Activation of Bentonite and Talc by Acetic Acid as a Carbonation Feedstock for Mineral Storage of CO2

The average global temperature has been slightly increasing by 0.76 °C over last 150 years. If the current state will continue, average Earth temperature will increase at the end of this century for about 1.1 – 6.3 °C according to applied emission scenario. Main reason of the observed global warming is the increasing contents of greenhouse gases (GHG), such as carbon dioxide (CO2), methane (CH4) a nitrous oxide (NO2), in the Earth atmosphere. The most important greenhouse gas is CO2. Carbon dioxide is considering as responsible for about two-third of the enhanced “greenhouse effect”. Its atmospheric concentration has risen from the pre-industrial levels of 280 ppm to 380 ppm in 2005. Human emissions of greenhouse gases are very likely responsible for global warming of the planet surface (IPCC, 2007). The increasing carbon dioxide content in the atmosphere and its long-term effect on the climate has led to increasing interest and research of the possibilities of capture, utilization and long-term storage of carbon dioxide (Yang at al., 2008; Jiang, 2011) Fossil fuels have been used as the world’s primary source of energy upon over the 20th century and this trend is expected to continue throughout the 21st century (Yang at al., 2008; Maroto-Valer at al., 2005). There is a direct link between emissions of carbon dioxide (Ce), human population (P), economic development that is indicated by gross domestic product (GPD), production of energy (E), amount of carbon-based fuels used for production of energy (C) and CO2 sinks (SCO2):


Introduction
The average global temperature has been slightly increasing by 0.76 °C over last 150 years.If the current state will continue, average Earth temperature will increase at the end of this century for about 1.1 -6.3 °C according to applied emission scenario.Main reason of the observed global warming is the increasing contents of greenhouse gases (GHG), such as carbon dioxide (CO 2 ), methane (CH 4 ) a nitrous oxide (NO 2 ), in the Earth atmosphere.The most important greenhouse gas is CO 2 .Carbon dioxide is considering as responsible for about two-third of the enhanced "greenhouse effect".Its atmospheric concentration has risen from the pre-industrial levels of 280 ppm to 380 ppm in 2005.Human emissions of greenhouse gases are very likely responsible for global warming of the planet surface (IPCC, 2007).The increasing carbon dioxide content in the atmosphere and its long-term effect on the climate has led to increasing interest and research of the possibilities of capture, utilization and long-term storage of carbon dioxide (Yang at al., 2008;Jiang, 2011) Fossil fuels have been used as the world's primary source of energy upon over the 20th century and this trend is expected to continue throughout the 21st century (Yang at al., 2008;Maroto-Valer at al., 2005).There is a direct link between emissions of carbon dioxide (C e ), human population (P), economic development that is indicated by gross domestic product (GPD), production of energy (E), amount of carbon-based fuels used for production of energy (C) and CO 2 sinks (S CO2 ): The emissions of anthropogenic carbon dioxide are increasing with population (P), standard of living (GPD/P); the energy intensity of economy (E/GPD) and the carbon intensity of the energy system (C/E).On the contrary C e is decreasing with S CO2 .Examination of the Eq.1.1, in principle, proposes that there are five ways to reduce atmospheric emissions of anthropogenic CO 2 , of which the first two, i.e. reduction in population and/or decline in economic output are naturally unacceptable.Reducing the carbon intensity of the energy system can be achieved by using hydrogen-rich fuels and renewable energy sources.The "solubility trapping".The chemical reactions inducted by CO 2 injection are described by Eq.1.1 and 1.2 (Xu at al., 2004).The weathering of alkaline rocks, such as alkaline or alkaline earth silicates is thought to have played a great role in the historical reduction of the atmospheric CO 2 content in atmosphere of Earth (Kojima at al., 1997).
Total estimated storage capacity of geological reservoirs is about 920 Gt CO 2 in depleted oil and gas fields, 400 -10 000 Gt in deep saline reservoirs and 20 Gt in coal mine coal deposits.
The cost for carbon dioxide capture and following storage in geologic formations is estimated about 4 -48 EUR/t CO 2 (Friedmann at al., 2006;Gale, 2004).The research works concerning in risk assessment of CO 2 geological storage is mentioned in work (Gale, 2004).
Deep-sea storage of anthropogenic CO 2 is an attractive concept that offers large storage capacity comparing to other options.However, storing CO 2 in oceans is limited by its high cost, technology development, potentially high environmental impact, because the storage capacity of the ocean has not been defined.The oceanic processes are controlled long-term processes and large scale storage has been discussed only in general terms.Addition of anthropogenic CO 2 would change the CO 2 chemistry in the ocean by reducing pH at the site.
The effects of long-term influence of low pH on planktonic ecosystem and oceanic biological processes are virtually unknown.Addition and CO 2 storage would probably dissolve carbonate deposits on the seafloor and suppress oxidation of organic matter (Wong & Matear, 1998;Bachu & Adams, 2003).Mineral storage based on carbonation is a promising CCS method for long-term storage of CO 2 in continental inland utilization.The carbon dioxide is stored through mineral trapping mechanism that requires the participation of cations, including Ca 2+ , Fe 2+ , and Mg 2+ , that can form stable solid carbonate phases (Giammar at al., 2005).This processing accelerates the natural weathering of silicate minerals, where these minerals react with CO 2 and form carbonate minerals and silica.Although the calcium silicate has been successfully carbonated at temperatures and pressures relevant for industrial processes, its natural resources are too small and expensive to be of practical interest.Therefore, current research activities focus mostly on carbonation of magnesium silicates (Teir at al., 2007).Overall course of carbonation process of wollastonite (CaSiO 3 ), olivine (Mg 2 SiO 4 ) and serpentine (Mg 3 Si 2 O 5 (OH) 4 ) may be described by Eq.1.4-1.6, respectively (Alexander, 2007;Wouter at al., 2007).
The magnesium bearing minerals typically contain about 40 % of magnesium, whereas the content of calcium is approximately 10 -15 %.R e a c t i v i t y o f o l i v i n e i s h i g h e r t h a n serpentine, but serpentine reactivity is strongly increasing by physical and chemical activation.Physical activation such as heat pre-treatment (calcination) at approximately 630 °C may remove water (dehydroxylation) from serpentine structure.The conversion to magnesite (MgCO 3 ) is higher (59.4 %) than the value (7.2 %) found for untreated samples (Alexander at al., 2007).Carbon dioxide sequestration capacity some of major rock forming minerals is listed in  (Xu at al., 2004).
If the rate-limiting step in the aqueous carbonation scheme is leaching of calcium or magnesium, then the production of carbonates may by accelerate via acceleration of dissolution stage.Inorganic (HCl, H 2 SO 4 , H 3 PO 4 ) as well as organic acids (CH 3 COOH), complexing agents and hydroxides (NaOH) were used for chemical activation of minerals.Hydrochloric acid enhances the magnesium ions liberation, however energy intensity production of Mg(OH) 2 has been increasing.Complexing agents were used to polarize and weaken the magnesium bonds within the serpentine structure.The most effective is treatment by H 2 SO 4 which increases the surface area from 8 to 330 m 2 •g -1 .Sulphuric acid pre-treatment enables aqueous carbonation of Mg(OH) 2 under milder condition.Temperature and pressure were reduced from 185 on 20 °C and 12.7 to 4.6 MPa.Process may by write as follows (Alexander at al., 2007;M.-Valer at al., 2005): Industrial by-products, such as iron and steel slags and cement based material, may contain very height percentage of calcium and magnesium oxides and therefore they may be carbonated and exploited for CO 2 mineral storage.Calcium and magnesium can be leached out by acetic acid.Such a process consists of two main steps.The first one, where calcium ions are extracted from natural calcium silicate mineral: And the second one, where carbon dioxide was introduced into the solution after removing of SiO 2 and calcite has been precipitated from the solution according to Eq.1.11.Acetic acid is recovered in this step and recycled for using of extraction in the first step (Eq.1.10).Similar reaction proceeds with magnesium silicates: (1.13)However, there are also small contents of many other compounds from iron and steel slags (such as heavy metals) which would be released by acetic acid (Teir at al., 2007).

Kinetics of silicate minerals, rocks, glass and raw materials dissolution
The main reasons for investigation of dissolution and precipitation reactions of silicate minerals and raw materials is in importance to understand the extent and environmental significance of the chemical weathering in nature (Cama at al., 1999;), study of its potential to utilization as the source of the divalent cations that is necessary for the sequestering of carbon dioxide into carbonates (Saldi at al., 2007), in order to improve their catalytic activity (Komadel & Madejová, 2006;Pushpaletha at al., 2005), study the puzzolanic activity in mortars and cements (Massazza, 1993) drug delivery (Viseras at al., 2010), synthesis of geopolymers (Buchwald at al., 2009), zeolites (Baccouche at al., 1998) and organic-clay composites (Yehia at al., 2012).The kinetics of mineral dissolution is an area in geochemistry that has received considerable attention over the past several years (Knauss at al., 2003).Hence, numerous works dedicated to investigation of clay mineral dissolution kinetics can be found in the current literature (Table 1.2).A basic concept in chemical kinetics is that reactions consist of a series of different physical and chemical processes that can be broken down into different ''steps''.For dissolution, these steps generally include at a minimum (Morse & Arvidson, 2002;Dorozhkin, 2002): 1. Diffusion of reactants through solution to the solid surface; 2. Adsorption of the reactants on the solid surface; 3. Migration of the reactants on the surface to an ''active'' site (e.g., a dislocation); 4. The chemical reaction between the adsorbed reactant and solid which may involve several intermediate steps where bonds are broken and formed, and hydration of ions occurs;  (a) Under low pH values. (b) Forming of rate-controlling precursor complex. (c) Under pH = 2.6.(Ptáček at al., 2011).
A central concept in dissolution kinetics supposes that one of these steps is the slowest than other.The reaction cannot proceed faster than the rate limiting step.Above mentioned steps 1 and 7 involve the diffusive transport of reactants and products through the solution to and from the surface.When this process is rate-limiting, the reaction is said to be diffusion controlled.Steps 2-6 occur on the surface of the solid and when one of them is rate controlling the reaction is said to be surface controlled (Morse & Arvidson, 2002;Dorozhkin, 2002).The dissolution of solids in liquids (or melts) consists of a surface chemical reaction and transport of the reaction components to the reaction boundary (Šesták, 1984).Many multicomponent silicate minerals under acidic condition are dissolved incongruently.The Ca 2+ ions were replaced by H 3 O + ions and leached layer of silica was formed.This layer wasn't homogeneous and its structure was changing with time as a consequence of polymerization of silanol groups (Weissbart & Rimstidt, 2000): Monosilic acid may be liberated from silicates which contain SiO 4 4-ions separated by metal cations -nesosilicates.Besides the temperature the solubility of an amorphous silica layer depends on pH and shows the minimum at pH 7. The accurate data are still missing because there is an extreme variation in the forms in which the amorphous silica can occur.The rate of dissolution is proportional to the concentration of H 3 O + and OH − ions in the range from 0 to 2 and from 3 to 6, respectively.The rate of diffusion or desorption of the silicic acid from the surface limits the rate of dissolution if pH is higher than 6 (Iler, 1979).
The dissolution mechanism of each multioxide silicate can be deduced from its structure.Note that in some cases, not all metal-oxygen bonds present in the structure need to be broken to completely destroy a mineral.Dissolution proceeds via the sequential equilibration of metal-proton exchange reactions until no further viable structure remains.The last of these sequential exchange reactions destroys the structure and it is irreversible in most cases.Assuming that at acidic conditions, the sequence of metal-proton exchange reactions during the dissolution of a multioxide silicate follow the order prescribed by the relative reactions rates of the single oxide dissolution as illustrated in Fig. 1.1 (Oelkers, 2001).The dissolution rate of the clay minerals seems to be continuously decreasing with elapsed time due to the preferred dissolution of reactive edge surfaces.As edge surfaces are selectively dissolved, the percentage of these reactivity reactive sites decrease with time leading to a decrease in the average reactivity of the overall clay surface (Köhler at al., 2005).The derivation of rate law for congruent dissolution of silicate multioxides at close to equilibrium conditions will be derived using a general formula M (1) z1 n1 M (2) z2 n2 M (3) z3 n3 O Σ(n(i)z(i))/2 , which is representative for oxide composition of nesosilicates related to phenakite (M For example, the members of olivine subgroup such as calcio-olivine, forsterite, fayalite, tephroite... for that M (1) = Ca, Mg, Fe 2+ , Mn..., trivalent cations does not present and M (3) = Si, are then dissolved according to following reaction scheme: The kinetics of this reversible chemical reaction involving competition between two elementary -forward (+) and reverse (-) reactions, can be easily expressed by applying the Van't Hoff law such that: The equilibrium constant K of forward and reverse Q reaction 1.15 can be then expressed as follows: The saturation state of a fluid is often expressed in terms of the ratio (Q/K); if by common convention the dissolving mineral appears on the left side of the reaction, values of (Q/K) < 1 indicate undersaturation of the fluid with respect to the mineral, and conversely, (Q/K) > 1 is representative of supersaturation (Hellmann at al., 2009).
The dissolution rate can be described via combination of Eq.1.17with law 1.18 and 1.19 by following kinetic equation: where the k represents the reaction rate constant.The chemical affinity of described reaction is defined as follow (Hellmann at al., 2009;Gérard at al., 1998): (1.21) so that can be derived that:

Activation of Bentonite and Talc by Acetic Acid as a Carbonation Feedstock for Mineral Storage of CO 2 229
The R is the universal gas constant (J·mol -1 ·K -1 ) and  r G = -A r denotes Gibbs energy (J·mol -1 ) and chemical affinity (J·mol -1 ) of reaction.The dissolution rate at near to equilibrium conditions when r + + r -≈ 0 requires that Q ≈ K and the ratio k + /k -≈ K: The overall dissolution rate should through combination of Eq.1.22with Eq. 1.23 expressed as: The temperature dependence of dissolution rate constant is given by Arrhenius law (Oelkers, 2001): The combination of Eq.1.24and Eq.1.25leads to equation: where A is pre-exponential (frequency) factor and E a is apparent activation energy.Under conditions that are not far from equilibrium conditions (please refer to Eq.1.23)where exp ( r G/RT) ≈ 1 can be dissolution rate expressed as: The kinetic parameter of dissolution process can be then estimated from Arrhenius plot as the slope (-E a /R) of the dependence of ln r on reciprocal temperature.Assuming information about ionic product of released cations (∏a M(i) n(i) ), the value of A can be calculated from the intercept with y-axis.A general scheme for the dissolution of a mineral or glass can be written as follow (Wieland et al.,1988): The precursor complex has the same chemical formula as the activated complex, but the activated complex has more energy.Within the context of transition-state theory (TST), the activated complex is in equilibrium with other species that precede it in the reaction sequence.It follows that a mineral dissolution rate can be considered to be proportional to the concentration of this "rate-controlling" precursor complex at the surface in accord with (Oelkers, 2001): where k + refers to a rate constant consistent with the P precursor complex and X P stands for the mole fraction of the precursor complex at the surface.
The dissolution mechanism of this mineral or glass is often initiated by the formation of the precursor complex through one or more exchange reactions.The process leads to formation of the leached surface through the metal-proton exchange.The next part of the dissolution reaction is destruction of the leached surface (Oelkers, 2001), i.e. incongruent dissolution takes place.The overall mechanism then may consist of a series of "i" elementary steps: The exponent  is generally known as Temkin's average stoichiometric number, which is equal to the ratio of the rate of destruction of the activated or precursor complex relative to the overall dissolution rate.The  value is related to the stoichiometric number of precursor complexes that can be formed from one mole of the commonly adopted chemical formula of a mineral or glass and it can have a value other than one (Aagaard & Hegelson, 1982).The average stoichiometric coefficient for the overall dissolution process that consists from isteps can be defined as follows (Gin at al., 2008): For reaction near to equilibrium we obtain: From the general law of mineral dissolution proposed by Aagaard and Helgeson, 1982 it can be derived by the same way as before: As it was pointed by Gin at al., 2008, the Eq.1.24is often presented as direct application of transition state theory.In fact, this law may be derived using simple kinetic concepts (notably the Van't Hoff law) irrespective of any hypotheses concerning the reaction mechanisms.The notion of an activated complex associated with an elementary step is theoretically compatible with the kinetic law 1.24, assuming an equilibrium existing between the activated complex and reactants in the forward and reverse directions.However, this notion is not required to obtain Eq.1.24and indeed leads to a paradox that lies in the fact that equilibrium was assumed between the activated complex and reactants in the forward direction, but that a second equilibrium was also assumed between the activated complex and the product in the reverse direction.This implies equilibrium between the products and the reactants, so the net rate should be zero.This paradox, of course, does not call into question the expression of the kinetic constants: the forward rate simply offsets the reverse rate.Postulating equilibrium between the reactants forming the activated complex in both directions and the activated complex therefore implies that Eq.1.24is valid only at equilibrium.

Clay minerals
Human life and the existence of many organisms on this planet are connected with clays.Clay minerals are the basic constituents of clay raw materials and clay raw material has always played the substantial role in human life (Table 1.3) due to their wide-ranging properties, high resistance to atmospheric conditions, geochemical purity, easy access to their deposits near the earth's surface and low price.A majority of clays is known for its plasticity.However, many clay raw materials are not plastic, or they are semi-plastic such as clay stones, clay shales, talc, pyrophyllite, vermiculite and coarser mica.The properties of clay minerals also reflect the state and distribution of the electrostatic charge of the structural layers.The negative charge is a result of the ionic substitutions in the octahedral and tetrahedral sheets of clay minerals (Konta 1995;Murray;2000).

Bentonite
Table 1.3.Traditional application area of clay minerals (Konta 1995;Murray;2000).A significant role for clay minerals in the origin of life was postulated by Bernal, 1967.Clay surface could adsorb and concentrate organic substances and some hypothesis supposed that clay crystals could function as the earliest genetic information storing material (C.-Smith, 1966 and1982) and iron-rich clay have significant importance in the origin of the photosynthetic organisms (Hartman, 1975).Clay minerals, the essential constituents of argillaceous rocks, can be classified in seven groups according to their crystal structure and crystal chemistry.These groups are listed together with their properties and the most important members in the Sepiolite, palygorskite (1) Interlayer ions that are present predominantly are marked by bold.
(4) Chanel containing water and exchangeable hydrated cations.Water can be withdrawn without structural lattice changes similar to zeolites.
Table 1.4.Classification of phyllosilicates (Martin et al., 1991;Konta, 1995)."T" or by [AlO(OH)] 6-octahedrons which are signed as "O".The interior of tetrahedrons and octahedrons contains smaller metal cations, their apices are occupied by oxygen's from which some are connected to protons (as OH).All these fundamental structural elements are arranged to form a hexagonal network in each sheet (Caglar at al., 2008;Konta 1995).

Properties and mineralogy raw materials main minerals -montmorillonite and talc
Bentonite occurs in the form of lenses in other sediments mostly as a weathering product after igneous material settled in water.It also commonly occurs as a product of supergene or hydrothermal alteration of some volcanic rocks, e.g.rhyolites, porphyres, phonolites, dacites, andesites and basalts.Smectites are especially formed through the decomposition of volcanic glass.The chemical composition of smectite, the dominant mineral of bentonites, is variable.It varies between montmorillonite (Al 1.67 (Mg,Fe 2+ ) 0.33 Si 4 O 10 (OH) 2 0.5Ca 0.33 • nH 2 O) and beidellite (Na 0.5 Al 2 (Si 3.5 Al 0.5 )O 10 (OH) 2 • nH 2 O).In the interlayer space of both smectites different cations are adsorbed, especially alkalis and alkaline earths (Konta 1995).
Smectites are an important class of clay minerals; they are utilized in many industrial processes due to their high CEC, swelling ability, and high surface area (Madejová at al., 2006).Montmorillonite was the name given to a clay mineral found near Montmorillon in France as long ago as 1874 (Grimshaw, 1971).Montmorillonite is classified as a dioctahedral clay mineral with the 2:1 type of layer linkage that is related to the group of smectites (Caglar at al., 2008).Dioctahedral layered structure of 2:1 type represents T-O-T sheet layered mineral with two tetrahedral and one octahedral layer where the centre of octahedron are predominantly occupied by trivalent cations such as Al 3+ , Fe 3+ , Cr 3+ , V 3+ , etc.The structure of montmorillonite is shown in Fig. 1.2.).Among its many uses, talc is an important raw material for magnesium ceramics (steatites, cordierite, enstatite and forsterite products).As the ceramic raw material, its thermal decomposition behaviour is of considerable interest (MacKenzie & Meinhold, 1994).Talc and pyrophyllite crystallize during metamorphic or hydrothermal processes (Konta, 1995).The structure of talc is shown in Fig. 1.2.Leaching procedure was performed using the well stirred suspension of clay mineral in diluted solution of acetic acid (Lachema, p.a.) of concentration 3 dm 3 ·mol -1 .Temperature of leaching bath ranged from 22 to 50 •C.The temperature of double wall glass reactor was adjusted using external water flow of temperature controlled water bath (thermostat).Sample was poured on by solution of acetic acid that was preheated to the applied leaching temperature in water bath of thermostat.Hence, the stirring of system by magnetic stirrer was used.Suspension contained 12.5 g of wollastonite per dm 3 of leaching solution.The pH value of dispersing medium for 24 h leaching experiment was continuously measured by pH meter connected to PC (Fig. 2.1).Solid part of suspension was separated by filtration through dense filter paper (red strip) after leaching.Filter cake was washed three times by slightly acidified (acetic acid) distilled water.The quantities of ions in original sample and leachate were determined by the Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES; ICP IRIS Iterdip II XSP duo).Filter cake was dried at 110 •C; its properties and composition were subsequently investigated by simultaneous TG-DTA-EGA, FT-IR, BET and SEM.Thermal analysis -simultaneous termogravimetry, differential thermal analysis and effluent gas analysis (TG-DTA and EGA) were performed with TG-DTA analyzer (Q600, Thermal Instruments) connected with FT-IR spectrometer (iS10, Thermo Scientific) through TGA/FT-IR interface (Thermo Scientific) heated to temperature 200 °C.That enables to study the composition of gas phase that was formed during processes which take place in heated sample.All experiments were performed with heating rate 20 •C·min −1 using argon with flowing rate 100 cm 3 ·min −1 as the carrier gas, i.e. in the inert atmosphere.Infrared spectra were collected upon mid-IR region via KBr pellets technique using FT-IR spectrometer iS10.Specimens were ground with dry spectroscopic grade KBr powder using the sample to KBr mass ratio of 1 : 100.The spectrum was obtained from 128 scans collected with resolution of 8 cm -1 .Scanning electron microscopy (SEM) was performed with a model BS 340 (Tesla).The X-ray diffractometer Siemens D500 with CuK radiation at 40 kV and 40 mA was utilized for identification the phase composition of raw material and leached samples.Brunauer-Emmett-Teller (BET) analysis (Chembet 3000, Quantachrome Instruments) was used to determine of leached samples specific surface.

Evaluation of leaching test
The method applied for monitoring of the leaching process is the same as for study of leaching of calcium from wollastonite (Ptáček at al., 2010).The buffer system of weak acid (CH 3 CO 2 H) and its salt (Ca(CH 3 CO 2 ) 2 or Mg(CH 3 CO 2 ) 2 ) with a strong base, i.e.Ca(OH) 2 or Mg(OH) 2 , was formed during dissolution of raw material.With respect to reaction stoichiometry, the amount of formed acetate ions was double to concentration of Ca 2+ ions released from wollastonite.Hence following subform of well known Henderson buffer equation may be used for estimation of the course of leaching process: where pK a denotes dissociation constant of acetic acid at given temperature.All variables in Eq.2.1 depend on the temperature.

Evaluation of leaching process kinetics
The monitoring of the progress of leaching experiment reflects the following facts and presumptions: 1.The amount of calcium and magnesium released into the solution is much higher than other elements extracted from raw material during leaching experiments, i.e. the amount of other metals in the solution is negligible; 2. Large excess of acetic acid in the system ensures its stable concentration level; 3. Henderson-Hasselbach buffer equation (Eq.2.1) can be applied for the reaction mixture; 4. Leached calcium was instantaneously transported out of surface by intensive stirring of the system.The steady-state dissolution rate for applied temperature r + (T) (mol·m -2 ·s -1 ) can be calculated using following equation (Oelkers, 2001): where [M 2+ ] i and [M 2+ ] t are an initial t i and general time t concentrations of M 2+ = Ca 2+ and Mg 2+ ions, respectively.The initial time of the process means the beginning of an induction period, so that the amount of Ca and Mg released during dissolution of calcite and dolomite can be excluded.The quantities V, ν M(Ac)2 and S are a volume of the system, stoichiometric number of M(Ac) 2 (ν M(Ac) 2 ≈ 0,3 for the Ca-montmorillonite and ν M(Ac) 2 ≈ 0,3 for talc) and total surface area of sample introduced into the reactor, respectively.The term Δ[M 2+ ]/Δt of Eq.2.2 can be determined as the slope of the linear part of the plot of concentration vs. time (Cama, 1999).This method of r + (T) value estimation is in particular favourable for the systems with very complicated stoichiometry of ongoing reactions such as in studied montmorillonite clay.
The reached stage of the system during the leaching process can be characterized by fractional conversion (degree of conversion) as follows: where bottom index i, t and ∞ denotes the initial (beginning of the induction period), currently measured and final value of M 2+ ions concentration.The degree of conversion can hold values from 0 to 1 and its time dependence enables to estimate mechanism and kinetics of leaching process by linearization procedure.The method is based on the formula: where k is the rate constant of the process.If the kinetic function g(y) corresponding to the proper mechanism was chose, the dependence of g(y) on t should be straight line with the slope k on wide interval of y.The mathematic expression of the kinetic function can be found in published literature (Vlaev at al., 2008;Duan at al., 2008;Saikia at al., 2002;Šesták, 1984).The variation of mineral dissolution rates with temperature is commonly described using the empirical Arrhenius law -Eq.1.25(Oelkers, 2001;Cama at al., 1999).The estimation of the apparent activation energy and the pre-exponential (frequency) factor (A) is based on the logarithmic form of the Arrhenius law: using values of r + determined for several temperatures.The plot of ln k vs. T −1 (Arrhenius plot) should be straight line, where the slope (−E a /R) yields to the apparent activation energy of the process and y-axis intercept is then equal to the ln A. For the early stage of dissolution process, the concentration of M 2+ ions in leaching solution is increasing with time almost linearly.It stands to the reason that the initial part of dissolution process enables to estimate the dissolution rate constant as: (2.6)

Results and discussion
There are many factors affecting the course of experiment such as pH of leaching solution, kind and solvent composition, temperature, pressure, particle size distribution and particle shape, concentration of solid in the suspension and stirring intensity.Hence, the initial state of raw material serving as the source of clay mineral should be characterized.The surrey of used raw materials composition and properties are listed in the Table 3.1.1.13 (1)  1.76 (2)  1.38 (3) ---  (11) [mV]
(2) Determined composition of clay mineral (dry state of sample).
Table 3.1.The composition and properties of clay raw materials.

Thermal analysis
Results of thermal analysis allow identification of main mineral phases and estimate their content in the clay raw material.The typical TG-DTA and EGA patterns of clay raw materials that were used as the source of montmorillonite and talc are shown in Fig. 3.1.The DTG curve is plotted in order to reach higher sensitivity to distinguish between individual steps of thermogravimetric analysis.The dehydroxylation of clay minerals, decomposition of carbonates and burning of organic admixtures are the main overlapping processes whose take place within temperature interval from 380 to 600 °C.The DTA shows broad endothermic peak having a composed structure at temperature 533.9 °C.The bands of carbon dioxide and water are well visible on EGA plot.These processes are affected together via partial formed gas species.For example the water formed by dehydroxylation of montmorillonite slows down the diffusion of oxygen into burning organic material and shifts the organic matter process to the higher temperatures, while water vapour formed by combustion of organic admixtures leads to increasing of partial pressure of water vapours.That results into decreasing rate of dehydroxylation of clay minerals (Ptáček at al., 2010).Oxygen deficiency leading to reduction condition during TA is indicated by bands of carbon monoxide on the results of EGA.
The effects of carbonates on the above mentioned processes should be explained using the Richardson's diagrams (Richardson, 1974) as follows.The Bell-Boudoir's reaction (Eq.3.1)shows thermodynamic equilibrium at temperature 720 °C, so that the carbon monoxide is the more stable at higher temperature than carbon dioxide.That means that CO 2 formed by the thermal decomposition of carbonates at temperatures near to temperature of equilibrium or higher facilitates the residual carbon removing process.
The two carbonates are identified in the analysis sample -siderite (FeCO 3 ) and dolomite (CaMg(CO 3 ) 2 ).Thermal decomposition of siderite that takes place at temperatures up to 410 °C are participate on the broad DTA endothermic effect at 533.9 °C.Annealing dolomite is decomposed within two steps that are represented by reactions 3.2 and 3.3.The first step takes place at 602.7 °C and second at 718.3 °C.The both processes are well visible on EGA.
The formation of SO 2 was detected on EGA upon temperature interval from 800 to 870 °C due to presence of traces of pyrite.The endothermic peak at temperature 848.2 °C is related to the formation of cordierite that is connected with destruction of the phylosilicate structure of clay minerals.The eutectic melt was detected at temperature 1141.4 °C.
During thermal analysis of talc raw material performed up to temperature 1250 °C (Fig. 3.2) is mass of the sample decreasing for about 13.12 %.The adsorbed water is removed up to 143 °C.The mass of sample was reduced for about 0.21 % during this process.The dehydroxylation of talc which takes place in temperature range from 720 to 970 °C and two steps of thermal decomposition of dolomite at 450 and 720 °C are the main occurring processes.The SO 2 bands in EGA plot indicate the presence of small amount of pyrite.

Infrared spectroscopy
The infrared spectrum of montmorillonite and talc clay is shown on Fig. 3.3.The data published in literature (Eren & Afsin, 2008;Molina-Montes at al., 2008;Madejová at al., 2006;Tyagi at al., 2006;Kloprogge at al., 2005) were used for interpretation of raw material spectral features.The OH stretching bands are located at 3695 and 3626 cm -1 .The bending of AlAlO-H, AlFeO-H a AlMgO-H groups show bands at 916, 877 and 837 cm -1 .The stretching and bending band of physical adsorbed water are located at 3427 and 1639 cm -1 .The most intensive band at 1035 cm -1 is related to antisymmetric stretching of the ≡Si-O-Si≡ bridge.The deformation mode is placed at 524 cm -1 .The dolomite and quartz are identified by infrared spectroscopy as the main admixtures of clay raw material that was used as the source of montmorillonite.
The infrared spectrum of talc (Fig. 3.3) shows stretching of MgO-H groups at wavenumber 3626 cm -1 .The modes are located at 670 and 646 cm -1 .The band of antisymmetric stretching and bending mode of ≡Si-O bond shows maximum absorption intensity at 1017 and 453 cm -1 , respectively.The other bands belong to admixture mineralsclinochlore and dolomite.
The particle size analysis of raw materials, i.e. bentonite clay and talc, used for leaching experiments are shown at Fig. 3.4.The shape of particle size distribution curve of bentonite raw material reflects the complicate phase composition of sample that contains a significant amount of carbonates and other admixture minerals of different hardness compared to clay, i.e. minerals with different grindability.These admixtures are responsible for the right shoulders of the particle size distribution curve.The talc raw material with high content of clay phase shows almost ideal Gaussian profile of particle size distribution curve with median 29.33 m (Table 3.1).(3.4) where y = 2z -x + 0,6, p = 5,4 -2z + x and q = 6z + n -6.On the other hand, with regard to the montmorillonite structure that is described in chapter 1.3, the release of cations from interlayer space is participating on the process.These ions are being exchanged by H 3 O + according to Eq.3-2.It was found by (Adams, 1987;Jovanovič and Janačkovič, 1991) that acid-activated (HCl or H 2 SO 4 of different molar concentrations) bentonite leads to a dissolution or removal of the octahedral sheets and interlayer cations.Its resulting in an increase of the pore volume and pore diameter, an enrichment of residual amorphous SiO 2 and an increase of sorption properties.
The pH change of solvent during leaching process performed upon temperatures within range from 22 to 50 °C is shown in the Fig. 3.7.The dependence of fractional conversion on the time was calculated according to formula 2.1 and 2.3 from measured pH on time dependence.The results of leaching experiment on montmorillonite clay show that mechanism of process is significantly affected by temperature.Linearization procedure leads to conclusion that the leaching process is handled by the stationary three-dimensional diffusion (D 4 ) at temperatures up to 25 °C, i.e. the course of leaching process can be characterized by Valensi-Ginstling-Brounstein (VGB) equation (Valensi, 1936;Ginstling and Brounstein, 1950): The Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation shows the best results for experiments performed upon temperature interval from 30 to 40 °C.The kinetic function corresponding to the mechanism of random nucleation and subsequent growth of nuclei (F 1 or A 1 ) can be described by Eq.3.7.At temperatures higher than 40 °C the leaching process is forced by chemical reaction of ¾th order (F ¾ ), i.e. by mechanism non-invoking equation: The Arrhenius plot is shown on Fig. 3.8.The value of apparent activation energy that was determined upon the above mentioned temperature interval is listed in the Table 3.2.The results of ICP-OES analysis (Fig. 3.9) of solvent after the leaching experiment show that predominantly extracted elements are Ca, Mg, Mg, Fe and Al.The amount of extracted per gram of clay raw material is listed in the Table 3.3.With except of calcium where extracted amount is not correlated with temperature (Table 3.3), the amount of extracted elements is generally increasing with temperature.The higher temperature then enables to reach better activation of bentonite by acetic acid using higher temperatures due to increasing content of leached Fe and Mg.That behaviour results from the structure of mineral of smectite groups (Fig. 3.2).751.84 20.112 10.758 7.558 10.19 24.33 21.082 57.054 0.778 4.838 8238 1320 25220 4410 25 743.18 19.642 10.484 7.522 9.526 23.194 14.552 58.856 0.76 4.628 7850 1844 23780 4576 30 722.36 20.326 11.992 8.546 11.608 25.148 18.97 65.142 0.778 4.496   While calcium is placed in place interlayer space and should be then easily replaced by sodium by cation exchange process, magnesium is bonded in brucite sheet of T-O-T complex and it can be released only after its dissolution.That is also the reason for observed correlation of Mg on the amount of extracted Al and other cation (Fe 3+ , Cr 3+ , V 3+ ...) coordinated octahedrally in the "O" layer.The solid rest that is resulting from the leaching process was analysed by TA, IR and SEM to determine its properties for the usage in cements due to estimated puzzolanic activity or as absorption agents.Thermal decomposition of formed carbonates that takes place upon temperature interval from 700 to 900 °C is well visible on DTA as well as EGA pattern.
Fig. 3.11.Thermal analysis of solid rest after leaching process.
The SEM analysis of the clay after dissolution experiment is shown in Figure 3.12.The admixture of carbonate minerals (please see Fig. 3.5) are dissolved at early stages of leaching process.The leached silica layer was formed on the surface of bentonite aggregates.

Dissolution of talc
The process of the dissolution of Talc in diluted solution of acetic acid should be described by following equation: The measured dependence of pH on the time of dissolution and fractional conversion time dependence calculated according to Eq.2.1 and 2.3 is shown on Fig. 3.13.To compare with bentonite clay, the course of talc activation process seems to be less affected by the temperature of leaching bath.Hence only the limit temperatures are plotted in the Fig. 3.13.The kinetic of leaching process should be described by the kinetic law: where kinetic exponent (Avrami's factors) has value of 1.2.

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There it is obvious that the amount of extracted magnesium and iron is strongly affected by the temperature while the calcium content is slightly decreasing with increasing temperature of solvent.It should be thus supposed that Ca come to solution in very short time after pouring the solvent during dissolution of the admixture of carbonates in the raw material.The negative temperature dependence is probably caused by absorption of calcium on leached layer that is formed on the surface of talc aggregates.The increasing content of calcium in the leaching bath (please refer to Table 3.7) as well as the correlation between extracted amount of Al (Table 3.8) should be explained analogically with leaching test of montmorillonite clay.

Conclusion
The initial stage of bentonite leaching process is on exchange of Ca and K from the interlayer space of montmorillonite and illite.The dissolution of T-O-T complex that is promoted by higher temperature then leads to the release of Mg and other octahedrally coordinate ions.Storage capacity of bentonite clay for CCS should be then significantly improved by activation process performed at elevated temperature.Increasing temperature promotes the rate of incongruent leaching process.The process of activation of talc shows also significant influence of leaching bath on the process.While amount of extracted calcium remains constant or slightly decrease due to absorption phenomena, the amount of extracted calcium should be significantly improved with increasing temperature of leaching bath.The capacity for CO 2 caption is at about 35 % higher for the clay of montmorillonite.This difference is decreasing with increasing temperature of leaching bath.

Acknowledgment
This paper is supported by the research project of ERDF no.CZ.1.05/2.1.00/01.0012''Centres for Materials Research at FCH BUT''.

Fig. 1
Fig. 1.1.Mechanism of dissolution of some minerals and basaltic glass at acidic condition according to Oelkers, 2001.
All experiments reported in this work were performed on bentonite from locality Obrnice (Czech Republic) produced by the company Keramost a.s., that was used as the source of Na, Ca -montmorillonite, and talc produced by Združena v.d.Spišká nová Ves, plant Gelnica from locality Gemerská poloma (Slovak Republic).The composition of montmorillonite 2 Ca 0,1 Al 2 Si 4 O 10 (OH) 2 (H 2 O) 10 and Mg 3 Si 4 O 10 (OH) 2 , respectively.

Fig. 3
Fig. 3.1.TG-DTA and EGA pattern of montmorillonite clay.TA of bentonite performed up to 1250 °C shows that mass of sample is decreasing for about 15.42 % within to the series of six endothermic steps.Evaporation of adsorbed water leads to the first endothermic peak of the maximum at temperature about 99.4 °C.The mass of sample was up to 165.2 °C (ousted point of DTG peak) reduced at about 3.71 %.The water vapour released from the sample is also well visible on EGA.The water can be also detected in the spectrum of gas phase upon the temperature interval ranged from 225 to 260 °C, where water molecules has been ousted from the interlayer space of montmorillonite and admixture of illite.The process shows maximum rate at temperature 245.0 °C.

Fig. 3
Fig. 3.4.SEM and particle size distribution analysis of clay raw material.The layered structure of talc aggregates is shown at Fig.3.6.The average size of (001) planes was via several measurements estimated on 200 m.The calcite was identified as the main admixture mineral of talc raw material.

Fig. 3
Fig. 3.7.The pH of leaching bath for experiment performed under different temperature and time dependence of fractional conversion.
Fig. 3.10.Infrared spectrum of bentonite leached by acetic acid.The results of thermal analysis (Fig.3.11)indicate introducing the salt of acetic acid into interlayer space of bentonite.The evaporation of acetic acid and burning of acetic salt are well visible on EGA.Thermal decomposition of acetates that is according to EGA connected with formation of acetone and carbon dioxide.Presence of carbon monoxide and dioxide bands upon the same temperature interval indicates the partially reduction condition of process that leads to formation of the calcium and magnesium carbonates:

Fig. 3 .
Fig. 3.13.The change of pH of leaching solution during activation of talc (a) and fractional conversion on time dependence (b).

Fig. 3 .
Fig. 3.14.The Arrhenius plot for the talc dissolved in diluted acetic acid.The Arrhenius plot that is shown in Fig.3.14 was used for determination the apparent activation energy of the leaching test from the dependence of 160 ± 3 J•mol -1 .The results of ICP-OES analysis of solvent after leaching tests performed within the temperature interval from 22 to 50 °C are plotted in Fig.3.15.

Fig. 3 .
Fig. 3.16.Infrared spectroscopy of solid rest after activation of talc by acetic acid.

Table 1 .
Table.1.1.1. Carbon dioxide sequestration potential of some major rock according to work Activation of Bentonite and Talc by Acetic Acid as a Carbonation Feedstock for Mineral Storage of CO 2 www.intechopen.com

Table 1 .2. Dissolution kinetics of silicates. Table is extracted from the work
Table 1.4.

Table 3 .
3. Influence of temperature on the extraction process.

98 0.95 0.98 0.98 1.00 1.00 0.98 0.94 1.00 0.90
-0.35 0.98 0.85 0.62 1.00 Table 3.4.Correlation table showing mutual relationships between temperature and amount of leached elements.The significant correlation is marked by bold.The increasing efficiency of extraction process is shown in Table.3.5 as the calculated amount of carbon dioxide that may be captured by the extracted element in formed carbonate.The results indicate that extraction efficiency should be significantly improved by activation process performed at higher temperatures.
Table 3.6 show that higher specific surface of leaching rest should be obtained for the sample prepared at temperature 35 °C.Table 3.6.Influence the temperature of leaching bath on the specific surface of solid rest.

Table 3 .
8 Correlation table showing mutual relationships between temperature and amount of leached elements.The significant correlation is marked by bold.The increasing efficiency of extraction process is shown in Table.3.9.The results indicate that extraction efficiency should be significantly improved by increasing of extracted Mg amount at higher temperatures.Table3.9.Bentonite clay activation efficiency.Table3.10show that higher specific surface of leaching rest after dissolution experiment.

Table 3 .
10. Influence the temperature of leaching bath on the specific surface of solid rest.