Formation of Scales of Calcium Carbonate Polymorphs: The Influence of Magnesium Ion and Inhibitors

Optimization of salinity and composition of injected low salinity water into sandstone reservoirs with minimum scale deposition

In this study, a mechanistic and comprehensive examination of the impact of the scale formation situation of different diluted seawater levels was conducted to investigate the influence of important factors on the performance and efficiency of low salinity water. To clarify the effective participating mechanisms, scale precipitation by compatibility test, field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) analysis, zeta potentials as surface charge, ion concentration changes, contact angle, pH, CO2 concentration, electrical conductivity, and ionic strength were analyzed. The results showed that increasing the dilution time to the optimal level (10 times-diluted seawater (SW#10D)) could effectively reduce the amount of severe precipitation of calcium carbonate (CaCO3) and calcium sulfate (CaSO4) scales. However, the reduction in CaCO3 scale precipitation (due to mixing different time diluted seawater with formation brine) and its effect on the wettability alteration (due to the change in surface charge of OLSW/oil and sandstone/OLSW) had higher impacts. The zeta potential results have shown that OLSW with optimum salinity, dilution, and ionic composition compared to different low salinity water compositions could change the surface charge of OLSW/oil/rock (- 16.7 mV) and OLSW/rock (- 10.5 mV) interfaces toward an extra negatively charged. FESEM and contact angle findings confirmed zeta potential results, i.e. OLSW was able to make sandstone surface more negative with diluting seawater and wettability changes from oil-wet toward water-wet. As a result, SW#10D was characterized by minimum scaling tendency and scale deposition (60 mg/l), maximum surface charge of OLSW/oil/rock (- 16.7 mV), and the potential of incremental oil recovery due to wettability alteration toward more water-wetness (the oil/rock contact angle ~ 50.13°) compared with other diluted seawater levels.

Synthesis, Characterization and Mechanism Study of Green Aragonite Crystals from Waste Biomaterials as Calcium Supplement

In present work, environmentally benign green aragonite crystals were synthesized from waste chicken eggshells and bivalve seashells through a simple and low-cost wet carbonation method. This method involves a constant stirring of calcium oxide slurry and magnesium chloride suspension in aqueous solution with constraint carbon dioxide injection at 80 °C. The physicochemical properties of the synthesized aragonite were further compared with the aragonite synthesized from commercial calcium oxide. The morphological analysis, such as acicular shape and optimum aspect ratio (~21), were confirmed by scanning electron microscopy. The average crystal size (10–30 µm) and specific surface area (2–18 m2 g−1) were determined by particle size and Brunauer–Emmett–Teller analysis, respectively. Moreover, a schematic crystal growth mechanism was proposed to demonstrate the genesis and progression of aragonite crystal. Green aragonite can bridge the void for numerous applications and holds the potential for the commercial-scale synthesis with eggshells and bivalve seashells as low-cost precursors.

Investigation of Scale Inhibition Mechanisms Based on the Effect of HEDP on Surface Charge of Calcium Carbonate

1-Hydroxyethylidene-1,1-diphosphonic acid is a widely used CaCO3 scale inhibitor. To probe its inhibition mechanisms, the effect of 1-Hydroxyethylidene-1,1-diphosphonic acid on surface charge and crystalline form of CaCO3 scale was investigated. The results show that CaCO3 originated from the equimolar mixture of Ca2+ and CO3 2 − is negatively charged and 1-Hydroxyethylidene-1,1-diphosphonic acid has no obvious effect on the zeta potential of CaCO3. Analysis of scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction indicated that the crystalline form of CaCO3 was altered in presence of 1-Hydroxyethylidene-1,1-diphosphonic acid. With the increase of the scale inhibition efficiency, more vaterite appeared in the particle. So a conclusion was drawn that the formation and transformation of the metaphase was inhibited by 1-hydroxyethylidene-1,1-diphosphonic acid, then the whole process of CaCO3 precipitating was slowed greatly.

Calcium Carbonate

Calcium carbonate is a chemical compound with the formula CaCO3 formed by three main elements: carbon, oxygen, and calcium. It is a common substance found in rocks in all parts of the world (most notably as limestone), and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. CaCO3 exists in different polymorphs, each with specific stability that depends on a diversity of variables.

The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite

The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5-25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73±10 and 66±2 kJ mol(-1), respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5-40 °C) is also presented.

Effect of antiscalants on precipitation of an RO concentrate: metals precipitated and particle characteristics for several water compositions

Inland brackish water reverse osmosis (RO) is economically and technically limited by the large volume of salty waste (concentrate) produced. The use of a controlled precipitation step, followed by solid/liquid separation (filtration), has emerged as a promising side-stream treatment process to treat reverse osmosis concentrate and increase overall system recovery. The addition of antiscalants to the RO feed prevents precipitation within the membrane system but might have a deleterious effect on a concentrate treatment process that uses precipitation to remove problematic precipitates. The effects of antiscalant type and concentration on salt precipitation and precipitate particle morphology were evaluated for several water compositions. The primary precipitate for the synthetic brackish waters tested was calcium carbonate; the presence of magnesium, sulfate, minor ions, and antiscalant compounds affected the amount of calcium precipitated, as well as the phases of calcium carbonate formed during precipitation. Addition of antiscalant decreased calcium precipitation but increased incorporation of magnesium and sulfate into precipitating calcium carbonate. Antiscalants prevented the growth of nucleated precipitates, resulting in the formation of small (100-200 nm diameter) particles, as well as larger (6-10 microm) particles. Elemental analysis revealed changes in composition and calcium carbonate polymorph with antiscalant addition and antiscalant type. Results indicate that the presence of antiscalants does reduce the extent of calcium precipitation and can worsen subsequent filtration performance.

The inhibition of calcium carbonate crystal growth by the cysteine-rich Mdm2 peptide

The crystal growth of calcite, the most stable calcium carbonate polymorph, in the presence of the cysteine-rich Mdm2 peptide (containing 48 amino acids in the ring finger configuration), has been investigated by the constant composition technique. Crystallization took place exclusively on well-characterized calcite crystals in solutions supersaturated only with respect to this calcium carbonate salt. The kinetic results indicated a surface diffusion spiral growth mechanism. The presence of the Mdm2 peptide inhibited the crystal growth of calcite by 22-58% in the concentration range tested, through adsorption onto the active growth sites of the calcite crystal surface. The kinetic results favored a Langmuir-type adsorption model, and the value of the calculated affinity constant was k(aff)=147x10(4) dm(3)mol(-1), a(ads)=0.29.

Investigation of Calcium Carbonate Scaling Inhibition and Scale Morphology by AFM

The calcium carbonate scale inhibition by two inhibitors, polyacrylic acid (PAA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), has been studied in two heat transfer systems: recirculating cooling water and pool boiling systems. It is found that PBTCA has a better inhibition effect than PAA under identical conditions. The inhibition effect increases with increasing fluid velocity for the cooling water system, whereas in the presence of inhibitors, the fluid velocity has less effect on the scaling behavior. When the initial surface temperature increases, the inhibition efficiency decreases. In the presence of inhibitors, the scaling behavior is insensitive to the change of surface temperature. The relationship between the inhibition effect and the fractal dimension has also been investigated. The results show that the fractal dimension is higher in the presence of inhibitors. The better the inhibition effect, the higher the fractal dimension. XRD and FTIR analyses demonstrate that for the CaCO(3) formed in the pool boiling system, the content of vaterite increases with the increase of inhibition effects. The metastable crystal forms of vaterite and aragonite are stabilized kinetically in the presence of inhibitors. The step morphology has been observed by atomic force microscopy. It is shown that the step space on the CaCO(3) surface increases in the presence of inhibitors. Moreover, with the increase in inhibition effect, both the step space and the fractal dimension increase. Step bunching is also found and discussed in this paper. Copyright 2001 Academic Press.

Crystallization and Transformation Mechanism of Calcium Carbonate Polymorphs and the Effect of Magnesium Ion

The crystallization of calcium carbonate was carried out by mixing CaCl(2) and Na(2)CO(3) solutions. The morphology of precursor formed prior to the nucleation of the polymorphous crystals (calcite and vaterite) varies depending on the feed concentration. The faster nucleation rate of polymorphous crystals in 0.2 mol/L than in 0.05 mol/L solution results in the prompt disappearance of the precursor at 0.2 mol/L. In 0.05 mol/L solutions the lifetime of the precursor is relatively long. The crystallization fraction of vaterite increases with the feed concentration and decreases with the addition rate of Na(2)CO(2) solution. Vaterite takes on the various morphologies of the aggregates of the primary flocculation body (spherulite) depending on the crystallization conditions. Vaterite transforms to calcite by a direct solution-mediated mechanism. During crystallization the concentration attains a stationary value, which increases with the feed concentration and decreases with the addition rate of Na(2)CO(2) solution. This may be due to the crystal size decrease expected from the Gibbs-Kelvin equation. Magnesium ion suppresses the transformation of vaterite by inhibiting the growth of the calcite. Magnesium ion is selectively included in calcite and causes the increase of the attained concentration and the remarkable change in the morphology of calcite especially in 0.05 mol/L solution. Copyright 2001 Academic Press.

Crystalline properties of carbamazepine in sustained release hydrophilic matrix tablets based on hydroxypropyl methylcellulose

The influence of hydroxypropyl methylcellulose (HPMC) on the crystal habit properties of carbamazepine in sustained release matrix tablets and in aqueous solutions was investigated using differential scanning calorimetry (DSC), X-ray powder diffraction and scanning electron microscopy (SEM). The results suggest that HPMC inhibits the transformation of carbamazepine to carbamazepine dihydrate in the gel layer of hydrated tablets and in aqueous solutions (depending on HPMC concentration), participates in its crystallization process and induces amorphism of carbamazepine crystals. The mechanism which explains these effects envisages the polymer serving as a template or microsubstrate for nucleation in the crystallization process. We assume that the interaction between the drug and polymer occurs by hydrogen bonding. The hydroxyl groups of the polymer may attach to the drug at the site of water binding, and thus its transformation to the dihydrate form, is inhibited. A more specific interaction involves structural matching (similar bond spacing distances) between inter-atomic distances in the crystal lattice of carbamazepine dimer and intra-atomic distances along the polymer chain.

The Role of Bicarbonate Ion in Calcite Scale Formation

Summary.

In this paper, we study the influence of the seed surface area, supersaturation ratio, bicarbonate ion concentration, and pH on the calcite precipitation rate. All other things being constant, the rate is a nearly precipitation rate. All other things being constant, the rate is a nearly linear function of seed surface area and supersaturation ratio. The rate also, surprisingly, depends on the concentration of bicarbonate ion, which is not a thermodynamically relevant species. There is no discernable effect of pH on the rate after the effects of pH on the supersaturation ration and bicarbonate ion concentration are accounted for.

Introduction

Calcite is one of the primary scale-forming minerals responsible for the fouling of oilfield production wells and equipment. Because of its importance, its rate of formation and the influences of various metal ions and other compounds on that rate have been studied extensively. Virtually all these other studies either implicitly assume or explicitly state that precipitation rate in a well-mixed system is a function only of the amount of seed and the saturation ratio (SR).

The primary goal of this work is to solve a puzzle that we had observed some time ago that conflicts with the assumptions stated above: the rate of calcite scale formation appears to proceed faster at lower pH than at higher pH. This is not predicted by any published model, nor pH. This is not predicted by any published model, nor has it been reported in the literature to the best of our knowledge. Another goal is to determine, if possible, what mechanism determines the rate of calcite scale growth. These are part of the overall goal: to predict scaling severity from water chemistry and physical parameters.

Theoretical treatments of the rate of crystallization start from the premise that nucleated precipitation rates depend only on surface properties and the free energy change involved in crystallization. The free energy change is proportional to the saturation index (SI), which is proportional to the saturation index (SI), which is proportional to log of SR, or SR-1 for SR near one. proportional to log of SR, or SR-1 for SR near one. The relevant surface property to be considered depends on the model considered. For diffusion-limited growth, the relevant property is simply the surface area. Crystallization rate is known to be diffusion-limited in a stagnant pool. In wells, production equipment, and our experiments, the flow is turbulent or swiftly moving and the rate is not likely to be limited by bulk diffusion. Even in turbulent flow, however, a stagnant boundary layer exists around each calcite particle. If diffusion through this layer is rate-determining (i.e., diffusion is slower than incorporation into the lattice), then the rate should be strictly proportional to the seed surface area.

If the rate is diffusion-limited, it should also be proportional to the concentration or activity difference between proportional to the concentration or activity difference between the surface and the bulk solution outside the boundary layer. This follows from Fick's law. If incorporation is fast, the SR at the surface is unity; the rate will then be proportional to the bulk SR minus unity for all SR where the proportional to the bulk SR minus unity for all SR where the rate is limited by diffusion through the boundary layer. It is generally agreed that for crystalline growth to occur at low supersaturations, growth units must be incorporated into a crystal along the self-propagating surface step that results when a line defect in the bulk crystal intersects the surface. This surface step twists itself into a spiral-shaped curve during crystal growth, and this model is called the spiral growth model. The spiral growth model was originally developed to describe the crystalline growth that occurs when neutral molecules are deposited from a vapor onto a crystalline surface. Incorporation of molecules into the crystal at the step has been shown to be the rate-controlling step in that case. Such surface spirals have unequivocally been shown to exist on ionic crystals grown from solutions and can be shown to be necessary to explain the "high" growth rates observed for such crystals. Whether this incorporation step is the rate-determining step for ionic crystallization from solution is an open question. It is generally believed that this is the step in crystal growth with which threshold inhibitors interfere.

The spiral growth law predicts a rate proportional to the number of growth spirals involved, with some slight modification because of spiral cooperation and interference. The number of spirals can be argued to be proportional to the initial seed mass, to the seed mass present proportional to the initial seed mass, to the seed mass present at any time, or to the seed area. The spiral growth law also predicts a rate that is proportional to the SI at high SI and proportional to the square proportional to the SI at high SI and proportional to the square of the SI at low SI. A rate that depends on the square of the SI at low SI is usually taken as proof that the rate is controlled by incorporation into the spiral. The determination of a rate law consequently gives an indication of the controlling mechanism.

Experimental Procedure

All experiments were run in a jacketed 400-cm3 beaker kept at 40.0 degrees C [104 degrees F] with circulating water from a thermostatted bath. The beaker was fitted with a Teflon lid scaled to the beaker with a Viton O-ring.

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