Factors affecting interaction of radiocesium with freshwater solids

The paper aims at the analysis of principal factors affecting the interaction of radiocesium with freshwater solids, important for the migration of radiocesium in rivers. Uptake of radiocesium by bottom sediments and suspended solids from small streams was studied as a function of pH and composition of aqueous phase, of the concentration of cesium in water and of the composition of freshwater solids, using laboratory model experiments. pH had negligible effect on the uptake in the pH range 5–9, the uptake decreased at pH values less than 3–5 depending on the nature and concentration of the solids. Addition of cations suppressed the uptake in the order K⁺>Na⁺>Ca²⁺, the suppression began at 0.001, 0.01 and 0.1 mol.dm^?3 concentration, respectively. Increase in cesium concentration in water caused a decrease of radiocesium uptake, but at very low concentrations of cesium combined with higher concentration of sediment (2g·dm^?3) the uptake was independent of cesium concentration. Removal of carbonates, oxidic coatings and organic matter from a sediment did not affect the sorption properties of the sediment. The nature of the effects found confirms that cesium is sorbed mainly by clay components of freshwater solids. Results obtained are compared with literature data and conclusions are drawn on the importance of the factors studied for modelling of radiocesium migration in rivers.     

Factors affecting interaction of radiostrontium with river sediments

Uptake of radiostrontium by sediments from two small streams was studied as a function of pH and composition of aqueous phase, of the concentration of strontium, of contact time, temperature and liquid-to-solid ratio (V/m), using laboratory model experiments. Between pH 5 and 12 the uptake increased with pH and shifted to higher pH values with increasing V/m ratio. Addition of cations suppressed the uptake in the order Na⁺<K⁺<Ca²⁺. Increase in strontium concentration had negligible effect up to 10^–5–10^–4 mol·dm^–3 concentration due to high concentrations of dissolved and exchangeable strontium present in the systems. The V/m ratio had no influence on K_d in the range of V/m=20–446 cm³ · g^–1 but K_d value for V/m=0.79 cm³ · g^–1 was significantly lower. Two-step kinetics of the uptake was observed in most cases with a rapid first step (<100 min) followed by a slow increase. No difference was found between the uptake at 10°C and 22°C. Adsorbed radiostrontium could be easily desorbed with river water. The easiness of desorption decreased with repeated desorption. Drying of sediment did not affect the first desorption, repeated desorptions slightly decreased. Conclusions were drawn on the mechanism of radiostrontium uptake and on the importance of the factors studied for modelling of radiostrontium migration in rivers.     

Analysis of the interaction of radionuclides with solid phase in surface waters using laboratory model experiments: Methodical problems

Use of laboratory model experiments for analysis of interaction of radionuclides with surface water solids is connected with methodical problems concerning selection of solid phase, sampling, storage and pretreatment of solid phase, concentration of radionuclide, selection of liquid to solid ratio, adsorption of radionuclide on vessel walls, choice of experimental procedures and change in radionuclide speciation in the solid phase. These problems are discussed on the basis of literature data and of experiments with radiocobalt or radiocesium in a system river water-suspended solids or bottom sediments. Possible ways of solution of the problems are shown. Two modifications of batch method are described in detail and their merits or drawbacks evaluated. Comparison of the modifications shows their possible use as complementary methods for the study of radionuclide behaviour in surface waters.     

Effect of hydrogen-ion concentration on the extraction of cobalt, nickel, cadmium and lead with APDC/MIBK: time stability of the extracts

The extraction of cobalt, nicke cadmium and lead ions by means of APDC/MIBK has been studied at various acidities of the aqueous phase (pH 0.2–6). Lead and nickel are extracted equally well over this pH-range, while cobalt and cadmium require pH> 1. The time stability of the extracted complexes in MIBK increases in the order cadmium < lead < nickel < cobalt. The decomposition of the complexing agent or the metal complexes is rapid in the two-phase system MIBK/water.     

Factors affecting interaction of radiocesium with freshwater solids

The paper aims at the analysis of principal factors affecting the interaction of radiocesium with freshwater solids, important for the migration of radiocesium in rivers. Uptake and release of radiocesium by bottom sediment and suspended solids from a small stream were studied as a function of contact time during the uptake and releases, of concentration of the solid phases and of temperature, using laboratory model experiments. Kinetics of the uptake were found to be singificantly affected by temperature and concentration of the solid phase. The kinetics and the concentration effect can be quantitatively described using kinetic model of two parallel or consecutive reactions. Kinetic parameters for the model were determined. Distribution coefficient K_d is independent of sediment concentration in the range of 20–70 mg·dm^?3 but passes through a maximum at higher concentration values. Release of radiocesium adsorbed on the freshwater solids was found to be quite rapid and a simple kinetics of the release from freshwater solids was observed. The amount released decreased with increasing contact time of radiocesium with solid phase. Quantitative evaluation of the release revealed partial irreversibility of radiocesium uptake on the solids studied. Results obtained are compared with literature data and conclusions are drawn on the importance of the factors studied for modeling of radiocesium migration in rivers.     

Removal of Cobalt Ions from Aqueous Solution by Adsorption onto Cross-Linked Calcium Alginate Beads

The removal of cobalt ions from dilute aqueous solutions using cross linked calcium alginate beads as the adsorbent is reported in this article. The influence of various experimental parameters such as pH, initial metal ion concentration, contact time and solid to liquid ratio were studied. The adsorption data were applied to Langmuir and Freundlich isotherm equations and various static parameters were calculated. It was observed that the uptake of cobalt ions was found to increase with time and that maximum adsorption was obtained within the first 60 minutes of the process. These results indicate that the cross linked calcium alginate beads have potential for removing cobalt ions from industrial waste water.     

Studies on removal of cobalt from an alkaline waste using synthetic calcium hydroxyapatite

The removal of cobalt from an alkaline waste solutions containing sodium was carried out using a radiotracer in a batch method using synthetic calcium hydroxyapatite (HAP). The influence of different parameters such as solution pH, contact time, cobalt concentration, and presence of other ions like sodium on cobalt removal was studied. The sorption process followed pseudo-second-order kinetics with necessary time of around 23–25 h to reach equilibrium and the cobalt uptake was quantitatively evaluated using the Freundlich model. The results indicated that the mechanism of cobalt removal by HAP was mainly due to chemisorption on a heterogeneous surface. In the presence of sodium, the sorption of cobalt on HAP was not affected. The sorption of cobalt on HAP was pH independent in the range from 4 to 8, because of its buffering properties. The adsorption of cobalt on HAP was fast and the percentage of cobalt sorption was >97 % during the first 30–40 min of the contact time.     

Removal of radiocobalt form aqueous solutions by inorganic exchangers

The sorption of radiocobalt from aqueous as well as organic solvents by natural and treated clays has been investigated. The effect of many factors, such as time, pH, carrier concentration, etc., were studied. In was found that the uptake is maximum in neutral, or slightly alkaline solutions. The rate of sorption depends on the velocity of shaking, which may indicate the operation of the film-diffusion mechanism, in addition to some contribution from particle-diffusion mechanism, but the dependence of the rate on shaking velocity could be attributed to an increase in the surface area of the clays. The conclusion is that natural clays are well suited for the removal of radioactive cobalt with slight, if any modification. These clays may be considered superior to synthetic exchangers for the removal of⁶⁰Co, if the availibility and prices of the former are taken into account.     

Sorption of the long-lived radionuclides cesium-134, strontium-85 and cobalt-60 on bentonite

The sorption of long-lived radionuclides of cesium, strontium and cobalt (¹³⁴Cs, ⁸⁵Sr and ⁶⁰Co) on bentonite under various experimental conditions, such as contact time, pH, sorbent and sorbate concentrations have been studied. The uptake of Cs and Sr was rapid and equilibrium was reached almost instantaneously in both the cases, while Co sorption was time dependent. The sorption of these nuclides increased by increasing pH. The uptake of Cs, Sr and Co increased with increasing the amount of the bentonite clay. The percentage sorption for Cs, Sr and Co decreased with increasing metal concentrations. The desorption studies with 0.01M CaCl₂ and ground water at low-metal loadings on bentonite showed that about 95% of Cs, 85-90% of Sr and 97% of Co were irreversibly sorbed. These results could be helpful for nuclear waste management, for waste water effluents containing low concentrations of cesium, strontium and cobalt.     

Determination of radiocobalt in seawater by successive extractions with the reagents of tris/pyrrolidine dithiocarbamato/bismuth/III/ and ammonium pyrrolidin-dithiocarbamate and back-extraction with bismuth/III/

Method for the isolation and radioactive cobalt /including⁵⁸Co and⁶⁰Co/ from a large volume of seawater and concentration in a small volume of chloroform as tris/pyrrolidine dithiocarbamato/cobalt/III/, Co/PDC/₃, is described. The seawater was extracted first with Bi/PDC/₃ in chloroform for removing parts of foreign metals like Hg, Ag, etc., and then added with ammonium pyrrolidindithiocarbamate, APDC, to complex with Co and possibly other ions and extracted into the organic phase. The final separation of Co from foreign ions in the organic phase was achieved by stripping with a Bi/III/ solution. The overall recovery of radiocobalt activity was found to be about 96%. The established method can be applicable for rapid and reliable determination of radiocobalt in seawater and other aqueous systems for environmental contamination.     

Comparative study on sorption of radiocobalt to montmorillonite and its Al-pillared and cross-linked samples: Effect of pH,ionic strength and fulvic acid

Effects of pH, ionic strength and fulvic acid on sorption of radiocobalt on montmorillonite and its Al-pillared and cross-linked samples were studied using batch technique. The results indicate that the sorption of cobalt is strongly dependent on pH values and independent of ionic strength. Fulvic acid enhances the sorption of cobalt slightly at low pH, but has no influence at high pH values. Surface complexation is considered the main mechanism of cobalt sorption to montmorillonite. The sequences of FA/Co²⁺ additions to the system did not affect cobalt sorption.     

Sorption of 60Co on a synthetic titanosilicate analogue of the mineral penkvilksite-2O and antimonysilicate

The ability of two different types of synthetic inorganic ion-exchangers to sorb radioactive cobalt-60 using a batch-type method was studied. The two materials examined were the analogue of the natural titanosilicate penkvilksite-2O (AM-3) and a synthetic antimonysilicate. Ion-exchange experiments were performed with solutions labelled with radioactive cobalt (⁶⁰Co). The sorption of ⁶⁰Co onto the two samples materials were compared in terms of distribution coefficient (K _d), sorption percentage and cobalt quantity removed in mg per gram weight of the material. Several parameters were investigated viz. contact time, cobalt concentration, and sorbent concentration. It was found that the batch factor and cobalt concentration had a significant influence on the sorption of cobalt onto both of the materials. This was associated with the difference in pH generated by suspensions of the materials in water which was alkaline for the penkvilksite-2O analogue, and acid for the synthetic antimonysilicate.     

Sorption interaction of phenanthrene with soil and sediment of different particle sizes and in various CaCl2 solutions

The objective of this investigation is to evaluate the influences of natural sorbent particle size and system Ca(2+) concentration on sorption of low-polarity organic chemicals. The physicochemical properties of the different particle size soil and sediment subsamples and the surface characters of the soil and sediment samples in various CaCl(2) concentrations were determined. The sorption behavior of phenanthrene (PHN) on the subsamples of different particle size and to the samples in various CaCl(2) solutions was examined. Batch experiments demonstrate that the sorption capacities increase with decreased particle size for both soil and sediment. It is presumably due to the higher total organic carbon (TOC) content for the finer particles. But the enhancements in sorption coefficients are not met with the equal increases in TOC contents. The effect of Ca(2+) on PHN uptake is strong in short contact time but slight in long contact time. With increasing Ca(2+) concentration, the sorption capacities for Beizhai soil increase first in the low Ca(2+) concentration range, and then decline. Nevertheless, the increase of Ca(2+) concentration greatly reduces the uptake of phenanthrene on Guanting sediment over the overall measured range. The different physicochemical properties, such as dissolved organic carbon (DOC) content, mineral and element composition, and surface characters, between soil and sediment may result in this discrepancy.     

Removal of radiocobalt from aqueous solution by different sized carbon nanotubes

Batch adsorption technique was applied to study the adsorption of radiocobalt on multiwalled carbon nanotubes (CNTs) with deferent sizes. The aim of this work was to examine the effect of contact time, pH, solid content, foreign ions and CNT particle sizes on the removal of Co(II) ions from aqueous solutions by CNTs. The results indicated that the adsorption of Co(II) was strongly dependent on pH and the adsorption capacity was in inverse proportion to the particle sizes of CNTs. The adsorption of Co(II) was weakly affected by ionic strength and foreign ions. Ion exchange and surface complexation were the main adsorption mechanisms. The kinetics of Co(II) adsorption on CNTs was described well by pseudo-second-order model. The Langmuir and Freundlich models were applied to interpret the adsorption data. The results are important to understand the physicochemical behavior of Co(II) with CNTs, and for the application of CNTs in the preconcentration of radiocobalt from large volumes of aqueous solutions.     

Removal of radiocobalt from aqueous solution by oxidized MWCNT

The study was undertaken to evaluate the feasibility of oxidized multiwalled carbon nanotube (oxidized MWCNT) for the removal of radiocobalt (⁶⁰Co) from aqueous solutions. The oxygen functional groups of oxidized MWCNT were characterized by FT-IR and XPS. Batch experiments were performed to study the sorption of cobalt as a function of contact time, solid contents, pH, ionic strength, foreign ions, and temperature. Two kinetic models viz. pseudo-first-order and pseudo-second-order were used to determine kinetic sorption parameters, and the kinetic sorption could be described more favorably by the pseudo-second-order model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on oxidized MWCNT was an endothermic and spontaneous processes. The results suggest that oxidized MWCNT can be used efficiently in the treatment of industrial effluents containing radioactive and heavy metal ions.     

Sorption of Radiocobalt on Bentonite and Kaolinite

The factors affecting the sorption of radiocobalt by bentonite and kaolinite were studied with the aim to assess important factors which should be included in modelling radiocobalt migration in soils and waters. The distribution coefficients of radiocobalt sorption on bentonite and kaolinite from aqueous solutions were determined by using the batch method, and it was found that they were insensitive to the loading, the initial pH, the ionic strength, the humic substance and the sorption direction. Thus, the sorption characteristics of radiocobalt on bentonite and kaolinite facilitated the mathematical modelling of radiocobalt migration. In addition, the sorption kinetics and the sorption mechanism of radiocobalt on bentonite and kaolinite were also examined.     

Behavior of some macroelements,trace elments and RE in the water-sediment system

The aim of this work was to estimate the processes of sorption or desorption which take place when water of slightly higher temperature and elevated concentrations of some elements, compared to groundwater, comes into contact with aquifer sediments under aerobic conditions. The behavior of some macro-elements, trace elements and RE in the water/sediment systems, prepared as five different granulometric fractions of the sediment, was followed by INAA, AAS and titrimetric methods, under simulated natural conditions. It was found that, for the majority of elements, desorption takes place. Opposite to this, Mg and Zn are sorbed from water on all sediment granulometric fractions. The concentration of Ca as a major cation is lingering about its initial value. Na, K, Ba, Sr, Fe, Hg, Au, Sc, Sb, U, La and Ce are desorbed from all sediment fractions. The desorption from finer sediment phase was less pronounced for Fe, Hg, Au, Sc, Sb and Ce. Sorption of some elements (like Co, Cr and Zr) on smallest sediment fraction (<90 m) appears. Sorption-desorption processes, as well as water pH changes, are time dependent, continuing for some weeks, especially in the coarse sediment system. The extents of sorption and desorption for most of the determined elements indicate that the specific surface area is not a key parameter     

Coupled mass transfer and reaction in water of an oil soluble chemical: A CT scan study

Chemical compounds of the family of alkoxysilanes, such as tetramethyl orthosilicate (TMOS), are soluble in oil but can be dissolved in water where they undergo a hydrolysis and a condensation reaction to form a stable silica gel. We have investigated in detail the coupled mass transfer–reaction process that takes place when oil with dissolved TMOS is brought in contact with water in a well-defined geometry. The main physical parameters (initial TMOS concentration in the oil phase, initial water to oil volume ratio, and water pH and salinity) were varied during the experiment. X-ray CT was used to visualize and quantify concentration changes in the oil and the water phases. We found that varying the initial concentration does not affect mass transfer rates out of the oil phase, but increasing initial concentrations do speed up gelation. The water to oil volume ratio has a larger impact on mass transfer, with a transfer rate that increases with increasing water to oil volume ratio. Low pH of the water phase promotes mass transfer, whereas high pH and addition of salt has no significant effect. Gelation is however more profoundly affected by both increasing pH and addition of salts.     

Separation and concentration of cobalt from ammoniacal solutions containing cobalt and nickel by emulsion liquid membranes using 5,7-dibromo-8-hydroxyquinoline (DBHQ)

The separation and concentration of cobalt from ammoniacal solutions containing nickel and cobalt by an emulsion liquid membranes (ELMs) using 5,7-dibromo-8-hydroxyquinoline as extractant has been presented. Membrane solution consists of a diluent (kerosene), a surfactant (Span 80), a modifier (tributylphosphate), and an extractant (DBHQ). Very dilute sulphuric solution containing EDTA as complexing agent, buffered at pH 5.0, has been used as a stripping solution. pH of ammoniacal feed solution containing cobalt and nickel was adjusted to 9.0 with hydrochloric acid. The important variables governing the permeation of cobalt have been studied. These variables are membrane composition, pH of the feed solution, cobalt and nickel concentrations of the feed solution, mixing speed, surfactant concentration, extractant concentration, EDTA concentration and pH of the stripping solution, and phase ratio. After the optimum conditions had been determined, it was possible to selectively extract 99.0% of cobalt from ammoniacal feed solution containing Co²⁺ and Ni²⁺ ions. The separation factors of cobalt with respect to nickel, based on initial feed concentration, have experimentally found to be of as high as 247.5 for about equimolar Co–Ni feed solutions.