SO4 H2O System Research Articles

Phase Equilibria in Quinary Na, K, Mg//Cl, SO4–H2O System at 25 °C

The phase equilibria in the quinary Na, K, Mg//Cl, SO4–H2O system at 25 °C were determined, and a total phase equilibria diagram of the system was constructed by means of the translation method. St...

Studies on Mutual Solubility of Salts in the NH4HCO3–(NH4)2SO4–H2O System

Mutual solubility of salts in a triple NH4HCO3–(NH4)2SO4–H2O system was studied in the temperature range of 293.15–323.15 K. The tests were performed using the isothermal solution saturation method...

Phase diagrams of the MgSO4-Al2(SO4)3-(NH4)2SO4-H2O system at 25 and 55 °C and their application in mineral carbonation

A route for the indirect mineral carbonation of blast furnace slag using (NH4)2SO4 as a recyclable reagent has recently been proposed. The main challenges associated with this route are reducing its energy consumption and improving its cost-efficiency. In this process, the recycling of (NH4)2SO4 by evaporation of the carbonation liquor make up a large proportion of the total energy consumption. Thus, controlling the water dosage during leaching of the products of roasting the blast furnace slag with (NH4)2SO4, which are mainly various sulfates of Ca, Mg, Al, and NH4+, is of great importance. In this study, the solubilities of the quaternary MgSO4-Al2(SO4)3-(NH4)2SO4-H2O system were measured at 25 and 55 °C using the isothermal method. The resulting phase diagrams are instructive for determining the lowest liquid-to-solid ratio required for leaching and for recovery of the value-added byproduct, ammonium alum, from the leachate. The results show that the crystalline region of NH4Al(SO4)2·12H2O dominates in the phase diagrams, indicating that it is easily crystallized out and that the use of this route for the separation of aluminum as ammonium alum is feasible. The liquid-to-solid ratios for the leaching unit were calculated to be 4.55 and 1.97 mL/g at 25 and 55 °C, respectively. The liquid-to-solid ratio at 55 °C was reduced by 56.7% compared to the ratio at 25 °C.

Thermodynamics of metal ion complex formation in the Zn2SiO4-NH3-(NH4)2SO4-H2O system (II): Analysis of Si(IV) components and experimental verification

The thermodynamics of Si(IV) complex equilibrium and effect of [NH3]/[NH3]T molar ratio on the components in the Zn2SiO4-NH3-(NH4)2SO4-H2O system were studied. Mass conservation, simultaneous chemical equilibrium, and electronic charge neutrality principles were employed. By varying the concentration of the total ammonia (0–7 mol/L), the pH values were calculated and the Si(IV) complexes in the system identified. The obtained results were then employed to plot the thermodynamic diagrams. Experimental verification based on thermodynamic analysis was carried out simultaneously. The results revealed that the [NH3]/[NH3]T molar ratio and the concentration of SiO2 in the leaching agent could be employed to predict the leaching behavior of Zn2SiO4 in the NH3-(NH4)2SO4-H2O system; The best leaching effect was observed at an [NH3]/[NH3]T molar ratio of 0.5; this is consistent with the results obtained from thermodynamic analysis.

Geochemical characterization of the geothermal system at Villarrica volcano, Southern Chile; Part 1: Impacts of lithology on the geothermal reservoir

Besides temperature, mineralogy, residence time and dilution are crucial for assessing water-rock interaction intensity. The geothermal system at the Villarrica-Quetrupillán-Lanín volcanic chain, Southern Chile, is located across a prominent lithological transition from plutonic rocks of the North Patagonian Batholith (NPB) to volcano-sedimentary units. With the goal to investigate the impact of lithology on medium-enthalpy geothermal fluids, 15 hot spring discharges were sampled and analyzed for anthropogenic tracers and isotopic composition and compared to the analyses of 31 reservoir rock analogues. Comparison of strontium isotope signatures between rock analogues and hot spring discharges allow an allocation of associated reservoir rocks. Chlorofluorocarbons quantify the dilution of the geothermal springs by shallow groundwater, ranging from almost CFC-free samples to dilution with modern meteoric water by up to 50 %. Fluids discharging from plutonic rocks have low proportions of dilution with modern waters, while hot springs discharging from the volcano-sedimentary rocks have a higher and variable dilution with modern waters. The fractionation of oxygen isotopes of the SO4-H2O system reveals reservoir temperature estimates of 80–100 °C in the plutonic sequence matching discharge temperatures. For the springs discharging from volcano-sedimentary units higher reservoir temperatures of 100–140 °C are calculated. On basis of the analysis, a conceptual reservoir model can be derived. Fast fluid ascent is indicated along Liquiñe-Ofqui fault system in the NPB by similar discharge and reservoir temperatures and low surficial dilution rates. Large differences in discharge and reservoir temperatures in the Cura-Mallín formation along with a high influx of surficial water may be attributed to a more branched pathway pattern. In conclusion lithology maybe an important factor when coming to the utilisation of geothermal resources.

Thermodynamics of metal ion complex formation in the Zn2SiO4-NH3-(NH4)2SO4-H2O system (I): Analysis of the Zn(II) complex equilibrium

Principles of mass conservation, simultaneous chemical equilibrium, and electronic charge neutrality, were employed to study the thermodynamics of Zn(II) complex equilibrium in the Zn2SiO4-NH3-(NH4)2SO4-H2O system. By varying the total ammonia concentration (0–7 mol/L), pH, and equilibrium concentration of total Zn, the concentrations of the Zn(II)-NH3, Zn(II)-OH−, and Zn(II)-NH3-OH– complexes in the system could be calculated and the thermodynamic diagrams plotted. The obtained results provide a theoretical basis for the development of a willemite leaching process and compensate for the lack of basic research in this area.

Chemical changes and reaction mechanism of hardened cement paste–(NH4)2SO4–H2O system

Physical performance and chemical composition of some hydration products in hardened cement paste are changed considerably in presence of NH4+ ions, which is closely related to long term durability of cement concrete. The dissolution of some hydration products and the newly formed reaction products in such system were thus studied. The results showed that the concentration of dissolved Ca2+ ions were increased with the concentration of (NH4)2SO4 solution in external environment; when dissolution process was reached equilibrium, the main product was gypsum; while koktaite was also detected in condition of higher concentration of (NH4)2SO4 solution, which was usually ignored or mistaken as ettringite. In this case, gypsum crystals experienced significant morphology change with the deceasing of particle size when the concentration of (NH4)2SO4 solution was increased. Moreover, by the dissolving of Ca2+ ion, [SiO4]4− tetrahedral chains polymerized into network structure and NH4+ ions were supposed to be doped into C-S-H network structure.

Solid-liquid phase equilibria of quaternary system NH4+//C1−, SO42−, H2PO4−–H2O and its subsystems NH4+//C1−, SO42−–H2O, NH4+//C1−, H2PO4−–H2O at 313.15 K

Solid–liquid phase equilibrium and physical properties of ternary systems NH4Cl-NH4H2PO4-H2O, NH4Cl-(NH4)2SO4-H2O and quaternary system NH4Cl-(NH4)2SO4-NH4H2PO4-H2O at 313.15K and atmospheric pressure were obtained by means of an isothermal solution method. The solid phases formed in the systems studied were determined by the Schreinemaker wet residue method. Based on the measured data, corresponding phase diagrams and the diagrams of physical properties versus composition were plotted. Neither complex salt nor solid solution is found in these systems at 313.15K. The ternary phase diagram of NH4+//C1−, H2PO4−–H2O contains one invariant point, and three crystallization regions (NH4H2PO4, NH4Cl, and (NH4Cl+NH4H2PO4)). The ternary phase diagram of NH4+//C1−, SO42−–H2O is similar to the previous one, also contains one invariant point, three crystallization regions ((NH4)2SO4, NH4Cl, and (NH4Cl+(NH4)2SO4)). The quaternary phase diagram of NH4+//C1−, SO42−, H2PO4−–H2O contains one quaternary invariant point, three crystallization regions ((NH4)2SO4, NH4Cl, and NH4H2PO4), and crystallization field of NH4H2PO4 is the largest one of them. All results obtained in this work can be used for the stripping process of solvent extraction in the production of potassium dihydrogen phosphate.

Solubility Investigations in the MgSO4–Al2(SO4)3–(NH4)2SO4–H2O Quaternary System at 40 and 80 °C

The separation of magnesium and aluminum bearing compounds from the (NH4)2SO4 aqueous solution is crucial for the ammonium sulfate roasting technique to extract Mg and Al from the magnesium–aluminum-bearing slag. Equilibrium solubility data for the quaternary system of MgSO4–Al2(SO4)3–(NH4)2SO4–H2O at 40 and 80 °C were therefore measured and compared with those of their ternary subsystems of MgSO4–(NH4)2SO4–H2O and Al2(SO4)3–(NH4)2SO4–H2O, respectively. The mutual salting-out effect between MgSO4 and Al2(SO4)3 in the quaternary system was further discussed. On the basis of the measured data, a strategy for effective separation of magnesium and aluminum compounds from the MgSO4–Al2(SO4)3–(NH4)2SO4–H2O system was developed.

Heterogeneous Nucleation of Trichloroethylene Ozonation Products in the Formation of New Fine Particles

Free radicals in atmosphere have played an important role in the atmospheric chemistry. The chloro-Criegee free radicals are produced easily in the decomposition of primary ozonide (POZ) of the trichloroethylene, and can react with O2, NO, NO2, SO2 and H2O subsequently. Then the inorganic salts, polar organic nitrogen and organic sulfur compounds, oxygen-containing heterocyclic intermediates and polyhydroxy compounds can be obtained. The heterogeneous nucleation of oxidation intermediates in the formation of fine particles is investigated using molecular dynamics simulation. The detailed nucleation processes are reported. According to molecular dynamics simulation, the nucleation with a diameter of 2 nm is formed in the Organic Compounds-(NH4)2SO4-H2O system. The spontaneous nucleation is an important process in the formation of fine particles in atmosphere. The model study gives a good example from volatile organic compounds to new fine particles.

Removal of Aluminum from Leaching Solution of Lepidolite by Adding Ammonium

Lepidolite is a kind of low-grade lithium ore (3.5–4.0% Li2O) which contains more than 22% Al2O3 and 8% K2O. Removal and utilization of the Al and K will be very important for the economic extraction of lithium from this ore. In this paper, a novel method is proposed to remove Al from the leaching solution of lepidolite by adding ammonium from (NH4)2SO4. The results indicate that adding NH4 + could remove more aluminum and have a smaller loss of lithium in comparison to adding K+ for removing aluminum in the leaching solution. The Al removal reached up to 80.44% at (K+ + NH4 +)/Al3+ molar ratio of 0.95, while the amount of Li+ (99.84%) still remained in the leaching solution. In addition, the phase equilibrium in the quaternary K2SO4-Al2(SO4)3-(NH4)2SO4-H2O system at 278.2 K was investigated to support the above conclusion. The results verify that the addition of ammonium could remove more Al3+ by easily forming potassium alum (KAl(SO4)2·12H2O) and ammonium alum (NH4Al(SO4)2·12H2O).

Phase Diagrams of the Na2SO4–MgSO4–(NH4)2SO4–H2O System at 60 °C and Their Application

The solubilities of quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O at 60 °C were measured by the isothermal method, and the corresponding phase diagram was studied. The analysis of the phase diagram shows that there are five crystalline fields, MgSO4·6H2O, Na2SO4·MgSO4·4H2O, Na2SO4, (NH4)2SO4, and MgSO4·(NH4)2SO4·6H2O, respectively. MgSO4·(NH4)2SO4·6H2O, and Na2SO4 crystalline fields are larger than other crystalline fields, which indicates that MgSO4·(NH4)2SO4·6H2O and Na2SO4 are crystallized out easily. On the basis of the analysis and calculation of the phase diagrams of the quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O and ternary system Na2SO4–(NH4)2SO4–H2O at 60 °C, a technology was designed to produce Mg–N compound fertilizers and Na2SO4 using (NH4)2SO4 as a salting-out agent to separate bloedite, which is easy to operate, fast to reach phases equilibrium, and can gain anhydrous Na2SO4 directly. On the basis of the Pitzer model of electrolyte solution theory, the solubilities of Na2SO4–MgSO4–(NH4)2SO4–H2O system at 60 °C were calculated. The results showed that calculated values were well consistent with experimental results.

Experimental method for determining mixed-phase precipitation kinetics from synthetic geothermal brine

A batch reactor design for determining precipitation kinetics from an experimental (i.e. laboratory made) geothermal brine is presented. The purpose of the method is to improve techniques for predicting scaling risks in basin-hosted, enhanced geothermal systems (EGS). The method is applied to determining kinetic rate laws for alkali-earth metal sulfate precipitation in the Na–Ca–Ba–Sr–Cl–SO4–H2O system, which are a set of components commonly found in sedimentary basin brines, worldwide. The method of integral rates was used to determine alkali-earth metal precipitation kinetic rate laws for solutions reacting over 4h at 75°C and 150°C. At 75°C, the rate law for total sulfate precipitation is rate=0.0137*[SO42−]2. At 150°C, the rate law for total sulfate precipitation is rate=0.011*[SO42−]2. All precipitants are found to be barite, with minor amounts of calcium and strontium incorporated into the barite structure. If only barite precipitation is considered, the rate coefficients become 0.045 and 0.025 at 75°C and 150°C, respectively. The precipitants’ specific reactive surface areas are estimated for each time step and temperature and are qualitatively observed to decrease as the reactions progress. The (1) the reaction order, (2) the rate coefficient and (3) the change in specific reactive surface area over time are the three parameters required to develop reactive transport models of mineral precipitation in a geothermal power plant. All three of these parameters can be determined with the method employed in this study. Results from these experiments confirm previous results that precipitation kinetics are dependent on both starting concentrations and background salinities. Experiments designed to predict scaling risks in real geothermal systems require adjustments to the method presented herein, specifically (1) experimental fluids must more closely approximate real geothermal brines, (2) a larger reactor is required to produce a greater precipitant mass and (3) full quantitative assessment of the precipitants’ specific reactive surface area are required to reduce the error of these measurements.

Predicting the solubility of SrSO4 in Na–Ca–Mg–Sr–Cl–SO4–H2O system at elevated temperatures and pressures

Precipitation of strontium sulfate (or SrSO4) has already been distinguished as one of the most costly and critical problems which may occur in process industries and oilfield operations. Costs due to scaling and remedial actions that need to be taken afterward are generally high owing to low solubility of SrSO4 in aqueous solutions. Therefore, a thorough understanding of the SrSO4 thermodynamic behavior under various operating conditions is vital to predict or even avoid the overall damage caused by scaling. The primary aim of this work is to develop a model based on Least Squares Support Vector Machine (LSSVM) and Coupled Simulated Annealing (CSA) referred to as CSA-LSSVM to predict strontium sulfate solubility as a function of pressure, temperature and ionic compositions. In this context, we have employed almost 1641 experimental data regarding strontium sulfate solubility to build a comprehensive model and to evaluate its reliability. The results show that the proposed model has a better performance in comparison with pre-existing empirical correlations used for predicting SrSO4 solubility and it is also in well accordance with experimental measurements. A comparison was also drawn between predictions of Pitzer ion interaction model with CSA-LSSVM model forecasts in terms of sensitivity analysis and single point solubility predictions. The whole dataset was analyzed at the end to diagnose the possible outliers and to investigate the reliability of recorded measurements. Based on the results obtained from this study, developed model could successfully be used in predicting SrSO4 solubility in aqueous Na–Ca–Mg–Sr–Cl–SO4–H2O system over temperature ranges from 2 to 253.5°C, and pressures from 1 to 568.51atm.

Prediction of the aqueous solubility of BaSO4 using pitzer ion interaction model and LSSVM algorithm

Deposition of barium sulfate (or BaSO4) has already been recognized as a devastating problem facing process industries and oilfield operations, mainly owing to its low solubility in aqueous solutions. Predicting and also preventing the overall damage caused by BaSO4 precipitation requires a profound knowledge of its solubility under different thermodynamic conditions. The main aim of this study is to develop a solubility prediction model based on a hybrid of least squares support vector nachines (LSSVM) and coupled simulated annealing (CSA) aiming to predict the solubility of barium sulfate over wide ranges of temperature, pressure and ionic compositions. Results indicate that predictions of the presented model are in well accordance with experimental measurements yielding overall correlation coefficient (R2) of 0.996 and total RMSE of 0.00077. Constructed model was also found to outperform a previously well-known correlation employed for predicting BaSO4 solubility in aqueous solutions. Solubility predictions based on Pitzer ion interaction model were also compared to CSA-LSSVM predictions in terms of single point estimations and sensitivity analysis. Results of this study suggest that CSA-LSSVM model could be implemented in assessing the solubility of BaSO4 in Na–Mg–Ca–K–Ba–Cl–SO4–H2O system over wide ranges of temperature from 0 to 279°C and pressures ranging from 1 to 1517 bars with an acceptable degree of accuracy.

Dissolution mechanism and solubility of hemimorphite in NH3-(NH4)2SO4-H2O system at 298.15 K

The dissolution mechanism of hemimorphite in NH3-(NH4)2SO4-H2O system at 298.15 K was investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The results show that hemimorphite is soluble in NH3-(NH4)2SO4-H2O system and its residue exists in the form of an amorphous SiO2 layer on the hemimorphite surface. The XPS data also indicate that the Si 2p3/2 and O 1s spectra of the hemimorphite are broadened and shift to higher binding energies and their binding energies are closer to silica with an increase of total ammonia and time. Solubility of hemimorphite in NH3-(NH4)2SO4-H2O system was measured by means of isothermal solution method at 298.15 K based on the study of the dissolution mechanism of hemimorphite. The results show that the solubility of zinc in solution increases firstly and then decreases with the increase of c T(NH3) (total ammonia concentration) at different NH3/NH4 + ratios. The solubility of silicon in solution decreases from 0.0334 mol/kg in c T(NH3)=4.1245 mol/kg NH3-(NH4)2SO4-H2O solution to 0.0046 mol/kg in c T(NH3)=7.6035 mol/kg NH3-(NH4)2SO4-H2O solution.

Phase diagrams of Na2SO4–MgSO4–(NH4)2SO4–H2O system at 25 °C and their application

Bloedite (Na2SO4·MgSO4·4H2O) is a kind of abundant natural resources. So far, it has not been developed and utilized effectively. In order to process and develop bloedite, a new technology to produce Na2SO4 and Mg–N compound fertilizers by a (NH4)2SO4 salting-out method to separate bloedite was proposed, the phase equilibrium of the quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O at 25°C was studied. The solubilities of the quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O were measured using isothermal method, and the phase diagram of this system was investigated. According to this phase diagram, there are six solid phases crystalline zones, which correspond to MgSO4·7H2O, MgSO4·Na2SO4·4H2O, Na2SO4·10H2O, Na2SO4·(NH4)2SO4·4H2O, (NH4)2SO4 and MgSO4·(NH4)2SO4·6H2O respectively. MgSO4·(NH4)2SO4·6H2O has the largest crystalline zone among these crystalline zones, which indicates that the double salt MgSO4·(NH4)2SO4·6H2O is the most easily to crystallize out. Based on the analysis and calculation of the phase diagrams, a new technology to produce Mg–N compound fertilizers and Na2SO4·10H2O using bloedite and (NH4)2SO4 as raw materials shows the advantage of non-evaporation of water and low energy consumption.

Phase Equilibrium of the Quaternary System Na2SO4–MgSO4–(NH4)2SO4–H2O at 0 °C

The solubilities of the ternary system MgSO4–(NH4)2SO4–H2O and the quaternary system Na2SO4–MgSO4–(NH4)2SO4–H2O at 0 °C were measured, and the phase diagrams of these two systems were plotted. On the basis of the phase diagrams obtained, we analyzed each saturation point and crystalline region. It indicated that ammonium sulfate as the salting-out agent can form double salt MgSO4·(NH4)2SO4·6H2O with magnesium sulfate, realizing better separation of sodium sulfate and magnesium sulfate. On the basis of the Pitzer model of electrolyte solution theory, the ionic strength function was introduced to express the interaction parameters between two kinds of electrolyte at 0 °C. The interaction parameters were regressed from the experimental data of the ternary systems, and the solubilities of Na2SO4–MgSO4–(NH4)2SO4–H2O system at 0 °C were calculated. The results showed that the calculated values were well consistent with experimental results.

Thermodynamic modelling of high salinary phosphate solutions. I. Binary systems

A comprehensive set of interaction parameters for the thermodynamic modelling of PO43−, HPO42− and H2PO4− in concentrated solutions in the Na–K–Cl–SO4–H2O system at 25°C was calculated by regression of experimental isopiestic and solubility data with the Pitzer formalism. The isopiestic method was used to generate additional sets of activity data, which complete and improve the statistical quality of data extracted from an extensive literature review. Thermodynamic properties of phosphate phases were calculated. In this first part, binary systems are presented.

Both initial concentrations of Fe(II) and monovalent cations jointly determine the formation of biogenic iron hydroxysulfate precipitates in acidic sulfate-rich environments

In order to accurately predict the types of biogenic iron hydroxysulfate precipitates in acidic, sulfate-rich environments facilitated by Acidithiobacillus ferrooxidans, different initial concentrations of Fe2+, K+, Na+, and NH4+ are selected and tested in batch experiments for the formation of the precipitates. The critical equations of jarosite formation in FeSO4–K2SO4–H2O system or FeSO4–(NH4)2SO4–H2O system could be described as Y=−22120.8077−0.04257x+0.006170x2 (R2=0.9979) or Y=0.03540−0.002950x+7.407E−5x2 (R2=0.9934), respectively, where Y is the threshold or critical values of the molar ratio of Fe/K or Fe/NH4 for jarosite formation, and x (mmol/L) is the initial concentration of Fe(II). Schwertmannite is the sole biogenic secondary ferric mineral when molar ratio of Fe/K or Fe/NH4 is higher than Y in the system with a given initial Fe(II) concentration. The precipitates are an admixture of schwertmannite and jarosite, or pure jarosite when the Fe/M molar ratio is lower than Y. The crystallinity of the secondary ferric minerals increased with the increase of initial Fe(II) concentration in the medium with a fixed K+ concentration. It is observed that the capacity of monovalent cation in promoting jarosite formation is K+>NH4+>Na+, as exhibiting that the capacity of K+ in this process is about 75 and 200 times greater than NH4+ and Na+, respectively. Obviously, both the initial concentration of Fe(II) and molar ratio of Fe to monovalent cation determine the types of biogenic iron hydroxysulfate precipitates.