Modeling solid–liquid equilibrium of NH₄Cl‐MgCl₂‐H₂O system and its application to recovery of NH₄Cl in MgO production

Abstract

A new method to recover NH 4 Cl from NH 4 Cl-rich aqueous solutions generated in the magnesia (MgO) production is developed on the basis of modeling the solid-liquid equilibrium (SLE) for the NH 4 Cl-MgCl 2 -H 2 O system with the Pitzer model embedded in Aspen Plus TM platform. The SLE values for the ternary system were determined from 278.15 to 348.15 K. The new standard-state chemical potentials of NH 4 Cl and MgCl 2 Á6H 2 O were judicially obtained. The resulting equilibrium constants were used to determine new interaction parameters for the NH 4 Cl-H 2 O and MgCl 2 -H 2 O systems. These new parameters, together with the mixing parameters determined from correlating the experimental values, were used to correlate the equilibrium constant for NH 4 MgCl 3 Á6H 2 O, which plays a key role in NH 4 Cl recovery. The results could extend SLE calculation for the NH 4 Cl-MgCl 2 -H 2 O system from 278.15 to 388.15 K, satisfying the process identification and simulation requirement involved in the recovery process. The phase-equilibrium diagram generated by modeling was illustrated to identify the process alternatives for recovering NH 4 Cl. The resulting course to recover NH 4 Cl by three fractional crystallization operations was finally proved feasible.

Kinetic analysis for crystal growth rate of NH4Cl in the NaCl‐MgCl2‐H2O system with a thermodynamic approach

“…The accuracy of Pitzer model in prediction of SLE in NH 4 ClMgCl 2 -H 2 O system has been illustrated in our previous work 6 and is not demonstrated again in the present work. A comparison of experimental data 26,27 with the prediction from the Pitzer model embedded in Aspen Plus TM platform by use of parameters taken from Ji et al 16 is shown in Figure 1 for the SLE in the NH 4 27 It is shown that the solubilities of NH 4 Cl increase with increasing temperature both in NH 4 Cl-NaCl-H 2 O and NH 4 Cl-MgCl 2 -H 2 O systems.…”

“…4 Cl in the soda process, the recovery of NH 4 Cl in MgO production process is also composed by the two consecutive cooling and salting-out operations. 6 In the case of cooling crystallization, as shown in Figure 14, the crystal growth rate increases with increasing concentration of MgCl 2 at the same supersaturation of Dm NH 4 in solution. Further, the increment is gradually magnified as increasing concentration of MgCl 2 , suggesting that the presence of MgCl 2 facilitates the growth of NH 4 Cl.…”

“…Referring to the soda combination process, a new crystallization process to recover crystalline NH 4 Cl as saleable product was successfully proposed and underdeveloped in our laboratory with the addition of MgCl 2 to the NH 4 Cl-rich solution generated in the process of MgO production. 6 The new method mainly consists of three crystallization steps: crystallization of ammonium chloride, crystallization of ammonium carnallite, and decomposition of ammonium carnallite. To recover the crystalline ammonium chloride, a series of strategies and operations, including temperature swing and addition of MgCl 2 , are used to carry the feed NH 4 Cl-rich solution to the desired crystallization region, where pure solids of the targeted components can be isolated.…”

Phosphorus recovery from urine with different magnesium resources in an air-agitated reactor

“…[7] China is also rich in saline brine resources that include considerable amounts of mainly Mg. [8] Therefore, enhancing current understanding on the effect of Mg resources on P recovery and crystal quality from urine is essential to improve P recovery from waste. Struvite crystallization does not only require a high PO 3− 4 -P removal efficiency but also a high product quality (i.e.…”

Thermodynamic and kinetic studies of the MgCl2‐NH4Cl‐NH3‐H2O system for the production of high purity MgO from calcined low‐grade magnesite

“…The calculated results were quite consistent with the experimental values with an overall average relative deviation (ARD) of 2.55%. For the binary NH 4 Cl-H 2 O and MgCl 2 -H 2 O systems, the model's prediction based on OLI parameters and the experimental data taken from literature 30,31 were compared over the temperature range from 0 C to 100 C. As shown in Figure 3b, the existing model again gave a good result for the solubility of NH 4 29 Regardless, the recalcualted results were in good agreement with the experimental values as shown in Figure 5 (solid line). Thus, it was confirmed that the new set of MSE model parameters are better at calculating phase equilibria of ternary and quaternary systems involving NH 4 Cl and MgCl 2 .…”