Το ανθρακικό ασβέστιο είναι ένα άλας που οι ιδιότητές του το κάνουν μοναδικό. Αποτελεί το 20% του στερεού φλοιού της γης και είναι αδιάσπαστα συνδεδεμένο με τη ζωή, την ανάπτυξη του πολιτισμού και την καλλιτεχνική δημιουργία του ανθρώπου. Αν και λόγω των φυσικών ιδιοτήτων του είναι κατάλληλο για πολλές βιομηχανικές χρήσεις είναι επίσης πηγή πολλαπλών και σοβαρών προβλημάτων στη βιομηχανία λόγω του σχηματισμού δυσδιαλήτων αποφρακτικών αλάτων, τα οποία γίνονται περισσότερο ενοχλητικά σε υψηλές θερμοκρασίες εξ αιτίας της αντίστραρης καμπύλης διαλυτότητός του. Στην παρούσα διατριβή χρησιμοποιήθηκε η τεχνική της αναπτύξεως των κρυσταλλικών φύτρων σποράς και η μελέτη της κρυσταλλικής αναπτύξεως των καλά χαρακτηρισμένων κρυσταλλικών φύτρων σποράς ασβεστίτη σε μετασταθή υπέρκορα διαλύματα ανθρακικού ασβεστίου έγινε με τις ακόλουθες μεθόδους: α) τη μέθοδο της διατηρήσεως σταθερού pH και β) τη μέθοδο της σταθερής συστάσεως του διαλύματος. ... / Calcium carbonate is a ubiquitous salt. One—fifth of the earth’s crust is composed of calcium carbonate in one form or another. It is very closely related with the life and civilization of man, because it is encountered almost everywhere. Even though it’s physical properties render it important for industry and finds many uses, it is also the source of considerable concern industrially through the formation of scale, which becomes even more annoying at elevated temperatures due to its reverse solubility curves. Environmentally, calcium carbonate’s dissolution, precipitation and sorptive eapacity plays an important role in the regulation of p1-I and in the transport of various ions to and from the bottom of sea and lakes. Calcium carbonate exhibits polymorphic variation. Thus, three polymorphs are most commonly encountered in nature, in the order of decreasing soluhility they are vaterite, aragonite and calcite. There are also hydrated salts of calcium carbonate such as monohydrate or hydrocalcite and hcxahydrate or ikaite. The tendency of the thermodynamically least soluble phases to transform into the most stable calcite, especially in the presence of foreign ions may stabilize the less stable precursor phases. Although the precipitation of calcium carbonate in aqueous media has attracted the attention of a large number of researchers, the mechanism of precipitation has not yet been fully understood. In the present dissertation has been used the highly reproducible seeded growth technique. Well characterized aged seeds were added to metastable super- saturated solutions of calcium carbonate and the investigation of the precipitation pro- cess took place by two different experimental techniques: a) pH—stat method and b) a plethostatic experimental approach. ..

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- / Calcium salts are known as compounds and minerals and they have been extensively studied due to their rich morphology and applications. They are known as biominerals, cement additives. fillers, food additives etc. In the oil and gas production calcium sulfates, carbonates and silicates form tenaciously adhering scale deposits which may stop production if the problem is not tackled timely. The motivation for this work was the well known problem of sand production during oil recovery, which occurs when the production rate exceeds a critical value. The aim has been an attempt to develop an inexpensive and environmentally friendly method to consolidate soil and sand for building purposes. The work included in this thesis, is focused in the investigation of the physico-chemical conditions at which calcium salts precipitate acting as consolidating material for soil and sand. The marked differences in the physicochernical properties of the precipitating salts enabled us to investigate the relative efficiency of three different classes of calcium salts: sulfates, carbonates and phosphates. As a result. the present thesis is divided in three parts. In the first one, the spontaneous precipitation of calcium sulfate from supersaturated solutions and the inhibition by water soluble polymers was examined. Two kinds of polymers: three polyacrylates (PAA) with different molecular weights (2.000 (PAA1), 50,000 (PAA2) and 240.000 (PAA3)) and one co-polymer of polyacrylic with polystyrene sulfonate (PAA-PSS) were tested. Very low concentrations of all polymers tested, down to 6ppm, increased markedly the induction period preceding precipitation at supersaturations in which, in the absence of additives the precipitation was spontaneous. The “kinetic Langinuir” equation based on the assumption of Langmuir - type adsorption of the additives on the precipitating calcium sulfate dihydrate, gave satisfactory fit of the kinetic data. From the fit according to this model, the affinity constants for the polymer-gypsum surfaces were calculated. The order of the affinity was PSS>PAA3>PAA1>PAA2. The precipitation of calcium sulfate dihydrate in the presence of sand grains, resulted in crystals which formed weak bridges among the grains and the material in which precipitation took pace was rather poorly consolidated. The second part reports on the precipitation of calcium carbonate through the enzymatic production of carbonate ions. This newly proposed method is based upon the slow evolution of the supersaturation with respect to calcium carbonate in an aqueous environment, in which one of the components of the supersaturated solution (in our case carbonate) is slowly released by a source through the action of enzymes present in the aqueous medium. The work done concerning the development of the methodology of enzyme mediated calcium carbonate formation in aqueous media involved the following steps: (i) Investigation of the mechanism of urea (substrate) decomposition in the presence of jack bean urease (enzyme) through conductivity measurements. Urease exhibited a bell- shaped activity profile as a function of temperature with optimum value at 50CC. The reaction of urea decomposition in the presence of urease followed Michaelis-Menten type kinetics up to a concentration of about 250 mM. At concentrations exceeding 250 m.M, the reaction rate decreased as the carbonate source concentration increased, suggesting substrate inhibition. (ii) The effect of various parameters, such as temperature, enzyme and salts concentrations, the presence of sand etc. was studied upon the rate of precipitation and the morphology of the precipitate. The rate of precipitation increased with increasing temperature up to the optimum temperature of the enzyme activity. The experimental conditions identified through a series of batch type experiments were optimized for the consolidation of granular materials. Lab experiments done in loose sand packs have shown that consolidation may be achieved through bridges of calcium carbonate formed enzymatically. The consolidation efficiency was found to be strongly dependent on urease quality. Crude jack bean urease was more effective than refined one, due to impurities which promote calcitic rhombohedra to precipitate. Increasing the number of solution injections resulted in increased strength and reduced permeability, as expected. Resistance to uniaxial strength was found to be inversely proportional with temperature. The highest values were obtained for precipitates formed on sand grains at 25:C. The initial concentration of the supersaturated solutions were also found to affect the degree of consolidation, because of the different precipitation rates (higher at higher supersaturations) and of the amount of the material precipitated on the grains, which again was more, the higher the solution supersaturation with respect to calcium carbonate. Next, the heterogeneous nucleation and growth of calcite was investigated both in unstable and stable solutions at supersaturations sufficiently low to allow for the measurement of induction times preceding the onset of precipitation. In the unstable regions the induction times were inversely proportional and the rates of precipitation increased with the solution supersaturation. The high order dependence of the rates of precipitation on the solution supersaturation suggested a polynucleation mechanism. Fit of the induction time-supersaturation data according to this model yielded a value of 49 mJ/m2 for the surface energy of the calcite nucleus forming. In the stable domain of the supersaturations, seeded growth experiments showed a second order dependence on the rates of crystal growth of calcite seed crystals, while quartz seed crystals failed to induce nucleation. Raising supersaturation to reach the unstable domain showed interesting features: calcite seed crystals yielded crystal growth kinetics compatible with the polynucleation model, without any induction time contrary to the quartz seed crystals that triggered secondary nucleation. The kinetics data in the latter case were consistent with the polynuclear model and the surface energy for the newly forming embryo was calculated equal to 13 mJ/m2, confirming the fact that the process is dominantly heterogeneous. In the third part of this dissertation an attempt is presented to apply the idea of enzymatic precipitation of salts to the case of calcium phosphate formation. For this purpose, two kinds of phosphatases were tested for their PO4/3 release capacity from polyphosphates. Each type of the enzyme functioned at a different pH, so that a wide pH-range was covered (5.50-9.80). A seven-fold increase in the enzyme concentration resulted in the increase of the hydrolytic substrate decomposition percentage from 38% to 82% at pH 5.50. At pH 9.80, increasing the amount of alkaline phosphatase by a factor of five, the percentage of hydrolytic decomposition increased from 800o to 100%. The temperature dependence of the enzymes’ activity allowed for the determination of the maximum rate and the Michelis-Menten constant. At 25oC, Rmax and Kmwere calculated equal to 3.2x104 mol/h and 2.15x l0 mol/l for acid phosphatase, while the values for alkaline phosphatase were 5.9x10 mol/h and 4.26x10-3 mol/l, respectively. The activation energies were calculated to be 31 and 74 kJ/mol for acid and alkaline enzymes respectively. In terms of precipitation, the enzymic hydrolysis method is applicable for concentrations of the substrate and of the cation of the precipitating salt lower than 0.05 mol/l. For higher concentrations, insoluble complexes of Ca-substrate were formed and the precipitation of calcium phosphate was not favored. The presence of sand promoted both precipitation and hydrolysis when acid phosphatase was used, while with alkaline phosphatase the effect of the presence of sand was negligible. Consolidation experiments conducted in loose sand packs indicated that this method may be applicable only to stabilize sand with a few applications of the working solution, since the amount of the precipitate is small for the concentration levels suggested by the results of the present work. For strong consolidation, and for the composition of the solutions suggested in this work, a large number of injections is needed.

Το κίνητρο της παρούσας εργασίας είναι η μελέτη των μηχανισμών καταβύθισης μέσω της in-situ ανάμειξης και καταβύθισης δυσδιάλυτων αλάτων( ανθρακικό ασβέστιο) πάνω στις επιφάνειες αλλά και κατά μήκος των πορώδων υλικών. Οι επικαθίσεις δυσδιάλυτων αλάτων σε πορώδη σχηματισμούς, αποτελεί ένα σημαντικό πρόβλημα σε βιομηχανικές εφαρμογές. Για παράδειγμα, στην παγκόσμια βιομηχανία πετρελαίου και φυσικού αερίου πολλές περιοχές άντλησης πετρελαίου αντιμετωπίζουν τεράστιο πρόβλημα επικαθίσεων αλάτων, με αποτέλεσμα την δραματική μείωση της παραγωγής πετρελαίου. Επιπλέον, προβλήματα εναπόθεσης αλάτων μειώνουν την εκμετάλλευση γεωθερμικής ενέργειας, τη διάρκεια ζωής μεμβρανών αφαλάτωσης, καθώς και την απομόνωση του CO2 σε υπόγεια πηγάδια, κτλ. Οι επικαθίσεις αλάτων σε πηγάδια άντλησης πετρελαίου προέρχονται είτε από απευθείας καταβύθιση των διαλυμένων αλάτων που βρίσκονται στο νερό που υπάρχει σε υπόγειες κοιλότητες και καταβυθίζονται εξαιτίας της διαφοροποίησης των τοπικών συνθηκών(κυρίως πίεσης και θερμοκρασίας), είτε από τις μεγάλες ποσότητες νερού που χρησιμοποιείται για την εκτόπιση του πετρελαίου στα πηγάδια παραγωγής. Ένα από τα σημαντικότερα προβλήματα που αντιμετωπίζουν οι εταιρίες εξόρυξης πετρελαίου είναι οι μειωμένοι ρυθμοί άντλησης λόγω της μείωσης του τοπικού πορώδους και της διαπερατότητας από τη δημιουργία και την ανάπτυξης επικαθίσεων στα πηγάδια εξόρυξης. Οι επικαθίσεις αλάτων μπορούν επιπλέον να φράξουν τις σωληνώσεις ή να σχηματίσουν ένα λεπτό στρώμα στα τοιχώματα των σωληνώσεων που χρησιμοποιούνται στην παραγωγή. Ο σχηματισμός επικαθίσεων έχει σαν αποτέλεσμα την δημιουργία λειτουργικών προβλημάτων και δυσκολιών, που οδηγούν σε επιπλέον κόστος και σε εξαιρετικές περιπτώσεις στην εγκατάλειψη του πηγαδιού άντλησης πετρελαίου. Αρχικά έγινε μελέτη της αυθόρμητης καταβύθισης του ανθρακικού ασβεστίου σε αντιδραστήρες διαλείποντος έργου. Μελετήθηκε επίσης και η επίδραση της ίδιας ποσότητας άμμου σε διαφορετικούς αρχικούς υπερκορεσμούς κατά την αυθόρμητη καταβύθιση του ανθρακικού ασβεστίου. Καθ’ όλη τη διάρκεια των πειραμάτων συλλέγονταν δείγματα από τον αντιδραστήρα και ανιχνευόταν η μείωση της συγκέντρωσης των ιόντων ασβεστίων με τη μέθοδο της ατομικής απορρόφησης. Από τη μείωση της συγκέντρωσης των ιόντων ασβεστίου υπολογίστηκε ο ρυθμός καταβύθισης και στη συνέχεια η φαινόμενη τάξη της αντίδρασης και η σταθερά ταχύτητας. Σε όλα τα πειράματα ανιχνεύτηκε με περίθλαση ακτίνων Χ και ηλεκτρονική μικροσκοπία σάρωσης, ο ασβεστίτης ως η μοναδική καταβυθιζόμενη φάση. Κατά την αυθόρμητη καταβύθιση του ανθρακικού ασβεστίου απουσία άμμου, ο κύριος μηχανισμός καταβύθισης βρέθηκε ότι είναι η επιφανειακή διάχυση των δομικών μονάδων σε κατάλληλες θέσεις στην επιφάνεια των κρυστάλλων, ενώ στα πειράματα παρουσία ποσότητας άμμου οι κρύσταλλοι αναπτύσσονται με βάση το πολυπυρηνικό πρότυπο. Στην παρούσα εργασία μελετάται επίσης η διεργασία καταβύθισης του δυσδιάλυτου άλατος του ανθρακικού ασβεστίου (CaCO3) σε δισδιάστατα πορώδη δοκίμια Plexiglas®. Μέσω της οπτικής παρατήρησης της ανάπτυξης των επικαθίσεων, επιχειρήθηκε η εξαγωγή ποιοτικών και ποσοτικών πληροφοριών που αφορούν τους μηχανισμούς και τον τρόπο με τον οποίο αναπτύσσονται οι κρύσταλλοι ανθρακικού ασβεστίου στα τοιχώματα του προσομοιωτή πορώδους μέσου κάτω από ρεαλιστικές συνθήκες ροής, θερμοκρασίας και συγκέντρωσης. Δύο ευδιάλυτα διαλύματα χλωριούχου ασβεστίου, CaCl2, και όξινου ανθρακικού ασβεστίου, NaHCO3, αναμιγνύονταν λίγο πριν την είσοδό τους στο πορώδες μέσο με τη βοήθεια εμβολοφόρων αντλιών. Η καταβύθιση του ανθρακικού ασβεστίου λάμβανε μέρος μέσα στο πορώδες γραμμικό μέσο. Χρησιμοποιώντας ένα οπτικό μικροσκόπιο σε συνδυασμό με βιντεοκάμερα ήταν δυνατή η παρακολούθηση και η καταγραφή των κρυστάλλων που εμφανίζονταν καθώς και η ανάπτυξη τους κατά μήκος του καναλιού, στις θέσεις 2 cm, 6 cm, 8 cm και 10 cm από την είσοδο του. Σε κάθε θέση μετρήθηκε η μεταβολή του pH και της συγκέντρωσης του ασβεστίου με το χρόνο και επιπλέον καταγράφηκε ο σχηματισμός των κρυστάλλων του ανθρακικού ασβεστίου με τη βοήθεια της κάμερας του μικροσκοπίου. Για τη μέτρηση της συγκέντρωσης των ιόντων ασβεστίων χρησιμοποιήθηκε η φασματοφωτομετρία ατομικής απορρόφησης ενώ ο υπολογισμός του μεγέθους των κρυστάλλων έγινε με τη βοήθεια του προγράμματος Adobe Photoshop CS5.1. Κατά την διάρκεια του πειράματος ο υπερκορεσμός μειωνόταν κατά μήκος του καναλιού, ως αποτέλεσμα της in situ ανάμειξης των διαλυμάτων του χλωριούχου ασβεστίου και ανθρακικού νατρίου. Τέλος, κοντά στην είσοδο του καναλιού ο αριθμός και το μέγεθος των κρυστάλλων που καταβυθιστήκαν ήταν μεγαλύτερο, συγκριτικά με αυτούς που καταβυθιστήκαν κοντά στην έξοδο. / The deposition of sparingly soluble salts in porous formations is a severe problem encountered in industrial applications. For example, in international oil and gas industry many oil fields in operation face the major problem of scale which reduces dramatically oil production. Moreover, scaling problems limit the utilization of geothermal energy, the operational life of desalination membranes, in CO2 sequestration in subsoil wells, etc. Scale deposits encountered in oil fields are formed either by direct precipitation of the dissolved salts present in the formation water and precipitate because of the change of the local conditions (mainly pressure and temperature) or because of the large quantities of the injection water used for the displacement of the oil in the production wells. In the course of scale formation and development at wellbores, both local porosity and permeability may be reduced resulting in lower oil recovery rates. Scale deposits may also block flow by clogging perforations or by forming a thick layer on the wall of the production tubing. The formation of scales may result in a series of operational problems and difficulties, and in turn, result to additional capital cost, substantial operating cost and in extreme cases in the abandonment of the oil wells. The injection water (sea water) used in oil production is a stream most often incompatible with the well formation water. Mixing the incompatible streams interact chemically resulting in the precipitation of minerals. The high concentrations of SO42- in sea water and the low concentrations of Ba2+/Sr2+ in the formation waters constitute solutions where the concentrations of SO42- are low while the concentrations of Ca2+, Ba2+ and Sr2+ are high. Mixing of these streams, there is a high probability of CaSO4, BaSO4 and/or SrSO4 precipitation. Some of the more common ions frequently encountered in oil field waters and cause precipitation in incompatible waters are Ca2+, Ba2+, Sr2+, Fe2+, HCO3- and SO42-. In most cases, the low solubility and tenaciously adhering calcium carbonate and barium sulfate scale deposits are the most commonly salts found in well scale deposits. Knowledge of the mechanisms underlying the formation of scale deposits and the concomitant effects on the changes of the local porosity and permeability is of paramount importance for the efficient design of scale control processes. On the other hand there are beneficial applications involving the precipitation of insoluble salts. The controlled precipitation of sparingly soluble salts may be used for the effective consolidation of unconsolidated or poorly consolidated formations, like the sandy soils or granular materials (applications: protection of cultivated soils from erosion by raining water, protection of sandy reservoirs from the intrusion of sand grains within the oil wells, waterproofing of underground constructions, e.g. tunnels or other concrete constructions, etc). The main motivation for the present work is the investigation of the precipitation mechanisms through in-situ mixing and the precipitation of sparingly soluble salts (calcium carbonate) in porous materials. The proposed method may be applicable for the prevention of sand entrainment into well bores during oil production in poorly consolidated oil reservoirs. In the present study two series of experiments were done in order to investigate the kinetics of calcium carbonate precipitation in batch reactors using calcium chloride and sodium bicarbonate as the initial reagents in the absence and presence of sand. In all supersaturated solutions used in the present work, the stoichiometric of total calcium ions to total bicarbonate ions was equal to 1:1. During the experiments samples were taken, filtered through membrane filters and analyzed for total calcium by atomic absorption spectroscopy. The analysis of the kinetic data showed that in spontaneous precipitation experiments the crystals grow with spiral mechanism (n=2) and in the presence of sand kinetics data were best fitted by the polynuclear model (n>2). At the end of each experiment, the fluid suspension was filtered with a 0.22 μm filter and the solids were collected, dried at room temperature, and characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Finally, also a series of experiments were done using two dimensional porous (Plexiglas®) medium models in which insoluble salts were nucleated from supersaturated solutions. Through the direct observation of the evolution of the deposits it was attempted to obtain qualitative and quantitative information concerning the mechanisms and pattern of deposition and growth of calcium carbonate scale on pore walls under realistic geometrical, flow, temperature and concentration conditions. Two soluble salts of calcium chloride, CaCl2, and sodium bicarbonate, NaHCO3, were mixed just before the injection point using syringe pumps. Precipitation of calcium carbonate took place within the porous medium. Using an optical microscope in combination with a video- camera it was possible to monitor crystal appearance and growth at a steady state. The growth of the calcium carbonate crystals in different positions within the etched linear porous medium as a function of time was observed. The visual observation of the crystal growth took place in different positions along the channel (2 cm, 6 cm, 8 cm and 10 cm from the inlet of the channel). In every position the changes of the pH and calcium concentration were measured and the formation of crystals was recorded through image capture. During the flow of the mixture through the channel, supersaturation decreased as a result of the in situ mixing of calcium and bicarbonate ions. As it was expected precipitation was favoured near the inlet of the cell and few crystals were precipitated near the outlet. Furthermore, the size of the crystal was bigger near the inlet of the channel in comparison to the crystals that have precipitate near the outlet of the channel.

Στο πλαίσιο της παρούσας εργασίας έγινε προσπάθεια για την ανάπτυξη αναλυτικών μεθοδολογιών με στόχο την ταυτοποίηση και την ποσοτική ανάλυση σε περιπτώσεις ταυτόχρονης συνύπαρξης και των τριών φάσεων του άνυδρου κρυσταλλικού ανθρακικού ασβεστίου. Η Φασματοσκοπία Raman και η Φασματοσκοπία Υπερύθρου ήταν οι δύο αναλυτικές τεχνικές οι οποίες χρησιμοποιήθηκαν σαν βάση για την ανάπτυξη των ανάλογων αναλυτικών μεθοδολογιών. Η χρήση της Φασματοσκοπίας Raman οδήγησε στην ανάπτυξη μιας μη καταστροφικής αναλυτικής μεθοδολογίας, στην οποία όμως μόνο τα σχετικά ποσοστά των τριών φάσεων έγινε δυνατόν να προσδιοριστούν. Για την δημιουργία των ευθειών αναφοράς, κατασκευάστηκαν δυαδικά μίγματα, ενώ χρησιμοποιήθηκαν οι κορυφές στα 711cm-1 για τον ασβεστίτη, στα 700cm-1 για τον αραγωνίτη και στα 750cm-1 για τον βατερίτη. Τα όρια ανίχνευσης προσδιορίστηκαν 0.13mol%, 0.18mol% και 1.3mol% για τον ασβεστίτη, αραγωνίτη και βατερίτη αντίστοιχα, ενώ τα σφάλματα κατά τον προσδιορισμό τριαδικού μίγματος γνωστής σύστασης βρέθησαν να είναι 1.6mol% για τον ασβεστίτη, 0.3mol% για τον αραγωνίτη και 1.1mol% για τον βατερίτη. Στην προσπάθεια επιλογής των κατάλληλων δονήσεων Raman, έγινε μελέτη των φασμάτων Raman των καθαρών κρυσταλλικών φάσεων και απόδοση των κορυφών. Τέλος με την χρήση της Φασματοσκοπίας IR έγινε δυνατός ο προσδιορισμός των απόλυτων ποσοστών των τριών φάσεων, κάνοντας χρήση των δονήσεων στα 714cm-1 για τον ασβεστίτη, στα 700cm-1 και 714cm-1 για τον αραγωνίτη και στα 745cm-1 για τον βατερίτη. Οι απόρροφητικότητες των κορυφών (σε mg-1CaCO3 mm-2) βρέθηκαν ίσες με: α 63.38 714 = για τον ασβεστίτη, α .30 700 = 19 και α .43 714 = 40 για τον αραγωνίτη και α .79 745 = 21 για τον βατερίτη. Τα όρια ανίχνευσης (σε mgCaCO3/mm2) προσδιορίστηκαν σε: 714 -4 C O.A. =6.6 ×10 για τον ασβεστίτη, 700 -3 A O.A. =2.2 ×10 και 714 -3 A O.A. =1.1×10 για τον αραγωνίτη και 745 -3 V O.A. =1.9 ×10 για τον βατερίτη. / In the present work new analytical methodologies were developed for the study of calcium carbonate polymorphs (calcite, aragonite, vaterite). Two vibrational techniques were employed for the simultaneous quantitative analysis of mixtures of crystalline materials; Raman Spectroscopy (non-destructive technique), Infrared Spectroscopy (destructive technique). Using binary mixtures from known quantities of the crystal phase the calibration curves were constructed using the Raman bands at 711cm-1 for calcite, 700cm-1 for aragonite and 750cm-1 for vaterite. Detection limits (DL) were found to be 0.13, 0.18 and 1.3mol % for calcite, aragonite and vaterite, respectively, while the relative errors in determining the mol % of a known ternary mixture of calcium carbonate polymorphs were 1.6% for calcite, 0.3% for aragonite and 1.1% for vaterite. Infrared Spectroscopy was used, in order to determinate the absolute concentration of the calcium carbonate crystal phases, using the bands at 714cm-1 for calcite, at 700cm- 1 and 714cm-1 for aragonite and at 745cm-1 for vaterite. The asborptivities were found to be α 63.38 714 = for calcite, α .30 700 = 19 and α .43 714 = 40 for aragonite and α .79 745 = 21 for vaterite. The detection limits were also established and found to be 714 -4 C D.L. = 6.6 ×10 for calcite, 700 -3 A D.L. = 2.2 ×10 and 714 -3 A D.L. =1.1×10 for aragonite and 745 -3 V D.L. = 1.9 ×10 for vaterite.