Adsorption of organic acids in oil on crushed marble at varying temperatures and ambient pressure

their


Graphical Abstract
Adsorption of organic acids in oil on crushed marble at varying temperatures and ambient pressure Mohammad Sarlak, Khosro Jarrahian, Alan J McCue, James A Anderson, Yukie Tanino Displacement of one fluid by another within a porous medium is relevant to many processes such as oil and gas recovery from hydrocarbon reservoirs.Immiscible displacement encountered in the oil and gas recovery is influenced, at the pore scale, by the properties of the grains (size distribution, roughness, mineralogy) and how they are arranged (pore topology and geometry) [1,2,3,4,5], the fractional volumes of the fluids initially occupying the pores [6,7,8], the velocity of the fluids [9,10], and the properties of the fluids (chemical and physical constituents, which in turn alter fluidfluid-grain contact angle, fluid-fluid interfacial tension, viscosity, and density) [6,11,12].Constituents in the oil phase can affect pore scale displacement via several Email addresses: m.sarlak@abdn.ac.uk (Mohammad Sarlak), ytanino@abdn.ac.uk (Yukie Tanino) pathways, one of which is sorption and subsequent alteration of the wettability of grain surfaces towards hydrophobic conditions.
Temperature controls both fluid-fluid and fluid-rock interactions [49,50,51].A number of studies have explored the impact of adsorption of stearic acid and cyclohexanepentanoic acid on the calcite surface at varying temperatures by measuring contact angle and interfacial tension [15,41,42,43,44].
Rezaei Gomari et al. [41], Rezaei Gomari and Hamouda [44], Jarrahian et al. [45], Norrman et al. [46], Haagh et al. [47] and Al-Shirawi et al. [48] studied the effect of carboxylic acids (stearic acid and cyclohexanepentanoic acid) structure and chemical composition, water composition, temperature and pH on calcite, mica, dolomite and limestone surface wettability using advancing and receding contact angles, interfacial tension measurements, zeta potential measurements, Thermogravimetric Analysis, vapor adsorption isotherm, Fourier Transform Infrared, Atomic Force Microscopy, X-ray Photoelectron Spectroscopy, Time-Of-Flight Secondary Ion Mass Spectrometry and Gas Chromatography Mass Spectrometry.They concluded that stearic acids changed calcite surface wettability from water-wet to strongly oil-wet at pH less than 7 and were more strongly adsorbed on the calcite compared to the mica, the limestone and the dolomite.
The aim of this paper is to improve our understanding of adsorption of stearic acid and cyclohexanepentanoic acid on marble (carbonate rock) as well as their adsorption strength through a series of adsorption experiments at various times.Stearic acid and cyclohexanepentanoic acid have been investigated in the literature to determine the impact of organic compounds available in the reservoir oil on carbonate rock [42,43,44,45,46,47,48].Although there is a large body of research available about organic compounds available in the reservoir oil, stearic acid and cyclohexanepentanoic acid adsorption has not been comprehensively investigated.This paper presents impact of time and temperature on adsorption of stearic acid or cyclohexanepentanoic acid on marble at ambient pressure.The amount of adsorbed acids on the marble grains was measured using GC-FID.Contact angles were measured to demonstrate the impact of adsorption of stearic acid or cyclohexanepentanoic acid on the wettability of the marble.The adsorption kinetics, isotherm adsorption parameters using common models in literature and thermodynamic parameters were calculated.PSA, SEM, and BET were also performed to characterise substrate (marble).

Materials and Methods
In this study marble was used to represent carbonate rock as it is a common form of CaCO 3 under ambient conditions.Carbonate pore spaces are mainly rounded and marble was used to obtain rounded calcite when is crushed [52,53].Crushing most limestones would produce semi-rounded and partially rhombic calcite of a mixture of grain sizes.Marble often has rounded moreequally dimensioned grains of calcite (sometimes called sucrosic or homoblastic).
Solutions of stearic acid or cyclohexanepentanoic acid in n-hexadecane was prepared to model oil phase.N-hexadecane was used to simplify the complexity of crude oil composition and minimise oil evaporation due to running the experiments at elevated temperature for a long period of time, whereas n-decane and toluene were used as model oil/solvent in previous researches [15,37,42,44].A simple synthetic brine was also used for contact angle measurements.

Model carbonate rock
Following Bowden et al. [3], Tanino et al. [9] and Zacarias-Hernandez et al. [54], marble from Carrara, Italy was used as an analogue for carbonate rock.A block of marble was first ground by use of Tema mill (Fritsch) and then sieved to collect the fraction which was finer than 45 µm.Grains were cleaned with methanol, dichloromethane and methanol, sequentially [3].The grains were then air dried in a fume hood for 24 hours before being heated at 373K for 48 hours to evaporate any residual methanol.
The marble grains were subsequently submerged in low concentration (approximately 2 vol.%) hydrochloric acid solution at 298 K for approximately 5 minutes to remove fine fractions [3] and then rinsed with distilled water.On completion of treatment, the grains were submerged in methanol, dichloromethane and methanol for 24 hours, sequentially.Finally, the grains were then allowed to dry in a fume hood for 24 hours prior to heating to 333 K for 48 hours to evaporate any residual methanol.
The  A.1). XRD result for treated marble is also shown in Figure A.3b.The main mineral constituents on treated marble is calcium carbonate.The result confirms that the sample is predominately calcium carbonate with approximately 0.5% of dolomite and 1-2% of potassium aluminosilicate.
Marble from Carrara, Italy was also used for contact angle measurements.Marble was cut into pieces approximately 10×10×5 mm in size with a diamond saw (Malvern Lapidary, 245 mm diameter) and a horizontal grinder (Jones & Shipman 1400).The two 10×10 mm surfaces were polished using a lap wheel with a solution of MicroPolish II Alumina 0.3 µm (Kent 3 Automatic Lapping and Polishing Unit, Engis Ltd).

Test fluids
Test oils comprised various concentrations (200 to 2200 mg/L) of stearic acid (Sigma-Aldrich, ≥ 98.5%) or cyclohexanepentanoic acid (Sigma-Aldrich, 98%) dissolved in n-hexadecane (Fisher Scientific, 99%).The molecular structure of stearic acid and cyclohexanepentanoic acid are shown in Table 1.The brine in the contact angle measurements were 5 wt.%NaCl and 1 wt.%KCl [2] in deionised water.The density and viscosity of test fluids used in this paper are listed in Tables B.1 to Table B.3.

Contact angle measurements
Three polished marble blocks were cleaned with methanol (Fisher Scientific, ≥ 99.8%), dichloromethane (Fisher Scientific, ≥ 99.8%) and methanol sequentially to remove any hydrocarbons, salt and water.After drying in an oven at 333 K, one of the blocks was fully submerged in n-hexadecane in a glass cuvette, and the other two were fully submerged in 2000 mg/L of cyclohexanepentanoic acid or stearic acid in n-hexadecane for 72 hours at 298 K following the procedure developed by Christensen and Tanino [55].After 72 hours, a drop of brine (equilibrated with test oils for 72 hours) was manually dispensed onto the substrate using sessile drop method with FTA instrument (FTA100, First Ten Angstroms) and imaged using a camera (FLIR USB 2.0-FMVU-03MTM-CS: 0.3 MP, 60 FPS, Aptina MT9V022, Mono) (Figure 1).At least six oil-brine contact angle measurements for each of the three oil phases were performed.

Adsorption and adsorption strength experiments
Three sets of experiment were designed to simulate the rock and fluid interactions and determine adsorption and adsorption strengths of stearic acid and cyclohexanepentanoic acid.Approximately 0.50 g of marble grains were placed into glass vials and exposed to 4 mL of model oils for 336 hours (the required time to achieve equilibrium).The mixture was agitated using a shaking water bath (Grant GLS Aqua Plus) at constant temperature of either 298, 313, 333 K.An aliquot of 100 µL was taken after 168, 336, and 504 hours and analysed by GC-FID (varian cp-3800, ZB-FFAP GC column 30 m × 0.25 mm × 0.25 µm) to measure the amount of stearic acid or cyclohexanepentanoic acid adsorbed on the substrate.
333 K was chosen as the maximum temperature considered as approximately 25% of world oil reservoirs are around 333 K [56].The adsorption experiments were performed at ambient pressure.To do adsorption experiments at reservoir pressure, it was required to design a high pressure vessel, capable to homogenise fluids prior to sampling and take aliquots at reservoir pressure.The experiments at reservoir conditions are also very time consuming.We could not outsource a setup or fabricate it internally to meet our experimental requirements in short term.Investigating the impact of pressure on the adsorption of stearic acid and cyclohexanepentanoic acid is a topic for future work using more sophisticated laboratory apparatus.
To determine the amount of strongly held adsorbates and its dependence on temperature, the remaining mixtures from adsorption experiments were centrifuged and liquid was decanted.The remaining grain was then exposed to 4 mL of fresh n-hexadecane.The mixture was agitated using a shaking water bath (Grant GLS Aqua Plus) at constant temperature (298, 313, or 333 K) and aliquots of 100 µL were taken after 168, 336, and 504 hours and analyzed using GC-FID.
The equilibrium concentrations (C e ), mass of adsorbate per volume of adsorbent, was calculated using GC-FID and the adsorbent loading (Q e ), the mass of adsorbate per adsorbent mass, was also determined using the following expression: Where C i is the initial concentration of the solution, ρ is the density of the solvent, m i and m r are the initial and remaining mass of the solution, and X is the mass of marble which is assumed to remain constant.

Adsorption kinetics, Langmuir model and thermodynamic parameters
Interaction mechanism between adsorbate and adsorbent are determined from kinetics of adsorption.Adsorption kinetics could predict adsorption rate and provide information about the mechanism of adsorption [50].Pseudo-first-order, pseudo-second-order and intra particle diffusion are the most common adsorption kinetic models used to understand the mechanism of adsorption of stearic acid and cyclohexanepentanoic acid on the marble [57,58].
Pseudo-first-order kinetic model was introduced by Lagergren (1898) for solid-liquid interface adsorption  process as given in below [50]: Where Q e (mg/g) is the equilibrium adsorbing loading and Q t (mg/g) represents the amount of adsorption on the marble at time t.K 1 (1/min) is constant rate of pseudo-first-order model and is calculated from slope of ln (Q e -Q t ) versus t.Pseudo-second-order kinetic model was also introduced by Lagergren at 1898 as below [50]: Where K 2 is constant rate of pseudo-second-order model and is obtained from the plot of t/Q t versus t.
The first and second-order kinetic models are used to understand the type of reaction and constant rates during adsorption of stearic acid and cyclohexanepentanoic acid on the marble.Intra-particle diffusion model is used for internal and external diffusion mechanisms [59,60,61].
Where k i is the intraparticle diffusion rate constant [M/MT 1/2 ] and P i [M/M] is the value of Q t at t= 0. Intra particle diffusion is the main mechanism if P i = 0 and the other mechanisms (external diffusion and adsorption onto the active sites) are involved in adsorption process if P i 0 [62].
There are several models in the literature to quantify adsorption processes and evaluate adsorption equilibriums such as Henry's, Freundlich's, Temkin's and Langmuir's isotherm.Crocker and Marchin [63], Madsen et al. [64] and Dubey and Waxman [65] suggested that the Langmuir's isotherm is the most suitable model to investigate the adsorption of crude oil organic components on reservoir rocks.Based on the results obtained in this paper Langmuir's isotherm is a reliable model to examine adsorption of stearic acid and cyclohexanepentanoic acid on a marble surface after sufficient time (Sec.3.3).
The general form of Langmuir's model [66] for solidliquid adsorption processes is given by: Where Q m is the maximum adsorption capacity (mass of adsorbate per mass of adsorbent) and K v is the volumetric adsorption constant (volume of adsorbent per mass of adsorbate).Rearranging Eq (5) yields the linear form of the Langmuir equation: Freundlich model proposes a multi-layer adsorption onto a heterogeneous surface [67] and defined by: Where K f is Freundlich constant and shows the adsorption capacity of stearic acid or cyclohexanepentanoic acid on the marble and 1/n is heterogeneity factor and relates to adsorption intensity [66,67,68].
Temkin model is also a linear isotherm and represent as follows [50,69]: Where B is the adsorption surface capacity per unit binding energy and K t is adsorption constant.
Thermodynamic parameters such as free energy change (∆G • ), enthalpy change (∆H • ) and entropy change (∆S • ) are a key parameter to determine the spontaneity of adsorption process and can be calculated from the variation of the thermodynamic equilibrium constant K T with the change in temperature and given by: Where α s is the activity of the adsorbed adsorbate, α e is the activity of adsorbate in the equilibrium solution, C s is the amount of adsorption in mmol of adsorbate per gram of adsorbent, C em is the adsorbate concentration in the equilibrium solution (mmol/mL), ν s is the activity coefficient of the adsorbed adsorbate and ν e is the activity of adsorbate in the equilibrium solution.As adsorbate concentration in the solution decreases and approaches to zero, K T is obtained by plotting ln(C s /C em ) vs C s [70,71].With calculating K T , thermodynamic parameters (∆G • , ∆H • , and ∆S • ) can be calculated by Van't Hoff equations [72,73,74]: Where T is absolute temperature and R is the universal gas constant (8.314J/(K mol)) J o u r n a l P r e -p r o o f Journal Pre-proof

Impact of stearic and cyclohexanepentanoic acid on contact angle
Images of selected static brine droplets dispensed on marble surfaces aged for 72 hours in n-hexadecane, 2000 mg/L of cyclohexanepentanoic acid in nhexadecane, and 2000 mg/L of stearic acid in nhexadecane at 298 K, are presented in Figure 2(a, b  and c).The mean of contact angles measured in nhexadecane, 2000 mg/L of cyclohexanepentanoic acid in n-hexadecane, and 2000 mg/L of stearic acid in pure n-hexadecane were 71 • ±4, 115 • ±13, and 136 • ±7 respectively (Figure 2d).This demonstrates that the wettability of marble surface is altered from water-wet to oil-wet through exposure to cyclohexanepentanoic acid or stearic acid solutions , consistent with previous measurements [2,55,75].

Effect of time on adsorption
In wettability studies, the duration a substrate and fluid are in contact is regarded as an important parameter.The effect of time on adsorption studies is not fully understood and has not been studied by many authors [50].The time required for adsorption of organic components in the oil phase on rock surface, can be used as an index to restore the wettability of the geological samples to their initial state in the laboratory [34].
Alotaibi et al. [76] reported in their study, Isoelectric point (IEP) for carbonate at (101.35 kPa, 298.15 K) falls within the range 9.8-11.9,and Farooq et al. [77] stated the range is between 8.2-8.5 at (101.35 kPa, 298.15 K).The rock surface charge will be positive if the pH of the flowing fluid adjacent to the reservoir rock surface is below IEP of the rock.Since the pH of the brine used in this study was measured 7.85, the marble grain surface carries positive charges and, accordingly, the adsorption layer is formed with the carboxyl group oriented towards it for both acids (Figure 3).
With having adsorbed amounts for stearic acid and cyclohexanepentanoic acid on marble and surface area measured for marble, surface area per molecule can be calculated from the following correlation [78]: Where σ is surface area per molecule, S A is specific surface of marble (0.13 m 2 /g), Γ is the adsorbed amount of stearic acid or cyclohexanepentanoic acid (moles per marble mass) and N A is Avogadro's number, 6.022 × 10 23 molecules per mole.For example, surface area of a molecule of stearic acid on marble is 2.98×10 −2 nm 2 .The equivalent value for cyclohexanepentanoic acid is 1.43×10 −2 nm 2 .Figures 4 and 7 show the impact of time on adsorption of stearic acid or cyclohexanepentanoic acid on marble grains at 298 K using pseudo-first-order, pseudo-second-order and intra-particle diffusion models [79].As shown, adsorption of stearic acid and cyclohexanepentanoic acid are in good agreement with pseudo-second-order model.From intra-particle diffusion model result for both acids in Figure 4c and 7c, it can be understood that adsorption mechanism is mainly due to intra-particle diffusion (linear portion of curve).The intercept of the plot reflects boundary layer effect and relates to boundary layer thickness.The adsorption rates for stearic acid and cyclohexanepentanoic acid increase substantially in first 168 hours at different initial concentrations, and then reach equilibrium gradually after 336 hours.A significant increase in adsorption is observed for both acids when the experimental time is increased from 168 to 336 hours.Subsequently, the adsorption capacities do not change significantly when increasing the experiment time from 336 hours to 504 hours, this suggests that the system is approaching equilibrium conditions at some point after the 336 hours experiment.The equivalent adsorption isotherms for both acids are also shown in Figure 4d and Figure 7d.
The impact of time on stearic acid or cyclohexanepentanoic acid adsorption at 313 and 333 K are also shown in Figures 5, 6, 8, 9. Likewise Figures 4 and  7, the adsorption rates increase substantially in first 168 hours at different initial concentrations, and then reach equilibrium gradually after 336 hours for the majority of concentrations.The adsorption kinetic parameters for stearic acid and cyclohexanepentanoic acid on marble for variable concentrations and temperatures are given at Table 2.
Barati et al. [50] studied the impact of time on the adsorption of a nonionic surfactant with varying concentrations on carbonate surfaces.They found that the adsorption increases with exposure time and reached an equilibrium after a certain time.As mentioned previously, due to the low BET surface area measured for treated marble, the mass of adsorption to unit mass is expected to be low.

Effect of temperature on adsorption and strength of adsorption
Figure 10 presents adsorption capacities at three temperatures for various concentrations of stearic acid or cyclohexanepentanoic acid dissolved in n-hexadecane on an treated marble substrate.The adsorption of stearic acid and cyclohexanepentanoic acid on marble was observed to follow a Langmuir model at all three temperatures considered, in line with literature [13,50].Adsorption was found to increase for all concentrations with increasing temperature which is in agreement with the results obtained by Strand et al. [80] and Barati et al. [50].The increase in adsorption capacities with temperature was observed to be significant from 298 to 313 K for both acids, with more modest increase observed when increasing the temperature from 313 to 333 K.
For stearic acid, the change in adsorption was 2.301 mg/g at C e =270 mg/L when the temperature was increased from 298 to 313 K; whereas from 313 to 333 K the increase was 0.149 mg/g at C e =260 mg/L.Similarly, for cyclohexanepentanoic acid, the change in adsorption was 1.310 mg/g at C e =290 mg/L compared to 0.246 mg/g at C e =280 mg/L from 313 to 333 K. Key adsorption parameters for stearic acid and cyclohexanepentanoic acid on marble grain such as Langmuir max-              3.
As shown in Table 3.
To further compare, the uptake of stearic acid or cyclohexanepentanoic acid on grain marbles, thermodynamic parameters (∆G • , ∆H • , and ∆S • ) were calculated (Table 4).∆G • , ∆H • , and ∆S • were calculated using different models in the literature.From Table 4, adsorption of stearic acid or cyclohexanepentanoic acid on marble grains is a spontaneous process as ∆G • is negative [81,82].The adsorption of stearic acid on marble grains is an endothermic reactions (negative sign of ∆H • ), whereas for cyclohexanepentanoic acid shows an exothermic reactions (positive sign of ∆H • ) [81].Affinity of stearic acid adsorption is greater than cyclohexanepentanoic acid based on ∆S • calculated [81,82].Some of the stearic acid and cyclohexanepentanoic acid adsorbed on the marble grains returned to solution after exposure to fresh n-hexadecane for 504 hours, with the amount returned increased with temperature.The remaining stearic acid (mass) is greater than cyclohexanepentanoic acid on the marble after 504 hours at 298, 313 and 333 K as listed in Table 5 (data for earlier times can be found in Appendix C).This shows that stearic acid bounds to marble grains are stronger than cyclohexanepentanoic acid.
Physical and chemical adsorption process can also be determined from ∆G • value.The free energy change ranges from ∆G • = 20 to 0 kJ/mol for physical adsorption, and for chemical adsorption, it ranges between −80 and −400 kJ/mol.∆G • values fall within the range −20 to −80 kJ/mol (Table 4 ), which suggests that both physical and chemical adsorption is involved [82,83].
It has previously been reported that stearic acid and naphthenic acids adsorbed on calcite [15,37,75] and dolomite [45] desorbed into distilled water [37,75].Following Thomas et al. [84]'s observation, the hightemperature loss corresponded to a monolayer of the adsorbate (chemisorption), and the low-temperature loss was interpreted as physisorption on top of the monolayer and readily removed.Our interpretation of the present experiments is that the acid returned into the fresh n-hexadecane is physi-sorbed mass, and what remains on the grains comprise a monolayer of chemisorbed acids.

Conclusions
The effect of time and temperature on the adsorption behaviour of organic acids in n-hexadecane on marble as well as their adsorption strengths were investigated in this study.Organic acids in the crude oil were represented by stearic acid and cyclohexanepentanoic acid.PSA, NAD, SEM and XRD were utilized to examine the properties of marble.The wetting properties of the marble surface were also evaluated using adsorption and adsorption strength measurements.The main findings are as follows: 1. Stearic acid and cyclohexanepentanoic acid adsorb on marble in the absence of water.Adsorption for both acids increases with temperature over the range considered presently, i.e., from 298 to 333 K. 2. Cyclohexanepentanoic acid mass adsorbed on marble is slightly greater than stearic acid.This may be attributed to the molecule surface area of cyclohexanepentanoic acid being smaller than that of stearic acid.3. Contact angle measurements indicate that adsorption of stearic acid and cyclohexanepentanoic acid alters the wettability of marble even in the absence of an aqueous phase.4. A portion of acid adsorbed on the marble surface was removed when submerged in fresh nhexadecane, indicating that stearic acid and cyclohexanepentanoic acid adsorbed on marble grains are desorbed to an extent.Value of ∆G • calculated also suggests that both physical and chemical adsorption were involved for adsorption of stearic acid or cyclohexanepentanoic acid on marble grains.Greater adsorption affinity of stearic acid on marble grains compared to cyclohexanepentanoic acid was resulted from ∆S • calculated.This is also confirmed by less stearic acid returned to solution compared to cyclohexanepentanoic acid.the size distribution of treated marble.Laser diffraction spectrometry gives an estimation of the percentage of particles belonging to a certain size using the principle of light scattering.On completion of cleaning, the grains were dispersed in water to separate particles individually.
The textural properties of treated marble were investigated using NAD technique and Brunauer-Emmett-Teller (BET) surface areas were calculated.The samples were analyzed using a BET instrument (Micromeritics ASAP 2020).
Approximately 0.50 g was placed into a glass cell and degassed under reduced pressure and elevated temperature (approximately 473 K) using a heating mantle to remove water and other contaminants.After the sample was degassed, the cell was moved to the analysis port and a dewars of liquid nitrogen was used to cool the sample and maintain it at a constant temperature.
For SEM, approximately 0.50 g of treated marble was mounted onto aluminum stubs and carbon coated.The measurements were carried out using a Carl Zeiss Gemini SEM 300-high resolution Field Emission SEM (FE-SEM) with Secondary Electron (SE), Back Scattered Electron (BSE) and Cathodoluminescence (CL) detectors at magnifications from 100 to 1500x.
XRD was performed using a Panalytical Empyrean powder diffractometer with Johansson monochromator to quantify/identify the types of minerals present within treated marble.Approximately 2.0 g of dried and cleaned samples were used.Each sample was analyzed between 5 • and 80 • 2-theta (θ) and a step size of 0.013 • .Samples were exposed to x-ray radiation, which was emitted from a copper anode at 35 kV, 30 mA.BET surface area for untreated and treated marble was calculated from NAD measurements.As expected, exposure to hydrochloric acid reduced the surface area (Table A.1), consistent with the removal of the finest marble grains captured in SEM images (Figure A.1).This also corresponds well with PSA result, as the loss of the smallest particles in the system correlates with a significant drop in surface area.
XRD results for untreated and treated marble are shown in Figure A.3.It can be clearly observed that the main mineral constituents on untreated and treated marble is calcium carbonate.The result for untreated marble confirms approximately 95% calcium carbonate, 2% calcium magnesium carbonate (dolomite), and 3% magnesium silicate.On treated marble, the sample is predominately calcium carbonate with a much-reduced proportion of dolomite (approximately 0.5%) and 1-2% of potassium aluminosilicate.Comparing the XRD result for both untreated and treated marble shows that there is no significant difference in mineralogy.As discussed previously, acid has only removed the fine fractions which are mainly calcium carbonate.
SEM images at different magnifications, particle size distribution of marble are shown in Figure A.1(b,d,f) and Figure A.2b, respectively.BET surface area calculated from NAD measurement was 0.13 ± 0.01 m 2 /g (Table

Figure 1 :
Figure 1: Marble block preparation for contact angle measurements

Figure 2 :Figure 3 :
Figure 2: Contact angle of a brine droplet on marble surface aged in (a) n-hexadecane, (b) 2000 mg/L cyclohexanepentanoic acid in n-hexadecane, (c) 2000 mg/L stearic acid in n-hexadecane for 72 hours at 298 K and (d) contact angle measurements for each solution; vertical bars depict standard deviation.Note that the brine droplet volumes differ between in (a), (b) and (c).N-hexadecane, cyclohexanepentanoic acid in n-hexadecane and stearic acid in n-hexadecane are depicted by +, × and ⋆ respectively.Measurement means are also shown in ⊕.

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Appendix A.
Impact of HCl treatment on crushed marble properties Particle size distribution was measured using a laser diffraction analyzer (Beckman Coulter LS13 320 with an aqueous liquid module attachment) to characterize J o u r n a l P r e -p r o o f Journal Pre-proof

Figure A. 1
shows the SEM images of untreated and treated marble grain surfac.It is readily evident that exposure to hydrochloric acid removed fine grains (sizes < 0(1) µm).
Figure A.2 shows particle size distribution for untreated and treated marble.Exposure to hydrochloric acid preferentially removed particles smaller than 20 µm.

Table 1 :
Structural formula and molar masses of the organic acids considered.

Table 2 :
Adsorption kinetic parameters for stearic acid or cyclohexanepentanoic acid on marble grains.
L ), Freundlich adsorption constant (K f ), and Temkin adsorption constant (K t ) are given in Table

Table 3 :
Isotherm adsorption parameters for stearic acid or cyclohexanepentanoic acid on marble grains.

Table 4 :
Thermodynamic parameters for adsorption of stearic acid or cyclohexanepentanoic acid on marble grains.

Table 5 :
Stearic acid and cyclohexanepentanoic acid returned to the solution at 298, 313, and 333 K after 504 hours.

Table B .
1: Densities and viscosities of the synthetic brine.

Table B .
2: Densities and viscosities of the stearic acid solutions.Table B.3: Densities and viscosities of the cyclohexanepentanoic acid solutions.Table C.1: Stearic acid and cyclohexanepentanoic acid returned to the solution at 298, 313, and 333 K after 168 hours.