Single Salt Solutions Research Articles

Magnetic field–influenced nanofiltration membrane blended by CS–EDTA–mGO as multi–functionality green modifier to enhance nanofiltration performance, efficient removal of Na2SO4/Pb2+/RR195 and cyclic wastewater treatment

Magnetic field–influenced nanofiltration membrane by blending of magnetic multi–functionality green modifier (CS–EDTA–mGO) was fabricated via phase inversion processes. Migration of superparamagnetic nanofiller particles into top surface layer of M6 NF–membrane by incorporating external magnetic–filed during casting phase improved the hydrophilicity, as well as formation of large pores diameters (1.57 nm) which offer a flux enhancement (84.2 kg/m2h), excellent fouling resistance (Rr of 26.4%, Rt of 39.4% and Rir of 25.0%) and highest flux recovery ratio (75.9%). The order of salt rejection for all modified NF–membranes was Na2SO4 > MgSO4 > NaCl and the efficiency of the membranes to reject salts follows the order of M6 > M4 > M0. The performance of M6 as magnetic field–influenced membrane in rejection of RR195 and MB was 21% and 42% higher than unblended membrane (M0), respectively. The highest removal efficiency of Pb2+ and Cd2+ observed for M6 (98.2% and 93.6%, respectively). M6 was more efficient in concurrent removing pollutants from mixed–solute feed. In this case, the existing of Na2SO4 enhanced the retention of RR195 from 97.2% to 99.3%. Long–term operation tests demonstrated the excellent stability of M6 for 18 h filtration with a limited reduction in rejection and water flux of single salt solution. M6 membrane has found potential application in cyclic textile wastewater treatment which the water flux was found to be constant over 3–repeated filtration cycles.

Effect of formation water salinity on interfacial tension of reservoir fluids

The interaction of surface-active species within crude oil with ions in the aqueous phase can have a major influence on the interfacial tension (IFT) between these two phases. Herein, the influence of salinity on IFT is investigated systematically. Brines with different salinities, including seawater and reservoir formation water, are considered. The measurements clearly show distinct IFT trends depending on the composition and concentration of salts in the aqueous phase as well as on the crude oil chemical species, as represented by the API values. The results show that complex brine systems have a stronger effect on IFT than individual single salt brine systems. It is possible to derive distinct additive correction factors for the respective tested brine systems based on the averaged values of deviation from the respective cases in deionized water. On average for the tested 10 oils, and in comparison to measurements in DI water, IFT was reduced by 3.4 mN/m in 100 kppm CaCl 2 solution, by 5.3 mN/m in 100 kppm NaCl solution, by 6.8 mN/m in formation water and by 8.2 mN/m in seawater. • Systematic investigation of salinity influence on IFT. • Single salt solutions, seawater and formation water considered. • Light, medium and heavier oils analysed. • Stronger IFT reduction in presence of complex brines. • IFT correction factors suggested.

Artificial neural network modelling for solubility of carbon dioxide in various aqueous solutions from pure water to brine

Predicting the solubility of CO2 in various aqueous solutions, such as pure water, brackish water, saline water and brine, has become increasingly important because of the interdisciplinary significance of carbon dioxide solubilization, particularly in the energy and environmental fields. Despite experimental difficulties, the solubility of CO2 in various aqueous solutions of single and multi-salt was measured under limited conditions for specific purposes. In this study, artificial neural network (ANN) model was applied to the solubility data of CO2 (2406 experimental data) in salt-dissolved solutions over a wide range of pressures (0.92–712.31 bar), temperatures (273.15–473.65 K), concentrations of electrostricted water molecules (0–90.12 mol/kgw), and overall mole fractions of dissolved salts (0–25.39 mol%), including supercritical condition of CO2. Compared with the conventional thermodynamic models using many parameters, the accuracy of ANN model with only four input variables was comparable for salt solutions and even feasible for brine-rock systems. While the average of the absolute relative deviation of the thermodynamic model with respect to CO2 solubility data in pure water and single-salt solution (1556 data of total 2406 data) was 5.44 %, that of the developed ANN model for the corresponding data was 4.90 %. The developed ANN model presented the capability of dimensional extrapolation in the prediction of CO2 solubility in salt solutions without over-fitting when the thermodynamic-based input variable was used. The model for the solubility prediction of non-polar gases in salt solutions could be a useful approach in complex salt solutions under a wide range of temperature and pressure.

Performance prediction of flat sheet commercial nanofiltration membrane using Donnan-Steric Pore Model

The rejection of sodium chloride (NaCl) and calcium chloride (CaCl2) single salt solutions were carried out for commercial nanofiltration NFDK membrane. Results showed that the NFDK membrane had a negative surface charge and had a higher observed rejection of 93.65% for calcium (Ca2+) ion and 78.27% for sodium (Na+) ions. Prediction of rejection for aqueous solutions of both salts was made using Donnan Steric Pore Model based on Extended Nernst-Planck Equation in addition to concentration polarization film theory. A MATLAB program was developed to execute the model calculations. Absolute Average Relative Error (% AARE) was found below 5% for real rejection of the NFDK membrane. This research could be used successfully to assess the membrane characterization parameter using a proposed procedure which can reduce the number of experiments.

Electrochemical Migration of Immersion Silver Plated Printed Circuit Boards Contaminated by Dust Solution

Due to the severe air pollution, printed circuit boards (PCB) in electronic products are apt to be covered by airborne dust deposition. The trace amounts of soluble salts in the dust particles increase ion concentration in the moisture condensed on the PCB surface so that the electrode reaction of electrochemical migration (ECM) is aggravated and the time to insulation failure also changes. In this article, based on the ion compositions analysis of soluble salts in natural dust collected indoor in northwest Beijing and eastern Shanghai, China, the effect of the anions in typical soluble salts (NaCl, Na2SO4) in natural dust on insulation failure mechanism and TTF of ECM of PCB is investigated by water drop tests on parallel wires on immersion silver plated PCB. Compared with PCB contaminated by single salt solution with different concentrations, the ECM characteristics of PCB covered by natural dust solution of various mass concentrations are analyzed. A failure physics-based life model of ECM of PCB under contamination of salt solution is fitted by the simulation tests of both the single salt solution and natural dust solution respectively. The mechanism and degree of action of soluble salts in natural dust on the ECM failure on PCB is discussed finally.

Efficient and controlled nano-catalyst solid-oxide fuel cell electrode infiltration with poly-norepinephrine surface modification

There is a growing attention to enhance the performance of solid oxide fuel cell (SOFC) electrodes through the incorporation of nano-catalyst materials within the electrodes’ active sites. In this study, we report a technique for increased efficiency and microstructural control of the nano-catalyst infiltration process through polymerized norepinephrine (pNE) treatment. Nano-CeO2 catalysts were incorporated within both electrodes of commercial anode-supported SOFCs using a single salt solution step after a coating of pNE within the porous microstructure. The optimization of catalyst loading was performed by varying the cerium nitrate solution concentrations between 0.4 and 2.0 M. The ceria nanoparticles are distributed at the near-electrolyte region in both electrodes, but with microstructural variance due to the precursor molarity and solid loading. The time-dependent polarization resistance (Rp) variation was categorized into three zones by the nano-catalyst loading. Zone I referred to the baseline performance for the low-catalyst loading and fluctuating Rp. However, the cells in Zone II and III showed a continuous time-dependent activation as low as 0.275 Ω cm2 at 750 °C. The results suggest that the nano-CeO2 film reduces coarsening and related degradation of the backbone. In addition, the pNE-assisted dip infiltration enhanced infiltrant deposition efficiency by reducing the number of infiltration steps.

Hofmeister effects in the gelling of silica nanoparticles in mixed salt solutions

Understanding the nature of specific interaction of ions with the charged silica nanoparticles is vital not only to produce gels for applications such as grouting but also for determining their long term stability. Interaction of silica nanoparticles in single salt solutions has been thoroughly investigated but in mixed salt solutions is rarely investigated. In this work we have investigated the gelling of silica nanoparticles in the mixtures of monovalent ions as well as in the mixtures of divalent and monovalent ions. To gain an understanding of the interaction of ions with the charged silica surface at molecular level we have performed molecular dynamics (MD) simulations. Our overall goal was to find out if in salt mixtures ions silica interactions follow the Hofmeister series or not and how ion specific interactions may change when chaotropic ions are successively replaced by kosmotropic or vice versa. The gelling results show that generally monvalent ions in salt mixtures follow the Hofmeister series, e.g., the gel times in the mixtures of lithium and sodium chlorides are much longer than in the mixtures of lithium and potassium chlorides. On the other hand, gel times in the salt mixtures containing divalent ions do not follow the expected Hofmeister series e.g. mixtures of magnesium and sodium chlorides show shorter gel times than that of calcium and sodium chlorides. However, pH dependent gelling revealed that at pH values less than 9 gelling in these mixtures follow the normal Hofmeister series i.e., longer gelling time in magnesium and sodium chlorides than in calcium and sodium chlorides. This reversal of Hofmeister series for divalent and monovalent salt mixtures at pH > 9 and normal Hofmeister series at pH < 9 is reported for the first time in literature. Such a revesal at pH> 9 is explained due to enhanced surface charge, ordring of surface water layer which leads to enhanced ion specificity of strongly hydrated ions such as Mg2+. Moreover, in mixtures having the same divalent salt but different monovalent salts such as magnesium chlorides mixtures with lithium, sodium and potassium chlorides a normal Hofmeister series prevails. MD simulations results revealed that Mg2+ ions retain their strong hydration shell while interacting with the oppositely charged silica surface which means that the shorter gelling times obtained in magnesium salts mixtures are not due to inner sphere complexation of magnesium with the silica surface. Instead magnesium interacts with the silica surface through its hydrating water molecules.

Automated simultaneous determination of total dissolved nitrogen and phosphorus in seawater by persulfate oxidation method

This paper describes an automated persulfate oxidation method for the simultaneous determination of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) in seawater using a gas-segmented continuous flow analyzer. Automation of simultaneous oxidation and colorimetric determination of TDN and TDP was performed by installing a heating oil bath unit with a long Teflon tube and an air compressor on the analyzer. Blank selection using single and mixed salt solutions dissolving sodium chloride, sodium sulfate, potassium bromide, and/or sodium hydrogen carbonate in pure water indicated that the single sodium chloride solution was most appropriate. The recoveries of various N and P compounds varied from 101% to 108% and 86% to 100%, respectively. Calibration curves showed suitable linearity ranges of 0–80 μM for the TDN analysis and 0–8 μM for the TDP analysis (r2 = 1.00). The detection limits for TDN and TDP analyses were 0.17 and 0.04 μM, respectively. A throughput of 17 samples per hour was achieved. Application to oceanic water samples showed that TDN and TDP concentrations in the upper 300 m varied from 3.8 μM to 11.0 μM and 0.08 μM to 0.41 μM, respectively, with the coefficients of variation of <7%. These concentrations were not significantly different from those obtained from conventional methods. This proposed method has simple, fast, and economical characteristics and is suitable for simultaneous analyses of TDN and TDP, which help our understanding of N and P dynamics in the ocean.

A Comparative Study for Application of Pitzer and ePC-SAFT Equations to Predict Volumetric and Saturation Properties in “Formation” Water

Predictions of salt solubility, brine vapor pressure and density are necessary to plan subsurface and surface operations. In this work, a comparative study was conducted to investigate prediction capabilities for salt solubility, equilibrium and volumetric properties of several minerals in “Formation” water by the Pitzer model (a commonly used industrial model) and by the ePC-SAFT equation of state (EOS). To achieve this, several validation and comparison steps were considered for reliable implementation of both models. Firstly, solubility, brine densities and vapor pressures for single-salt solutions were predicted. Afterward, the models’ applications were extended to several mixtures of two salts to predict solubility compared to experimental data from available literature. ePC-SAFT shows promising accuracy. The average relative deviation for prediction of liquid density (which cannot be estimated with the Pitzer model) for single-salt solutions of NaBr, KCl, NaCl and Na2SO4 are 1.13%, 0.70%, 1.02% and 0.36%, respectively. The average relative deviation from experimental data of vapor pressure for mixtures of NaCl and KBr is 0.75% and for mixtures of NaBr and KCl is 0.74% for systems with different concentrations. Moreover, a stochastic regression procedure is presented to evaluate the ePC-SAFT parameters. This technique is used for strontium in different salt solutions. The average relative deviation for mean ionic activity coefficients calculated by ePC-SAFT from experimental data using the ePC-SAFT parameters of strontium from the work of Held et al. [1] for single-salt solutions of strontium chloride, strontium bromide, strontium iodide, strontium nitrate and strontium perchlorate are 19.73%, 19.96%, 15.15%, 14.95% and 25.70%, respectively. These values using the ePC-SAFT parameters of strontium regressed in this work are 6.98%, 10.13%, 8.33%, 9.59% and 10.08%, respectively. Finally, the solubility of different salts was studied for mixing of formation water (FW) and injection water (SW).

Monovalent/Divalent salts separation via thin film nanocomposite nanofiltration membrane containing aminated TiO2 nanoparticles

Nanofiltration is widely used in separation of ions with different sizes and charges. However, thin-film composite nanofiltration membrane is hard to reach satisfied selectivity for monovalent ions from divalent ions. In this study, polyamide thin film nanocomposite (TFN) nanofiltration membranes were prepared via interfacial polymerization of piperazine and trimesoyl chloride on a PES substrate by incorporation of aminated titanium dioxide (APTES-TiO2). Surface morphology, roughness of the TFN membranes with varied concentration of aminated TiO2 were tested by SEM, AFM and Zeta analysis. The results showed membrane containing 0.3(w/v%) amino-modified titanium dioxide with ion-selective properties had greatly improved pure water flux while the Na2SO4 rejection keeps at a relative high level (>95%). For the separation of single salt solution, 0.3(w/v%) TFN has a higher rejection for sodium chloride (23.2%) and sodium sulfate (99.7%). For monovalent/divalent mixed salt solution has a separation factor of 477.89 in terms of chloride ion (Cl−) and sulfate (SO42−) in the mixed solution with a salt concentration ratio of 1:19, which was higher than that of the conventional commercial NF membranes, such as Desal-DL, NF 270. This method provides the possibility of recovering concentrated brine and industrial separation of monovalent and divalent ions.

Experimental and Theoretical Analysis of Lead Pb2+ and Cd2+ Retention from a Single Salt Using a Hollow Fiber PES Membrane.

The present work reports the performance of three types of polyethersulfone (PES) membrane in the removal of highly polluting and toxic lead Pb2+ and cadmium Cd2+ ions from a single salt. This study investigated the effect of operating variables, including pH, types of PES membrane, and feed concentration, on the separation process. The transport parameters and mass transfer coefficient (k) of the membranes were estimated using the combined film theory-solution-diffusion (CFSD), combined film theory-Spiegler-Kedem (CFSK), and combined film theory-finely-porous (CFFP) membrane transport models. Various parameters were used to estimate the enrichment factors, concentration polarization modulus, and Péclet number. The pH values significantly affected the permeation flux of the Pb2+ solution but only had a slight effect on the Cd2+ solution. However, Cd2+ rejection was highly improved by increasing the pH value. The rejection of the PES membranes increased greatly as the heavy metal concentration rose, while the heavy metal concentration moderately affected the permeation flux. The maximum rejection of Pb2+ in a single-salt solution was 99%, 97.5%, and 98% for a feed solution containing 10 mg Pb/L at pH 6, 6.2, and 5.7, for PES1, PES2, and PES3, respectively. The maximum rejection of Cd2+ in single-salt solutions was 78%, 50.2%, and 44% for a feed solution containing 10 mg Cd/L at pH 6.5, 6.2, and 6.5, for PES1, PES2, and PES3, respectively. The analysis of the experimental data using the CFSD, CFSK, and CFFP models showed a good agreement between the theoretical and experimental results. The effective membrane thickness and active skin layer thickness were evaluated using the CFFP model, indicating that the Péclet number is important for determining the mechanism of separation by diffusion.

Bio-inspired co-deposited preparation of GO composite loose nanofiltration membrane for dye contaminated wastewater sustainable treatment

The fully separation of dye/salt through loose nanofiltration membranes is of great significance for the sustainable development paradigm of textile wastewater. However, the current loose nanofiltration membranes suffer low separation efficiency and complex preparation. Herein, by one-step co-deposition, we develop graphene oxide (GO) composite loose nanofiltration membranes with low negatively charged surface. Our membrane possesses unconventional high pure water permeation of 71.7 LMH/bar, 92.9 % rejection for Methyl blue (MB) and 98.8 % rejection for Congo red (CR). Benefiting from the large interlayer distance of GO nanosheets and low negatively charged surface, membrane achieves high dyes/salts separation with satisfactory permeation to salts (94.3 % of Na2SO4, 97.6 % of MgSO4, 98.3 % of MgCl2 and 99.0 % of NaCl). The CR/salt mixed solutions exhibit similar removal rates to their constituents’ single dye or salt solutions (CR rejection is up to more than 97 % and the permeations of all salts are above 93 %). At the same time, binary dyes mixtures (Congo red and Methyl orange) can also be effectively separated. Furthermore, the membrane shows a relatively desirable antifouling property. The flux recovery still remains at 85.9 % after three cycling filtrations. This study provides a facile approach to prepare highly-efficient loose nanofiltration membranes for wastewater sustainable remediation.

Thermodynamic modeling of [formula omitted] solubility in saline water using NVT flash with the cubic-Plus-association equation of state

The accurate estimation of CO2 sequestration potential in deep saline aquifers requires the knowledge of CO2 solubility in brine, thus placing importance on reliable thermodynamic models that account for the effect of different salts and their mixtures over wide ranges of pressure, temperature and salt concentration. Most literature investigated CO2 solubility in a single-salt solution as a replacement of real saline water, which may significantly overestimate CO2 sequestration potential through solubility trapping. In order to accurately estimate CO2 sequestration potential over geological conditions, the Peng-Robinson Cubic-Plus-Association (PR-CPA) equation of state (EOS) is used in this study to model both aqueous and nonaqueous phases. A promising flash technique at given moles, volume and temperature, known as NVT flash, is employed and the salting-out effect is reproduced by correcting the chemical potential of aqueous nonelectrolyte components. To represent real saline environments, five salts are considered, including sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl2), magnesium chloride (MgCl2) and sodium sulfate (Na2SO4). With taking into account the electrostatic contribution caused by salts, the combination of the salt-based PR-CPA EOS and NVT flash accurately models the solubility behavior of CO2 in mixed-salt solutions and the numerical results agree with experimental data very well. Moreover, the proposed CPA model exhibits neck-to-neck accuracy to the more sophisticated electrolyte CPA EOS, thus making it promising to accurately estimate carbon sequestration potential in saline aquifers through solubility trapping.

The Behavior of Gangue During the Flotation of a Sulfidic PGM-Bearing Ore in Response to Various Monovalent and Divalent Ions in Process Water.

Mineral concentrators are becoming increasingly aware of the importance of the quality of the water that they feed into their milling and flotation circuits. It is speculated that different inorganic constituents of process water may yield different flotation results owing to the electrolyte–reagent–mineral interactions occurring in the pulp phase. These interactions are said to be specific to ion type, reagent type, and mineral or ore type. It therefore stands to reason that there is a need to develop an understanding of the specific ion effects on both the pulp phase and the froth phase phenomena, such that the chemistry and the quality of process water can be monitored and controlled in a manner that does not negatively affect the flotation performance. Previous research has shown that inorganic electrolytes may impact the hydrophobicity and the floatability of mineral particles and could in turn affect froth stability, entrainment, and thus mineral grades and recoveries. In this study, the floatability of a Cu-Ni-PGM-bearing Merensky ore is tested on a bench-scale flotation system in various single salt solutions, viz., CaCl2, CaSO4, Ca(NO3)2, MgCl2, Mg(NO3)2, MgSO4, NaCl, NaNO3, and Na2SO4, in order to examine specific ion effects on gangue recovery. Coagulation and zeta potential tests are conducted in order to establish the nature of the impact that specific ions have on the behavior of gangue in flotation. The findings of this work have shown that single salt solutions containing ions resulted in a strong depression of gangue compared to those solutions containing Cl− and SO42− ions. It was also shown that the divalent Ca2+ and Mg2+ showed a stronger depression of gangue compared to the monovalent Na+. Ca2+, in comparison to Na+, resulted in an increase in the coagulation of the ore as well as an increase in the zeta potential of talc. Overall, the findings of this paper suggest that the presence of Ca2+ and Mg2+ in process water would most likely create conditions that promote gangue depression.

Single and binary ion sorption equilibria of monovalent and divalent ions in commercial ion exchange membranes

The co-ion and counter-ion sorption of monovalent (Na+, K+, Cl− and NO3−) and divalent ions (Ca2+ and SO42−) in commercial Neosepta ion exchange membranes were systemically studied in both single and binary salt systems. The new generation of Neosepta cation exchange membrane (CSE) showed a significant difference in water uptake and co-ion sorption compared to the earlier generation (CMX). Use of the Manning model confirmed that there were significant differences between these membranes, with the estimated value of the Manning parameter changing from 1.0 ± 0.1 for CMX to 2.8 ± 0.5 for CSE. There were fewer differences between the two Neosepta anion exchange membranes, AMX and ASE. In single salt solutions, potassium sorbed most strongly into the cation exchange membranes, but in binary salt mixtures, calcium dominated due to Donnan exclusion at low concentrations. While these trends were expected, the sorption behaviour in the anion exchange membranes was more complex. The water uptake of both AMX and ASE was shown to be the greatest in Na2SO4 solutions. This strong water uptake was reflected in strong sorption of sulphate ions in a single salt solution. Conversely, in a binary salt mixture with NaCl, sulphate sorption fell significantly at higher concentrations. This was possibly caused by ion pairing within the solution, as well as the strongly hydrophobic nature of styrene in the charged polymer. Water uptake was lowest in NaNO3 solutions, even though sorption of the nitrate ion was comparable to that of chloride in these single salt solutions. In the binary mixture, nitrate was absorbed more strongly than chloride. These results could be due to the low surface charge density of this ion allowing it to bond more strongly with the hydrophobic polymeric backbone at the exclusion of water and other ions.

Nanofiltration of Simulated Acid Mine Drainage: Effect of pH and Membrane Charge

Acid mine drainage (AMD) is a severe form of environmental pollution that has the potential to contaminate surface and ground waters by introducing heavy metals and lowering the pH. The feasibility of using nanofiltration (NF) as a potentially attractive and cost-effective remediation method to treat acid mine drainage was investigated in this study. The performance of an acid-stable NF membrane focusing on the effects of the water pH and membrane charge on ion rejection was systematically studied. A single salt solution experiment showed that Mg, Cu, and Mn containing species were highly rejected at above 97%. Below the membrane iso-electric point (IEP), Mn showed an increased rejection of 99%, while Mg and Mn rejections were relatively constant within the investigated pH range of pH 2 to 7. Rejection of monovalent Cl− decreased with increasing concentration of an accompanying divalent SO42−, showing that Donnan related effects are more prominent at higher ionic concentrations. The sulfate rejection decreased drastically below pH 3 due to the formation of HSO4−, which permeated through the membrane, which can be utilized as a way of separation of the metals from the accompanying sulfur-containing compounds. For mixed salt solutions, rejection of silicate dropped from 52% to 38% when magnesium sulfate was added, owing to shielding of the membrane surface charge by Mg2+ ions. The NF process performance with a simulated AMD solution was found to be similar to that with model salt solution experiments, both in terms of ion rejection values and general pH-dependent rejection trends. The results obtained can be used as a fast preliminary tool for evaluating the feasibility of using NF for treating AMD with a given ionic composition and pH.

A general model for prediction of BaSO4 and SrSO4 solubility in aqueous electrolyte solutions over a wide range of temperatures and pressures

The aqueous solubility of BaSO4 and SrSO4 in salt-containing solutions plays a crucial role in process industries and oilfield operations. Small variations in thermodynamic conditions result in precipitation and co-precipitation of these salts, mainly owing to their limited solubility in aqueous solutions. Understanding the environmental chemistry of BaSO4 and SrSO4 requires accurate knowledge of their solubility and thermodynamic behaviors. In this study, a general solubility prediction model based on a least square support vector machine and differential evolution algorithm was developed that is able to handle solubility predictions for BaSO4 in single salt solutions containing NaCl, CaCl2, MgCl2, KCl, KBr, Na2SO4, and Na2B4O7, and for SrSO4 solubility, it can handle predictions for single, binary, and ternary salt solutions containing NaCl, CaCl2, and MgCl2 over a wide range of temperatures and pressures. Model predictions agree excellently with experimental measurements, yielding an overall correlation coefficient (R2) of 0.9911 and an Average Absolute Error of 6.24%. A comparison of the general solubility prediction model with the Pitzer ion-interaction model revealed that both the models perform well in single salt solutions, while the Pitzer model fails to produce accurate solubility predictions when the aqueous system is extended to binary and ternary electrolyte mixtures.

Prediction of CO2 solubility in multicomponent electrolyte solutions up to 709 bar: Analogical bridge between hydrophobic solvation and adsorption model

Prediction of CO2 solubility in electrolyte solution is important for the design of various industrial processes using CO2. A large amount of experimental data is needed to predict the solubility accurately, as a consequence of the complex composition of electrolyte solution. 1384 experimental CO2 solubility data in various electrolyte solutions (containing mostly Na+, Ca2+, Mg2+, K+, SO42−, and Cl−) from 30 references were used as training and validation data for developing a solubility model. According to the analogy between the hydrophobic solvation of CO2 and the adsorption phenomena, the novel solubility model with only four parameters (m0, α, k0, and k1) was developed to predict the CO2 solubility in solution with various ions. The model was correlated with the CO2 pressure and system temperature. The effect of dissolved electrolytes on the CO2 solubility was indicated by the concentration of electrostricted water molecule (ha) in the model, which was calculated using the concentration and hydration number of dissolved ions. The developed model with four parameters—obtained from experimental CO2 solubility data in water and single-salt solutions—reproduced the CO2 solubility well in complex electrolyte solutions, including the solutions after CO2–brine–rock reactions. Of the 1384 data, 94% were within a 95% prediction interval of the model. The model parameters can be used to estimate the heat of CO2 solvation, maximum CO2 solubility in water, and decay constant of the CO2 solubility with respect to the ha value. The developed model was further validated with single-salt solutions containing minor ions such as Li+ or Br−.

Modeling of Gas Solubility Using the Electrolyte Cubic Plus Association Equation of State

The prediction of the solubilities of carbon dioxide and methane in aqueous solutions of inorganic salts is important for geological carbon storage, enhanced oil recovery, gas hydrate formation, and seawater desalination. Few electrolyte equations of state can be used for accurate gas solubility calculations over wide ranges of temperature, pressure, and salt molality. This work presents a thermodynamic modeling study on the solubilities of carbon dioxide and methane in aqueous solutions of several inorganic salts with the electrolyte cubic plus association equation of state. The binary interaction parameters between ions and gas are obtained by fitting the experimental data of gas solubility in single-salt solutions. It is shown that the equation of state can satisfactorily correlate the gas solubility over a wide range of conditions, with deviation less than the reported experimental uncertainties (7%) for most systems. The equation of state is then used to predict the gas solubility in multi-salt solut...

Effect of the membrane exclusion mechanism on phosphate scaling during synthetic effluent desalination

Calcium phosphate scaling is one of the main limitations in effluent desalination using membranes. This may be overcome by tailoring membranes with lower rejection of the scalant ions.In this study, we systematically examined the use of negatively and positively charged membranes, rejecting ions mainly based on Donnan exclusion, as a low-scaling alternative to dielectric-exclusion-dominated polyamide NF membranes for effluent desalination.The two charged membranes exhibited a lower calcium and especially phosphate rejection than the polyamide membrane. Consequently, the calcium phosphate supersaturation and then the propensity to scaling of the charged membranes were much lower than the polyamide membrane. This also allowed filtering at a much higher recovery ratio with the charged membranes. It was also found that, despite the fact that the charged membranes had an opposite fixed charge, their scaling behavior was similar. Apparently, although these membranes showed opposite selectivity towards scalant ions (phosphate and calcium) in single salt solutions, the rejection pattern in mixed salt solutions resulted in similar saturation indices, much lower than for polyamide membrane.The scale formed on all three membranes was identified as amorphous calcium phosphate (ACP), although its saturation index was lower than its solubility factor. This was explained by concentration polarization which increases the saturation index in the solution adjacent to the membrane surface.Tests in absence of permeate flux showed a much slower precipitation that took a few days compared with filtration conditions (few hours). In addition, under these conditions, the effect of the scaling on the membrane permeability was generally reduced and the scale contained crystalline calcium phosphate products, different from ACP.The results indicate that the ion rejection and resulting polarization next to the membrane surface plays a crucial role in scaling. Thus, tuning ion selectivity of NF membranes towards scalant ions presents a promising alternative for scaling mitigation during effluent desalination.