Les cryptokarsts de Beez (Namur, Belgique) se sont développés au dépens de calcaires dolomitiques viséens, à la faveur de drains constitués par les filons sulfurés Fe-Pb-Zn, sous une couverture composée de pélites gréseuses viséo-namuriennes et de sables oligocènes. À Khamouda (Kasserine, Tunisie), les poches karstiques se sont développées suivant la stratification sub-horizontale des calcaires sénoniens de la Formation Douleb à partir d'une faille normale les mettant au contact de la couverture sableuse miocène (Formation Béglia). Dans les deux sites, des paragenèses riches et complexes s'installent aux interfaces entre encaissant carbonaté et remplissages karstiques. Des argilites blanches, principalement composées de phases silico-alumineuses et alumineuses, ainsi que des croûtes ferrugineuses sont toujours présentes. À Beez, l'argilite est constituée d'halloysite et de gibbsite. À Khamouda, elle s'enrichit de phases zincifères plus rares, telles que la sauconite, ainsi que d'un phyllosilicate à 7 Å et d'un hydroxyde de zinc amorphe. Des sulfates sont également néoformés, notamment du gypse, dissout par la suite mais dont les croûtes ferrugineuses comportent encore des indices, ainsi que de la jarosite à Beez. D'un point de vue fondamental, les systèmes cryptokarstiques, qui opposent une barrière carbonatée à la migration de fluides acides, sont des structures privilégiées pour l'étude et la compréhension de la migration et la fixation des éléments chimiques dans le domaine supergène. Dans les deux cas, les fluides météoriques acquièrent leur acidité (pH ~2 à Beez et pH~4 à Khamouda) par lessivage de la couverture sédimentaire sus-jacente et notamment par oxydation des sulfures qu'elle contient (pyrite à Beez, pyrite et sphalérite à Khamouda). Les principaux éléments mobilisés à Beez sont Si et Al et dans une moindre mesure Fe, Mn et les Terres Rares ; tandis qu'à Khamouda, les principaux éléments mobilisés sont Si, Al et Zn, et dans une moindre mesure Fe, Pb et les Terre Rares. La neutralisation des fluides au contact du mur carbonaté conduit dans un premier temps à la formation de sulfates (gypse, jarosite) et d'oxy-hydroxydes de fer, puis d'halloysite et d'hydroxydes d'aluminium à partir de pH 4,8-5,4. À Khamouda, les phases zincifères ne se forment que plus tardivement (pH < ~9,5). Dans les deux cas étudiés, nous avons mis en évidence l’évolution de phases minérales depuis des gels silico-alumineux jusqu’à des minéraux bien cristallisés, tels que l’halloysite, ou moins bien organisés, tels que certains oxydes de manganèse à Beez. Dans les deux gîtes, le microfaciès tubulaire de l'halloysite, correspondant à une croissance fissurale, prédomine par rapport au faciès sphéroïdal se développant habituellement au sein des masses de gel ; ce qui suggère une fracturation répétée des masses de gels précurseurs. Nous avons également établi que ces gels continuent à incorporer des cations des solutions percolantes, notamment du manganèse à Beez. La difficulté majeure de l'étude des altérations cryptokarstiques réside dans la détermination des âges des phénomènes. L'âge des couvertures sédimentaires impliquées dans les poches karstiques donne une première approximation. Ainsi, la phase majeure d'altération à Beez est post-oligocène suivie d'une réactivation quaternaire ; tandis que l'altération est post-miocène à Khamouda. Le site de Beez propose un éventail de minéralisations pouvant faire l'objet de datations radiométriques. Ces datations "absolues" doivent constituer une priorité forte à l'avenir. __________________________________________________________________________________________________ Résumé en anglais : The cryptokarsts from Beez (Namur, Belgium) were settled in dolomitic Visean limestones, in which vertical Fe-Pb-Zn sulphides veins play an important role as karstic drains. The sedimentary cover is made up of Viseo-Namurian siliceous shales and Oligocene sands. The cryptokarsts from Khamouda (Kasserine, Tunisia) were found in Senonian limestones (Douleb Formation). They expand from a down fault, which has brought limestones into contact with Miocene sands (Béglia Formation), following the sub-horizontal stratification. In both sites, complex paragenesis settled at the limestone/karst-filling interface. White clays, principaly composed of Si-Al and Al phases, and ferruginous crusts are the main paragenesis. In Beez, the white clays are made up of halloysite and gibbsite, while in Khamouda, they are enriched with uncommon zinciferous phases as sauconite (Zn-smectite), a 7Å-phyllosilicate and an amorphous Zn­hydroxide. Sulphates have also been found, as imprints of gypsum crystals in both sites, and as jarosite in Beez. Acid fluids percolated in the overlying sedimentary cover (pH~2 in Beez and pH~4 in Khamouda). The acidity is due to the oxidation of some sulphides (pyrite in Beez; pyrite and sphalerite in Khamouda). Cryptokarsts basically play an important role in chemical elements mobilization and trapping processes. In Beez, Si and Al have mainly been mobilized. Fe, Mn and the Rare Earth Elements (REE) have been mobilized too. In Khamouda, the main mobilized elements are Si, Al and Zn. Fe, Pb and REE have been mobilized too. The acid fluids are neutralized at the limestone karst-wall. It leads first to the neogenesis of sulphates (as gypsum and jarosite) and iron oxi-hydroxides (pH < 4,8). Then, halloysite and Al-oxi-hydroxides are formed (from pH~4,8-5,4 upward). In Khamouda, zinciferous phases developed lately (from pH~9,5 upward). In both studied systems, we clearly show the development of mineral phases from a Si-Al gel to well-crystallized minerals, as halloysite, or badly organized minerals, as some Mn-oxides from Beez. In both deposits, tubular halloysite, which usually develops in cracks, is prominent in comparison to spheroidal halloysite, which usually growths in gel masses. It suggests an extreme fracturing of the gel masses. We established that these gel masses mix cations from the percolating solutions. The main difficulty in cryptokarstic environments is to determine ages of weathering processes, nevertheless the age of overlying deposits give an idea. Thus, the major weathering stage in Beez is post-Oligocene (followed by a Quaternary reactivation), while weathering in Khamouda is post-Miocene. The cryptokarsts from Beez contain several mineral phases, which could be dated with radiometric methods. This "absolute" dating has to be the next step.

THEREDA (Thermodynamic Reference Database) is a collaborative project, which has been addressed this challenge. The partners are Helmholtz-Zentrum Dresden-Rossendorf, Karlsruhe Institute of Technology (KIT-INE), Gesellschaft für Anlagen- und Reaktorsicherheit Braunschweig mbH (GRS), TU Bergakademie Freiberg (TUBAF) and AF-Consult Switzerland AG (Baden, Switzerland). The aim of the project is the establishment of a consistent and quality assured database for all safety relevant elements, temperature and pressure ranges, with its focus on saline systems. This implied the use of the Pitzer approach to compute activity coefficients suitable for such conditions. Data access is possible via commonly available internet browsers under the address http://www.thereda.de. One part of the project - the data collection and evaluation for uranium – was a task of the Helmholtz-Zentrum Dresden-Rossendorf. The aquatic chemistry and thermodynamics of U(VI) and U(IV) is of great importance for geochemical modelling in repository-relevant systems. The OECD/NEA Thermochemical Database (NEA TDB) compilation is the major source for thermodynamic data of the aqueous and solid uranium species, even though this data selection does not utilize the Pitzer model for the ionic strength effect correction. As a result of the very stringent quality demands, the NEA TDB is rather restrictive and therefore incomplete for extensive modelling calculations of real systems. Therefore, the THEREDA compilation includes additional thermodynamic data of solid secondary phases formed in the waste material, the backfill and the host rock, though falling into quality assessment (QA) categories of lower accuracy. The data review process prefers log K values from solubility experiments (if available) to those calculated from thermochemical data.

In this thesis, the response of uranium minerals and poorly crystalline phases to changes in geochemical conditions through geological time has been assessed in order to understand the mobility of natural uranium in the fracture network of a proposed site for a spent nuclear fuel repository in Forsmark, Sweden. Identification and characterization of solid phase uranium have been performed through electron microprobe analysis and optical petrography (Article I). The identified uraninite, haiweeite, and uranophane crystals have been dated using U-Pb and Pb-Pb isotope ratios obtained from secondary ion mass spectrometry and laser ablation-inductively coupled plasma-mass spectrometry (Article II). The mobility of uranium in current Forsmark groundwaters and fracture system has been modelled using the PHREEQC geochemical program and Ra and Rn isotope systematics (Article IV). The rate of submarine groundwater discharge (SGD) from the Forsmark coast to Öregrundsgrepen has also been modelled using Ra isotopes (Article V). Results from these studies support a geologically early (~1200 Ma) oxidation of U(IV) to U(VI). It is further suggested that the old U(VI) minerals present in the bedrock are soluble at the pe values and alkalinities observed in the Forsmark groundwaters. At pe &lt; −4.6 and alkalinity &lt; 60 mg/L, U(VI) can be reduced to U(IV) and deposited in the fracture network. Although a non-negligible rate of SGD has been observed, this cannot be attributed to the discharge of deep (&gt;200 m.b.s.l.) Forsmark groundwaters on the basis of current data. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: In press. Paper 4: Manuscript. Paper 5: Manuscript.</p>

Inverse geochemical modelling has been used frequently in groundwater systems between wells along a known flowpath and between precipitation and stream waters in catchments. This research expands the use of inverse geochemical modelling through a reaction path model (RPM) between waters in an alpine catchment to determine the geochemical connections and disconnections within the catchment. The data for this study are from the Green Lake 4 catchment in the Colorado Front Range during the 1996 snowmelt season, which has been divided into discrete time intervals based on snowmelt hydrology. Unique combinations of geochemical connections occur during these time intervals, and they show a dynamic hydrologic system. RPM results show notable disconnections; soil water is not geochemically connected to any other end member. These changes reflect changes in weathering reactions in the catchment that are dependent on the duration and timing of snowmelt. Previously end-member mixture analysis (EMMA) models have been used to discern the water sources in catchments. The combination of RPM and EMMA approaches offers the opportunity to connect the source of water to the internal hydrologic structure of the catchment, to better understand how catchments might respond to changes in climate or atmospheric deposition.

La carbonatation minérale est une technique alternative de capture et stockage du CO2 anthropique. L'abondance des matériaux carbonatables sur terre en fait une solution à fort potentiel. En particulier, la carbonatation directe en voie aqueuse a été présentée dans la littérature comme la voie la plus intéressante d'un point de vue énergétique pour la carbonatation minérale ex-situ, à la condition que les cinétiques naturellement lentes de dissolution des silicates magnésiens en phase aqueuse puissent être accélérées de plusieurs ordres de grandeur. Cette thèse étudie en détail les verrous et mécanismes de cette réaction en présence d'additifs organiques tels que l'oxalate, connus pour leur capacité à accélérer la dissolution des silicates magnésiens. Dans un premier temps, la carbonatation en voie aqueuse sans additif d'une olivine modèle est étudiée de manière à mettre en évidence la nature des phénomènes limitants. Ensuite le travail se concentre sur l'étude du rôle de l'additif oxalate à travers des essais spécifiques et une analyse fine de la phase solide. Il est démontré que pour différentes concentrations de suspension et sous 20 bar de CO2, cet additif conduit à la formation de complexes aqueux stables du magnésium avec l'oxalate et à la précipitation de MgC2O4,2H2O (glushinskite), qui empêchent toute précipitation quantitative de magnésite. La simulation géochimique complète du système a été réalisée et a permis d'expliquer les résultats des essais par un mécanisme de dissolution à grain rétrécissant. L'extension de l'étude à un autre silicate (harzburgite) et à d'autres ligands organiques accélérateurs de la dissolution des silicates tels que le citrate et l'EDTA n'a pas non plus permis d'obtenir la formation quantitative de carbonate, à cause d'une forte complexation en phase aqueuse du Mg extrait du minerai. Ces travaux remettent en doute la perspective de développement d'un procédé industrialisable de minéralisation du CO2 en présence d'additifs organiques. / Mineral carbonation is an interesting option for mitigation of anthropogenic CO2 emissions. Direct aqueous mineral carbonation has been presented by many as a promising strategy for ex-situ mineral carbonation, on the basis that organic additives such as oxalate increase the rate and extent of dissolution of magnesium silicates several folds. This thesis discusses and extends the current understanding of this process through geochemical modelling and detailed solid characterization. First, mineral carbonation is investigated in water alone, without additives, in order to understand and quantify the actual limitations of the process with specific magnesium silicate ores. Dissolution kinetics being critical with this process, the role of disodium oxalate as a dissolution accelerating agent is thoroughly examined with olivine, through dedicated experiments and comprehensive analysis of both solid and liquid phases. Under 20 bar of CO2, and irrespective of the conditions used, it is found that the formation of strong oxalate-magnesium complexes in solution and precipitation of MgC2O4,2H2O (glushinskite) impede any chance of precipitating significant amounts of magnesium carbonate. Geochemical modelling permits successful simulation of the dissolution kinetics of magnesium silicate using a shrinking particle model. Other promising ligands from a dissolution perspective, namely citrate and EDTA, were also investigated. Contrary to oxalate, these do not form any solid by-products with magnesium, and yet they do not produce better carbonation results. The results and findings from this work cast strong doubts about the possibility of developing a viable direct aqueous mineral carbonation process using organic salts.

>Magister Scientiae - MSc / Fly ash is the most abundant of the waste materials generated from coal combustion in coal-fired power stations. South Africa uses more than 100 million tonnes of low grade bituminous coal annually to produce cheap electricity thereby generating huge amounts of fly ash each year. The disposal of fly ash has been a major concern to the world because of its potential environmental impact due to the possible leaching of the toxic elements contained in fly ash. This study centres on the chemical characterization and leaching behaviour of the fly ashes generated from SASOL Synfuels and ESKOM power station at Secunda and Tutuka in South Africa respectively. The aim is to understand the composition of the fly ashes and to determine the leachability of species from the ashes in order to predict the environmental effect of the different ash handling system of the coalfired stations (wet disposal system in Secunda and dry disposal system in Tutuka). Several leaching methods were employed in this study in order to develop a methodology for evaluating and modelling ash system and were able to discriminate between ash types and model ash handling system. Fly ashes from the two South African coal-fired stations were subjected to total acid-digestion and XRF analyses in order to determine the total amounts of major and minor species contained in the fly ashes. The total acid-digestion test and the XRF analysis revealed that the major species such as Al, Si, Ca, Na, Mg, K, Sr, Ba and S04, and minor species such as Fe, Ti, V, Mn, Cr, Ni and Cu were present in both fly ashes in fairly similar concentrations. The mineralogical characterization by XRD of Secunda and Tutuka fly ashes revealed mullite and quartz as the major mineral phases with minor peaks of CaO and calcite. Several leaching tests and different leaching conditions were employed in this study in order to develop a standardized replicable methodology for environmental impact assessment and for modelling the impact of different ash handling scenarios. The fly ashes were exposed to these different leaf leachant of different pHs on the leachability of species from the fly ashes. To achieve this, DIN-S4, TCLP and ANC tests were employed. The natural pH of the fly ash leachates were very high ranging between 12.56 and 13.08. The DIN-S4 leaching test revealed that the easily soluble species of the fly ashes include Ca, Mg, Na, K and S04 and various toxic elements. The leachates from the TCLP test recorded higher concentrations of Ca, Mg, Na, K and S04 which was attributed to the slight decrease in the pH due to the addition of a acidic leachant with a pH of 2.88. Comparison of the amount leached (DIN-S4) from the fly ashes with the total concentrations of each of the components of the fly ashes (determined by the total acid-digestion), the percentage of each of the readily soluble species ranged from 15-24.23% for Ca, 0.23-0.45% for K, 0.58-0.82% for Na, 0.0047-0.007% for Mg, 0.96-3.33% for Ba and 0.012-1.51 % for S04 per dry mass of each component in the fly ash. The ANC test revealed the effect of a leachant of specified pH on the release of species from the fly ashes with concentrations of the major and minor species leached out of the fly ashes found to be higher than the concentrations released into the leachates when DIN-S4 and TCLP test were considered at specific pH and showed the pH dependence of the solubility and release of species. These tests also showed the effect of the liquid to solid ratio upon leachability of species. In addition to the batch leaching tests mentioned above, dissolution kinetics and up-flow percolation tests were carried out on the fly ashes to determine the leaching behaviours of the fly ashes over time and the factors controlling the release of species from the fly ashes in the long term. The dissolution kinetics test was done for an extended period of 60 days with recycle of the leachant and the up-flow percolation test was carried out with constant leachant renewal until a liquid/solid ratio of 20 was attained (:::::;9d0ays). The geochemical computer code PHREEQC and MINTEQ database was used for geochemical modelling of the leachates at various reaction times and LIS ratios. The geochemical modelling results revealed that the release of the species from the fly ashes is controlled by the solubility of mineral phases in many case except for Na. The release of Ca, S04, Mg, Ba and Sr in the leachates of the fly ashes were predicted to be controlled by portlandite, gypsum, brucite, barite and celestite respectively while birnessite, magnetite, BaCr04, CaMo04 and Ba(As04h were predicted to be the mineral phases controlling the release of Mn, Fe, Cr, Mo and As respectively. The pH of the leachates plays a significant role in the leaching of both major and minor species from the fly ashes. The concentrations of species leached into solution at low pH (ANC and TCLP) were higher than the concentrations released at high pH (DIN-S4, dissolution kinetics and up-flow percolation tests). The amounts of the toxic elements such as As, Se, Cd, Cr and Pb that leached out of the fly ashes when in contact with demineralized water (DIN-S4) were very low and below the target water quality range (TWQR) of South African Department of Water Affairs and Forestry (DWAF), but the amounts of As and Se leached out by acidic leachant applied in the TCLP test and at lower pH ranging between 8 and 10 the case of the ANC test were slightly higher than the TWQR, which is an indication that the pH of the leaching solution and the contact time playa significant role on the leaching of species out of the fly ashes. This study revealed that the leaching of species from the fly ashes depends on various factors which include: physical and chemical characteristics and mineralogical composition of the fly ashes, the total concentrations of species in the ash, the rate of flow through the ash system and more importantly the pH of the leachant to which the ash system is exposed to. The results of different experiments and analysis carried out on the two South African fly ashes (Secunda and Tutuka fly ashes) showed that, despite the high concentrations of soluble species or leachable elements in the fly ashes, the leaching of major, minor and trace elements into the soils and the groundwater could be minimized if certain conditions such as avoiding acidic precipitation that could reduce the pH of the ash system are adhered to. The leaching trends of the species and the geochemical modelling data also showed that the formation of secondary mineral phases could reduce the release of toxic elements, the release of which would require aggressive low pH leachants, high flow rate, high recharge and long-term leaching for the dissolution of the formed mineral phases. In conclusion, the combination of the leaching tests employed in this study gives information on the leaching behaviour of the Secunda and Tutuka fly ashes and the factors controlling the leaching of the elements from the fly ashes. This study has been able to show that elements are leached out of the fly ashes at both alkaline and acidic pH. It is also revealed in the study that the disposal techniques employed by the coal-fired stations which were simulated by using the dissolution kinetics and up-flow percolation tests are adequate methods for modelling of the ash disposal scenario. These two methods show that the dry disposal system at Tutuka will encourage equilibration of the ash/water system thereby facilitating the precipitation of mineral phases that could control the release of both major and minor species from the fly ash, whereas the wet ashing system at Secunda may expose the ash to sufficient flow to rapidly leach species out into the environment.

THEREDA (Thermodynamic Reference Database) is a collaborative project, which has been addressed this challenge. The partners are Helmholtz-Zentrum Dresden-Rossendorf, Karlsruhe Institute of Technology (KIT-INE), Gesellschaft für Anlagen- und Reaktorsicherheit Braunschweig mbH (GRS), TU Bergakademie Freiberg (TUBAF) and AF-Consult Switzerland AG (Baden, Switzerland). The aim of the project is the establishment of a consistent and quality assured database for all safety relevant elements, temperature and pressure ranges, with its focus on saline systems. This implied the use of the Pitzer approach to compute activity coefficients suitable for such conditions. Data access is possible via commonly available internet browsers under the address http://www.thereda.de. One part of the project - the data collection and evaluation for uranium – was a task of the Helmholtz-Zentrum Dresden-Rossendorf. The aquatic chemistry and thermodynamics of U(VI) and U(IV) is of great importance for geochemical modelling in repository-relevant systems. The OECD/NEA Thermochemical Database (NEA TDB) compilation is the major source for thermodynamic data of the aqueous and solid uranium species, even though this data selection does not utilize the Pitzer model for the ionic strength effect correction. As a result of the very stringent quality demands, the NEA TDB is rather restrictive and therefore incomplete for extensive modelling calculations of real systems. Therefore, the THEREDA compilation includes additional thermodynamic data of solid secondary phases formed in the waste material, the backfill and the host rock, though falling into quality assessment (QA) categories of lower accuracy. The data review process prefers log K values from solubility experiments (if available) to those calculated from thermochemical data.

The origin of compositional gaps in volcanic deposits remains controversial. In Akaroa Volcano (9.6 to 8.6 Ma), New Zealand, a dramatic compositional gap exists between basaltic and trachytic magmas. Previously, the formation of more evolved magmas has been ascribed to crustal melting. However, the interpretation of new major and trace element analysis from minerals and bulk-rocks coupled with the mechanics of crystal-liquid separation offers an alternative explanation that alleviates the thermal restrictions required for crustal melting models. In a two-stage model, major and trace element trends can be reproduced by polybaric crystal fractionation from dry melts (less than 0.5 wt.% H2O) at the QFM buffer. In the first stage, picritic basalts are separated from an olivine-pyroxene dominant mush near the crust-mantle boundary (9 to 10 kbar). Ascending magmas stagnated at mid-crustal levels (5 to 6 kbar) and fractionated an olivine-plagioclase assemblage to produce the alkali basalt-hawaiite trend. In the second stage, trachyte melt is extracted from a crystal mush of hawaiite to mugearite composition at mid-to-upper crustal levels (3 to 5 kbar) after the melt has crystallised 50 vol.%. The fractionated assemblage of plagioclase, olivine, clinopyroxene, magnetite, and apatite is left in a cumulate residue which corresponds to the mineral assemblage of sampled ultramafic enclaves. The results of trace element modelling of Rayleigh fractionation using this extraction window is in close agreement with the concentrations measured in trachyte (= liquid) and enclaves (= cumulate residue). The compositional gap observed in the bulk-rock data of eruptive products is not recorded in the feldspar data, which show a complete solid solution from basalt and co-magmatic enclaves to trachyte. Complexly zoned plagioclases further suggest episodical magma recharge events of hotter, more mafic magmas, which lead to vigorous convection and magma mixing. In summary, these models indicate that the Daly Gap of Akaroa Volcano formed by punctuated melt extraction from a crystal mush at the brittle-ductile transition.

Um software de modelagem de especiação geoquímica é responsável pelo cálculo da distribuição das espécies dissolvidas entre solutos e complexos aquosos, e também computar os índices de saturação para diferentes minerais. Neste trabalho nós apresentamos SHPECK, um software desenvolvido para modelar sistemas de equilíbrio geoquímico usando condições de balanço de massa baseadas no conceito da lei de fases (GARRELS; CHRIST, 1965). SHPECK gera um sistema de equações de ação de massa acopladas com restrições de equilíbrio e resolve com a utilização do método se Newton-Raphson. Nosso software aceita qualquer combinação de elementos, espécies e reações, permitindo ao usuário criar diferentes ambientes de simulação e, portanto, controlar qualquet aspecto e configuração do modelo. SHPECK contém uma interface de interação com o usuário e também um banco de dados estruturado que controla todo o gerenciamento dos dados termodinâmicos utilizados para a modelagem geoquímica. Aliado a isso, apresentamos também os conceitos básicos necessários para compreenção da modelagem geoquímica seguida por uma revisão de opções de software disponíveis para modelagem geoquímica. Para finalizar, fizemos uma validação do SHPECK através da modelagem de um sistema de reações diagenéticas observadas em um reservatório asiliclástico e realizamos um estudo comparativo dos resultados do SHPECK com outros software disponíveis. Também para validação, realizamos uma avaliação de tempo de acesso ao banco de dados e pode-se notar um aumento de performance considerável através do uso de um banco de dados relacional comparando-se aos approaches existentes. / A geochemical speciation modeling software is responsible for calculating the distribution of dissolved species between solutes and aqueous complexes, and also computes saturation indexes for different minerals. In this work we introduce SHPECK, a software program developed to model geochemical equilibrium systems using the mass-balance conditions based on the phase rule concept (GARRELS; CHRIST, 1965). SHPECK composes a system of mass-action equations coupled with equilibrium constraints and solve using Newton-Raphson method. Our software accepts any general combination of elements, species, and reactions, allowing the user to create different environments, simulations and, therefore, fully control any aspect and configuration of the model. It provides an interactive user interface as well as the support of a builtfrom- the-ground database structure that handles the management of the whole thermodynamic data used for the geochemical modeling. Also, we present the basic concepts for geochemical modeling followed by a computer science based review about the available geochemical modeling software. Finally, we validate SHPECK by modeling the diagenetic reactions observed in asiliciclastic reservoir and by performing a comparative study with other modelling software package. In addition to this, a database comparison was addressed and the results demonstrate a substantial improvement on the performance by the use of the SHPECK’s relational database comparing to the existent approaches.

Um software de modelagem de especiação geoquímica é responsável pelo cálculo da distribuição das espécies dissolvidas entre solutos e complexos aquosos, e também computar os índices de saturação para diferentes minerais. Neste trabalho nós apresentamos SHPECK, um software desenvolvido para modelar sistemas de equilíbrio geoquímico usando condições de balanço de massa baseadas no conceito da lei de fases (GARRELS; CHRIST, 1965). SHPECK gera um sistema de equações de ação de massa acopladas com restrições de equilíbrio e resolve com a utilização do método se Newton-Raphson. Nosso software aceita qualquer combinação de elementos, espécies e reações, permitindo ao usuário criar diferentes ambientes de simulação e, portanto, controlar qualquet aspecto e configuração do modelo. SHPECK contém uma interface de interação com o usuário e também um banco de dados estruturado que controla todo o gerenciamento dos dados termodinâmicos utilizados para a modelagem geoquímica. Aliado a isso, apresentamos também os conceitos básicos necessários para compreenção da modelagem geoquímica seguida por uma revisão de opções de software disponíveis para modelagem geoquímica. Para finalizar, fizemos uma validação do SHPECK através da modelagem de um sistema de reações diagenéticas observadas em um reservatório asiliclástico e realizamos um estudo comparativo dos resultados do SHPECK com outros software disponíveis. Também para validação, realizamos uma avaliação de tempo de acesso ao banco de dados e pode-se notar um aumento de performance considerável através do uso de um banco de dados relacional comparando-se aos approaches existentes. / A geochemical speciation modeling software is responsible for calculating the distribution of dissolved species between solutes and aqueous complexes, and also computes saturation indexes for different minerals. In this work we introduce SHPECK, a software program developed to model geochemical equilibrium systems using the mass-balance conditions based on the phase rule concept (GARRELS; CHRIST, 1965). SHPECK composes a system of mass-action equations coupled with equilibrium constraints and solve using Newton-Raphson method. Our software accepts any general combination of elements, species, and reactions, allowing the user to create different environments, simulations and, therefore, fully control any aspect and configuration of the model. It provides an interactive user interface as well as the support of a builtfrom- the-ground database structure that handles the management of the whole thermodynamic data used for the geochemical modeling. Also, we present the basic concepts for geochemical modeling followed by a computer science based review about the available geochemical modeling software. Finally, we validate SHPECK by modeling the diagenetic reactions observed in asiliciclastic reservoir and by performing a comparative study with other modelling software package. In addition to this, a database comparison was addressed and the results demonstrate a substantial improvement on the performance by the use of the SHPECK’s relational database comparing to the existent approaches.