NH4Cl H2O Research Articles

Solid-liquid phase equilibrium for the hexamethylenetetramine–NH4Cl–H2O system: Solubility determination, model correlation and molecular simulation

The phase equilibrium of the hexamethylenetetramine (HMTA)–NH4Cl–H2O ternary system was investigated to optimize the crystallization separation process for HMTA in industrial wastewater treatment. The solubility of HMTA and NH4Cl in water was measured by the dynamic dissolution equilibrium method. Four isothermal ternary system phase diagrams were generated at 293.15, 303.15, 313.15, and 323.15 K. The solubility data were correlated by the Extended UNIQUAC model, which showed that the model predictions fit well with experimental values. Intermolecular interactions were analyzed by molecular simulations to describe the solubility behavior of the solute in the solvent from a microscopic perspective.

Ammoniacal leaching behavior and regularity of zinc ash

AbstractIn this work, a new hydrometallurgical process was developed to treat zinc ash produced from the hot galvanizing industry. The theoretical analysis shows the feasibility of dissolving zinc ash in the NH3–NH4Cl–H2O system, and the dissolution products are predominantly composed of Zn (NH3)42+. The impacts of different experimental conditions were examined, and the leaching ratio of zinc was as high as 96.4% under the conditions of NH3/NH4+ratio of 1:1, liquid/solid of 9:1, total ammonia concentration of 8 mol/L and the stirring speed of 250 rpm at 313 K for 120 min. The kinetics of the leaching process were investigated and the calculated apparent activation energy was approximately 4.69 kJ/mol, which indicated that the zinc ash leaching process was controlled by diffusion-controlled. As revealed by the determination of impurity ions, on one hand, there were fewer impurities in the leaching solution, and the concentrations of Fe2+and Pb2+in solution are less than 0.02 mg/L and 0.05 mg/L respectively; on the other hand, there was no need for further impurity removal in this process. The proposed process has a certain application value in treating zinc ash.

Solid–Liquid Phase Equilibria of NaCl–NH4Cl–MgCl2–H2O and Its Subsystems NaCl–NH4Cl–H2O and NaCl–MgCl2–H2O at T = 303.15 K

Solid–Liquid Phase Equilibria of NaCl–NH₄Cl–MgCl₂–H₂O and Its Subsystems NaCl–NH₄Cl–H₂O and NaCl–MgCl₂–H₂O at <i>T</i> = 303.15 K

High-temperature thermodynamics of ZnO–NH4Cl–H2O system

On the basis of the principles of simultaneous equilibrium, conservation of mass, and aqueous electronic charge neutrality and the correspondence principle of ion entropy, the high-temperature thermodynamics of the ZnO–NH4Cl–H2O system was studied to predict solubility and construct Zn species distribution. The model was constructed precisely by using the MATLAB program. The total Zn2+ concentration in the solution was affected significantly by temperature and total ammonium concentration. ZnNH3Cl3− was the predominant species in the ZnO–NH4Cl–H2O system. The solubility of zinc diammine chloride in NH4Cl solution (>2 mol·L−1) in the temperature range of 303–353 K was determined using equilibrium experiments, which had results that agreed well with the theoretical value. The data and high-temperature thermodynamic model used in this paper are reliable.

Specifics of Phase Equilibria Studies in the NH4H2PO4–(NH4)2HPO4–(NH4)2SO4–NH4Cl–H2O at 25°C System by the Optimized Sections Method

Phase equilibria in the NH4H2PO4–(NH4)2HPO4–(NH4)2SO4–NH4Cl–H2O five-component water–salt system and in its boundary systems have been studied at 25°С by an optimized sections method. The efficiency of the algorithm for predicting the compositions of eutonic solutions in the system has been shown. The methodology of experimental design and its implementation in studies of in-, mono-, di-, and invariant equilibria by the optimized sections method is described. The system under study is a simple eutonic type; its eutonic solution is saturated with the initial salt components. Monovariant equilibrium lines and salt cocrystallization surfaces have been studied. Experimental data have been used to plot the phase diagram of the system and its projection on the salt base. The boundaries of areas where one, two, three, or four salts crystallize together have been designated on the salt projection.

Measurements and Modeling of the Phase Equilibria in AlCl3 + NaCl + CaCl2 + H2O and AlCl3 + CaCl2 + NH4Cl + H2O Systems

Solid–liquid phase equilibrium for chloride salt systems plays a vital role in the utilization of liquid wastes generated from soda ash production by the Solvay process. The equilibrium data for ternary systems AlCl3–NaCl–H2O, AlCl3–NH4Cl–H2O, and CaCl2–NH4Cl–H2O from 283 to 353 K were determined by a dynamic method. A chemical model for these systems was developed with the mixed-solvent electrolyte model parameterization with the average absolute relative deviation less than 5%. The new model is capable of calculating solubilities of NaCl and NH4Cl in the AlCl3–CaCl2–H2O system, and the average absolute relative deviation of predicted points is less than 6%. The experimental and calculated phase equilibria have been used in developing a recovery method for NaCl and CaCl2 in the liquid wastes from the Solvay process and the subsequent utilization of CaCl2.

Hydrometallurgical Process for Zinc Recovery from C.Z.O. Generated by the Steelmaking Industry with Ammonia–Ammonium Chloride Solution

In this research, some experimental steps were investigated to recover zinc contained in crude zinc oxide (C.Z.O.). In the first stage, the C.Z.O. was treated in NH3–NH4Cl–H2O solution to dissolve the metals. The optimized leaching conditions in batch experiments were obtained: agitation speed 250 rpm, concentration of ammonia and ammonium chloride 2.5 mol/L and 5 mol/L, respectively, time 30min, temperature 40 °C, and L/S = 6 mL/g. The extraction percentage of zinc was over 81% under the optimized leaching conditions. The kinetic study indicates that zinc extraction from the C.Z.O particles was very rapid. In the second stage, the solution from the leaching process was purified by adding zinc dust to the solution. The Cu, Cd, Pb, Sb, and As could be reduced to levels of 0.03, 0.09, 0.87, 0.22, and 0.12 mg/L after the purification process. Finally, the electrowinning process was used to recover dissolved Zn from the final solution. The zinc content in the electrowon zinc was more than 99.99%.

Isopiestic Measurements of Osmotic and Activity Coefficients of NiCl2–NH4Cl–H2O Systems at 308.15 K

In this work, the osmotic coefficients and water activities of NiCl2–NH4Cl–H2O ternary system and its two subsystems were obtained by isopiestic measurements at 308.15 K. The mean ion activity coefficients of NiCl2–H2O and NH4Cl–H2O systems with different molalities at 308.15 K were calculated by the Pitzer ion interaction model. Meanwhile, the self-consistency of experimental data was validated by Gibbs–Duhem equation, showing the calculated results have a good self-consistency between Pitzer ion interaction model and Gibbs–Duhem equation in the whole experimental molality range for NH4Cl–H2O system. Whereas for the NiCl2–H2O system, the Pitzer equation has its limitation of the molality range. Similarly, the osmotic coefficients of NiCl2–NH4Cl–H2O ternary system with different ionic strength can be obtained. Furthermore, the relative deviation between the experimental and calculated results indicated that the mixing parameters of Pitzer equation can be ignored in estimating the osmotic coefficients at the ionic strength of less than 2.5 mol·kg–1, whereas it cannot be omitted at the higher ionic strength.

Phase Diagram of the Quaternary System KCl–MgCl2–NH4Cl–H2O at t = 60.00 °C and Their Application

Based on the requirement for the comprehensive exploitation and utilization of the salt lake resources magnesium chloride and potassium chloride, a new technology to produce KCl and ammonium carnallite (NH4Cl·MgCl2·6H2O) by using NH4Cl as salting-out agent to separate carnallite is proposed. The solubilities of quaternary system KCl–MgCl2–NH4Cl–H2O were measured by the isothermal method at t = 60.00 °C and the corresponding phase diagram was plotted and analyzed. The analysis of this phase diagram shows that there are seven saturation points and eight regions of crystallization. These eight regions of crystallization represent salts corresponding to KCl, NH4Cl, MgCl2·6H2O, (K1−n(NH4)n)Cl, ((NH4)nK1−n)Cl, (K1−n(NH4)n)Cl·MgCl2·6H2O, KCl·MgCl2·6H2O and NH4Cl·MgCl2·6H2O. According to the phase diagram analysis and calculations, ammonium carnallite (NH4Cl·MgCl2·6H2O) and KCl can be obtained using carnallite as raw materials and ammonium chloride as salting-out agent at t = 60.00 °C. The new technology shows the advantages of being easy to operate and having low energy consumption. The research on this quaternary phase diagram is the foundation for reasonable development of carnallite resources and comprehensive utilization of the salt lake brines.

In Situ Observation of Crystal Rain and Its Effect on Columnar to Equiaxed Transition

The investigation of a columnar to equiaxed transition (CET) and grain refinement is of high commercial importance for the improvement of the solidification structure of metal castings. The crystal rain from the free surface is frequently generated to produce grain refinement and promote a CET in alloys under the application of electromagnetic fields. However, the mechanism underlying the CET influenced by the generated crystal rain is not clear because the employed metallic alloys are opaque. In the present paper, the crystal rain in a transparent NH4Cl–H2O solution is produced by blowing a cooled nitrogen gas on the free surface to observe in situ its impact on the occurrence of a CET. The results show that the crystal rain can significantly promote a CET even in a high temperature gradient and that a CET only can occur when the temperature gradient is almost close to zero in the reference experiment. Finally, the most likely mechanism is discussed and clarified.

Study of simultaneous solubility of salts in the ammonium nitrate–ammonium chloride–water system

Ternary eutectic of the NH4NO3–NH4Cl–H2O system at–23.6°С has been found using a set of theoretical and experimental methods. According to the data of visual-polythermal and differential thermal analyses data, crystallization surface of the system has been plotted at–23.6 to 100°С.

Phase Diagrams of the Quaternary System NaCl–MgCl2–NH4Cl in Water at 0 and 25 °C and Their Application

On the basis of the comprehensive utilization of the Na–Mg salt deposit, a new process to produce NaCl and ammonium carnallite (MgCl2·NH4Cl·6H2O) by using NH4Cl and the solution left after the preparation of potassium salt as raw materials was proposed. For this, the phase equilibrium of the quaternary system NaCl–MgCl2–NH4Cl–H2O at 25 and 0 °C was studied. The solubilities of the quaternary system NaCl–MgCl2–NH4Cl–H2O were measured by an isothermal method, and the corresponding phase diagrams were drawn out. From the phase diagrams: there are four solid phase crystalline zones, which correspond to NaCl, MgCl2·6H2O, NH4Cl, and MgCl2·NH4Cl·6H2O respectively. NaCl and MgCl2·NH4Cl·6H2O have larger crystalline zones at 25 °C than at 0 °C, and NH4Cl has a smaller crystalline zone at 25 °C than at 0 °C. It indicates that NaCl and MgCl2·NH4Cl·6H2O are easy to crystallize out. On the basis of the analysis and calculation of the phase diagrams, the appropriate conditions for the process were identified. In the pro...

Materials balance of pilot-scale circulation leaching of low-grade zinc oxide ore to produce cathode zinc

The pilot-scale production of cathode zinc from low-grade zinc oxide ore through periodic extraction in NH3–NH4Cl–H2O system was studied. Leachant balance in circulation process was controlled by parameters of recycling rate (γ) and relative concentration error (De) between CMeLn and CMeL∞ according to the equation . The concentration of zinc in leach liquor was enriched in 39·085 g/L after five recirculation leaching cycles, which was consistent with the predicted value theoretically when recycling rate was supposed to 0·467.Cathode product containing more than 99·9% of Zn and current efficiency of 97·02% were obtained after purification of two-stage treatment. The liquid loss was confirmed to exist in electrowinning operation and the problem of solution balance was solved through partial diverging cycle and addition of washing water in residue washing unit. Mineralogical analysis results showed that about 90% of ammonia-soluble Zn (ZnCO3 + ZnSO4) dissolved out from zinc ore.

Nucleation and growth orientation of zinc electrocrystallization in the presence of gelatin in Zn(ii)–NH3–NH4Cl–H2O electrolytes

Nucleation and growth orientation of zinc electrocrystallization in the presence of gelatin in Zn(ii)–NH3–NH4Cl–H2O solutions were studied.

Phase Equilibria for the Glycine–Methanol–NH4Cl–H2O System

An investigation of the phase equilibria of the glycine–methanol–NH4Cl–H2O system was carried out with the objective of optimizing the monochloroacetic acid (MCA) process for the production of glycine. Phase equilibrium of the glycine–NH4Cl–H2O system at temperatures over the range of 283.2–353.2 K was determined for concentrations ranging up to the multiple saturation points. The solubilities of both glycine and NH4Cl were found to increase with increasing temperature, as well as with increasing concentration of other solutes. The Bromley–Zemaitis model for ions and the Pitzer formulation for glycine neutral species implemented in the OLI platform were used in the regression of the experimental solubilities. The average absolute deviations between the regressed solubility values and the experimental data were found to be 1.4% for glycine and 0.93% for NH4Cl. Three binary interaction parameters of the Pitzer formulation were newly obtained and coupled with the Bromley–Zemaitis parameters documented in OLI’s databank to predict the multiple saturation points of the system. Additionally, the solubility of glycine in methanol–H2O mixtures was also measured from 283.2 to 323.2 K, and a sharp decline was observed as a function of the content of methanol. Such thermodynamic information is definitely useful for improving the existing industrial process, as well as providing fundamentals for the development of new glycine production processes.

Filling-box process during solidification of a liquid hypoeutectic binary solution

Solidification of binary solutions often occurs in many industrial applications, including the casting of binary alloys. In this study we consider the effect of a side cooling wall on the development of double-diffusive convection during solidification of a hypoeutectic aqueous ammonium chloride (NH4Cl–H2O) solution. To study flow development during solidification of this solution, we used the shadowgraph technique, particle image velocimetry, and a thermochromic-liquid-crystal slurry. In addition, the transient temperature distribution within the test cell was measured by type-T thermocouples. The results of these experiments revealed that the filling-box process originated from the bottom of the test cell to the top. This process induced several double-diffusive layers and counterclockwise roll cells in the melt, mainly caused by double-diffusive convection. Consequently, the filling-box process may cause serious V-segregates and material defects in solidified ingots.

Theoretical analysis of aqueous solutions of mixed strong electrolytes by a smaller-ion shell electrostatic model

In spite of the great importance of mixed electrolytes in science and technology, no compelling theoretical explanation has been offered yet for the thermodynamic behavior of such systems, such as their deviation from ideality and the variation of their excess functions with ionic composition and concentration. Using the newly introduced Smaller-ion Shell treatment - an extension of the Debye-Hückel theory to ions of dissimilar size (hence DH-SiS) - simple analytic mathematical expressions can be derived for the mean and single-ion activity coefficients of binary electrolyte components of ternary ionic systems. Such expressions are based on modifying the parallel DH-SiS equations for pure binary ionic systems, by adding to the three ion-size parameters - a (of counterions), b+ (of positive coions), and b- (of negative coions) - a fourth parameter. For the (+ + -) system, this is "b++," the contact distance between non-coion cations. b++ is derived from fits with experiment and, like the other b's, is constant at varying ion concentration and combination. Four case studies are presented: (1) HCl-NaCl-H2O, (2) HCl-NH4Cl-H2O, (3) (0.01 M HX)-MX-H2O with X = Cl, Br, and with M = Li, Na, K, Cs, and (4) HCl-MCln-H2O with n = 2, M = Sr, Ba; and n = 3, M = Al, Ce. In all cases, theory is fully consistent with experiment when using a of the measured binary electrolyte as the sole fitting parameter. DH-SiS is thus shown to explain known "mysteries" in the behavior of ternary electrolytes, including Harned rule, and to adequately predict the pH of acid solutions in which ionized salts are present at different concentrations.

Solubilities of NH4VO3 in the NH3–NH4+–SO42––Cl––H2O System and Modeling by the Bromley–Zemaitis Equation

The solubility of ammonium metavanadate (NH4VO3) in ammonium salt solution is significant for the precipitation of NH4VO3from the vanadium-containing solution. The solubilities of NH4VO3 in the (NH4)2SO4–H2O, NH4Cl–H2O, and (NH4)2SO4–NH3–H2O systems were measured using dynamic method in the temperature range from (298 to 343) K. The investigated concentration is up to 3.0 mol·kg–1, 2.5 mol·kg–1, and 5.2 mol·kg–1 for (NH4)2SO4, NH4Cl, and NH3, respectively. The solubility of NH4VO3 decreases sharply with the addition of (NH4)2SO4 or NH4Cl while the solubility of NH4VO3 in the mixed NH3 and (NH4)2SO4 (0.10 mol·kg–1) solution increases first and then levels off with increasing NH3 concentration. The solubility product constant (KSP) of NH4VO3 was also determined using the standard-state thermodynamic data. The Bromley–Zemaitis model was applied to model the solubility of NH4VO3 in the systems mentioned above, and five pairs of new model parameters were obtained via the regression of the experimental solubili...

Liquid–Solid Equilibrium of the KCl–NH4Cl–NH3–H2O System with Different NH3 Contents at (273.15 and 298.15) K

The KCl–NH4Cl–H2O system is common in the potash industry, but it is difficult to obtain pure KCl in this system because of the mixed crystals of KCl and NH4Cl. Therefore, phase diagrams of the KCl–NH4Cl–NH3–H2O system at (273.15 and 298.15) K were determined in this paper. The results showed that the phase diagrams of the KCl–NH4Cl–5 % NH3–H2O system at (273.15 and 298.15) K, KCl–NH4Cl–10 % NH3–H2O system at 273.15 K, and KCl–NH4Cl–15 % NH3–H2O system at 298.15 K were consist of four crystallization fields, that are, NH4Cl, NH4Cl + (K, NH4)Cl, (K, NH4)Cl, and KCl, respectively. However, for the KCl–NH4Cl–15 % NH3–H2O system at 273.15 K and the KCl–NH4Cl–23 % NH3–H2O system at 298.15 K, there are only three crystallization fields corresponding to NH4Cl, NH4Cl + KCl, and KCl. It can be concluded that, with increasing NH3 contents, the crystallization area of the mixed crystal disappears gradually. To clarify the mechanism of the phase field changes, a Fourier transform infrared spectroscopy (FTIR) method w...

Suppressing freckles during solidification due to periodic motion of top liquid layer

In the past, one main area of focus in the solidification of a liquid binary alloy has been the investigation of strategies for the elimination or minimization of the presence of “double-diffusive convection”, the main cause of poor quality alloys. In particular, “freckles” occurring in the solidification process cooled from the bottom can result in severe material defects in the final product. The objective of this study is to investigate the effect of a periodic lid-driven flow on the development of double-diffusive convection during solidification from below to aid in the removal or reduction of the occurrence of this convection that causes the formation of freckles. A hyper-eutectic aqueous ammonium chloride (NH4Cl–H2O) solution was used as the test sample and was contained in an enclosure cooled from the bottom to study flow development and heat and mass transport phenomena during solidification. Flow visualization using the shadowgraph technique and measurements of the temperature distribution, the concentration distribution, and the movement of the liquid–mush interface were conducted during solidification. The experimental results revealed that the imposed periodic lid-driven flow had a positive effect on the process by suppressing the plumes emanating from the channels and reducing the strength of the double-diffusive convection.