Looking for the salt with the greatest ability to effect the release of Ammonia gas from aqueous ammonia at a pressure of about 1.4MPa (i.e. salt not precipitating out of solution) and at a temperature of about 35 degrees Celsius (i.e. about 308 Kelvin). A salt which has an ammonia solubility being of 14 Molal or less at 1.4MPa at 35 degrees Celsius in 0.5 Molar solution of the salt would suit my needs. Thanks for the help!
One option could be sodium monobasic phosphate (NaH2PO4) at acidic pH.
Thanks. Wouldn’t the acid ph result in excess Hydrogen ions which in turn will increase rather than decrease the Ammonia solubility (per Le Chatelier’s principle)?
In the following all systems are supposed to equilibrate with gas phase containing NH3(g).
1. Systems without likely precipitation (biphasic):
I. Most ammonium salts are rather soluble in water. Even so, note that such salts generally behave as acidic in presence of a strong base like NaOH, e.g.: NH4Cl + NaOH ⇌ NaCl + NH3 + H2O.
II. Ammonium bicarbonate, (NH4)HCO3, converts to ammonium carbonate, (NH4)2CO3, or conversely; depending on partial pressure of NH3(g), which can be dissolved and either captured or released by these salts: (NH4)2CO3 ⇌ NH4HCO3 + NH3.
III. Analogously, both ammonium bisulfate and ammonium sulfate could be considered. Ammonium sulfate can form possibly interesting double salts (ammonium metal sulfates) for the intended application, namely of lower solubility. Depending on partial pressure, NH3(g) can be dissolved and either captured or released by these salts: (NH4)2SO4 ⇌ NH4HSO4 + NH3.
2. Systems with U(VI) uranyl/diuranate precipitants for likely precipitation (triphasic):
IV. It may possibly be found worthy to give some attention at the ammonium diuranate (ADU) ((NH4)2U2O7; (NH4)2U2O7·xH2O(s)↓) / uranyl hydroxide (UO2(OH)2; UO2(OH)2·H2O(s)↓) / ammonia (NH4OH; NH3) aq. sol. system. The following equilibrium can translate hydroxide-assisted uranyl/diuranate conversion: 2UO2(OH)2 + 2NH4OH ⇌ (NH4)2U2O7 + 3H2O.
V. The aq. system tetra-ammonium uranyl tri-carbonate ((NH4)4UO2(CO3)3(aq.; s↓) / ADU / uranyl carbonate / uranyl bicarbonate / ammonium carbonate / ammonium bicarbonate / ammonia (NH4OH; NH3) / dissolved (aq.) carbon dioxide (CO2; H2CO3), seems also worth some attention. The following equilibrium can be considered for bicarbonate-assisted uranyl/diuranate conversion: 2UO2(HCO3)2 + 6NH4OH ⇌ (NH4)2U2O7 + 4NH4HCO3 + 3H2O.
VI. The aq. system uranyl nitrate (UO2(NO3)2; UO2(NO3)2·6H2O(s)↓ / ADU / ammonium nitrate / ammonia (NH4OH; NH3) may also worth some attention. The following equilibrium can be accepted for nitrate-assisted uranyl/diuranate conversion: 2UO2(NO3)2 + 6NH4OH ⇌ (NH4)2U2O7 + 4NH4NO3 + 3H2O.
VII. Also the aq. system ammonium uranyl phosphate (NH4UO2PO4; NH4UO2PO4·3H2O(s)↓; NH4UO2PO4·4H2O(s)↓ / uranyl orthophosphate ((UO2)3(PO4)2; (UO2)3(PO4)2·xH2O(s)↓ (x = 4, 6)) / uranyl hydrogenphosphate (UO2HPO4; UO2HPO4·xH2O(s)↓ (x = 3, 4)) / ADU / uranyl hydroxide / (NH4)3PO4 / (NH4)2HPO4 / ammonia (NH4OH; NH3) can possibly be found of interest. The following equilibrium can be considered for (UO2)3(PO4)2/UO2HPO4 interconversion: H2O + (UO2)3(PO4)2 ⇌ UO2HPO4 + 2UO22+ + PO43- + OH-. Hydroxide-assisted uranyl/diuranate conversion can possibly occur: 2UO2(OH)2 + 2NH4OH ⇌ (NH4)2U2O7 + 3H2O.
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