Common Ion Effect Research Articles

Chelating agent-introduced unconventional compound acid for enhancing coal permeability

The low permeability of coalbed methane (CBM) reservoirs can be attributed to cementing minerals, which make it difficult for water/gas to flow in the pores and fractures. Acid stimulation is considered a promising method to enhance coal permeability by dissolving these inorganic minerals. Laboratory experiments were carried out to investigate the interactions between acids and coal samples from the Qinshui Basin. XRD and SEM-EDS analyses showed that these coal samples contained a large amount of clay minerals, and some carbonates, pyrite, etc. Considering the complexity of the mineral concentration, three kinds of acids (organic acids, chelating agents, and fluoroboric acid) were optimized via static leaching tests, ICP-OES, etc. Based on the results, out of the four chelating agents, HEDTA showed the highest chelating amount for Ca2+ (380.38 mg/g) and Fe3+ (476.4 mg/g), and 1 wt% HEDTA (pH = 2) yielded the highest dissolution rate. For the organic acids, the dissolution rate decreased with an increase in acid concentration because of the common ion effect. The dissolution rate with 2.5 wt% OA-1 was 8.02% while that with 20w% HCl was only 7%. In addition, 639 mg/L Ca was detected in the 5 wt% OA-1 leachate, which was higher than that for the 5 wt% HCl (575 mg/L). Afterward, orthogonal methods were used to optimize the compound acid system which consisted of 1.5 wt% HEDTA +4 wt% OA-1 + 5 wt% HBF₄. According to the core-flooding test results, after acid injection for approximately 100 PV (pore volume), the porosity of coal core sample increased from 3.36% to 4.95%, and the permeability increased 3.29 times. In general, previous studies have been limited to the conventional acids (HCl and mud acid), yet the drawbacks such as clay breakage, migration, and precipitation cannot be neglected. Accordingly, this paper proposed a set of chelating agent-introduced compound acid and it shows great promise in the application of enhanced CBM recovery.

Transformation Kinetics of Burnt Lime in Freshwater and Sea Water.

Calcium oxide (CaO), also known as burnt lime, is being considered as a possible treatment to reduce the negative impact of sea urchins on tare forests in northern coastal waters and blue-green algal blooms in the surrounding of fish-farms. In this respect, the reaction kinetics of burnt lime in contact with sea water has been elucidated and compared to its behaviour in fresh water. In the first minutes of contact between burnt lime and water, it “slaked” as CaO reacted with water to yield calcium hydroxide (Ca(OH)2). Subsequently, calcium hydroxide reacted with magnesium, sulphate and carbonate from the sea water to yield magnesium hydroxide (Mg(OH)2), calcium sulphate dihydrate (gypsum, CaSO4·2H2O) and calcium carbonate (CaCO3), respectively. In a closed system of 1% CaO in natural sea water (where the supply of sulphate, magnesium and carbonate is limited), more than 90% reacted within the first 5 h. It is foreseen that in an open system, like a marine fjord, it will react even faster. The pH 8 of sea water close to the CaO particle surface will immediately increase to a theoretical value of about 12.5 but will, in an open system with large excess of sea water, rapidly fall back to pH 10.5 being equilibrium pH of magnesium hydroxide. This is further reduced to <9 due to the common ion effect of dissolved magnesium in sea water and then be diluted to the sea water background pH, about 8. Field test dosing CaO particles to sea water showed that the pH of water between the particles stayed around 8.

Studies on Boiling Point Elevation of Water and it’s Correlation with Salt Concentrations for Application in Evaporator Design

The boiling point of a solution increases with the increase of non-volatile solute concentration as the vapor pressure of solvent reduces due to addition of solute in it. Thus the solution need to be heated to a higher temperature in order to get the vapor pressure to become equal to the external pressure at the boiling point. Experiment shows that the change in boiling point of the solvent above a solution from that of the pure solvent is directly proportional to the molal concentration of the solute. Since evaporators dealing with boiling solutions, and in particular with solutions with non-volatile solutes, any problems related with heat transfer on it must account for the effect of boiling point elevation in designing the evaporator. In this experimental studies the boiling point elevations of water due to presence of individual sodium and potassium salts like NaCl, NaOH, KCl, KNO3 as well as mixtures consisting of both NaCl & NaOH and KCl& KNO3 have been correlated to salt concentrations and solubility of the salts. The correlations are based on combination of Clasius-Clapeyran relation with Raoult’s law considering wide range of salt concentrations from 1.4 to 16 wt. %. The correlation takes care of two factors namely interaction between the salts and water common ion effect of the cations together.

Solid–Liquid Phase Equilibria of the Aqueous Ternary System (Li2CO3 + Na2CO3 + H2O) at (278.15 to 308.15) K

The phase equilibria of the ternary system (Li2CO3–Na2CO3–H2O) at 278.15 ≤ T/K ≤ 308.15 K were investigated by isothermal dissolution equilibrium. On the basis of the experimental data, the phase diagrams and densities versus mass fraction (100w) of sodium carbonate were plotted. For the ternary system, there is one invariant point, two univariant curves, and two crystallization regions corresponding to lithium carbonate (Li2CO3, LC) and sodium carbonate decahydrate (Na2CO3·10H2O, NC10) or thermonatrite (Na2CO3·H2O, NC). No solid solution or double salt was found in the ternary system at the experimental temperature; the ternary system was a simple eutectic type. In a comparison of the phase diagrams from 278.15 to 308.15 K in the system, the crystallization region of NC10 existed at 278.15, 288.15, and 298.15 K, and the equilibrium solid phase corresponding to sodium carbonate was dehydrated and transformed to thermonatrite at 308.15 K. The crystallized area of lithium carbonate expands with increasing temperature, while the crystallized areas of sodium carbonate demonstrate an opposite trend. The components of Na2CO3 in solution have a common ion and salting-in effect to Li2CO3, and the salting-in effect increases with increasing concentration. This indicates that a large amount of excess sodium carbonate could not improve the yield of lithium in the carbonated precipitated lithium process. The density of this ternary system changes regularly with the changing concentration of sodium carbonate, and it was represented by empirical equations as functions of concentration.

Removal of chloride ions from acidic solution with antimony oxides

This study aims to investigate the removal of Cl- from acidic solution with antimony oxides. The effects of the adsorbent type, reaction time, reaction temperature, Sb/Cl mole ratio and acidity on adsorption performance and the regeneration of loaded adsorbent were systematically studied. The results shows that Sb2O3·xH2O has the highest adsorption rate (97.64%) among Sb2O3·xH2O, Sb2O5·xH2O, Sb2O4·xH2O and Sb2O3 in the solution containing 1.25mol/L H2SO4 under the condition of Sb/Cl mole ratio 3:1 and stirring for 2h at room temperature, and the concentration of Cl- in the acid solution can be reduced to 280mg/L. Then the residual Sb in the adsorbed solution can be decreased from 48.21mg/L to 16.09mg/L by C-SbA which is made by Sb2O5·xH2O. The C-SbA which has been used can be reused after calcining at 400℃ for 2h. The loaded adsorbent was completely regenerated by adding it into NaOH or Na2CO3 solution whose pH is equal or more than 9.5 according to S/L ratio 1:6g/mL and was stirred for 0.5h at room temperature. The Cl- in the regenerated solution was crystallized and precipitated in the form of NaCl without evaporation and concentration according to the common ion effect of Na+, and the purity of NaCl was more than 99%.

Removal of lincomycin from aqueous solution by birnessite: kinetics, mechanism, and effect of common ions

The removal of lincomycin (LIN) from aqueous solution by birnessite was investigated by batch experiments. When the dosage of birnessite is 500 mg L-1 and the initial concentration of LIN is 15.5 μmol L-1, more than 90% of LIN was removed within 240 min at pH 4.90. Under different conditions, the reactions were well fitted with the second-order model (R2 > 0.95). The removal kinetics and the reaction mechanism were described. The presence of cations (e.g., K+, Ca2+, Mg2+, Fe2+, and Mn2+) inhibited the removal of LIN by birnessite, following the order: Mn2+ > Fe2+ > Ca2+ > Mg2+ > K+ ≈ Na+, due to the sorption of cations on birnessite, companying with the electron transfer and precipitation of oxides (for Mn2+ and Fe2+). The addition of Cu2+, SO42-, or NO3- improved the reactions. The presence of Cu2+ could oxidize antibiotics, and the repulsion between SO42-or NO3- and birnessite might disperse the birnessite suspensions during the reactions. Mn(IV) and Mn(III) were the core Mn species that play an important role in LIN removal. These findings will help to understand the removal process of LIN and illustrate the influence of cations and anions on the removal of similar pollutants by birnessite.

Impact of evaporation on groundwater salinity in the arid coastal aquifer, Western Saudi Arabia

Understanding groundwater salinization and pollution in the arid coastal aquifer is crucial due to complex geochemical processes and sources. This study intends to evaluate the impact of evaporation on groundwater salinity in the arid coastal aquifer, Al Lusub basin, Saudi Arabia using geochemical and multivariate statistical tools. Groundwater samples were collected (n = 52) and analysed for major and minor ions. Groundwater is brackish and shallow wells have higher salinity compared to deeper ones. Hierarchical cluster analysis (HCA) classified the wells into three groups (CG1, CG2, CG3). In these cluster groups, salinity is in the order of CG1(1448 mg/l) < CG2 (3704 mg/l) < CG3(11018 mg/l). PHREEQC modelling reveals that groundwater in this basin is saturated with carbonate, sulphate (CG2, CG3), fluorite (CG3) and silicate minerals, and under-saturated with chloride and hydroxide minerals. Thermodynamic stability diagrams confirm the silicate weathering and kaolinite equilibrium. Precipitation of carbonate minerals at high salinity due to evaporation reduces Ca activity in the groundwater, which triggered the solubility of gypsum and fluorite through common ion effect. Pearson correlation analysis, principal component analysis, ionic ratios (Na/Cl, Cl/Br and F/Cl) and ionic deltas (+ΔBr, +ΔF, +ΔCa, +ΔSO4, +ΔNO3, −ΔNa and −ΔK) justified that non-saline sources and processes, namely evaporation, reverse ion exchange, mineral dissolution and wastewater infiltration predominantly affected the water chemistry in this aquifer. Repeated irrigation practice with high salinity groundwater leads to salt accumulation in the vadose zone due to evaporation, which flushed by the subsequent irrigation events and resulted in higher salinity and NO3− in the groundwater. Hence, sustainable groundwater management and smart irrigation should be implemented.

Noncorrosive necking treatment of the mesoporous BaSnO3 photoanode for quantum dot-sensitized solar cells

The perovskite structure BaSnO3 is regarded as a promising photoanode material, and an effective necking treatment strategy is necessary for the electrical connectivity of mesoporous BaSnO3 photoanode-based solar cells. The often-adopted necking strategy involves the treatment in TiCl4 solution with low pH, which can lead to the leaching of barium cations from BaSnO3 and impair the effect of the necking treatment. To address this issue, we report herein a novel noncorrosive necking strategy based on the common ion effect. The strategy involved treating the mesoporous BaSnO3 photoanode with a mixture solution of TiCl4 and BaCl2. Compared with the common TiCl4 necking treatment, the treatment with TiCl4 and BaCl2 mixture solution negligibly affected the formation of the TiO2 overlayer on the surface of BaSnO3 particles, but it maintained the crystallinity of the BaSnO3 particles. The TiCl4 and BaCl2 mixture solution treated BaSnO3 photoanodes were assembled into CdSe/CdS co-sensitized quantum dot-sensitized solar cells (QDSSCs), which showed ca. 37% increase in power conversion efficiency in comparison with the TiCl4 treated photoanode. The charge extraction, electrochemical impedance spectroscopy, and intensity-modulated voltage/photocurrent spectroscopy measurements showed that the QDSSCs fabricated from the TiCl4 and BaCl2 mixture solution treated BaSnO3 photoanode contained fewer trap states and exhibited less charge recombination and longer electron lifetime than those based on the common TiCl4 treated photoanodes, demonstrating the effectiveness of the noncorrosive necking treatment.

MODEL MENTAL MISKONSEPSI PADA KONSEP KESETIMBANGAN KELARUTAN

Study on students' mental model's analysis was done to identify misconceptions about solubility equilibria concept. The method employed in the study was a case study uses a qualitative approach. The participants were 23 students of class XI of a senior high school in Bandung. The instrument used in the study was the Diagnostic Test on Mental Model-Prediction, Observation, Explanation (TDM-POE). The results showed that there were diverse of students' misconceptions about the precipitate formation of a reaction, the effect of common ions and decrease in pH on solubility. Based on the results of the study, many misconceptions occur in the subconcept of the effect of common ions on solubility. Misconceptions arise because students have incomplete mental models at the submicroscopic level.

Phase equilibria of ammonium scandium fluoride phases in aqueous alcohol mixtures for metal recovery by anti-solvent crystallization

This paper investigates the phase equilibria of ammonium scandium fluoride phases in pure water, aqueous NH4F solutions and in mixtures of NH4F and alcohols. The solubility of the solid phases was determined at 25 °C. It was observed that (NH4)3ScF6 transforms into NH4ScF4 when contacted with pure water for 24 h. Solid phase transformation was also noted in NH4F solutions of concentration ≤ 0.5 mol/L. At NH4F concentrations ≥ 0.8 mol/L, no phase change has been observed, and the solubility of (NH4)3ScF6 decreases with increasing NH4F concentration due to the common ion effect. In NH4F-alcohol mixtures, the solubility of (NH4)3ScF6 decreases in the order: methanol > ethanol > 1,3-propane-diol > 2-propanol. This aligns with the decrease in the effective dielectric constant of the resulting solvent mixture, which is very similar for NH4F-alcohol mixtures formed by ethanol and 1,3-propane-diol.

Effect of Common Ions on Adsorption of Hg(II) and Cr(VI) using Chemically Activated Biosorbent By Column Studies

Effect of Common Ions on Adsorption of Hg(II) and Cr(VI) using Chemically Activated Biosorbent By Column Studies

Machine-Vision-Enabled Salt Dissolution Analysis.

Salt formation is a well-established method to increase the solubility of ionizable drug candidates. However, possible conversion of salt to its original form of free acid or base—disproportionation—can have a drastic effect on the solubility and consequently the bioavailability of a drug. Therefore, during the salt selection process, the salt dissolution behavior should be well understood. Improved understanding could be achieved by a method that enables simultaneous screening of small sample amounts and detailed dissolution process analysis. Here, we use a machine-vision-based single-particle analysis (SPA) method to successfully determine the pH-solubility profile, intrinsic solubility, common-ion effect, pKa, pHmax, and Ksp values of three model compounds in a fast and low sample consumption (<1 mg) manner. Moreover, the SPA method enables, with a particle-scale resolution, in situ observation of the disproportionation process and its immediate effect on the morphology and solubility of dissolving species. In this study, a potentially higher energy thermodynamic solid-state form of diclofenac free acid and an intriguing conversion to liquid verapamil free base were observed upon disproportionation of the respective salts. As such, the SPA method offers a low sample consumption platform for fast yet elaborate characterization of the salt dissolution behavior.

Composite crystallization fouling characteristics of normal solubility salt in double-pipe heat exchanger

The fouling behavior of normal solubility pure salt (Na2SO4) and mixed salt (Na2SO4 and NaCl) in counter-current double-pipe heat exchanger was investigated. Through real-time monitoring of inlet and outlet temperatures of hot and cold fluids, the influences of various factors such as the inlet temperature, inlet velocity of hot solution and solute mass ratio on the fouling thermal resistance were determined. The results show that the fouling thermal resistance is determined by the sodium sulfate content at the experimental temperature and the change of the solubility of sodium sulfate within the temperature difference of heat transfer. With the increase of the inlet velocity of hot solution, the thermal resistance of fouling decreases gradually, indicating that the fouling process is controlled by chemical kinetics. In the fouling experiment of mixed salt solution, the main deposition material is sodium sulfate. Due to the common ion effect, sodium chloride greatly affects the saturated solubility of sodium sulfate, with the increase of the mass ratio of sodium chloride, the fouling thermal resistance and the fouling rate decreases gradually, and the time when the fouling thermal resistance reaches the asymptotic value is prolonged. The research results can provide theoretical guidance for scale inhibition of cooling surface of double-pipe heat exchanger in the treatment of wastewater containing sodium sulfate.

The preparation of high purity MgO and precision separation mechanism of Mg and Ca from dolomite

High purity MgO is widely used in various fields as an important magnesium compound. The separation of Mg and Ca is of great importance for the preparation of high purity MgO from dolomite. In this study, the key effects of carbonization temperature and nano-calcium carbonate agglomeration on the separation mechanism of calcium and magnesium have been investigated. The results indicated that the reaction in the carbonization process was stepwise. Precise control of the carbonization temperature was essential for the formation of Mg(HCO3)2 due to its low reaction efficiency at lower temperatures or decomposition markedly at higher temperatures. Meanwhile, there was a common-ion effect in solutions containing Mg2+ and Ca2+. Nano-CaCO3 particles were formed during carbonization and agglomerated with the prolongation of static time. A product with a purity of 99.56% MgO and 0.16% CaO was obtained under the optimized conditions: ratio of liquid–solid 30 L/g, carbonization temperature 22–25 °C, carbonization time 1 h, and refining time 4 h. This work has important guiding significance for the preparation of high purity magnesium oxide from dolomite.

Degradation of AO7 with Magnetic Fe3O4-CuO Heterogeneous Catalyzed Sodium Percarbonate System

Magnetically recyclable Fe3O4-CuO was synthesized by a one-step hydrothermal method and characterized by scanning electron microscopy coupled with energy dispersive spectrometer (SEM-EDS) and X-ray diffraction (XRD). The degradation of azo dye acid orange 7 (AO7) by percarbonate (SPC) activated with Fe3O4-CuO was studied. The effects of Fe3O4-CuO catalyst loading, SPC concentration, pH value, and common chloride ions on AO7 degradation in the Fe3O4-CuO/SPC system were evaluated. The main reaction mechanism of AO7 degradation was analyzed. The results show that Fe3O4-CuO could effectively activate SPC to degrade AO7 and the reaction was accelerated with the increase of Fe3O4-CuO dosage. The increase of SPC dosage was favorable for the degradation of AO7, but excessive SPC dosage inhibited the degradation of AO7. Common ions (e.g., Cl-) in dye wastewater could promote the degradation of AO7, and the degradation rate increased with increasing concentration of Cl-. The reaction mainly occurred on the surface of the catalyst, and·OH was identified as the main active species for the degradation of AO7. The catalyst Fe3O4-CuO showed excellent stability owing to the high catalytic activity remaining after 4 cycles of repeated use. The Fe3O4-CuO/SPC system achieved a high mineralization rate in the process of decolorization of AO7.

Thermodynamic analysis of proton- and urea-induced dissociation of tobacco mosaic virus: stoichiometry, common ion effect, cooperativity, heterogeneity of subunits and the effect of urea as a homogenizer

The urea- and pressure-induced dissociation of tobacco mosaic virus (TMV) and proton involvement were investigated using a thermodynamic approach that considered the extent of reaction for protons and urea. The stoichiometry of these effectors was determined, as were the Gibbs free energy of dissociation (ΔGD), the volume change associated with dissociation (ΔV) and the Hill coefficient (H). At low pressure, the proton release ($$\mu_{{H^{ + } }}$$) was 1.9 and 1.4 mol H+/mol of TMV at pH 4.8 and 6.8, respectively. Below pH 4.5 and at pH 6.2, there was proton absorption ($$\mu_{{H^{ + } }}$$ < 0). The urea stoichiometry at atmospheric pressure (µU) indicated urea uptake throughout the pH range examined, with values of µU from − 1.8 to − 2.2 mol U/mol of TMV subunit at a urea concentration (expressed in pU) of − 0.18 and − 0.55, respectively. The presence of urea resulted in a much smoother dissociation profile, as indicated by the values for ΔGD, ΔV and µU. This finding suggested an important role for urea in promoting homogenization, as previously reported in the literature. Overall, compared to available methods, the thermodynamic procedure described here allowed a much more detailed analysis of the thermodynamic parameters involved and the detection of properties associated with homogenization by urea.

Effects of common groundwater ions on the transformation and reactivity of sulfidized nanoscale zerovalent iron

Sulfidized nanoscale zerovalent iron (S-nZVI) is an Fe-based reactant widely studied for its potential use for groundwater remediation. S-nZVI reactivity has been widely investigated testing various contaminants in various water matrices, but studies on S-nZVI corrosion behaviour and reactivity upon exposure to complex groundwater chemistries are limited. Here, we show that anoxic aging of S-nZVI for 7 days in the absence and presence of key groundwater solutes (i.e., Cl−, SO42−, Mg2+, Ca2+, HCO3−, CO32−, NO3−, or HPO42−) impacts Fe0 corrosion extent, corrosion product and reduction rates with trichloroethene (TCE). White rust was the dominant corrosion product in ultrapure water and in SO42−, Cl−, Mg2+ or Ca2+ solutions; green rust and/or chukanovite formed in HCO3− and CO32− solutions; magnetite, formed in NO3− solutions and vivianite in HPO42− solutions. The aged S-nZVI materials expectedly showed lower reactivities with TCE compared to unaged S-nZVI, with reaction rates mainly controlled by ion concentration, Fe0 corrosion extent, type(s) of corrosion product, and solution pH. Comparison of these results to observations in two types of groundwaters, one from a carbonate-rich aquifer and one from a marine intruded aquifer, showed that S-nZVI corrosion products are likely controlled by the dominant GW solutes, while reactivity with TCE is generally lower than expected, due to the multitude of ion effects. Overall, these results highlight that S-nZVI corrosion behaviour in GW can be manifold, with varied impact on its reactivity. Thus, testing of S-nZVI stability and reactivity under expected field conditions is key to understand its longevity in remediation applications.

Chitosan-induced Synergy for Extended Antimicrobial Potency and Enhanced In Vitro Drug Release of Free Base Ciprofloxacin Nanoplexes.

Ciprofloxacin free base is practically insoluble in aqueous medium (0.0011 and 0.09 mg/mL at 25 and 37°C respectively). Its inorganic salt form (ciprofloxacin hydrochloride) is more soluble in water (1.35 mg/mL) however when administered orally, it exhibits decreased solubility in the stomach due to common ion effects. Ciprofloxacin free base was used in this study because of its greater hydrophobicity than its hydrochloride salt, which is required for effective permeability and potent antibacterial activity. The purpose of this study is to enhance oral solubility and bacterial cell permeability of the free base ciprofloxacin (CPX) using a single step CPX-chitosan (CT) selfassembly to form nanoplexes with organic counterions. It was envisioned that this would allow the delivery of larger amounts of active drug into the microorganisms. Ciprofloxacin-chitosan nanocomplex (nanoplex) was prepared using low energy electrostatic self-assembly technique previously described. Formation of eutectic nanoplex was confirmed using FTIR, DSC, TGA and SEM. The saturated solubility, in vitro release kinetics and mechanism of drug release were determined using mathematical models. Potency and synergism were determined from the inhibition zones, minimum inhibitory concentration (MIC) and Fractional Inhibitory Concentration (FIC) of the nanoplexes using Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Formation of CPX-CT eutectic adduct polymeric nanoplexes was confirmed with FT-IR and DSC and SEM revealed the conversion of rod-like crystals of CPX (117 μm long) into spherical nanostructures (23-503 nm) dictated by pH, ionic strength and concentration of CT. The solubility of free base CPX increased to a maximum of 32.77 mg/mL compared to 0.0011-0.09 mg/mL reported in literature and dissolution efficiency increased to a maximum of 100% within 72 h. The synergistic effect of CT on antimicrobial activity of CPX was quantified, for the first time, using Fractional Inhibitory Concentration (FIC) of the nanoplexes. FIC was less than 0.5 in both Gram positive (0.031-0.250) and Gram negative (0.036-0.281) microorganisms used in this study, confirming synergistic enhancement of antimicrobial efficacy of CPX. It is evident that the design of drug-polymer nanocomplex formulation provides a platform for the synergistic enhancement of therapeutic potency of antibiotics.

Assessing the slake durability of red stratum sandstone in different solution environments by a novel dual rotation test

This paper proposed a novel dual rotation slaking test with minimum mechanical and artificial disturbance that can better correlate slaking characteristics. The robustness of the proposed method was validated through a comparison of the results of the proposed test with those of the standard slake durability test. Theoretical analysis was conducted to reveal the micro-mechanism of the air-breakage phenomenon of red stratum sandstone from the perspective of surface tension, then the possibility of employing surfactant as a restrainer to retard slaking was proposed. Finally, the dual rotation slaking test was employed to evaluate the effect of various chemical additives in the slaking fluid on the durability of the red stratum sandstone. Test results showed that the surfactant sodium dodecyl sulphate (SDS) could retard deterioration by reducing the air-breakage phenomenon at its critical micelle concentration (CMC, 0.05 mol/L). Sodium chloride (NaCl) and magnesium chloride (MgCl2) can inhibit mineral dissolution through the common ion effect. The precipitation generated by sodium carbonate (Na2CO3) and potassium carbonate (K2CO3) acts as cement, increasing the durability of the red stratum sandstone. However, acidic agents generated by the hydrolysis of Al2(SO4)3 make the minerals highly susceptible to be attacked, and the significant volumetric expansion of the precipitated calcium sulphate (CaSO4) in sodium sulphate (Na2SO4) solution can contribute to the breakdown of the red stratum sandstone.

Separation and Recycling of Concentrated Heavy Metal Wastewater by Tube Membrane Distillation Integrated with Crystallization.

Tube membrane distillation (MD) integrated with a crystallization method is used in this study for the concurrent productions of pure water and salt crystals from concentrated single and mixed system solutions. The effects of concentrated Zn2+ and Ni2+ on performance in terms of membrane flux, permeate conductivity, crystal recovery rates, and crystal grades are investigated. Preferred crystallization and co-crystallization determinations were performed for mixed solutions. The results revealed that membrane fluxes remained at 2.61 kg·m−2·h−1 and showed a sharp decline until the saturation increased to 1.38. Water yield conductivity was below 10 μs·cm−1. High concentrated zinc and nickel did not have a particular effect on the rejection of the membrane process. For the mixed solutions, membrane flux showed a sharp decrease due to the high saturation, while the conductivity of permeate remained below 10 μs·cm−1 during the whole process. Co-crystallization has been proven to be a better method due to the existence of the SO42− common-ion effect. Membrane fouling studies have suggested that the membrane has excellent resistance to fouling from highly concentrated solutions. The MD integrated with crystallization proves to be a promising technology for treating highly concentrated heavy metal solutions.