal ion complexation is one of the most important processes in seawater; especially, most bioactive trace metals, such as Fe(III) and Cu, exist as complexes with ligands in dissolved organic matter. The organic ligands in seawater are characterized with metal ions selected by the HSAB concept. A strong organic ligand, which originates from marine microorganisms, is classified as a hard base including carboxylates. The free organic ligand concentrations in seawater are buffered by complexation with excess amounts of Ca and Mg in seawater. The chemical equilibrium model suggested that the concentrations of bioactive free metal ions are at an optimal level to activities of marine microorganisms. For chemical speciation, it is important to have a better understanding of the ecological roles of trace metals in seawater.     

A preliminary study to assess the effect of some seawater components on the speciation of plutonium

Since Pu(IV) and Pu(V) exhibit very different sediment sorption behaviour, the transport of Pu in the aquatic environment is dependant upon oxidation state and the rate of interconversion between the species. A number of laboratory experiments have been carried out to determine possible parameters which influence the rate of Pu redox reactions and the extent of sorption by suspended particulate in the marine environment. Results suggest that, although the initial sorption of Pu(IV) did not appear to be dependant upon the major cations present in seawater, the sorption of Pu(V) was decreased in the presence of Ca²⁺ and Mg²⁺ ions. Both the rates of oxidation of dissolved Pu(IV) and reduction of dissolved Pu(V) increased with increasing suspended particulate concentration.     

Redox speciation of plutonium in natural waters

Data on the stability of Pu(V) as the dominant oxidation state of tracer concentrations of plutonium in natural waters is reviewed. Laboratory experiments for solutions of 0.1 and 1.0M (NaCl) ionic strength and pH 3–10 confirm the dominance of Pu(V) as the state in solution. Humics in the waters can cause reduction to Pu(IV).     

A new method of plutonium speciation in sea water

A new method of plutonium speciation in large volume of sea water was developed by using adsorption of Pu(IV)-Xylenol Orange chelate and Pu-Arsenazo chelate on XAD-2 resin, respectively. The tetravalent plutonium ion reacts selectively with Xylenol Orange in acid solution and that adsorbed on XAD-2 resin. Total plutonium can be collected onto the resin in the form of its Arsenazo-III complex. The determination of plutonium then was carried out by alpha-ray spectrometric method after decomposition of organic complexes and ion exchange separation. The present method is confirmed for convenient and rapid preconcentration procedure for plutonium shipboard chemistry.     

Chemical separation of plutonium

Plutonium in nanogram quantities was isolated from uranium targets irradiated with charged particles. High decontamination was achieved using a method that combines anion exchange with extraction chromatography in tributyl phosphate/hydrochlorid acid solution system.     

Environmental plutonium: The curious case of seawater

A method for quantitatively estimating the fractions of plutonium oxidation states that derive from disproportionation, or other oxidation-reduction reactions, is illustrated with data for seawater. The results agree with experiment and can be checked numerically. Attention is drawn to a discrepancy in what we think is known about seawater.     

The speciation of arsenic in seawater and marine species

Dissolved inorganic arsenic species were determined in natural waters and selected marine species. Prior to irradiation by NAA samples were preconcentrated and the As(III) and As(V) species separated by APCDT-chloroform extraction. Marine samples were digested by microwave heating. Interpretation of data was achieved by comparing the ratio of As(III)/As(V) in the samples and correlating it with the prevailing environmental conditions.     

The extraction, determination and speciation of tributyltin in seawater

Summary Methods have been developed for the determination, by carbon-furnace atomisation atomic absorption spectrophotometry, of inorganic and of total butyltin in seawater. Concentration/separations are based on the solvent extraction of organotin species directly into toluene and of inorganic tin as its tin(IV) 8-hydroxyquinoline chelate into chloroform. Detection limits are 0.7–0.8 ng.

---

Extraktion, Bestimmung und Speziation von Tributylzinn in Seewasser

     

A robust procedure for the determination of plutonium and americium in seawater

A new procedure for the analysis of Pu and Am in large water samples is presented. In this procedure, the actinides are first preconcentrated from 200 liter water samples with combined MnO₂ and Fe(OH)₃ co-precipitation. Pu and Am are then separated from the large amount of Mn by performing a second precipitation of Fe(OH)₃ at pH 6. The final separation of Pu and Am from interfering elements and from each other is achieved with the use of a single extraction chromatographic column of TRU-ResinÔ. The -activities are then determined using -spectrometry after source preparation by CeF₃ micro co-precipitation. The procedure described is faster, simpler, more robust and gives higher chemical yields then procedures normally used for routine analysis of Pu and Am. The chemical yields of Pu and Am, when analysing 200 liter sea water samples, are between 80-85%.     

Chemical speciation of radionuclides migrating in groundwaters

In order to more accurately predict the rates and mechanisms of radionuclide migration from lowlevel waste disposal facilities via groundwater transport, ongoing studies are being conducted at field sites at Chalk River Laboratories to identify and characterize the chemical speciation of mobile, long-lived radionuclides migrating in groundwaters. Large-volume water sampling techniques are being utilized to separate and concentrate radionuclides into particulate, cationic, anionic, and nonionic chemical forms. Most radionuclides are migrating as soluble, anionic species which appear to be predominately organoradionuclide complexes. Laboratory studies utilizing anion exchange chromatography have separated several anionically complexed radionuclides, e.g.,⁶⁰Co and¹⁰⁶Ru, into a number of specific compounds or groups of compounds. Large-volume ultra-filtration experiments have shown that significant fractions of the radionuclides are being transported in these groundwaters in the form of macromolecules having molecular weights ranging from less than 3,000 to 100,000.     

Chemical speciation of mercury in natural waters

Improved sensitivity of the cold-vapour atomic absorption method for mercury can be obtained by equilibrating the reduced sample with a small volume of air at 90°C. An automated system has been developed that has a detection limit of 1 ng Hg l^-1. By changing the reducing conditions three species of mercury can be differentiated and determined, inorganic mercury, arylmercury compounds such as phenylmercury(II) chloride, and alkylmercury compounds such as methylmercury(II) chloride. Speciation of mercury in natural waters is possible.     

Environmental plutonium: What is the redox potential of seawater?

The potential of seawater has recently been reported as 0.8 V. This number conflicts with many literature sources on oceanography.Mount is operated for the U.S. Department of Energy by EG&G Mound Applied Technologies Incorporated under contract No. DE-AC04-88DP43495.     

Chemical speciation of nanoparticles surrounding metal-on-metal hips

Spectromicroscopy of tissue surrounding failed CoCr metal-on-metal hip replacements detected corroded nanoscale debris in periprosthetic tissue in two chemical states, with concomitant mitochondrial damage. The majority of debris contained Cr(3+), with trace amounts of oxidised cobalt. A minority phase containing a core of metallic chromium and cobalt was also observed.     

Chemical dissolution of total content of fallout plutonium in deep-sea sediment

Simple nitric acid leaching and alkali fusion techniques for the determination of the total content of fallout^239,240Pu in deep-sea sediment were compared. Leaching neither with boiling conc. HNO₃ nor with boiling conc. HNO₃+H₂O₂ was found to be sufficient. The sodium hydroxide fusion technique yielded reproducible analytical results and is proposed as an optimum dissolution method for quantitative determination of the total content of fallout^239,240Pu in deep-sea sediment.     

化学形态分析软件CHEMSPEC及其应用

放射性核素在地质层中的吸附和迁移行为与其所处的化学形态密切相关．为了预测在处置库受损情况下放射性核素的时间和空间分布,需要建立化学形态分析与水力学计算相耦合的数学模型及计算软件．为此,我们编写了化学形态分析软件CHEMSPEC．本文在简要介绍该软件的原理和程序结构后,着重介绍该程序为防止质量平衡方程组迭代求解过程的发散所采取的措施,提出用“预报－校正法”处理沉淀－溶解平衡的算法,以及用“冻结”和“解冻”氧化态的策略处理包含氧化还原反应和沉淀反应的化学平衡的计算．本文用4个典型例子说明CHEMSPE在现阶段能解决些什么问题．最后讨论了存在的问题和尚待完成的工作．     

Chemical speciation code CHEMSPEC and its applications

The adsorption and migration behavior of a radionuclide in geological media heavily depends on its chemical forms in a given chemical environment. In order to predict the temporal and spatial distribution of radionuclides around a disposal site when its canister is damaged, it is necessary to develop coupled chemical speciation-solute transport models and relevant software. For that reason, we wrote a new chemical speciation program CHEMSPEC. In this paper, the principles and structure of CHEMSPEC are briefly described, and the strategy and algorithms that were used in this code are interpreted in some detail, such as the measures adopted to prevent divergence in iteratively solving the mass balance equations, the “predictor-corrector” algorithm for calculation of the number and quantities of solid species formed, and the alternate use of “freezing” and “defreezing” oxidation states in handling of co-existent redox and precipitation equilibria. Four examples are given to illustrate CHEMSPEC’s features and capabilities.     

Determination of plutonium isotopes in seawater samples by Semiconductor Alpha Spectrometry,ICP-MS and AMS techniques

Analysis of plutonium isotopes by Semiconductor Alpha Spectrometry (SAS), ICP-sector field mass spectrometry (ICP-MS) and Accelerator Mass Spectrometry (AMS) was carried out in seawater samples collected from the Northeast Atlantic Ocean (nuclear waste dumping sites) and Northwest Pacific Ocean. No particularly elevated levels of the atom ratios of ²⁴⁰Pu/²³⁹Pu compared to global fallout ratio (0.18) were found in the Northeast Atlantic Ocean seawater samples. The higher levels of atom ratios of ²⁴⁰Pu/²³⁹Pu were found in the Northwest Pacific Ocean. This is mainly due to contribution from the local fallout from nuclear weapon tests carried out at the Pacific Proving Grounds at the Marshall Islands.