Abstract
In this study, nickel nanoparticles (NiNPs) were synthesized and utilized for removing dispersed oil from oilfield-produced water in Sudan. The synthesis process involved using two concentration of hydrazine as a reducing agent and sodium hydroxide as solvent. Physiochemical characterizations, such as X-ray diffraction (XRD) and transmission electron microscopy (TEM), confirmed the successful preparation of NiNPs. The TEM analysis revealed an average particle size ranging from 70 to 90 nm, with a change in morphology from star-shaped to monodispersed spherical particles. The crystal structure analysis confirmed the face-centered-cubic (FCC) configuration of the NiNPs, validating their structural properties. Significantly, the NiNPs demonstrated an impressive capability to remove oil form produced water, achieving a remarkable efficiency of 98% in eliminating dispersed oil from produced water. The oil removal process followed Freundlich isotherms, as evidenced by the high value of the linear regression coefficient. Additionally, the kinetics of the oil removal process conformed well to the pseudo-second-order model, indicating a rapid reaction. This study successfully demonstrated the efficient removal of dispersed oil from produced water using nickel nanoparticles, which interacted physically with the oil particles. These findings highlight the potential of NiNPs as an effective adsorbent for treating oilfield-produced water and mitigating environmental contamination.
HIGHLIGHTS
Nickel has been synthesized by two different concentrations of hydrazine.
This is the first time testing metallic nickel nanoparticles for this purpose in Sudan.
INTRODUCTION
Produced water is a byproduct of gas and oil production from both onshore and offshore wells (Spoonamore 2011; Alkhazraji & Alatabe 2021). Produced water is a mixture of oil, organic compounds, salts, heavy metals, radioactive elements, and dissolved oxygen. However, oil is dispersed in produced water during oil and gas operations. Produced water composed of different mixtures, BTEX (benzene, toluene, ethylbenzene, and xylene), classified as low molecular weight (382.59 g/mol). Another central combination of high molecular weight, less-soluble PAHs (polyaromatic hydrocarbons), and phenols (≈760 g/mol) were found. Experimental data showed that most oils in produced water are polar; however, dispersed oil is oil suspended in the aqueous phase (Igunnu & Chen 2014).
The amount of dispersed oil depends upon the density and viscosity of the oil, the water–oil tension interface, and the droplet history (Bretz et al. 1994). The ratio of oil to produced water varies widely from zero to more than 50% (2% oil and 98% water). The volume of produced water is directly proportional to the production of gas and oil (Henderson et al. 1999). Many techniques have been applied to separate and remove dispersed oil from produced water, such as biological, adsorption, membrane filtration, ionic surfactant, hydrocyclones, chemical oxidation, and electrochemical methods (Igunnu & Chen 2014). Nevertheless, there exist various limitations associated with these techniques, including high energy consumption during pressure plumb operations, the need for chemical usage in some cases, the potential requirement for pre- and post-treatment processes, and the overall costs being dependent on the volume of produced water (Pichtel 2016).
Nanoparticles offer several advantages as a potential technique for the treatment of produced water.
Enhanced contaminant removal: Nanoparticles have a high surface area-to-volume ratio, which allows for efficient adsorption and absorption of contaminants present in produced water and nanoparticles can be engineered and functionalized to target specific contaminants or classes of pollutants. They can be modified with different coatings, surface charges, or functional groups to enhance their affinity for particular pollutants (Yap et al. 2021).
The low-cost adsorbent powder is a valuable material for removing tiny oil droplets from produced water due to its large surface area (Ko et al. 2014). The magnetite and surface-coated magnetic nanoparticles attract researchers for their applications in the separation and removal of oil from produced water (Igunnu & Chen 2014; Ko et al. 2014, 2017; Hosseini et al. 2018; Adewunmi et al. 2021).
Over recent decades, metallic nickel (Ni) and nickel oxide (NiO) nanoparticles have had various potential applications due to their remarkable properties, high ferromagnetic properties, high chemical stability, and coercive force. Therefore, they used adsorbents to purify water to remove heavy metals, anions, and dyes. They were also used as antimicrobial agents (Ravindhranath & Ramamoorty 2017; Jaji et al. 2020; Khoso et al. 2021). The magnetic nickel-ferrite nanoparticles (NFNs) are synthesized by co-precipitation and then used as adsorbents to remove heavy metals from wastewater (Khoso et al. 2021). The essential advantages and role of NiNPs as adsorbents for removing dispersed oil from produced water in oilfields (Jaji et al. 2020), top-down and bottom-up protocols prepare nickel nanoparticles (NiNPs). Therefore, NiNPs are fabricated by the bottom-up protocol by many methods such as sol-gel, spinning, chemical vapor deposition, pyrolysis, precipitation, and green methods. Trends in NiNP applications in fields such as biomedical, catalysis, supercapacitors, and dye-sensitized solar cells were explored.
Researchers recently synthesized a photocatalyst reactor for oil removal from produced water using zinc nanoparticles as a catalyst in batch and continuous systems (Alkhazraji & Alatabe 2021).
In Sudan oilfields, there is a problem with a tremendous amount of water accompanied by dispersed oil, contaminating the environment when discharged. Authors tried to find methods to remove dispersed oil from produced water. These methods include chemical and biological. To overcome this problem, the current study researchers synthesized NiNPs and then used them to treat spoiled oil in oilfield-produced water. To the best of our knowledge, this is the first time testing metallic nanoparticles for this purpose in Sudan.
MATERIALS AND METHODS
Sampling
Produced water samples were collected from Al-Fulah, an oil field in West Kordofan state in Sudan. In recent years, there has been a significant rise in the volume of produced water in Sudan's oil fields. This increase can be attributed to the growth in oil production and the aging of existing fields. Presently, approximately 1.2 million barrels per day of water are being produced in the national company (GNPOC) oil field in Sudan (Ahmed Khadam et al. 2009).
A colorimetric method was applied to determine oil concentration using DR6000 Spectrophotometer, HACH, USA. The calibration curve was constructed using a standard solution of 1000 mg L−1 of dispersed oil and n-hexane as an extraction solvent (Federation 1999). Quality control and assurance have been applied during the experiment.
Preparation of NiNPs
Nickel chloride hexahydrate (NiCl2·6H2O), absolute ethanol 99%, sodium hydroxide (NaOH), and hydrazine monohydrate (N2H4·H2O) were involved in the synthesis of NiNPs.
NiNPs were prepared by adopting Zhiyu methods; a mixing of nickel chloride (3 g) was dissolved in ethanol. While sodium hydroxide (NaOH) was dissolved directly in absolute ethanol, two appropriate amounts of hydrazine monohydrate (N2H4·H2O) (5.4 and 8.2 g) were added. Meanwhile, the ratio between (N2H4/Ni2+ was 10 and 15). Mixture Ni-1 and mixture Ni-2, respectively, were indexed. The temperature was controlled to 60 °C with continuous stirring for 1 h and constant pH.
Characterization procedure
The particle size of NiNPs was determined by a TEM model H700H.
Batch adsorption experiment
During experiments, qe can be calculated in different forms, and it represents the adsorption capacity (mg g−1), whereas Ci and Ce represent the initial and equilibrium concentrations (mg L−1) of the adsorbate, and V and W stand for solution volume (L) and mass (g) of the adsorbent, respectively.
The main benefits of isotherms are considered equilibrium and interaction mechanisms between the adsorbent and the adsorbate at static temperature. Therefore, this equilibrium can be described by a set of models from one to five parameters. Langmuir and Freundlich cover two parameters (Liu et al. 2019; Jaji et al. 2020).
Adsorption and kinetics models
In the linear equation, 1/qe vs. 1/Ce were plotted as a mathematics function, therefore, KL and qmax were calculated directly from the value of slope and intercept, respectively.
Freundlich constant and Kf and n values can be obtained from the slope and intercept of plotting Log qe vs. Log Ce in the linear form of the equation.
Therefore, Kf is Freundlich's constant used to measure the adsorption capacity, and 1/n is the adsorption intensity. The value of 1/n demonstrates the adsorption process is either favorable (0.1 < 1/n < 0.5) or unfavorable (1/n > 2) (Ayawei et al. 2017).
In addition, the pseudo-first-order and pseudo-second-order have been applied to determine the time of oil adsorption on NiNPs and enhance experimental data to obtain the best results. To describe the mechanism of the kinetics of adsorption of dispersed oil on NiNPs, two models have been applied to Equations (10) and (11) in Table 1 (Li et al. 2012).
Kinetic models . | Equation . | Plot . | Constants and parameters . | Eq. no . | Ref . |
---|---|---|---|---|---|
Pseudo-first-order | (10) | Dehmani & Abouarnadasse (2020) | |||
Pseudo-second-order | (11) | Dehmani & Abouarnadasse (2020) |
Kinetic models . | Equation . | Plot . | Constants and parameters . | Eq. no . | Ref . |
---|---|---|---|---|---|
Pseudo-first-order | (10) | Dehmani & Abouarnadasse (2020) | |||
Pseudo-second-order | (11) | Dehmani & Abouarnadasse (2020) |
RESULTS AND DISCUSSION
Characterization results
Moreover, the average particle size determined by the Debye-Scherrer equation was found 12 nm for both ratios.
Parameters . | Maximum value . | Minimum value . |
---|---|---|
pH | 8 at T = 26.5 °C | 7.4 at T = 26.5 °C |
Oil and grease (mg L−1) | 300 | 200 |
TDS (mg L−1) | 1,217 | 950 |
Conductivity (μS/cm) | 4,200 | 3,800 |
Total oil (IR, mg L−1) | 380 | 59 |
Parameters . | Maximum value . | Minimum value . |
---|---|---|
pH | 8 at T = 26.5 °C | 7.4 at T = 26.5 °C |
Oil and grease (mg L−1) | 300 | 200 |
TDS (mg L−1) | 1,217 | 950 |
Conductivity (μS/cm) | 4,200 | 3,800 |
Total oil (IR, mg L−1) | 380 | 59 |
Adsorption and kinetics evaluation
W (g) . | Ci (mg L−1) . | Ce (mg L−1) . | qe (mg g−1) . | 1/Ce . | ln Ce . | 1/qe . | ln qe . | Removal (%) . |
---|---|---|---|---|---|---|---|---|
0.01 | 550 | 157 | 3932 | 0.0064 | 5.0547 | 2.5 × 10−4 | 8.28 | 71.5 |
0.02 | 550 | 100 | 2250 | 0.0100 | 4.6052 | 4.4 × 10−4 | 7.72 | 81.8 |
0.03 | 550 | 71 | 1598 | 0.0142 | 4.2569 | 6.3 × 10−4 | 7.38 | 87.2 |
0.04 | 550 | 54 | 1240 | 0.0185 | 3.9890 | 8.1 × 10−4 | 7.12 | 90.2 |
0.05 | 550 | 40 | 1020 | 0.0250 | 3.6889 | 9.8 × 10−4 | 6.92 | 92.7 |
W (g) . | Ci (mg L−1) . | Ce (mg L−1) . | qe (mg g−1) . | 1/Ce . | ln Ce . | 1/qe . | ln qe . | Removal (%) . |
---|---|---|---|---|---|---|---|---|
0.01 | 550 | 157 | 3932 | 0.0064 | 5.0547 | 2.5 × 10−4 | 8.28 | 71.5 |
0.02 | 550 | 100 | 2250 | 0.0100 | 4.6052 | 4.4 × 10−4 | 7.72 | 81.8 |
0.03 | 550 | 71 | 1598 | 0.0142 | 4.2569 | 6.3 × 10−4 | 7.38 | 87.2 |
0.04 | 550 | 54 | 1240 | 0.0185 | 3.9890 | 8.1 × 10−4 | 7.12 | 90.2 |
0.05 | 550 | 40 | 1020 | 0.0250 | 3.6889 | 9.8 × 10−4 | 6.92 | 92.7 |
The removal fits well with Freundlich's isotherm since the value of the linear regression coefficient (R2 = 0.98314) is higher than Langmuir's isotherm (R2 = 0.9775). The results illustrate that dispersed oil adsorbate forms a physical adsorption monomolecular layer into the internal surface of NiNPs.
The maximum adsorption capacity of NiNPs for dispersed oil was 22,841 mg g−1. The value of the separation factor (RL) for NiNPs is less than one (0.670), which favors the adsorption phenomenon. The data in Table 4 demonstrate Langmuir isotherm parameters information.
Intercept . | Slope . | qmax (mg g−1) . | KL (L mg−1) . | RL . | R2 . |
---|---|---|---|---|---|
0.000044 | 0.03905 | 22,841 | 0.001121 | 0.670 | 0.9775 |
Intercept . | Slope . | qmax (mg g−1) . | KL (L mg−1) . | RL . | R2 . |
---|---|---|---|---|---|
0.000044 | 0.03905 | 22,841 | 0.001121 | 0.670 | 0.9775 |
. | Intercept . | Slope . | qe (mg g−1) . | K-value . | R2 . |
---|---|---|---|---|---|
Pseudo-first-order | 2.64202 | 0.07329 | 14.04 | 0.0014658 | 0.238 |
Pseudo-second-order | 7.45E-04 | 0.0012 | 833.33 | 1.93 × 10−3 | 0.998 |
. | Intercept . | Slope . | qe (mg g−1) . | K-value . | R2 . |
---|---|---|---|---|---|
Pseudo-first-order | 2.64202 | 0.07329 | 14.04 | 0.0014658 | 0.238 |
Pseudo-second-order | 7.45E-04 | 0.0012 | 833.33 | 1.93 × 10−3 | 0.998 |
Oil dispersed removal from produced water quickly by magnetic nanoparticles as recorded in literature because of external magnetic field force. Therefore, it successfully separates oil droplets from attached water (Ko et al. 2014). Figure 4 shows the removal percentage vs. NiNP doses; it can be noticed that there are two adsorption processes. In the first step, the interaction between dispersed oil and the side surface of NiNPs before saturated, while in the second step, dispersed oil molecules saturated the pore size of the NiNPs, and adsorption was reduced due to weak concentration (Gerçel & Gerçel 2007; Bhatnagar et al. 2010).
Positively magnetic nanoparticles crafted by the amine functional group showed high removal of oil from emulsion solution found at 99.5, 97.9, and 96.4%, respectively, by electrostatic forces. Positively magnetic nanoparticles have destroyed the stabilization energy barrier between oil drops, and it separated from the water easily (Ko et al. 2017).
Meanwhile, nickel is essential to transition elements, its magnetic properties higher than the other elements rather than the iron family. The saturated magnetization (Ms) of NiNPs was estimated to be between 50 and 60 emu g−1 (Hwang et al. 1997; Simonsen et al. 2018). Different weights of NiNPs showed a high ability to remove dispersed oil from produced water. The removal percentage was 98% (40 mg L−1). Figure 4 represents the relationship between NiNP doses and removal percentage.
CONCLUSIONS
A new nickel-nanoparticle adsorbent was synthesized through a thermal decomposition process. Hydrazine and sodium hydroxide were employed as reducing agents and a solvent, respectively. When applied to treat oilfield-produced water, the findings indicated that the resulting water was effectively purified and suitable for agricultural reuse. The evaluation of fit quality and adsorption performance often involves the use of linear regression analysis due to its broad applicability in different adsorption data. Furthermore, several researchers have extensively employed nonlinear regression analysis to bridge the gap between predicted and experimental data. Consequently, it is crucial to determine and clarify the utility of both linear and nonlinear regression analysis in various adsorption systems.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.