Medium Ca2 Research Articles

A novel strontium(II)-modified calcium phosphate bone cement stimulates human-bone-marrow-derived mesenchymal stem cell proliferation and osteogenic differentiation in vitro

In the present study, the in vitro effects of novel strontium-modified calcium phosphate bone cements (SrCPCs), prepared using two different approaches on human-bone-marrow-derived mesenchymal stem cells (hMSCs), were evaluated. Strontium ions, known to stimulate bone formation and therefore already used in systemic osteoporosis therapy, were incorporated into a hydroxyapatite-forming calcium phosphate bone cement via two simple approaches: incorporation of strontium carbonate crystals and substitution of Ca2+ by Sr2+ ions during cement setting. All modified cements released 0.03–0.07mM Sr2+ under in vitro conditions, concentrations that were shown not to impair the proliferation or osteogenic differentiation of hMSCs. Furthermore, strontium modification led to a reduced medium acidification and Ca2+ depletion in comparison to the standard calcium phosphate cement. In indirect and direct cell culture experiments with the novel SrCPCs significantly enhanced cell proliferation and differentiation were observed. In conclusion, the SrCPCs described here could be beneficial for the local treatment of defects, especially in the osteoporotic bone.

A Role for the Excess Ryanodine Receptors in Excitation‐Contraction Coupling

A close interaction between the plasma membrane bound DHPR (dihydropyridine receptor, the sensor of electrical changes in the membrane) and the endoplasmic reticulum bound RyR (ryanodine receptor, the Ca2+ release channel to the cytosol) is central to excitation‐contraction coupled Ca2+ release (ECC) by skeletal muscle. We hypothesized that the 2:1 ratio of RyR:DHPR may reflect relative movement of DHPR and RyR accompanied by bursts of Ca2+ release. We tested the hypothesis by measuring the sensitivity of the RyR and DHPR to modulators of these proteins. The response of RyR (measured as Ca2+ appearance in the cytosol) to its namesake modulator ryanodine (Ry) was shifted to lower concentrations of Ry when cells were subjected to field depolarization. In a similar way, Ca2+ release in response to the DHPR activator BayK was also shifted to lower concentrations of BayK when cells were depolarized. However, sensitivity of Ca2+ release to these agents was not altered when either the direct RyR activator CMC (a caffeine‐like agent) or increased medium Ca2+ was applied. While some studies have suggested that RyR may not be essential in ECC, this was based on very high concentrations of Ry (above 100 μM). Yet, we found that cells incubated with Ry at 10 μM completely blocked ECC. Ry at concentrations greater than 50 μM compromised cell viability. Our findings support an interaction model of DHPR and RyR in ECC, a role for the excess number of RyR over DHPR, and indicate Ca2+ release for ECC is exclusively through the RyR.

Differentiation of Human Embryonic Stem Cells into Clinically Amenable Keratinocytes in an Autogenic Environment

Human embryonic stem cells (hESCs)-derived keratinocytes hold great clinical and research potential. However, the current techniques are hampered by the use of xenogenic components that limits their clinical application. Here we demonstrated an efficient differentiation of H9 hESCs (H9-hESCs) into keratinocytes (H9-Kert) with the minimum use of animal-derived materials. For differentiation, we established two microenvironment systems originated from H9-hESCs (autogenic microenvironment). These autogenic microenvironment systems consist of an autogenic coculture system (ACC) and an autogenic feeder-free system (AFF). In addition, we showed a stage-specific effect of Activin in promoting keratinocyte differentiation from H9-hESCs while repressing the expression of early neural markers in the ACC system. Furthermore, we also explained the effect of Activin in construction of the AFF system made up of extracellular matrix similar to basement membrane extracted from H9-hESC-derived fibroblasts. H9-Kert differentiated in both systems expressed keratinocyte markers at mRNA and protein levels. H9-Kert were also able to undergo terminal differentiation in high Ca(2+) medium. These findings support the transition toward the establishment of an animal-free microenvironment for successful differentiation of hESCs into keratinocytes for potential clinical application.

The effects of in vitro supplementation of capacitation medium with ascorbic acid on kinetic parameters of caprine epididymal sperm

The production of reactive oxygen species in seminal plasma is a normal physiological process which plays a critical role in inducing sperm capacitation or acrosome reaction. However, over generations of ROSs are known to disturb sperm’s movement, membrane and DNA integrity. Ascorbic acid (vitamin C) as a potent antioxidant is able to block lipid peroxidation and scavenge free radicals. Therefore, the aim of this study was to evaluate in vitro supplementation of a capacitation medium with ascorbic acid on motility and kinetic characteristics of caprine epididymal spermatozoa. Epididymal spermatozoa were obtained from 30 adult and apparently healthy goat testes in six replicates and incubated in the capacitation medium (Ca2+-free Tyrode’s medium, Sperm-TALP) supplemented with 0 (control group) and 50 μg/mL ascorbic acid (vitamin C group). Motion parameters were assessed using a computer-assisted sperm analysis system at 10, 30, 60, 120 and 240 min after sperm incubation at 37 °C and 6 % CO2. Exposure of spermatozoa to ascorbic acid caused a significant increase (p < 0.05) in total and progressive sperm motility, curvilinear and straightline velocity and the percentage of linearity compared with the control group from 30 up to 60 min. Despite of the primary reduction in the mean angular displacement (MAD, p < 0.05) and amplitude of lateral head displacement (ALH, p < 0.05), a significant increase was observed for MAD and ALH at 30 min after incubation. Vitamin C group showed the highest level of beat cross frequency at 120 min in which there was no significant difference to the control group. According to the results obtained, ascorbic acid supplementation increases sperm motility and improves sperm kinetic parameters of caprine epididymal sperm.

Effects of the presence of Fe(0) on the sorption of lanthanum and lutetium mixtures in smectites

The sorption of La and Lu mixtures was examined in two bentonites after incubation for three months at 20 and 80°C with Fe(0), as a laboratory approach to evaluate the effects of waste canister corrosion in a deep repository on the performance of clay engineered barriers. The sorption/desorption parameters were determined from batch tests in two ionic media: deionized water and, to consider the additional effect of cement leachates, 0.02molL−1 Ca.Results from XRD analyses showed the formation of crystalline FeO(OH), goethite, in a few samples and the degradation of the bentonites due to Fe(0) oxidation during incubation. Moreover, the EDX spectra showed that the lanthanides were sorbed primarily at smectite sites, although sorption onto goethite was also observed, whereas Fe(0) particles did not contribute to lanthanide sorption. The formation of goethite could explain the high Kd values measured in a few scenarios (e.g., those with single solutions or mixtures with the lowest initial concentration of the competitive lanthanide in which high affinity sites governed sorption), with up to 3-fold increases over the values obtained without Fe incubation. However, at higher lanthanide concentration, Kd values decreased or remained constant compared to the samples without Fe incubation, which could be explained by bentonite degradation. In the Ca medium, as much as 5 times lower Kd values were obtained, because of the competitive effect of the Ca ions, especially for Lu in the MX80 bentonite. This indicated that the small number of high affinity sites had been diminished.The sorption data were satisfactorily fitted to a two-solute Langmuir model. In addition, Kd values correlated well with desorption data, which showed that the larger the decrease in Kd, the larger the increase in sorption reversibility. It is suggested that corrosion products from the metal canister might compromise the long-term radionuclide retention of the clay-engineered barriers.

Infection with Mycobacterium avium subsp. paratuberculosis Results in Rapid Interleukin-1β Release and Macrophage Transepithelial Migration

Pathogen processing by the intestinal epithelium involves a dynamic innate immune response initiated by pathogen-epithelial cell cross talk. Interactions between epithelium and Mycobacterium avium subsp. paratuberculosis have not been intensively studied, and it is currently unknown how the bacterium-epithelial cell cross talk contributes to the course of infection. We hypothesized that M. avium subsp. paratuberculosis harnesses host responses to recruit macrophages to the site of infection to ensure its survival and dissemination. We investigated macrophage recruitment in response to M. avium subsp. paratuberculosis using a MAC-T bovine macrophage coculture system. We show that M. avium subsp. paratuberculosis infection led to phagosome acidification within bovine epithelial (MAC-T) cells as early as 10 min, which resulted in upregulation of interleukin-1β (IL-1β) at transcript and protein levels. Within 10 min of infection, macrophages were recruited to the apical side of MAC-T cells. Inhibition of phagosome acidification or IL-1β abrogated this response, while MCP-1/CCL-2 blocking had no effect. IL-1β processing was dependent upon Ca(2+) uptake from the extracellular medium and intracellular Ca(2+) oscillations, as determined by EGTA and BAPTA-AM [1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethyl ester)] treatments. Thus, M. avium subsp. paratuberculosis is an opportunist that takes advantage of extracellular Ca(2+)-dependent phagosome acidification and IL-1β processing in order to efficiently transverse the epithelium and enter its niche--the macrophage.

Caprine cauda epididymal sperm motility pattern in the capacitation medium supplemented with leptin

Leptin is an adipocyte-derived hormone with a role in the reproductive system through metabolic signals. Studies have suggested that binding of leptin to its receptors which have been found in human and boar sperm activates biochemical pathways leading to sperm capacitation. The present study was designed to explore the effects of leptin on sperm kinetic pattern during capacitation in vitro. Epididymal spermatozoa were obtained from 30 adult goat testes in six replicates and incubated in capacitation medium (Ca2+-free Tyrode’s medium, Sperm-TALP) supplemented with 0 (Con, control group), 10 and 100 ng/mL (L10 and L100 groups, respectively). Motion parameters were assessed using computer-assisted sperm analysis system at 10, 30, 60, 120 and 240 min after sperm incubation at 37°C and 6 % CO2. Exposure of spermatozoa to two different doses of leptin caused a significant increase (p < 0.05) in total and progressive sperm motility, curvilinear and straight line velocity, linearity (Lin), mean angular displacement, amplitude of lateral head displacement (ALH) and beat cross-frequency (BCF) compared to the control group specially up to 60 min. There was not any significant difference between L10 and L100 groups in the evaluated parameters except for the first 10 min that L100 had better result in increasing Lin, ALH and BCF (p < 0.05) and at the time of 240 min in which L10 showed a significant increase in all motion parameters. In conclusion, this study showed that leptin supplementation had significant effects on sperm motility patterns and so could enhance the sperm capacitation process.

Bioactive Ca-, P-, and Si-containing hydrogels based on silicon glycerolates and hydroxyapatite

The dispersive phase and the dispersive medium of the combined Ca-, P-, and Si-containing hydrogels obtained from silicon glycerolates in an excess of glycerol and hydroxyapatite colloid solution have been isolated and investigated by means of a number of physicochemical and physical methods. The formation mechanism and hydrogel framework scheme have been proposed.

Combined effect of ion concentration and functional groups on surface chemistry modulated CaCO3 crystallization

The effects of self-assembled monolayer templates terminated with carboxyl, hydroxyl, amino and methyl groups (–COOH, –OH, –NH2 and –CH3) on CaCO3 crystallization are compared in aqueous solutions of low, medium and high Ca2+ concentrations. On the –COOH surface, only calcite rhombohedra are crystallized in the solutions at three different concentrations, while size, shape and orientation of the formed calcites are distinct in various Ca2+ concentration solutions. In low Ca2+ concentration solution, vaterites (111) and (200) are formed on –OH and –NH2 surfaces respectively while no crystals are observed on –CH3 surface. In high Ca2+ concentration solution, calcite (104) is formed on the –OH surface. Calcites and small amounts of vaterites and aragonites are formed on –NH2 and –CH3 surfaces. In medium concentration solutions, the results are similar to the case of high concentration with a lower density of crystals. From the view of the two well-known mechanisms for biomineralization, ion absorption and particle-based crystallization, the results in our study are discussed. Our findings can advance the understanding of CaCO3 biomineralization in nature and also supply guidance for the design of advanced biomaterials.

Effect of calcium ion on the thermal denaturation of subfragment-1 and rod regions of squid myosin upon the heating of myofibrils

Thermal inactivation of Ca2+ ATPase of squid myofibrils was significantly suppressed in the presence of Ca2+. Monomeric myosin content decreased much faster than Ca2+ ATPase inactivation in Ca medium, which was well explained by fast rod denaturation. In contrast, rod denaturation was slower than S-1 in EDTA medium. The decrease in monomeric myosin content was explained by faster S-1 denaturation. Comparing the S-1 and rod denaturation rates at a fixed temperature, it was concluded that S-1 denaturation was suppressed by Ca2+ whereas the rod denaturation was not. An unfolding experiment with isolated myosin rod confirmed that there was no stabilizing effect of Ca2+ on myosin rod. It was concluded that significant stabilization of the S-1 portion by Ca2+ generated the apparently different myosin denaturation patterns in the two media.

Calcium Dependencies of Regulated Exocytosis in Different Endocrine Cells

Exocytotic machinery in neuronal and endocrine tissues is sensitive to changes in intracellular Ca(2+) concentration. Endocrine cell models, that are most frequently used to study the mechanisms of regulated exocytosis, are pancreatic beta cells, adrenal chromaffin cells and pituitary cells. To reliably study the Ca(2+) sensitivity in endocrine cells, accurate and fast determination of Ca(2+) dependence in each tested cell is required. With slow photo-release it is possible to induce ramp-like increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) that leads to a robust exocytotic activity. Slow increases in the [Ca(2+)](i) revealed exocytotic phases with different Ca(2+) sensitivities that have been largely masked in step-like flash photo-release experiments. Strikingly, in the cells of the three described model endocrine tissues (beta, chromaffin and melanotroph cells), distinct Ca(2+) sensitivity 'classes' of secretory vesicles have been observed: a highly Ca(2+)-sensitive, a medium Ca(2+)-sensitive and a low Ca(2+)-sensitive kinetic phase of secretory vesicle exocytosis. We discuss that a physiological modulation of a cellular activity, e.g. by activating cAMP/PKA transduction pathway, can switch the secretory vesicles between Ca(2+) sensitivity classes. This significantly alters late steps in the secretory release of hormones even without utilization of an additional Ca(2+) sensor protein.

Physiological and molecular responses of two Arabidopsis accessions to calcium amendment and salt constraint

The Arabidopsis thaliana NOK2 accession displays salt tolerance compared to more commonly known A. thaliana accessions, such as Col-0, but the basis of this phenotypic feature is unknown. This work was focused on determining whether salt tolerance in NOK2 plants is affected by calcium supplementation to the growth medium. A. thaliana seedlings were grown in pots containing a mixture of sand and peat under controlled conditions in a low-level Ca(NO3)2 medium supplemented with 0 or 50 mM NaCl with and without amendment with two higher levels of Ca(NO3)2. Calcium amendment was beneficial for salt-treated NOK2 plants, as shown by the increase in dry weight of NOK2 plants with and without NaCl, but had no impact on Col-0 biomass. Sodium accumulation decreased as a function of calcium amendment in NOK2, while Col-0 maintained its high Na levels under these conditions. Leaf K+ content, K+ uptake, and Ca content decreased in NOK2 and Col-0 plants growing in the low-level Ca medium when NaCl was added, but rose in leaves of both accessions with calcium amendment, although K remained low in both accessions in the absence of NaCl. K+/Na+ selectivity increased preferentially in NOK2 with increasing calcium in the presence of NaCl, but when Na was restricted and not under any conditions in Col-0. Preferential effects of calcium were not observed on the transcript accumulation of seven Na+, K+ or Ca2+ transport genes for either of the accessions, except for increased transcription of the CAX4 gene in NOK2 leaves at the highest calcium concentration used (5 mM). Leaf membrane leakage, which increased two-fold higher in Col-0 under salt application compared with the increase in NOK2, declined for both accessions in response to calcium supplementation, and in NOK2 this decline reached no salt levels when Ca2+ amendments were highest. Chlorophyll and carotenoid content dropped two-fold in Col-0 in response to salt, but were unchanged in NOK2 under these conditions. In contrast, leaf anthocyanins, which were normally tenfold higher in Col-0 than in NOK2 in the low-level Ca2+ medium, declined in Col-0 plants as a function of Ca2+ supplementation, but were maintained at low levels in NOK2 leaves regardless of salinity and calcium. In conclusion, NOK2 plants responded positively to calcium supplementation by improving biomass yield during salinity treatment, whereas this amendment only affected Col-0 by reducing its permeability and anthocyanin titre. K+/Na+ selectivity appeared to be an important characteristic of NOK2 response to calcium. The regulation of this response may involve the CAX4 Ca2+/H+ vacuolar transport gene, but does not appear to involve six other common ion transporters.

Natural antioxidants and vascular calcification: a possible benefit

Several studies have demonstrated the impact of vascular calcification on morbidity and mortality both in the general and chronic kidney disease populations. The process of vascular calcification involves complex mechanisms including the overexpression of genes and proteins associated with mineralization and increments of reactive oxygen species (ROS). Taking into account previous findings, we decided to analyze in vitro the likely inhibitory effect of natural antioxidants in the process of vascular calcification. Primary vascular smooth muscle cells (VSMCs) were cultured with either normal medium or normal medium supplemented with calcium and phosphorus (P + Ca) in combination with several antioxidants. Mineralization, intracellular reactive oxygen species levels and the protein expression of Cbfa1/RUNX2 and Mn-superoxide dismutase-2 (SOD-2) were investigated. Curcumin and silybin were the more effective, inhibiting both ROS increase and VSMC mineralization. Curcumin was able to prevent the increase in Cbfa1/RUNX2 expression, but did not modify SOD-2 expression in the VSMCs cultured with the P + Ca medium. These findings support the importance of performing further studies in this field, as some antioxidants might have potential benefits in the management of vascular calcification.

Morphological features and chromosome numbers in cultures of five Cephaleuros species (Trentepohliaceae, Chlorophyta) from Japan

SUMMARYThe morphological features and chromosome numbers were examined in cultures of five species of Cephaleuros; C. aucubae, C. biolophus, C. japonicus, C. microcellularis, and C. virescens, collected from Japan. On agar media of Bold's basal medium and CA medium, radial growth of the algal colonies was vigorous in C. virescens, moderate in C. aucubae, and poor in C. microcellularis, but varied from poor to moderate in isolates of C. biolophus and C. japonicus. Filaments of C. virescens branched at an angle less than 40° and just below the cross walls, while those of the other species branched at an angle greater than 40° without relation to the cross walls. The length of filamentous cells was significantly smaller in C. microcellularis than in the other species. The chromosome number differed with the species: n = 22 in C. aucubae, n = 34 in C. biolophus, n = 18 in C. japonicus, n = 12 in C. microcellularis, and n = 24 in C. virescens. The chromosome number did not vary between isolates from filaments and gametes in C. aucubae and C. biolophus and among those from filaments, gametes, and zoospores in C. japonicus and C. virescens.

Examination of competitive lanthanide sorption onto smectites and its significance in the management of radioactive waste

The competitive effect of La and Lu (analogues of radionuclides appearing in radioactive waste) in the sorption in four smectites was examined. Sorption and desorption distribution coefficients (Kd; Kd,des), and desorption rates (Rdes) were determined from batch tests in two media: deionized water and, to consider the influence of cement leachates, 0.02molL−1 Ca. The competitive effect was lower when high-affinity sites were available, as in the water medium at the lowest range of initial lanthanide concentration, with high Kd for La and for Lu (5–63×104Lkg−1). Lower Kd was measured at higher initial concentrations and in the Ca medium, where Lu showed a stronger competitive effect. This was confirmed by fitting the sorption data to a two-solute Langmuir isotherm. The desorption data indicated that sorption was virtually irreversible for the scenarios with high sorption, with an excellent correlation between Kd and Kd,des (R2 around 0.9 for the two lanthanides). Assuming that radioactive waste is a mixture of radionuclides, and that Ca ions will be provided by the cement leachates, this would reduce the retention capacity of clay engineered barriers.

The synergistic effect of calcium (Ca), alpha‐linolenic acid (ALA) and conjugated‐linoleic acid (CLA) on osteoblastogenesis and adipogenesis

Recent research points into connections between bone and adipose tissue with major players being Ca, ALA and CLA. The aim of this study was to investigate possible synergistic effects among ALA, CLA and Ca on preosteoblastic MC3T3‐E1, preadipocytic MC3T3‐L1 and stromal ST2 cell proliferation. Low or high (0.5 or 2 mM) Ca in media containing individual or mixture of ALA (8.75–50 μM; n‐6/n‐3=4/1) and CLA isomers (20 μM of c9, t11/t10, c12‐CLAs; 80/10, 90/10, 90/5% respectively) were treated for 6 days (triplicate). Cell proliferation was determined by resazurin salt solution, and florescence was measured at 590 nm. ST2 and 3T3‐E1 cell proliferation was higher at 0.5 mM and lower at 2 mM Ca; Reversed was true for 3T3‐L1 cells (p&lt;0.05). At both Ca levels, individual or mixture of ALA and CLA did not affect 3T3‐L1 cells. In ST2 cells, the effect of ALA was lowered by adding CLA (80/10; 90/10) at 0.5 mM Ca, whereas at 2 mM Ca, ALA+CLA (80/10) further enhanced proliferation. In 3T3‐E1 cells, even though ALA significantly increased proliferation at 0.5mM Ca, its effect was markedly lowered by addition of CLA at all combinations/both Ca levels. Overall, providing high Ca may reduce adipogenesis, but enhance osteoblastogenesis. In a proliferative stage, a synergistic effect among Ca, ALA and CLA on bone/fat cell may not be substantial, but is significant in increasing progenitor stromal cell formation. DMI#1673 and FSU‐CRC#119532Grant Funding Source: National Dairy Council

Binding of pemphigus vulgaris IgG to antigens in desmosome core domains excludes immune complexes rather than directly splitting desmosomes

Pemphigus vulgaris (PV) is characterized by autoantibodies against desmoglein (Dsg) 3 or both Dsg1 and Dsg3, i.e. desmosomal adhesion molecules. We examined whether or not PV IgG binding to Dsg3 directly impairs the adhesion of desmosomes. For immunofluorescence microscopy, keratinocytes were first incubated with PV IgG for 30 min in low Ca(2+) medium, in which no desmosomes were formed, and then for 1 h in high Ca(2+) medium to generate desmosomes. For immunoelectron microscopy, after a 30-min incubation with PV IgG in low Ca(2+) medium, cells were incubated with antihuman IgG with 5-nm gold particles for 5 min; after washing, cells were further incubated in high Ca(2+) medium for 1 h. For tracing of PV IgG/Dsg3 immune complexes formed in the desmosomal core domain, cells were first incubated with PV IgG for 5 min to allow PV IgG to bind the desmosomal core domain and were further incubated with PV IgG-free medium for different times. Immunofluorescence microscopy revealed that PV IgG bound in a random-punctate pattern on the cell surface in low Ca(2+) medium was translocated to the cell-cell contacts forming a dotted-linear distribution, suggesting desmosome generation even in the presence of PV IgG. Immunoelectron microscopy revealed that half-desmosome-like structures decorated with gold particles in low Ca(2+) keratinocytes coupled to form desmosomes and gold particles were sandwiched in the desmosomal core domain after Ca(2+) switch, even though their surfaces were covered with PV IgG/antihuman IgG 5-nm gold particles. In the tracing experiments, although PV IgG demonstrated a dotted-linear distribution along the cell-cell contacts colocalized with desmoplakin (DPK) after a 30-min tracing, it disappeared from cell-cell contacts after a 5-h tracing, leaving DPK and desmocollin 3. These results suggest that the PV IgG/Dsg3 immune complexes are excluded from the desmosomal core domain rather than directly splitting the desmosome.

Lanthanide sorption on smectitic clays in presence of cement leachates

Due to their potential retention capacity, clay minerals have been proposed for use in the engineered barriers for the storage of high-level radioactive actinides in deep geological waste repositories. However, there is still a lack of data on the sorption of actinides in clays in conditions simulating those of the repositories. The present article examines the sorption of two lanthanides (actinide analogues) in a set of smectitic clays (FEBEX bentonite, MX80 bentonite, hectorite, saponite, Otay montmorillonite, and Texas montmorillonite). Distribution coefficients ( K d) were determined in two media: water and 0.02 mol L −1 Ca, the latter representing the cement leachates that may modify the chemical composition of the water in contact with the clay. The K d values of the lanthanides used in the experiments (La and Lu) varied greatly (25–50 000 L kg −1) depending on the ionic medium (higher values in water than in the Ca medium), the initial lanthanide concentration (up to three orders of magnitude decrease inversely with lanthanide concentration), and the examined clay (up to one order of magnitude for the same lanthanide and sorption medium). Freundlich and Langmuir isotherms were used to fit sorption data to allow comparison of the sorption parameters among smectites. The model based on the two-site Langmuir isotherms provided the best fit of the sorption data, confirming the existence of sorption sites with different binding energies. The sites with higher sorption affinity were about 6% of the total sorption capacity in the water medium, and up to 17% in the Ca medium, although in this latter site sorption selectivity was lower. The wide range of K d values obtained regarding the factors examined indicated that the retention properties of the clays should also be considered when selecting a suitable clay for engineered barriers.

Reversibility of La and Lu sorption onto smectites: Implications for the design of engineered barriers in deep geological repositories

The sorption reversibility of La and Lu (considered as actinide analogues) onto a set of smectites (bentonite FEBEX; hectorite, HEC; MX80; saponite, SAP; Otay montmorillonite, SCa-3; and Texas montmorillonite, STx-1) was studied to estimate actinide retention by smectites that are candidates for use as engineered barriers in deep geological repositories. The sorption distribution coefficients ( K d) and the reversibility parameters (desorption distribution coefficients ( K d,des), adjusted distribution coefficients ( K d,adj), and desorption rates ( R des)) were determined from batch tests in two ionic media: deionized water and Ca 0.02 mol L −1. The latter simulates possible conditions due to the presence of concrete leachates. The results varied greatly depending on the ionic medium, the lanthanide concentration and the clay structure. The high values of K d,des obtained (up to 1.1 × 10 5 and 9.2 × 10 4 L kg −1 for La and Lu in water, and 2.8 × 10 4 and 4.1 × 10 4 L kg −1 for La and Lu in the Ca medium) indicate the suitability of the tested smectites for lanthanide (and therefore, actinide) retention. Based on all the data, SCa-3, HEC and FEBEX clays are considered the best choices for water environments, whereas in Ca environments the suitable clays depended on the lanthanide considered.

Preparation of α-calcium sulfate hemihydrate from FGD gypsum in K, Mg-containing concentrated CaCl 2 solution under mild conditions

To prepare α-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) byproduct under atmospheric pressure, the dehydration of FGD gypsum in a concentrated Ca and Mg chlorides solution medium at 95 °C was investigated, and the effects of K + ions were focused on. The crystal water content variation, material phases, and morphological characteristics of the dehydration products were examined and compared. The solubilities of α-HH in the mixed salt solutions with different K + ion concentrations were also determined. It was found that with low concentration of K + ions in the mixed salt solution (i.e. 0.001–0.035 M), the dehydration rate was enhanced, while with higher K + ion concentration (i.e. 0.087–0.263 M), this process was retarded. α-HH was the dehydration product when K + ion concentration was at appropriate level, while anhydrite (AH) occurred when K + ion concentration was above 0.173 M. K + ions were assumed to behave as a capping agent to control the morphology of the α-HH, resulting in crystals of lower aspect ratio. FGD gypsum can be successfully transformed into α-HH in concentrated Ca and Mg chloride solution under mild conditions, and K + ions play an important role in the process.