Calcite and barite precipitation in CaCO3-BaSO4 ...

Arab J Geosci (2017) 10:220 DOI 10.1007/s12517-017-3005-1

ICAGE 2016

Calcite and barite precipitation in CaCO3-BaSO4-NaCl and BaSO4-NaCl-CaCl2 aqueous systems: kinetic and microstructural study Hanen Azaza 1 & Lassaad Mechi 1 & Amira Doggaz 1 & Virgil Optasanu 2 & Mohamed Tlili 1,3 & Mohamed Ben Amor 2,3

Received: 28 October 2016 / Accepted: 25 April 2017 # Saudi Society for Geosciences 2017

Abstract During the production of hydrocarbons from subterranean reservoirs, scaling with calcium carbonate and barium sulfate causes flux decline and dangerous problems in production facilities. This work is intended to study the effect of calcium ions on the precipitation of barium sulfate (barite); then, the effect of the formed barite on calcium carbonate crystallization. The conductometric and pH methods were used to follow the progress of the precipitation reaction in aqueous medium. The obtained precipitates were characterized by FTIR, RAMAN, SEM, and XRD. It was shown that Ca2+ in the reaction media does not affect the microstructure of barite even for higher calcium–barium molar ratio. It influences the precipitation kinetics and the solubility of barite by the formation of CaSO4° ion pairing as a predominant role of complex formation (CaSO4) and the increase of the ionic strength. In Ca(HCO3)2-BaSO4-NaCl aqueous system, experiments have showed that added or formed barite in the reaction media accelerates calcite precipitation. No effect on the microstructure of heterogeneous formed calcite which remain

calcite shape. However the presence of carbonate ions affects slightly the microstructure of barite. Keywords Calcium carbonate . Barite . FTIR

Introduction Inorganic salts such as barium sulfate, calcium carbonate, and calcium sulfate are generated in water treatment systems, particularly in off-shore oil production, forming hard scales in production facilities. These unwanted minerals are a persistent and common problem encountered during the production of hydrocarbons from subterranean reservoirs, result of variation in chemical and thermodynamic parameters (Melo et al. 1988; Breen et al. 1991; Hamed et al. 2000). The mixture of incompatible fluids containing various ions is the main reason for the precipitation of more salts, may be combined to form scale on the wall of pipes, pumps, etc. This

This article is part of the Topical Collection on Georesources and Environmental Management * Lassaad Mechi [email protected] Hanen Azaza [email protected]

Mohamed Ben Amor [email protected] 1

Lab of Natural Water Treatment, Water Research and Technologies Center, Borj-Cedria Technopark University of Cartage, PO-box N°273, 8020 Soliman, Tunisia

2

ICB UMR 6303 CNRS, Université de Bourgogne Franche Comté, 9 av Alain Savary, 21078 Dijon Cedex, France

3

Department of Chemistry, Faculty of Science—King Khalid University, Abha 9033, Saudi Arabia

Amira Doggaz [email protected] Virgil Optasanu [email protected] Mohamed Tlili [email protected]

220

Arab J Geosci (2017) 10:220

Page 2 of 9

insoluble and very compact deposit can cause irreversible damage and dangerous for pipelines and production facilities (Editions TECHNIP 1976); e.g., in the sea of Miller field (North Sea), engineers were shocked by a drop in production of 4770 m3/d to zero in just 24 h (Crabtree et al. 1999). As mentioned above, calcium carbonate, barite, and calcium sulfate are the major scaling contributors. Having the lowest solubility, barium sulfate is the main disturbance in equipment of oil and it crystallizes instantly when water rich in sulfate is mixed with barium-rich water. This is the case of certain waters such as in Zarzaitine or Hassi Massaoud platforms. The literature presented important studies on the pure and mixed precipitation of these sparingly soluble salts. Coprecipitation of calcium carbonate with calcium sulfate (Sudmalis and Sheikholeslami 2000; He et al. 2009; Liu et al. 2012; Zarga et al. 2013), barium carbonate with calcium carbonate (L’vov and Ugolkov 2004), and barium sulfate with calcium sulfate (Zhu 2004; Naseri et al. 2015, Azaza et al. 2017) have been investigated to understand the mutual effect between these salts (the precipitation of one salt when another salt is present in a solid form). However, no study has been focused on the effect of barite formation on the kinetics of calcium carbonate precipitation. The aim of this paper is to study the effect of calcium ions on barium sulfate precipitation and to investigate the effect of the formed BaSO4 on calcium carbonate scale formation in synthetic solution. For this, precipitation tests were made in different aqueous media. The precipitation kinetic is evaluated using the conductometric method. The formed solids are recuperated by filtration and analyzed using FTIR, Raman, and XRD techniques.

Experimental procedure Materials For all precipitation tests, the experimental unit of Fig. 1 was conceived. A 1 L-closed thermostatic cell was used to maintain the solution at constant temperature by a thermostatic Fig. 1 Experimental assembly

liquid circulation (303 K). The magnetic stirrer was used to keep the solution homogeneous. The solution-pH and conductivity were recorded throughout the experience. Work solutions Used chemicals BaCl 2 .2H 2 O, Na 2 SO 4 , CaCl 2 .2H 2 O, NaHCO3, NaCl, and CaCO3 were of analytical grade from SIGMA-ALDRICH and Fluka. CO2 gas was supplied by air liquid in Tunisia. Calcium effect on barite precipitation To observe the effect of calcium ions in barium sulfate precipitation, five solutions were prepared (Table 1). Calcium ion concentration was varied from 0 to 57 × 10−4 M for constant barium and sulfate content ([Ba2+] = [Ca2+] = 3 × 10−4 M). The pH of all solutions was about 5.7. The precipitation test starts from the addition of sodium sulfate to the calcium chloride and barium chloride solution. Mixed precipitation of BaSO4-CaCO3-H2O system The experimental protocol performed for these reactions was carried out in two different operating modes with double decomposition method. –

–

Mode 1: Adding 0.7 of barite seeds to1 L of supersaturated, with respect to calcite, Ca(HCO3)2 solution prepared by dissolving 400 mg of pure CaCO3 in distilled water under CO2 bubbling. The temperature was maintained at 303 K and the pH was about 6.7 (Table 2). Mode 2: Supersaturated solutions of barium sulfate and calcium carbonate were prepared by mixing 250 mL of BaCl2.2H2O aqueous solution and 250 mL of Na2SO4 aqueous solution with 500 mL of supersaturated CaCO3 solution at 303 K. At the beginning of the experiment, the pH is equal to 6.7 (Table 2).

All experiments were repeated several times to ensure experimental results.

Arab J Geosci (2017) 10:220

Page 3 of 9 220

Table 1 Solutions composition for the study of Ca2+ effect on barite precipitation [Ba2+] (M) [SO42−] (M) [Ca2+] (M) R = [Ca2+]/[Ba2+] Experiment a Experiment b Experiment c Experiment d

3 × 10−4 3 × 10−4 3 × 10−4 3 × 10−4

3 × 10−4 3 × 10−4 3 × 10−4 3 × 10−4

0 0 9 × 10−4 3 30 × 10−4 10 57 × 10−4 19

Solid characterization The solid phase obtained was analyzed by FTIR, XRD, SEM, and Raman spectroscopy. Infrared spectra of the samples in KBr pellets were obtained by defusing reflectance by accumulating 40 scans on an Affinity-1C Schimadzu spectrophotometer, in the range of 4000–400 cm−1 with 4 cm−1 of resolution. MicroRaman spectrometry examination was obtained by using a Jobin Yvon high-resolution Raman spectrometer (brand: HORIBA Jobin Yvonet model: LabRam HR). Micro-Raman spectra were obtained with a LABRAM spectrometer (ISAJobin Yvon). XRD is carried out at room temperature with a Philips X’PERTPRO diffractometer in step scanning mode using Cu Kα radiation (λ = 0.15418 nm). The XRD patterns were recorded in the scanning range 2 h = 5–90°. A small angular step of 2 h = 0.017° and fixed counting time of 4 s were used. The XRD reflection positions were determined using BX-Pert HighScore Plus^ software.

Ba2þ þ SO2− 4 →BaSO4

ðR3Þ

Supersaturation is the driving force for the crystallization; thus, nucleation and crystal growth is initiated when the value of the supersaturation coefficient in the solution is greater than 1. Supersaturation coefficients Ωi for all sparingly soluble salts (i) which can form in the studied solutions were calculated as follow:

 γ Ca2þ Ca2þ γ HCO−3 HCO−3 :10pH−pK2 ΩCaCO3 ¼ ð1Þ k sp;CaCO3

2−  γ Ca2þ Ca2þ γ SO2− SO4 4 ΩCaSO4 ¼ ð2Þ k sp;CaSO4

2−  γ Ba2þ Ba2þ γ SO2− SO4 4 ð3Þ ΩBaSO4 ¼ k sp; BaSO4 Where [] is the molar concentration of the subscripted aqueous species, ksp is the solubility product, γ is the ionic activity coefficient of the subscripted aqueous species, and K2 is the second dissociation constant of H2CO3. For T = 303 K: k sp;CaCO3 (calcite) = 3.1 × 10−9 (Bischoff et al. 1993), k sp;CaSO4 2H2O = 4.25 × 10−5 (Marshall and Slusher 1966) and k sp; BaSO4 = 1.14 × 10−10 (Monnin 1999). γi is calculated us function of the ionic strength I by the following equation (Davies 1962).  pffiffi  I 2 pffiffi −0:3I logγ i ¼ −AZi 1þ I −3

where A ¼ 1:82  106 ðεTÞ =2 , ε is the dielectric constant of water and T is the temperature in K.

Thermodynamic analysis The calco-carbonic system is a three-phase system: CaCO3 (solid) CO2 (gas)-H2O (liquid) in which the precipitation reaction is represented by the following overall equation: Ca2þ þ 2HCO−3 →CaCO3 þ CO2 þ H2 O

ðR1Þ

Gypsum and barite precipitation reactions are accorded to the two following equations: Ca2þ þ SO2− 4 þ 2H2 O→CaSO4 :2H2 O

ðR2Þ

Table 2 Solutions used to study the crystallization in BaSO4-CaCO3H2O system [Ca2+] (M)

[HCO3−] (M)

Experiment 4 × 10−3 8 × 10−3 a Experiment 4 × 10−3 8 × 10−3 b Experiment 4 × 10−3 8 × 10−3 c

Mode 1:mBaSO4 Mode 2:[Ba2+] (g) (M) 0

0

0.7

0

0

3.10−3

Results and discussion Seeing that the solution composition differs for each experiment and in order to compare results, it was chosen to present the Δσ conductivity instead of the solution conductivity curves. Delta conductivity (Δσ) is the difference between the initial conductivity and the conductivity at the time t: Δσ = σinitial−σt Effect of calcium ions Calcium ions effect on barium sulfate precipitation is presented based on conductivity measurements and integrated by a morphological and structural investigation. Figure 2 shows precipitation curves in different solutions of Table 1. It clearly shows that the presence of calcium have an effect on barite precipitation kinetics. All curves are characterized by the presence of two zones; the first one, where Δσ increases linearly with time, corresponds to the nucleation, and crystalline

220

Arab J Geosci (2017) 10:220

Page 4 of 9

Fig. 2 Temporary delta conductivity variation (Δσ = σinitial−σt) in the barium sulfate precipitation at T = 30 °C with variables ratios R = [Ca2+]/ [Ba2+]: a R = 0, b R = 3, c R = 10, and d R = 19

growth steps. In the second one, where Δσ does not have a significant variation, equilibrium between the formed solid, and the free ionic species in the solution was established. The decrease of the linear part-slope with calcium content shows that the presence of this Ca2+ decelerates the precipitation rate of barite. However, the decrease of Δσ, when precipitation reaction is achieved and an equilibrium solid/liquid is established, with increasing calcium content can be explained by the formation of a more soluble precipitates in the solution. From a molar ratio R = 3 (Table 1), calcium ion has an effect on the precipitation kinetics of barite bat not on the solubility of the precipitate. It is only from R = 10 that a net effect on both precipitation rate and solubility were recorded. The precipitation kinetics was affected by the greater inhibitory effect of calcium ions which can adsorbed on barite nuclei during formation and growth (Jones et al. 2004); also, the formation of the calcium sulfate ion pairs CaSO4° decreases the free sulfate, hence the saturation state of the solution, as will be shown below. For the effect on the barite solubility, results are in agreement with those reported by Jones et al. 2004 who worked under nearly the similar conditions. The increase of the ionic strength can reduce the barium and sulfate activities and then solubility (Stanford and Watson 1974). Nevertheless, the ionic strength (I = 0.0189 mol/L) of the reaction media remains low even for the richest solution in salts where (R = 19, Table 1) and it cannot be the main responsible for the decrease of solubility. The formation of CaSO4°(aq) can play an important role. Indeed, the equilibrium constant of the reaction (R3) is the solubility product of barite. When expressed considering ion pairs such as BaSO4° and CaSO4°, the solubility product is given by:

 ð4Þ k sp ¼ Ba2þ : SO2− 4 :γ Ba2þ : γ SO2− 4 where [i] and γi are the molar concentration of free ions and the activity coefficients of the designed aqueous spices, respectively.

The equilibrium between an ion pair and an aqueous cation M (Ca2+ or Ba+2) and sulfate can be written as: Å

MSO4 ⇆M 2þ þ SO2− 4

ðR4Þ

The equilibrium dissociation constant is given by:
2þ 
2−  M : SO4 :γ M 2þ : γ SO2− 4
 k ip ¼ MSO04 :γ CaSO Å

ð5Þ

4

Combining Eqs. 4 and 5 (if the ion-pair CaSO4 is considered) leads to: h i k
Ca2þ :γ 2þ 1 sp Å CaSO4 ðaqÞ ¼ :
2þ  Ca : ð6Þ k ip Ba :γ Ba2þ γ CaSO4Å According to Table 1, barium concentration is constant. So, Eq. 6 demonstrates that the ion-pair concentration increase with the amount of the added calcium. Considering this ion-pair formation, the solubility (s) in presence of calcium ions can be expressed as function of the solubility product of barite as follow:  h i Å s s− CaSO4 ðaqÞ ¼ k sp

ð7Þ

Table 3 Solubility of barite in different aqueous media of Table 1 calculated with Eq. 7 [Ca2+] (M)

R = [Ca2+] /[Ba2+]

Experiment 0 0 a Experiment 9 × 10−4 3 b Experiment 30 × 10−4 10 c Experiment 57 × 10−4 19 d

[CaSO4°] (M)

Solubility (M)

0

1.2 × 10−5

2.0 × 10−5

1.8 × 10−5

5.1 × 10−5

3.6 × 10−5

7.9 × 10−5

4.8 × 10−5

Arab J Geosci (2017) 10:220

Page 5 of 9 220

Fig. 3 XRD patterns of barite obtained at R = 0 and R = 10

Equation 7 demonstrates that the solubility increases with the increase of the ion pairs. Both Eqs. 6 and 7 can now explain the increase of the solubility of barite with calcium contents observed in Fig. 2. Table 3 gives the solubility values estimated from Eq. 7 for different experiments of Table 1. The solubility calculation show that for R = 3, the formed calcium sulfate ionic complex does not affect significantly the solubility of barite. For this, the same amount of barite was precipitated despite the slight difference in the kinetics (Fig. 2). For R = 10 and 19, the solubility was increased by about 200 and 300%, respectively. This clearly explains the low amount of the precipitated barite for experiments c and d (Fig. 2). By EDAX analysis of barite formed in supersaturated solutions with

Fig. 4 Specters Raman: a R = 10, b R = 0 (barite pure)

different calcium content, Jones et al. (2004) have been detected small amounts of Ca in barite only for a high calcium content (250 × 10−4 M). So, they assumed that even for a small amount of calcium in the solution, the barite lattice can contain Ca but with amounts below the detection limit of the EDAX detector. The increase of the solubility, deduced from precipitation curves and not calculated by Jones et al. (2004), has been interpreted as a consequence of (i) an increase in the internal free energy of the crystal after incorporation of Ca2+ in the lattice or (ii) a decrease of free sulfate after ion-pairing formation. In order to decide between these two mechanisms, other techniques for the solid analysis (XRD, FTIR, and Raman spectroscopy), not used by Jones et al. (2004), are exploited in the present work.

220

Page 6 of 9

Arab J Geosci (2017) 10:220

Fig. 5 Temporary delta conductivity variation (Δσ = σinitial-σt) in the calcite precipitation at T = 30 °C: a without barium, b 0.7 g of barites, and c [Ba2+] = 3.10−3 M

As it was proposed by Jones et al. (2004), in such systems, the formation of solid solutions having their own thermodynamic properties can be expected. For this, a structural and morphological characterization of the obtained precipitates was carried out. Figure 3 illustrates XRD patterns of the compound obtained in the solution with R = 10 and the pure barite, synthesized at laboratory scale, as reference in the solution where R = 0. The X-ray characterization shows no differences between XRD patterns of the two compounds, in presence (R = 10) and absence (R = 0) of calcium ion. The same structure, which is of pure barium sulfate, was observed. This can excluded the insertion or substation of calcium cations in the sulfate barium lattice. Indeed, insertion or substitution phenomena can move and widen the diffraction. Recently, Azaza et al. (2017) have demonstrated that calcium insertion and substitution in barite lattice occurs if [SO42−] > [Ba2+] at acid medium to obtain a solid solution with dentritic form. However, in the studied solutions (Table 1), [SO42−] and [Ba2+] are equimolar. Further, Raman analysis (Fig. 4) confirms that the compound obtained with R = 10 and pure barite have the same microstructure. So, at light of these analyses, the decrease of the precipitation rate of barite and the increase of its solubility with increasing calcium content is due to: (i) the decrease of barium and sulfate activities because the increasing of the Fig. 6 Temporary pH variation over the calcite precipitation at T = 30 °C: a without barium, b 0.7 g of barite, and c [Ba2+] = 3.10−3 M

ionic strength and (ii) the decrease of the free sulfate ions which form aqueous complex with calcium CaSO4° as a predominant role against the ionic strength. So as possible mechanism, the insertion of Ca+2 in the barite lattice proposed by Jones et al. (2004) should be excluded. Mixed precipitation of BaSO4 and CaCO3 In order to investigate the effect of barite on calcium carbonate precipitation from kinetics and structural point of view, solutions of Table 2 were used. Figure 5 shows the correspondent precipitation curves. In the absence of barium ions and barite, calcium carbonate nucleation starts after 5520 s of the reaction time for a pH of 7.86 (Fig. 6) and a supersaturation coefficient ΩCaCO3 of about 21. The presence of BaSO4 whether in mode 1 (barite was added at solid form as seeds) or in mode 2 (barite was formed in the reaction medium following the reaction R3 before CaCO3 precipitation) has accelerated the nucleation of CaCO3. Here, it should be noted that BaCO3 cannot form in the reaction medium despite its low solubility (ksp = 2.58 × 10−9) which is of the same order of magnitude as calcite (ksp = 3.09 × 10−9). Indeed, for the pH 6.8 of the experiment beginning, the system, with respect to BaCO3 and CaCO3, is nearly at equilibrium; the calculated supersaturation coefficient with respect to these two salts do not

Arab J Geosci (2017) 10:220

Page 7 of 9 220

Fig. 7 Infrared analysis of: a pure BaSO4; b barite + calcite; c pure calcite

exceeds 2. However, the system is supersaturated on BaSO4 at the same conditions of pH; the supersaturation coefficient calculated from Eq. 3 was estimated to be 2.37 × 104 which is very high seeing the lower solubility constant of barite (ksp = 9.88 × 10−11). For such saturation state, instantaneous precipitation of barite occurs in a few seconds after the beginning of the experiment. The remaining barium ions amount in the solution is then very weak (remaining [Ba2+] = solubility of barite (~10−6 M). At light of the above presented results (Fig. 2), calcium ions present in the reaction medium ([Ca2+]/[Ba2+] = 1.3) cannot affect this solubility. So, the precipitation of BaCO3 even for the highest reached pH value (~7.7) is not possible given the low barium concentration. The nucleation time decreases from 5520 to 4680 s under mode 2 and 4200 s for the mode 1. From the slope of the linear part of growth step (Fig. 5), it seems that barite seeds slightly affect CaCO3 growth rate contrary to the nucleation step. This is manifested clearly in pH curves (Fig. 6) showing that Fig. 8 RAMA analysis of: a pure BaSO4; b barite + calcite; c pure calcite

nucleation starts at lower pH; 7.7 and 7.75 for mode 1 and mode 2, respectively. This pH decrease causes a decrease of the supersaturation coefficient (14 for mode 1 and 15 for mode 2) calculated from Eq. 3. So, the presence of barite either following mode 1 or 2 accelerates the calcium carbonate precipitation by acting as a support of CaCO3 heterogeneous nucleation. Figures 7 and 8 show FTIR and Raman analysis of barite, calcite, and calcite formed in presence of barite as for mode 1 or mode 2. This figure shows that the co-precipitated solid form presents all characteristic bands of sulfate vibration in the barium lattice and those of carbonate vibration in calcium carbonate calcite shape. As first observation, the precipitate is composed of two separate phases. This supports the above suggestion that barite plays the role of a support for heterogeneous precipitation of calcite. Detailed analysis shows that carbonate vibrations remains in their positions as for pure calcite. Thereby, barium solids affect only calcium carbonate precipitation rate

220

Arab J Geosci (2017) 10:220

Page 8 of 9

a

b

barite calcite

in Raman and FTIR analyses can be attributed to the presence of carbonate and bicarbonate ions which can form barium carbonate ion pairs. Carbonate species can absorb on BaSO4 lattice and partially substitute sulfate. SEM images indicate that the morphology of calcite (Fig. 9a) is slightly changed in the final product obtained in mode 1 and in mode 2; e.g., Fig. 9b shows solids of mode 1 experiment. This photo shows to separate precipitates of barite with a small size (