Optimal Physicochemical Conditions Research Articles

An innovative method for fractionating the milk fat globule membrane and the major buttermilk proteins

Buttermilk (BM) is a by-product of butter manufacturing that shares a similar composition to skim milk but contains a higher concentration of phospholipids due to milk fat globule membrane (MFGM) fragments released during cream churning. Despite its high added-value components, MFGM is underutilized mainly due to the challenge in separating its components from the other constituents of buttermilk. Our work has focused on the use of calcium phosphate particles, called hydroxyapatite (HA), to extract and separate the different components from buttermilk. This study investigated the impact of various physicochemical parameters (temperature, ionic strength, and pH) on the adsorption of a mixture of micellar casein (CM), whey proteins, and MFGM from BM onto HA surfaces. A box-Behnken design was utilized to predict optimal physicochemical conditions for selectively separating components in buttermilk. Ionic strength (IS) played a crucial role, with low IS having a minimal positive influence and high IS negatively influencing adsorption. pH influenced adsorption by altering protein and HA surface charges. The optimal conditions for adsorption were an IS of 100 mM for a pH of 7, for 90 % of CM, 37 % of β-lactoglobulin, 11 % of α-lactalbumin and 7 % of MFGM. Desorption experiments using citrate and alkaline pH showed promising results for CM recovery, with citrate efficiently releasing the adsorbed CM. Additionally, MFGM were separated from whey proteins through selective precipitation at a pH of 4.0, allowing sedimentation of MFGM (100 %) while keeping whey proteins soluble. The presence of β-lactoglobulin in the protein fraction of MFGM (31 %) and CM (37 %) was attributed to pasteurization, which denatured a portion of β-lactoglobulin and led to its attachment to MFGM surfaces and interaction with CM. This protocol produces a nearly pure fraction of MFGM with a simple method which is suitable for industrial production, representing significant valorization for the dairy sector.

The Impact of Physicochemical Conditions on Lactic Acid Bacteria Survival in Food Products

Lactic acid bacteria (LAB), due to their many advantageous features, have been utilized in food manufacturing for centuries. Spontaneous fermentation, in which LAB play a fundamental role, is one of the oldest methods of food preservation. LAB survival and viability in various food products are of great importance. During technological processes, external physicochemical stressors appear often in combinations. To ensure the survival of LAB, adjustment of optimal physicochemical conditions should be considered. LAB strains should be carefully selected for particular food matrices and the technological processes involved. The LAB’s robustness to different environmental stressors includes different defense mechanisms against stress, including the phenomenon of adaptation, and cross-protection. Recently established positive health effects and influence on human wellbeing have caused LAB to be some of the most desirable microorganisms in the food industry. A good understanding of LAB defense and adaptation mechanisms can lead to both optimization of food production and storage conditions, as well as to obtaining LAB strains with increased tolerance to stressors. Hopefully, as a result, the final food product with naturally present or added LAB can achieve outstanding quality and safety with health benefits that meet consumer expectations.

Role of Physico-Chemical and Cellular Conditions on the Bone Repair Potential of Plastically Compressed Collagen Hydrogels.

Since their first description nearly 20 years ago, dense collagen hydrogels obtained by plastic compression have become popular scaffolds in tissue engineering. In particular, when seeded with dental pulp stem cells, they have demonstrated a great in vivo potential in cranial bone repair. Here, we investigated how physico-chemical and cell-seeding conditions could influence the formation and in vitro mineralization of these cellularized scaffolds. A qualitative assessment demonstrated that the gel stability before and after compression was highly sensitive to the conditions of fibrillogenesis, especially initial acid acetic and buffer concentrations. Gels with similar rheological properties but different fibrillar structures that exhibited different stabilities when used for the 3D culture of Stem cells from Human Exfoliated Deciduous teeth (SHEDs) could be prepared. Finally, in our optimal physico-chemical conditions, mineralization could be achieved only using human dental pulp stem cells (hDPSCs) at a high cell density. These results highlight the key role of fibrillogenic conditions and cell type/density on the bone repair potential of cell-laden plastically compressed collagen hydrogels.

Bioproduction and Application of Orange and Yellow Pigments Obtained from Chryseomicrobium palamuruense and Micrococcus luteus

Colour is a fundamental and most likely one of the primary attributes to be observed by the human senses, making it an essential part of human life and culture. This study investigates the bioproduction and potential application of bacterial pigments obtained from abattoir wastewater. Bacteria isolates recovered from abattoir wastewater were screened for pigment production and identified using the 16S rRNA gene sequence. Optimal physicochemical conditions of parameters were investigated and harnessed for bulk pigment production. Pigments produced were characterised using UV-Visible Spectrophotometer and Fourier Transform Infra-Red (FTIR) Analysis. The antibacterial and dyeing ability of the extracted pigments were evaluated. Two bacteria namely, Chryseomicrobium palamuruense strain PUI and Micrococcus luteus strain 1k produced orange and yellow pigments respectively. The UV-visible spectrum of the orange pigment produced by Chryseomicrobium palamuruense showed surface plasmon resonance peaks at 262, 426, and 453 nm while that of the yellow pigment produced by Micrococcus luteus showed a single peak at 260 nm. The FTIR analysis of the extracted pigments indicated the presence of some functional groups namely hydroxyl (OH), C-H, primary and secondary C-O, and skeletal C-C vibrations. Chryseomicrobium palamuruense and Micrococcus luteus showed no antibacterial activity against the selected typed bacterial isolates assessed in this study. The orange pigment extracted from Chryseomicrobium palamuruense was retained on cotton and polyester producing different shades of colour on the two fabrics when used as a dyeing agent. The pigment-producing potentials of these organisms suggest their relevance as promising dyes in textile industry.

Toward application of biocontrol to inhibit wine spoilage yeasts: The use of statistical designs for screening and optimisation

Spoilage yeasts generate considerable economic losses in the wine industry, and although sulphur dioxide (SO2) is traditionally used for control, its use has become controversial because of its negative effects on health. Biocontrol has emerged as a partial alternative to SO2, and most research has focused on the selection of biocontrol yeasts and/or the mechanisms involved, while little research has been directed to the environmental conditions that make biocontrol effective for application. When there are two or more interacting yeasts, the physicochemical factors that affect their antagonism are many and therefore the application of biocontrol is complex. To reduce SO2, the present study aimed to elucidate biocontrol mechanisms of two yeast interactions and to establish optimal physicochemical conditions for biocontrol of the spoilage yeast during grape must fermentation. Through the use of statistical design, it was possible to find relevant physicochemical factors and optimise them. Wickerhamomyces anomalus “BWa156” developed an active supernatant against ZygoSaccharomyces rouxii “BZr6” while supernatant from Metschnikowia pulcherrima “BMp29” was ineffective. In mixed must fermentations, the first interaction (BWa156 vs. BZr6) showed fewer physicochemical factors impacting biocontrol compared to the second interaction (BMp29 vs. BZr6). However, the fewer factors of the first interaction had a stronger effect on the decline in the spoilage population. Validations showed that the optimal conditions for biocontrol with the first interaction could be predicted. Analysis of the results with BWa156 vs. BZr6 and BMp29 vs. BZr6 suggests that the first interaction is a competition that includes a killer toxin, while the second interaction involves competition for iron resources. Response surface methodology (RSM) allowed a reduction in the number of experiments and permitted to find the optimal biocontrol conditions (SO2: 0 mg mL-1; pH: 3.7; Reducing sugars: 23 °Brix) for the interaction between BWa156 and BZr6.

Исследование структурных характеристик Ni-Zn-Co феррошпинелей

Currently, in the modern scientific literature there is an increased interest in ferrites of all types. Among them, a special place is occupied by Ni-Zn ferrite with a spinel structure. It is known that the functional properties of ferrites can be significantly changed by partial or com-plete replacement of the cations of the initial matrix with other cations differing in magnetic moment and size. Such a change in the structure makes it possible to effectively vary the proper-ties of ferrites, i.e. to provide "tuning" of the material for the required properties. An analysis of the literature in this direction has shown that the cobalt ion Co2+ is an effective substitute cation. In this study we are dealing with the Ni-Zn ferrites of variable composition, with the fixed con-tent x(Co) = 0.1. The general formula is: Co0.1Zn0.9-xNixFe2O4, (where x = 0; 0.3; 0.6; 0.9). The aim of the presented work is to synthesize samples, as well as to study their density and porosity, which in turn have a direct effect on the performance properties of ceramic ferrites. The synthesis of the samples was carried out by the solid-phase reaction method, using a high-temperature furnace in an air atmosphere. Previous studies have made it possible to identify a set of optimal physicochemical conditions under which the initial charge ferritization occurs. The initial components for preparing the charge included oxides. X-ray phase analysis and X-ray structural analysis, electron microscopy and energy dispersive X-ray spectroscopy were used as research methods. As a result of X-ray phase analysis, it has been revealed that the obtained samples are monophasic and belong to spinels of the AFe2O4 type (where element A = Ni, Zn, Co). The study of the surface morphology of the samples has revealed the presence of many crystallites of various sizes, the natural faceting of which corresponds to crystallites with a cubic syngony. Investigations of the true and X-ray density of the obtained samples have been carried out. The dependence of the influence of the substitution value x(Ni) on the porosity (density), as well as on the parameters of the elementary crystal lattice, has been determined.

Biochemical and Molecular Characterization of a Thermostable Alkaline Metallo-Keratinase from Bacillus sp. Nnolim-K1.

Keratinases are considerably gaining momentum in green technology because of their endowed robustness and multifaceted application potentials, such as keratinous agro-wastes valorization. Therefore, the production of novel keratinases from relatively nonpathogenic bacteria grown in agro-wastes formulated medium is cost-effective, and also imperative for the sustainability of thriving bioeconomy. In this study, we optimized keratinase production by Bacillus sp. Nnolim-K1 grown in chicken feather formulated medium. The produced keratinase (KerBNK1) was biochemically characterized and also, the keratinase-encoding gene (kerBNK1) was amplified and sequenced. The optimal physicochemical conditions for extracellular keratinase production determined were 0.8% (w/v) xylose, 1.0% (w/v) feather, and 3.0% (v/v) inoculum size, pH 5.0, temperature (25 °C) and agitation speed (150 rpm). The maximum keratinase activity of 1943.43 ± 0.0 U/mL was achieved after 120 h of fermentation. KerBNK1 was optimally active at pH and temperature of 8.0 and 60 °C, respectively; with remarkable pH and thermal stability. KerBNK1 activity was inhibited by ethylenediamine tetra-acetic acid and 1,10-phenanthroline, suggesting a metallo-keratinase. The amplified kerBNK1 showed a band size of 1104 bp and the nucleotide sequence was submitted to the GenBank with accession number MT268133. Bacillus sp. Nnolim-K1 and the keratinase displayed potentials that demand industrial and biotechnological exploitations.

Bacillus sp. FPF-1 Produced Keratinase with High Potential for Chicken Feather Degradation.

Chicken feathers are predominantly composed of keratin; hence, valorizing the wastes becomes an imperative. In view of this, we isolated keratinase-producing bacteria and identified them through the 16S rDNA sequence. The process condition for keratinase activity was optimized, and electron micrography of the degradation timelines was determined. Keratinolytic bacteria were isolated and identified as Bacillus sp. FPF-1, Chryseobacterium sp. FPF-8, Brevibacillus sp. Nnolim-K2, Brevibacillus sp. FPF-12 and Brevibacillus sp. FSS-1; and their respective nucleotide sequences were deposited in GenBank, with the accession numbers MG214993, MG214994, MG214995, MG214996 and MG214999. The degree of feather degradation and keratinase concentration among the isolates ranged from 62.5 ± 2.12 to 86.0 ± 1.41(%) and 214.55 ± 5.14 to 440.01 ± 20.57 (U/mL), respectively. In the same vein, 0.1% (w/v) xylose, 0.5% (w/v) chicken feather, an initial fermentation pH of 5.0, fermentation temperature of 25 °C and an agitation speed of 150 rpm, respectively, served as the optimal physicochemical conditions for keratinase activity by Bacillus sp. FPF-1. The time course showed that Bacillus sp. FPF-1 yielded a keratinase concentration of 1698.18 ± 53.99(U/mL) at 120 h. The electron microscopic imaging showed completely structural dismemberment of intact chicken feather. Bacillus sp. FPF-1 holds great potential in the valorization of recalcitrant keratinous biomass from the agro sector into useful products.

Phenolic Constitution, Phytochemical and Macronutrient Content in Three Species of Microgreens as Modulated by Natural Fiber and Synthetic Substrates.

The present study examined the modulatory effects of natural fiber substrates (agave fiber, coconut fiber and peat moss) and synthetic alternatives (capillary mat and cellulose sponge) on the nutritive and phytochemical composition of select microgreens species (coriander, kohlrabi and pak choi) grown in a controlled environment. Polyphenols were analyzed by UHPLC-Q-Orbitrap-HRMS, major carotenoids by HPLC-DAD, and macro-minerals by ion chromatography. Microgreens grown on peat moss had outstanding fresh and dry yield but low dry matter content. Natural fiber substrates increased nitrate and overall macro-mineral concentrations in microgreens compared to synthetic substrates. The concentrations of chlorophylls, carotenoids and ascorbate were influenced primarily by species. On the contrary, variability in polyphenols content was wider between substrates than species. Out of twenty phenolic compounds identified, chlorogenic acid and quercetin-3-O-rutinoside were most abundant. Hydroxycinnamic acids and their derivatives accounted for 49.8% of mean phenolic content across species, flavonol glycosides for 48.4% and flavone glycosides for 1.8%. Peat moss provided optimal physicochemical conditions that enhanced microgreens growth rate and biomass production at the expense of phenolic content. In this respect, the application of controlled stress (eustress) on microgreens growing on peat moss warrants investigation as a means of enhancing phytochemical composition without substantial compromise in crop performance and production turnover. Finally, nitrate deprivation practices should be considered for microgreens grown on natural fiber substrates in order to minimize consumer exposure to nitrate.

Physical and chemical conditions for longterm functioning of restorations with zirconium-based framework: literature review

The aim of the study is to determine the optimal physico-chemical conditions and factors for the long-term perspective of zirconia-based restorations. Materials and methods Information was searched in English without time limits in the PubMed electronic database, a Google search and literature lists of relevant studies and reviews. Full-text articles from 2003 to 2018 were selected, in which studies of frameworks made of zirconium dioxide, a protocol for changing firing temperatures, and a description of the structure are described. Results. Totally 79 articles were identified. After the selection of articles on the inclusion criteria and removal of duplicate articles, the total number was 5. The review of the literature included studies of 3 types of zirconium: 3Y-TZP, ATZ, 12Ce-TZP. In a number of studies, the authors studied experimentally the influence of the oral environment on the long-term functioning of zirconium, and a number of authors conducted a study on the effect of heating and cooling gradients, as well as mechanical processing of zirconium frameworks. Conclusion. This literature review has shown the optimal physicochemical conditions and factors for the long-term prospects for restorations with a zirconia-based framework, starting from its composition, technical and laboratory stages, and pumping over the oral cavity factors. The combination of these factors can reduce the effect of the transition of zirconium dioxide from the tetragonal to the monoclinic phase, as well as reduce the stress outcomes resulting from the processing of zirconia frameworks and their facing layer.

Integrated Processing Technology for Calcium-Bearing Alumosilicate Raw Material

The undertaken research is aimed to reveal optimal physicochemical conditions for deep conversion of calcium-bearing alumosilicate raw material. An innovative technology of integrated extraction of nano-dispersion amorphous silica, alumina, calcium fluoride and other useful elements has been developed.

Enolase from Trypanosoma cruzi is inhibited by its interaction with metallocarboxypeptidase-1 and a putative acireductone dioxygenase

Purification of enolase (ENO) from the cytosol of Trypanosoma cruzi indicated that it may interact with at least five other proteins. Two of them were identified as metallocarboxypeptidase-1 (TcMCP-1) and a putative acireductone dioxygenase (ARDp). Subcellular localization studies confirmed the presence of ARDp in the cytosol, as is the case for ENO and TcMCP-1. Analysis of the ARDp sequence showed that this protein has two domains, an N-terminal ARD and a C-terminal TRP14 (thioredoxin-related protein) domain. The interactions between ENO, TcMCP-1 and ARDp were confirmed for the natural proteins from the trypanosome (using size-exclusion chromatography and co-immunoprecipitation from a cytosolic fraction) and recombinant forms (using ELISA ligand-binding assay and ENO activity assays). The ELISA ligand-binding assays permitted to verify the optimal physicochemical conditions for the interactions (representative for the physiological conditions) and to determine the affinity constants (Kd): ENO/ARDp: 9.54 ± 0.82 nM, ARDp/ENO 10.05 ± 1.11 nM, and ENO/TcMCP-1: 5.66 ± 0.61 nM. The data also show that the interaction between TcMCP-1 and ARDp is mediated by ENO acting as a “bridge”. Furthermore, considerable inhibition of the ENO activity, up to 85%, is observed when the enzyme interacts with TcMCP-1 and ARDp simultaneously. All these data confirm that the interaction between ENO, TcMCP-1 and ARDp, occurring in T. cruzi's cytosol, modulates the ENO activity and suggest a possible physiological mechanism for regulation of the ENO activity by the protein-protein interaction.

Mustard oil cake as an inexpensive support for production of chitin deacetylase by Penicillium oxalicum SAEM-51 under solid-state fermentation

Abstract Response surface methodology was employed to optimize the cultivation conditions of Penicillium oxalicum SAE M -51 for the enhancement of chitin deacetylase (CDA) production under solid-state fermentation. The enzyme catalyzes deacetylation of N -acetyl glucosamine subunits of chitin resulted in the production of chitosan, widely utilized biopolymer for drug delivery, waste water treatment and as nutraceutics. Among different agro-horticultural substrates evaluated, mustard oil cake had resulted into maximal CDA production. Entrapment of fungal mycelia onto the solid support was studied using scanning electron microscopy. Optimal physico-chemical conditions for maximal CDA production were found to be 4.906 g, 73.62% and 8.578% for substrate amount, moisture content and inoculum size, respectively. The experimental CDA production (1162.03±7.2 U gds −1 ) under optimized condition was observed in close agreement with the values predicted by the quadratic model (1137.85 U gds −1 ). The CDA production by P. oxalicum SAE M -51 was increased significantly by 1.3 fold, as compared to the un-optimized ones (877.56±8.9 U gds −1 ).

Captive Breeding and Hatchery Production of Mouth Brooding Jewel Cardinal Perch, Pterapogon Kauderni, (Koumanns, 1933) Using Brackish Water: The Role of Live Prey and Green Water Enrichment in Juvenile Production

An attempt was made to study the captive breeding and larval rearing of the Cardinal fish Pterapogon kauderni using brackish water for the first time in India. P. kauderni, a mouth brooder fish was procured from the traders at the size range of 4-6 cm and acclimatized under captive conditions. Suitable water quality parameters were maintained and standardized. The fish was fed with boiled clam meat, octopus, oyster, squid and trash fish thrice a day. Spawning took place after two months of rearing, in between 10:45-13:00 hrs and hatch out occurred after the sunset. Incubation was in the male’s mouth, which was extended up to 21-23 days and after hatch out, juveniles were separated from the parental tank. The tanks were maintained with optimal physico-chemical conditions as in the parent tanks. Different light intensities and diets were provided for the successful of juveniles rearing. Good survival (58%) was achieved by adopting the photoperiod 24L/0D. the results illustrated that the photoperiod and different diets given to the juveniles influences the physiological performance of the juveniles. SGR, FCR and AGR of juveniles of P. kauderni increased significantly with the increase of the photoperiod (P<0.05). Babies looked like their parents at birth and within a week, they obtained parental coloration. Comparatively higher growth rate was observed, when they were fed with algal enriched artemia than the Poly Unsaturated Fatty Acid (PUFA). Babies reached the marketable size within 45 days. This study deliberately reveals that, breeding and rearing of the marine fish P. kauderni using the estuarine water and also reveals the physiological response of juveniles of P. kauderni to the change of photoperiod and substantiated that photoperiod and different diets influences the juvenile growth, survival and feeding.

Bark, a suitable biosorbent for the removal of uranium from wastewater – From laboratory to industry

This paper shows that natural materials such as barks can successfully replace synthetic resins for industrial purposes. Evaluated in batch conditions, biosorption of uranium on suitably prepared Douglas fir barks took place in less than 10 min and appeared to be optimum at pH>4. The biosorption process of uranium (uranyl form UO) was characterized in the optimal physico-chemical conditions and could be mathematically modeled as a Langmuir isotherm. With a maximum uranium specific uptake q max value of 1.16 meq.g-1 (138 mgU.g-1 ) it was found that the sorption capability of Douglas fir barks was at least five times higher for uranium than for other heavy metals such as lead. Adsorption of uranium contained in water leached from a former uranium mine was then monitored over a one-month period in a laboratory-scale chromatography column. The fixation capacity remained fairly constant throughout the whole testing period. Water radioactivity decreased from 1500 mBq.L-1 (0.12 mgU.L-1 ) to (0.4 μ gU.L-1 ) at the column exit. This technology was successfully transferred and tested through a pilot project under industrial conditions with the support of AREVA NC.

Biochemical characterisation of the esterase activities of wine lactic acid bacteria

Esters are an important group of volatile compounds that can contribute to wine flavour. Wine lactic acid bacteria (LAB) have been shown to produce esterases capable of hydrolysing ester substrates. This study aims to characterise the esterase activities of nine LAB strains under important wine conditions, namely, acidic conditions, low temperature (to 10 degrees C) and in the presence of ethanol (2-18% v/v). Esterase substrate specificity was also examined using seven different ester substrates. The bacteria were generally found to have a broad pH activity range, with the majority of strains showing maximum activity close to pH 6.0. Exceptions included an Oenococcus oeni strain that retained most activity even down to a pH of 4.0. Most strains exhibited highest activity across the range 30-40 degrees C. Increasing ethanol concentration stimulated activity in some of the strains. In particular, O. oeni showed an increase in activity up to a maximum ethanol concentration of around 16%. Generally, strains were found to have greater activity towards short-chained esters (C2-C8) compared to long-chained esters (C10-C18). Even though the optimal physicochemical conditions for enzyme activity differed from those found in wine, these findings are of potential importance to oenology because significant activities remained under wine-like conditions.

Optimization of photocatalytic oxidation of 2,2′,3,3′-tetrachlorobiphenyl

Polychlorinated biphenyls (PCBs) are wide spread environmental pollutants. This research focused the optimum physico-chemical conditions under which photocatalytic oxidation (PCO) can be used to degrade 2,2′,3,3′-tetrachlorobiphenyl (tetra-CB). Among the optimal physico-chemical conditions studied were UV intensity, hydrogen peroxide (H 2O 2) and titanium dioxide (TiO 2) concentrations, initial pH, and possible reaction intermediates were also determined. The results indicate that the optimal physico-chemical conditions necessary for the degradation of tetra-CB by PCO were UV intensity at 3.16 mW/cm 2, 30 mM of H 2O 2 and 100 mg/l of TiO 2. In contrast to the results of PCO studies on other organic compounds, the optimum pH for PCO degradation of tetra-CB was 5.5. The removal efficiency was also higher under acidic conditions than alkaline conditions. Although degradation intermediates such as 1,3-bis(1,1-dimethylethyl)benzene, 2,4-bis(1,1-dimethylethyl)phenol, and 3,5-di- tert-butyl-4-hydroxybenzaldehyde were identified at an early stage in the reaction process, they were not completely degraded even after 7 h of PCO reaction.

Studies of synergism for lowering dynamic interfacial tension in sodium α-( n-alkyl) naphthalene sulfonate/alkali/acidic oil systems

Alkylnaphthalene sulfonates with high purity were selected as model components to research synergism for lowering interfacial tension (IFT) in surfactant/alkali/acidic oil systems. The dynamic IFTs between alkylnaphthalene sulfonates with different alkyl chain length and n-decane, oleic acid model oil, or Shengli crude oil were measured. The results showed that the alkylnaphthalene sulfonates with different alkyl chain lengths had different synergism with different acidic components and their ionized acids under the same conditions. The synergism for lowering dynamic IFT in alkylnaphthalene sulfonate/alkali/acidic oil systems was controlled by alkylnaphthalene sulfonate concentration, alkyl chain length, alkali concentration, alkali type, and oleic acid concentration: optimal physicochemical conditions were necessary to the best synergism. This indicates that the synergism among added surfactant acidic components in crude oil and their ionized acids is controlled by the ratio of their interfacial concentrations.

The uranium ore from Mina Fe (Salamanca, Spain) as a natural analogue of processes in a spent fuel repository

In the frame of the ENRESA natural analogue programme, the uranium ore from the “Mina Fe” (Salamanca, Spain) has been studied as a natural analogue of radioactive spent fuel behaviour. This uranium mine is hosted in highly fractured schistose rocks, a geological setting that has not been envisaged in the Spanish options for radioactive waste burial. However, some analogies with the processes that might be involved in the evolution of these geological repositories suggested this investigation. The pitchblende–pyrite–carbonate paragenesis has been studied “in situ” as natural analogue of the nuclear spent fuel behaviour under extremely oxidative dissolution conditions. Similarly, secondary Fe oxyhydroxides and clay minerals have also been considered as relevant analogue materials for the retention of uranium and other analogous trace metals. A multidisciplinary characterisation of the site has been performed in order to study these processes. Though the intense mining activities in the site hindered precise determination of the original hydrogeological and hydrochemical features of the investigated zone (Boa fault zone), the mineralogy and geochemistry of fracture fillings, mineralisation and associated clayey materials have allowed the geochemical evolution of the system to be established. Three geochemical zones have been clearly differentiated: (i) the oxidised zone, from the surface to approximately 20 m depth, (ii) the redox transition zone, from 20 to 50 m depth, and (iii) the reduced zone, located below the transition zone. The oxidised zone is characterised by the presence of the typical mineral association resulting from the strong acid conditions caused by the total oxidation of pyrite and other sulphides. The total oxidation, dissolution and leaching of U(IV), as uranyl–sulphate aqueous complexes, prevailed in this oxidised zone. The redox transition zone is characterised by the coexistence of the primary uranium paragenesis, oxidised minerals, as well as numerous secondary solid phases as a result of the physico-chemical changes in the environment. The optimal physico-chemical conditions for the coffinitisation of pitchblende and the co-precipitation of Fe(III)–U(VI) took place in this zone. In the reduced zone, where the primary uranium paragenesis is present, we currently find the necessary physico-chemical conditions to stabilise pitchblende, pyrite and carbonates. The physico-chemical conditions of the oxidised zone are not relevant to disposal conditions. In the transition zone, two main geochemical processes take place: (i) the coffinitisation of pitchblende, which may be an important process for the stability of spent fuel in reducing conditions, and (ii) the co-precipitation of the Fe(III) and U(VI) as oxyhydroxides, another relevant mechanism for the retention of uranium. The physico-chemical conditions that prevail below 50 m depth should be sufficient to stabilise a spent nuclear fuel repository, in the same way as they have been able to preserve the 34-Ma-old uranium deposit of the Mina Fe.

HEAVY METAL ADSORPTION BY CRUDE CONIFEROUS BARKS: A MODELLING STUDY

ABSTRACT Equilibria and mechanisms involved in the adsorption process of metal ions (Cr3+, Cu2+, Ni2+, Pb2+ and Zn2+) from aqueous solutions using coniferous barks as biosorbent substrate were investigated. Crude barks were used in this study since previous experiments showed a decreasing uptake for chemically treated barks in the considered granulometry. In our experimental conditions, the maximum binding capacity of barks followed the decreasing order Cr3+>Cu2+>Pb2+>Ni2+>Zn2+ whereas their general binding affinity decreased as: Pb2+>Cr3+> Ni2+>Zn2+>Cu2+. Adsorption isotherms at the optimal physico-chemical conditions were established and the adsorption phenomenon was described by the non-competitive Langmuir adsorption model which fitted well the experimental data. An evaluation of adsorption capability was carried out using model parameters which were graphically determined. Models for removal of cations have been discussed; they represent efficient tools for predicting the behaviour of the biosorbents in metal ion adsorption systems.