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Marble and limestone have been extensively used as building materials in historical monuments. Environmental, physical, chemical and biological factors contribute to stone deterioration. The rehabilitation of stone damage and the delay of further deterioration is of utmost importance. Inorganic nanoparticles having chemical and crystallographic affinity with building materials is very important for the formation of protective coatings or overlayers. In the present work, we have tested the possibility of treating calcitic materials with suspensions of amorphous calcium carbonate (am-CaCO3, ACC) and amorphous silica (AmSiO2). Pentelic marble (PM) was selected as the test material to validate the efficiency of the nanoparticle suspension treatment towards dissolution in undersaturated solutions and slightly acidic pH (6.50). Suspensions of ACC and AnSiO2 nanoparticles were prepared by spontaneous precipitation from supersaturated solutions and by tetraethyl orthosilicate (TEOS) hydrolysis, respectively. The suspensions were quite stable (nine days for ACC and months for AmSiO2). ACC and Am SiO2 particles were deposited on the surface of powdered PM. The rates of dissolution of PM were measured in solutions undersaturated with respect to calcite at a constant pH of 6.50. For specimens treated with ACC and AmSiO2 suspensions, the measured dissolution rates were significantly lower. The extent of the rate of dissolution reduction was higher for AmSiO2 particles on PM. Moreover, application of the nanoparticles on the substrate during their precipitation was most efficient method.

The lifespan of biological heart valve prostheses available in the market is limited due to structural alterations caused by calcium phosphate deposits formed from blood plasma in contact with the tissues. The objective of this work is to present a comparative methodology for the investigation of the formation of calcium phosphate deposits on bioprosthetic and tissue-engineered scaffolds in vitro and the influence of mechanical forces on tissue mineralization. Based on earlier investigations on biological mineralization at constant supersaturation, a circulatory loop simulating dynamic blood flow and physiological pressure conditions was developed. The system was appropriately adapted to evaluate the calcification potential of decellularized (DCV) and glutaraldehyde-fixed (GAV) porcine aortic valves. Results indicated that DCV calcified at higher, statistically nonsignificant, rates in comparison with GAV. This difference was attributed to the tissue surface modifications and cell debris leftovers from the decellularization process. Morphological analysis of the solids deposited after 20 h by scanning electron microscopy in combination with chemical microanalysis electron-dispersive spectroscopy identified the solid formed as octacalcium phosphate (Ca8(PO4)6H2·5H2O, OCP). OCP crystallites were preferentially deposited in high mechanical stress areas of the test tissues. Moreover, GAV tissues developed a significant transvalvular pressure gradient increase past 36 h with a calcium deposition distribution similar to the one found in explanted prostheses. In conclusion, the presented in vitro circulatory model serves as a valuable prescreening methodology for the investigation of the calcification process of bioprosthetic and tissue-engineered valves under physiological mechanical load.

In the present work, the effect of wettability on CaCO3 precipitation was approached by monitoring crystal formation in microchips of different wettability degree. Solutions of calcium chloride and...

BACKGROUND AND AIM OF THE STUDY Glutaraldehyde (Glut) fixed bioprosthetic valves fail due to progressive dystrophic calcification. Many treatments have been proposed to eliminate calcification but none have been entirely successful. Calcitonin (CT) and sodium bisulfite (BSF) have recently been introduced as independent anticalcification reagents. It is postulated that their combined effect, along with the addition of the detergent Tween 80 and alcohol at 37°C, may efficiently minimize tissue calcification due to aldehyde adduct formation and elimination of lipids. MATERIAL AND METHODS Three groups were created from porcine aortic leaflets: group I (Glut only), group II (Glut with 1% CT, 12.5% BSF, and 1.2% Tween 80 at 37°C), and group III (Glut with 1% CT, 10% BSF, 1.2% Tween 80, and 20% alcohol at 37°C). All tissues were implanted subdermally in three sets of eight (group I), six (group II), and five (group III) Wistar rats. After 4 months, the tissues were retrieved and lyophilized at -40°C at 100 mm Hg. The calcium was measured with a flat atomic absorption technique. RESULTS The preimplantation calcium (Ca) concentration in mg Ca/gram of tissue was 1.79 ± 0.14 in group I, 1.65 ± 0.28 in group II, and 0.72 ± 0.79 in group III (P = ns). After 4 months, the Ca concentration was 277.55 ± 32.52, 103.54 ± 5.39 (P

Background and aim of the study Calcification remains the major role of failure of implantable biomedical material and in particular of bioprosthetic valves. Various treatments have been proposed to mitigate calcification of glutaraldehyde-fixed bioprosthetic valves but none have succeeded in inhibiting or mitigating efficiently the calcification process of the implantable biological tissues. Since the discovery of calcitonin (CT) and its therapeutic role in treating hypercalcemic patients, CT has never been tried as an anticalcification treatment for biomaterials. It is postulated, that tissue calcification may be efficiently minimized by forming adducts with aldehyde groups thus eliminating the places of the biological tissues onto the calcium cations could be deposited. Material and methods Fresh porcine aortic leaflets were cut radially in three parts. Three groups of tissue were created. Group I (glutaraldehyde only), Group II (glutaraldehyde with 1% CT) and Group III (glutaraldehyde with 10% CT). All tissues were then implanted subdermally in three sets of 8 (Group I) and 9 (Group II and Group III) male Wistar rats of 12 days old. 21 days later the rats were euthanized by inhalation of CO2. The tissues were retrieved and after rinsing with distilled water 3 times, were lyophilized at −40 °C at high vacuum pressure of approximately 100 mmHg for 16 h. The calcium content was then measured with flat atomic absorption technique. Results The preimplantation values of Ca concentration as expressed in mg Ca/g of tissue were 1.79 ± 0.14 in Group I, 4.78 ± 0.0079 in Group II and 2.88 ± 0.17 in Group III (p = ns). 21 days later the values of Ca concentration were 126.95 ± 12.97 for Group I, 24.69 ± 2.71 for Group II (p Conclusion An anticalcification treatment based on calcitonin as an additive to buffered glutaraldehyde, mitigates the calcification process of the implantable biological tissues, as compared to glutaraldehyde treatment only.

Cardiovascular diseases are the first cause of death worldwide. Among different heart malfunctions, heart valve failure due to calcification is still a challenging problem. While drug-dependent treatment for the early stage calcification could slow down its progression, heart valve replacement is inevitable in the late stages. Currently, heart valve replacements involve mainly two types of substitutes: mechanical and biological heart valves. Despite their significant advantages in restoring the cardiac function, both types of valves suffered from serious drawbacks in the long term. On the one hand, the mechanical one showed non-physiological hemodynamics and the need for the chronic anticoagulation therapy. On the other hand, the biological one showed stenosis and/or regurgitation due to calcification. Nowadays, new promising heart valve substitutes have emerged, known as decellularized tissue-engineered heart valves (dTEHV). Decellularized tissues of different types have been widely tested in bioprosthetic and tissue-engineered valves because of their superior biomechanics, biocompatibility, and biomimetic material composition. Such advantages allow successful cell attachment, growth and function leading finally to a living regenerative valvular tissue in vivo. Yet, there are no comprehensive studies that are covering the performance of dTEHV scaffolds in terms of their efficiency for the calcification problem. In this review article, we sought to answer the question of whether decellularized heart valves calcify or not. Also, which factors make them calcify and which ones lower and/or prevent their calcification. In addition, the review discussed the possible mechanisms for dTEHV calcification in comparison to the calcification in the native and bioprosthetic heart valves. For this purpose, we did a retrospective study for all the published work of decellularized heart valves. Only animal and clinical studies were included in this review. Those animal and clinical studies were further subcategorized into 4 categories for each depending on the effect of decellularization on calcification. Due to the complex nature of calcification in heart valves, other in vitro and in silico studies were not included. Finally, we compared the different results and summed up all the solid findings of whether decellularized heart valves calcify or not. Based on our review, the selection of the proper heart valve tissue sources (no immunological provoking residues), decellularization technique (no damaged exposed residues of the decellularized tissues, no remnants of dead cells, no remnants of decellularizing agents) and implantation techniques (avoiding suturing during the surgical implantation) could provide a perfect anticalcification potential even without in vitro cell seeding or additional scaffold treatment.

Phosphorus removal from wastewaters is a great interest to avoid eutrophication of natural waters (i.e. rivers, lakes). Additionally phosphorus recovery is also important due to increasingly limited nutrient resources. Struvite (MgNH4PO4*6H2O) is of current interest as it is considered an alternative way for water remediation and potential use as a renewable fertilizer. Towards environmental sustainability, phosphorus and nitrogen removal and recovery from domestic, industrial, and/ or agricultural inputs, in the form of struvite may be an attractive alternative for the valorization of wastewaters (Mpountas et al., 2017).Direct observations of crystal dissolution and growth process at the nano- level are possible through the use of Atomic Force Microscopy (AFM). A considerable number of studies have investigated mineral dissolution and growth by in-situ AFM imaging in a fluid-cell (Vavouraki et al., 2008; 2010). These direct observations and measurements allow the investigation of possible process mechanisms at the mineral-solution interface. Previous study on AFM imaging indicated struvite micro- to nanocrystal morphology. Hövelmann & Putnis (2016) investigated the interactions of ammonium-phosphate solutions with brucite (Mg(OH)2) cleavage surfaces by AFM suggesting coupled brucite dissolution and struvite precipitation at the mineral-fluid interface. To the best of our knowledge, there are no records of nanoscale observations of dissolution and/ or growth of struvite surfaces. The aim of this study is to perform in situ AFM experiments using freshly cleaved struvite surfaces at flow conditions. Step retreat and/ or etch pit spreading were observed. Dissolution rates of struvite using doubly deionized water at different pH values were determined whereas growth rates at different saturation values and pH using magnesium and ammonium-phosphate bearing solutions were also measured . Raman and SEM analyses were carried out to assess chemical structure and morphology of the obtained struvite crystals before and after AFM experiments.Acknowledgments: The work has been supported by IKY-DAAD (2018-4) and KRHPIS II (Action PERAN). References: Hövelmann & Putnis, 2016. Env. Sci. Technol. 50, 13032−13041; Mpountas et al., 2017. J. Chem. Technol. Biotechnol. 92, 2075–2082; Vavouraki et al., 2008. Chem. Geol. 253, 243–251; Vavouraki et al., 2010. Cryst. Growth Des. 10, 60–69.

Calcification is among the principal causes of biological heart valve substitute failure. Glycosaminoglcans (GAGs) are negatively charged molecules, possessing anticoagulation and anti-inflammatory activity that make them a potential solution against calcification. In the present work, the anticalcification potential of heparin was investigated under constant supersaturation conditions with respect to hydroxyapatite (Ca 5 (PO 4 ) 3 OH; HAP). Heparin concentration in the supersaturated solutions was in the range between 0.25 and 3 ppm, at pH 7.40 and 37 °C. Heparin showed inhibitory activity, which was attributed to adsorption at the active crystal growth centres. Heparin concentration as low as ca. 50 μM, reduced the rate of HAP crystal growth by more than 80%, while further increase (up to 200 μM) failed to completely inhibit the process beyond 90%. Heparin uptake studies at equilibrium conditions and analysis of the kinetics data in the presence of heparin, strongly suggest that the inhibition is due to the adsorption of heparin onto the HAP crystals, which resulted in the poisoning of the active growth sites.

Recalcitrant barium sulfate (BaSO4) scale deposits are commonly encountered in industrial applications. They are hard to remove because of the pH-independence of their solubility. The formation of BaSO4 from supersaturated solutions was studied in two series of experiments: (a) the first series was performed under conditions of high supersaturation to determine the domain of stability of the system and (b) the second at low supersaturations, under conditions in which the supersaturated solutions were stable (seeded growth experiments). From the first series, the stability diagram of the system was determined. Through the second series of precipitation experiments, the effect of two types of triphosphonic acid additives on BaSO4 formation was assessed: the rigid aromatic 1,3,5-benzenetriphosphonic acid (BTP) and the flexible aliphatic amino-tris(methylenephosphonic) acid (AMP). Initially, the pH of the solutions was adjusted at 9.5 so that all phosphonate groups were deprotonated. For both additives, the rate of crystal growth of BaSO4 was inhibited. At low pH (3.60) a decrease of the rate of crystal growth with increasing additive concentrations was found. At pH 9.50 however, an irregular trend was observed showing a relative increase of the rates of crystal growth with increasing inhibitor concentration. These inconsistencies were attributed to changes of the solubility of BaSO4 in the presence of additives. The solubility changes in the presence of each test additive were quantified by measuring the apparent solubility of BaSO4 seed crystals. The measurements showed that the changes were negligible at pH 3.60. Kinetics measurements in the presence of the test additives suggested that their adsorption on the BaSO4 seed crystals was responsible for the inhibition. Modelling the adsorption according to the Freundlich isotherm gave a satisfactory fit of the kinetics data in the presence of BTP and AMP at pH 9.50. The presence of the test additives at both pH values did not affect the morphology of the growing BaSO4 crystals.

BACKGROUND In the present work, a combination of several physicochemical methods has been applied aiming at recovering phosphorus from olive mill wastewater (OMW) in the form of struvite (NH4MgPO4·6H2O, MAP) and at the same time achieving reduction of the chemical oxygen demand (COD) of the wastes. Phosphorus is a valuable raw material used for the production of fertilizers and numerous other products. RESULTS The experiments were conducted in a two-stage process, over a pH range between 5 and 10. The first step consisted of a batch process, in which MgCl2 or MgSO4 were used as coagulants of suspended particles of the OMW. During the second step, a nitrogen source (NH4OH(aq)) was added to the supernatant and solid precipitation took place without delay. The measured COD values of the fluid phase of the OMW was reduced by up to 73% of the initial value, while the final crystalline product consisted of a mixture of struvite and dittmarite (NH4MgPO4·H2O). CONCLUSION Over 90% dissolved phosphorus recovery from OMW samples in the form of struvite was achieved through the application of a two-step process together with a significant reduction of the COD of initial raw wastewaters. © 2017 Society of Chemical Industry

BACKGROUND Phosphorus and nitrogen recovery from municipal and/or industrial wastewater treatment plants in the form of magnesium ammonium phosphate hexahydrate (MgNH4PO4⋅6H2O, MAP, Struvite) is an attractive alternative for the valorization of wastes. Although efforts have been focused in the recovery of nitrogen and phosphorus nutrients from wastewater at alkaline pH, removal of these nutrients in weakly acid pH is still challenging. The advantage of acid pH is that the precipitation of heavy metals in the form of insoluble hydroxides is avoided on the condition that their concentrations are relatively low. RESULTS The metastable zone width of solutions, supersaturated with respect to MAP at pH 6.50 was investigated. The kinetics of MAP formation both in unseeded and in seeded solutions was investigated in batch reactors at constant supersaturation. The rates of crystal growth, of MAP on seed crystals showed a parabolic depenedence on the relative supersaturation. The concentration of the inoculating seed crystals affected the rates of crystal growth. CONCLUSIONS It is possible to crystallize MAP at pH values of 6.50 provided that the supersaturation is sufficient. From the rate dependence on relative supersaturation (parabolic) it was concluded that the crystal growth mechanism was surface diffusion controlled for the integration of the growth units at the active crystal growth sites. Secondary nucleation, depending on the solution supersaturation, was observed within the stable domain of the metastable zone. The morphology of MAP seed crystals remained unchanged, while the mean particle size increased reaching comparable sizes irrespective of the degree of supersaturation.

Calcification is a recurrent problem in patients suffering from heart valve disease and it is the main cause of failure in biological heart valve prostheses. The development of reliable calcification tests that consider both the material properties of the prostheses and the fluid composition is of paramount importance for the effective testing and subsequent selection of new cardiovascular implants. In this article, a fast, reliable, and highly reproducible method for the assessment of the calcification potential of biomaterials was developed. The developed method simulated closely the chemical environment in vivo , where the supersaturation levels of calcium and phosphate remain constant. Seeded hydroxyapatite (HAP) crystal growth experiments were used as the reference system and compared to the mineralization kinetics and extent of frozen untreated bovine and porcine pericardium, and glutaraldehyde-fixed bovine pericardium. Untreated pericardial patches did not calcify in the supersaturated calcium phosphate solutions whereas glutaraldehyde-fixed bovine pericardial patches mineralized at the same conditions. The present work suggested that the loose collagenous serosa side of the pericardium mineralized at lower rates compared to its dense collagenous fibrous side. Concordant with these findings, the mineralization of bioprostheses may also be attributed, to the structural deterioration of collagen-rich tissues, induced by chemical treatment used to control in vivo structural stability and immunomodulation of the implants.

Acinetobacter baumannii is a typically short, almost round, rod-shaped (coccobacillus) Gram-negative bacterium. It can be an opportunistic pathogen in humans, affecting people with compromised immune systems, and it is becoming increasingly important as a hospital-associated (nosocomial) infection. It has also been isolated from environmental soil and water samples. In this work, unlike conventional medical methods like antibiotics, the influence of atmospheric-pressure cold plasma on this bacterium is evaluated by means of a colony count technique and scanning electron microscopy. The plasma used here refers to streamers axially propagating into a helium channel penetrating the atmospheric air. The plasma is probed with high resolution optical emission spectroscopy and copious reactive species are unveiled under low-temperature conditions. Based on the experimental results, post-treatment (delayed) biochemical effects on Acinetobacter baumannii and morphological modifications appear dominant, leading to complete deactivation of this bacterium.

International audience; The crystal growth of aragonite was investigated at pH 7.8, 37 °C and constant solution supersaturation from aragonite-seeded supersaturated solutions. The effect of the presence of orthophosphate ions in the supersaturated solution on the kinetics of crystallization of aragonite was investigated over the range of orthophosphate concentrations of 0.25 μM–1 mM. In the presence of orthophosphate in the range of 0.25 μM–8 μM, the crystal growth rate of aragonite decreased with increasing phosphate concentration. At orthophosphate concentration levels exceeding 2 μM, induction times were measured and were found to increase with orthophosphate concentration. At orthophosphate concentration levels > 8 μM, the crystal growth of aragonite was inhibited, suggesting the blockage of the active growth sites by the adsorption of orthophosphate ions. Adsorption was confirmed by the investigation of orthophosphate uptake on aragonite, which was: i) found to depend on the equilibrium concentration of orthophosphate in aqueous solutions saturated with respect to aragonite; ii) not influenced by the ionic strength of the electrolyte up to 0.15 M NaCl, showing that electrostatic interactions between orthophosphate and CaCO3 did not play a significant role in this concentration range. Adsorption data of orthophosphate on the aragonite crystals gave satisfactory fit to the Langmuir adsorption model and was confirmed by XPS analysis.

The crystal growth of monetite (CaHPO 4 , DCPA), the least stable calcium phosphate has been investigated by the seeded growth method from solutions supersaturated exclusively with respect to this phase alone. The kinetics of crystal growth was measured at constant supersaturation at 37° C, pH 6.0. The measurements of the rates of crystal growth of DCPA showed a second order dependence on the relative supersaturation of the solutions with respect to DCPA, suggesting that the rate determining step is surface diffusion of the growth units to the active growth sites of the crystals. The heterogeneous crystallization of brushite (CaHPO 4 ·2H 2 O, DCPD) on DCPA seed crystals in solutions supersaturated with respect to both DCPD and DCPA showed that DCPD nucleation and growth took place selectively by heterogeneous nucleation on the DCPA seed crystals. The same parabolic dependence of the rates on the relative supersaturation of the solutions with respect to DCPD was found, showing that the mechanism was the same as in the case of growth of DCPA on DCPA seed crystals. Seeding of solutions supersaturated with respect to both DCPA and DCPD at pH 6.0, 37 °C with collagen type II in powdered form, resulted to the formation of an apatitic solid. The morphology of the crystals formed on the collagenous matrix suggested that the identified mineral was probably the result of rapid hydrolysis of metastable calcium phosphatephases. The formation of the mineral phase on collagen took place past long induction time periods inversely proportional to the relative supersaturation with respect to DCPD and showed that the collagen substrate did not stabilize calcium phosphate at the same conditions at which DCPA did.

Purpose To investigate the nature and characteristic features of deposits causing opacification of intraocular lenses (IOLs) based on the examination of clinical findings using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) analysis. Design Retrospective, observational case series. Methods This is a multicenter study of 6 hydrophilic acrylic IOLs (Lentis LS-502-1; Oculentis GmbH, Berlin, Germany) with a hydrophobic surface that were explanted from 5 patients because of opacification. Three patients had an uncomplicated phacoemulsification. One patient underwent combined phacoemulsification and pars plana vitrectomy for retinal detachment and later silicone oil endotamponade owing to redetachment. The last patient had a pars plana vitrectomy and silicone oil instillation combined with phacoemulsification for tractive retinal detachment and diabetic retinopathy. The explanted lenses were submitted to our laboratory and were examined by SEM and EDX in order to identify the morphologic features and the composition of the deposits. Results SEM and EDX analyses confirmed the presence of calcific deposits in the interior of the opacified hydrophilic IOLs, with a pattern showing the formation of lumps on the surface. The lumps were due to subsurface formation of calcium phosphate crystalline deposits. The crystallite clusters seemed to diffuse from the IOL interior to the surface. Conclusions We demonstrated the calcification pattern of the hydrophilic IOL (Lentis LS-502-1) with a hydrophobic surface. Although hydrophilic acrylic lenses have a hydrophobic surface, the development of calcification is a possible threat initiating from the hydrophilic subsurface of the IOLs.

Summarization: Chemical dissolution and salt crystallization are very important factors contributing to the deterioration and damage of the built cultural heritage consisting of marble and limestone. Understanding of the underlying mechanisms of the calcitic materials damage is necessary for the design of efficient strategy for the prevention of deterioration can be done only through the appropriate kinetics measurements. Kinetics of dissolution of calcitic materials and of the growth of salts of interest should be measured, precisely and reproducibly. In the present work, the rates of dissolution of calcitic marbles (>98% calcite) and sandstone were measured at constant undersaturation and were correlated with the respective solution undersaturation. The dissolution kinetics measurements showed that calcitic limestone at pH 8.25 had a lower dissolution rate constant in comparison with the respective value for Pentelic marble, a calcitic material (ca. 98% calcite). The mechanism was surface diffusion controlled at alkaline pH values. In more acid pH values mass transport became more significant. Reduction of the rates of dissolution was achieved by the addition of substances with functional groups, which may interact with the surface of the calcite crystals. Several inorganic ions (including orthophosphates, pyrophosphates, phosphonates, fluoride and sulfate) and one organic environmentally friendly compound, polycarboxymethyl inulin (CMI) (MW 15000) were tested and their effect on the rates of dissolution was discussed. Phosphonates, were found to have a beneficial effect on the control not only of marble dissolution, but also on the crystallization of damaging soluble salts like NaCl and Na2SO4·10H2O (mirabilite). Appearing in: Transdisciplinary Multispectral Modeling and Cooperation for the Preservation of Cultural Heritage. TMM_CH 2018

Heart valve diseases remain common in industrialized countries. Bioprosthetic heart valves, introduced as free of anticoagulation therapy alternatives to mechanical substitutes. Still they suffer from long term failure due to calcification. Different treatment methods introduced to inhibit calcification, have so far been limited in success. Glycosaminoglycans (GAGs) possess properties including high negative charge, anticoagulation and anti-inflammatory activity that make them a potential solution for calcification problem. In this study, heparin hydrogel was prepared and characterized both chemically and mechanically. After that, heparin hydrogel embedded bovine pericardial tissues, fixed with glutaraldehyde, were produced and tested for their mechanical behavior and anticalcifcation potential in vitro using the constant composition model. In the calcification experiments, tissues were divided into three groups: a) Controls without treatment, b) Hydrogel treated tissues and c) Tissues with raw heparin dissolved in the calcification solution. The results showed that embedding of tissue with hydrogel had no stiffening effect on its mechanical behavior. Calcification assessment showed a significant efficacy on inhibition of calcium phosphate deposition of hydrogel treated (second group) in comparison to untreated tissues (control, first group). Calcification inhibition potential was very similar in both the second and raw heparin (third group). Histological data confirmed the obtained results, suggesting that heparin treatment is a promising anticalcification agent.

Sparingly soluble salts precipitation, e.g. calcium carbonate or calcium sulfate, results in pore clogging in rock formations and in the concomitant reduction of the local permeability of oil wells during the oil extraction processes. On the other hand, in situ controlled salt precipitation is desirable in various applications e.g. waterproofing of concrete constructions suffering from leakages, etc. In the present study, calcium carbonate (CaCO3) precipitation in sandbeds was investigated, in the presence of organic solvents simulating the conditions prevalent in oil-well zones. CaCO3 precipitation was investigated from supersaturated solutions prepared by in-situ mixing of NaHCO3 and CaCl2.2H2O solutions before the inlet of sandbeds. The solution resulting from the mixing of the two solutions was supersaturated with respect to all calcium carbonate polymorphs. Three types of experiments were performed depending on the supersaturated solutions: a) aqueous solutions b) aqueous supersaturated solutions in contact with sandbeds pre-saturated with n-dodecane c) aqueous solutions containing monoethylene glycol (MEG). Results showed that oil–water interfaces enhanced the heterogeneity of the supersaturated solutions and accelerated crystal growth of calcium carbonate at the inlet of the sandbed, resulting in early pore clogging and limitation of local permeability. Maximum sandbed consolidation was obtained with the solutions containing MEG.

Although landfilling and disposal into the ocean present still the most common methods used in the sewage sludge management, the share of recycling and reuse based on drying and incineration procedures continuously increases during the last decades. In this paper, an energy-efficient thermal treatment of sewage sludge is proposed, aimed at its use in blended cements. A practical application of the designed treatment is performed for the sewage sludge obtained from the municipal wastewater treatment plant in Patras, Greece. The material characterization shows that the sludge thermally treated at 700 °C has significant amounts of silica, alumina, calcium oxide and iron oxide, while the content of amorphous phase is 41%, which results in a good pozzolanic activity. The mechanical properties of hardened cement pastes prepared using blended Portland cement-thermally treated sewage sludge binders are after the 28-days curing period not satisfactory yet, indicating that a substantial part of the sludge acts still as filler only. This discrepancy between the pozzolanic activity and mechanical tests can be explained by too coarse sludge particles which slow down the pozzolanic reaction. The results of chemical tests show that the safe limit for the practical use of sewage sludge as partial Portland cement replacement is 10%, which is mainly due to the relatively high content of chlorides and alkalis. This limit can though be increased by the removal of soluble salts from the raw sludge using water treatment. The life cycle assessment analysis of the blended cements shows that the decrease in energy consumption is nearly 10% for each 10% of sewage sludge in the blend. The emission of greenhouse gases during the thermal treatment of the sludge is found almost twenty times lower than in the Portland cement production. The cost analysis reveals substantial economical benefits related to the application of sewage sludge as partial cement replacement.

Visualization experiments using one-dimensional (1-D) porous media made of Plexiglas and two-dimensional glass porous networks were conducted to obtain qualitative and quantitative information concerning the precipitation and crystal growth of CaCO3 under varying flow and concentration conditions. Supersaturated solutions were prepared by mixing sodium bicarbonate and calcium chloride solutions before the pore networks. Nucleation and crystal growth were assumed to occur within the porous media. Changes in the initial and final solution composition were monitored. At low initial supersaturation values (SRinitial), a few crystals were observed within the flow channels and crystal growth took place exclusively on the newly formed crystals. As the SRinitial increased, more crystals were formed along the flow channels and new crystallites were continuously formed during the course of the experiments. Nucleation and crystal growth were not uniform. The crystal growth rates depended on the initial value of SR a...

Built heritage consists to a large part of calcitic minerals (marble, limestone) which are prone to dissolution over a wide pH range. Indeed, chemical is solution is among the most significant factors contributing to the deterioration and damage of the built cultural heritage. Carbon dioxide dissolved in atmospheric water contributes to the development of acid conditions on the surface of the calcitic materials which accelerate dissolution of calcite crystals. These effects are enhanced in the case of polluted atmosphere which contributes to more aggressive environment for the dissolution process. The measurement of parameters that determine the kinetics of dissolution is very important for the understanding of dissolution mechanism and hence the design of efficient strategy for the prevention of it. As a result, precise and reproducible methods are necessary for drawing reliable mechanistic information. In the present work, the dissolution kinetics were investigated at conditions of constant driving force for the dissolution process. The methodology used to measure the rates of dissolution of calcitic marbles (>98% calcite) and sandstone was both accurate and highly reproducible. The rates of crystal dissolution measured were correlated with the corresponding solution undersaturation. The dissolution kinetics measurements showed that calcitic limestone at pH 8.25 had a lower dissolution rate constant in comparison with the respective value for Pentelic marble, a calcitic material (ca. 98% calcite). The mechanism was the same, i.e., surface diffusion controlled at alkaline pH values. The prevention of dissolution strategy therefore shall depend either on the alteration of fluid dynamics at the acid pH values or on the modification of the surfaces at the alkaline domain. The latter can be achieved by the addition of substances with functional groups, which may interact with the surface of the calcite crystals. Several inorganic ions (fluoride and sulfate) and one organic environmentally friendly compound, polycarboxymethyl inulin (CMI) (MW 15000), have been tested, and their effect on the rates of dissolution was discussed.

Clays and muds have been used for centuries as cosmetics or pharmaceutical products for various therapies. The suitability of muds and clays for health- and beauty-related applications depends on their physicochemical properties, mineralogical composition, particle characteristics and toxicity. In this work, the physicochemical characterization of 12 mud specimens from different natural spa resorts in Greece and one from Israel (Dead Sea) is presented. All specimens were sterilized at 121 °C for 20 min, because of their intended use. The Greek mud specimens were collected from various locations in Macedonia, Western Greece and Northeast Aegean. All muds were characterized concerning their mineralogical, chemical components as well as their morphological characteristics using appropriate methods [powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), nitrogen absorption specific surface area measurements (BET), scanning electron microscopy and energy dispersive X-ray spectroscopy]. The concentrations of F−, Cl−, NO3− and SO42− anions at equilibrium with the mud specimens were measured by ion chromatography. Total calcium concentration was measured using atomic absorption spectroscopy, and the concentration of total N, C, H and S in the solids was measured using elemental analysis. Moreover, total phenolic concentration (TPC) in distilled water equilibrated with the mud specimens was measured as an index for their antioxidant properties. Several muds were found to present high TPC. Several of the examined mud specimens were found to have the potential use as pharmaceuticals or cosmetics. Based on the physicochemical characteristics of the mud specimens examined, possible improvement in their use and applicability has been suggested.

Chemical, physical, morphological, and mineralogical analysis of sewage sludge originating from a waste water treatment plant in Patras, Greece, is presented in the paper. The sewage sludge is firstly dried at 70°C, then oven-burned at 700°C for two hours and milled. The thermally treated material is analyzed using XRF and XRD, the particle size distribution is determined by a laser diffraction method. A potential use of sewage sludge in blended cements is investigated on the basis of the measurement of mechanical and basic physical properties of pastes containing the sludge in an amount of up to 60% of the mass of cement. Experimental results show that the thermal treatment of pre-dried sewage sludge and its grinding provides a material that can be successfully applied as a partial replacement of Portland cement. At a production of blended cements for high strength concrete, an up to 20% cement replacement level can be recommended.

The formation of inorganic scale deposits of the alkaline earth metals is a persistent problem. Dispersion of solid particles separating out from the fluids is also very important for fouling due to deposition. Scale formation and stabilization of suspensions are often overcome through the use of water soluble polymers. In the present work, a series of polymeric compounds were tested as inhibitors of calcium carbonate and calcium sulfate dihydrate (gypsum) precipitation and as dispersion agents of hematite (Fe2O3) suspensions in electrolyte solutions. Acrylic acid (AA) and maleic acid (MA) polymers were found to inhibit the precipitation of calcium carbonate and gypsum from supersaturated solutions to extents exceeding 90% at concentrations as low as 2 ppm. The molecular weight (MW) was an important parameter in determining the activity of the tested inhibitors. Lower MW polymers (ca. 2000) proved to be more efficient than higher MW polymers. A similar trend was exhibited for the dispersion ability of the hematite particles. AA and MA copolymers in which functional groups were introduced (pyrrole, sulfono and amide groups) were efficient precipitation inhibitors and dispersion agents, but the efficiency depended strongly on the co-polymer architecture. Copolymers containing sulfono groups improved inhibitory activity and dispersion ability and showed higher calcium ion tolerance.

Coagulation/flocculation process is considered as a nonexpensive and effective method to reduce organic and inorganic content of industrial wastewaters. In the present study series of polyelectrolytes were tested to optimize the existing procedure with new chemical reagents that resulted in removal percentages up to 93%. Organic load expressed in terms of chemical oxygen demand, particle size distribution, pH, and ζ potential of suspended particles were among the parameters that were investigated for the best coagulation/flocculation of particles suspended in paint industrial wastewaters. The target was to find the optimum concentration values of polyelectrolytes that neutralize the ζ potential and shrink the particle size distribution. The remaining organic compounds were further treated with a combined ultrafiltration/reverse osmosis system that almost eliminated the organic content, and the final permeate stream is suitable for reuse in the premises of the industry.

In the present work, the effect of the presence of strontium ions in supersaturated calcium phosphate solutions on the rates of crystal growth of octacalcium phosphate (Ca 8 H 2 (PO 4 ) 6 ·5H 2 O, OCP) and of hydroxyapatite (Ca 5 (PO 4 ) 3 OH, HAP) was investigated at 37 °C and at constant solution supersaturation. The presence of strontium reduced crystal growth rates of both calcium phosphate phases. The reduction of the OCP crystal growth was ca. 40% for strontium concentration of 1 mM while for HAP was significantly higher, reaching 70% for the same concentration of strontium in the solution. Higher retardation of the rates of HAP crystal growth was achieved at higher supersaturations in the presence of 1 mM strontium concentration. Moreover, strontium ions were shown to stabilize or delay the transformation of the unstable OCP that tends to hydrolyze to the thermodynamically more stable HAP. Strontium ions were incorporated into both OCP and HAP growing on the respective seed crystals.

The crystallization of sodium sulfate decahydrate (Na 2 SO 4 ·10H 2 O, mirabilite) from supersaturated solutions was investigated using stable supersaturated solutions seeded with mirabilite seed crystals. The experiments were done in batch, stirred reactors in which the supersaturated solutions were prepared either by dissolution of sodium sulfate anhydrous at 32 °C followed by cooling to 18 or 20 °C or by mixing equal volumes of equimolar ammonium sulfate and sodium hydroxide solutions at 20 °C. Inoculation of the solutions supersaturated only with respect to mirabilite with seed crystals was accompanied with temperature increase of the thermostated solution. Despite the fact that crystal growth was initiated with seed crystals, the process started past the lapse of induction times inversely proportional to the solution supersaturation. The rates of crystal growth were measured both from the temperature rise and from the concentration–time profiles, which were linearly correlated. The measured crystal growth rates showed a parabolic dependence on supersaturation at low supersaturations. For higher values this dependence changed to linear, a behavior consistent with the BCF spiral crystal growth model. The morphology of the crystals growing at 20 °C showed typical prismatic habit, while at 18 °C when crystallized from cooled sodium sulfate solutions changes in the crystal habit to a leaf like morphology were observed.

A new method for the consolidation of loose sand formations has been developed. The method involves in situ precipitation of a composite calcium phosphate–polyelectrolyte salt that binds together with loose sand grains, thus resulting to their consolidation. Three different polyelectrolytes (PE) were tested, i.e., polyacrylic acid (PAA), polyallylamine hydrochloride (PAH), and polyethylenimine (PEI). The effect of PE tested on the thermodynamics and the kinetics of precipitation of calcium phosphate salts was investigated. Three types of experiments were done. Investigation of the adsorption of PE on either hydroxyapatite (Ca5(PO4)3OH, HAP) crystals or on sand grains. Measurement of the kinetics of heterogeneous nucleation of HAP on the solid substrates and the mechanical properties of the obtained crystals in batch experiments of low and high supersaturation solutions, respectively. Evaluation of the consolidation in sand packs in order to investigate the effectiveness of the method. The crystallization rates, Rp, on HAP crystals in the presence of the PE tested were found in the order R p PAA > R p PEI > R p PAH , while nucleation and crystal growth on silicate sand took place only in the absence of adsorbed PE. PAH favored strongly the consolidation process, whereas PEI and PAA resulted in the formation of poorly consolidated grain agglomerates.

The hierarchically structured glass sponge Caulophacus species uses the first known example of a silica and calcite biocomposite to join the spicules of its skeleton together. In the stalk and body skeleton of this poorly known deep-sea glass sponge siliceous spicules are modified by the addition of conical calcite seeds, which then form the basis for further silica secretion to form a spinose region. Spinose regions on adjacent spicules are then joined by siliceous crosslinks, leading to unusually strong cross-spicule linkages. In addition to the biomaterials implications it is now clear, from this first record of a biomineral other than silica, that the hexactinellid sponges are capable of synthesizing calcite, the ancestral skeletal material. We propose that, while the low concentrations of calcium in deep sea waters drove the evolution of silica skeletons, the brittleness of silica has led to retention of the more resilient calcite in very low concentrations at the skeletal joints.