Study of Ammonium Oxalate Monohydrate Minerals Using Theoretical Solid-State Methods
Colmenero, Francisco. Journal of Physics and Chemistry of Solids, 2019, 125, 31-42.
In order to study the structural, spectroscopic and thermodynamic properties of the ammonium oxalate mineral oxalate monohydrate [(NH4)2(C2O4)H2O], a theoretical solid-state approach was adopted. This work investigates the use of plane waves and pseudopotentials in theoretical solid-state calculations based on periodic density functional theory (DFT).
Key properties of ammonium oxalate monohydrate
· The structural properties that were calculated, including lattice parameters, bond lengths and angles, and X-ray powder diffraction patterns, matched well with the experimental results obtained from low temperature X-ray diffraction data.
· The bands observed at 2344, 2161, 1933, and 1902 cm-1, as well as the 815 cm-1 band, were determined to be combination bands not accounted for in the computed spectrum. Additionally, it was confirmed that the band at 2879 cm-1 was an overtone.
· The calculated specific heat at 323 K was Cp=202.3 k/J/mol, which closely matched the experimental value. Additionally, the enthalpies and free energies of formation for oxammite were determined based on the elements and thermodynamic properties of its thermal decomposition reaction. These findings revealed that the crystalline material of ammonium oxalate monohydrate begins to decompose at a relatively low temperature of 288 K.
Ammonium Oxalate Leaching to Recover Vanadium from Vanadium Slag
Li, Meng, et al. Jom, 2017, 69, 1970-1975.
Ammonium oxalate [(NH4)2C2O4] can be used as a leaching medium to recover vanadium from vanadium slag after non-salt roasting. In this non-salt roasting ammonium oxalate leaching (NRAL) strategy, the chromium spinels in the raw vanadium slag cannot be converted into carcinogenic chromates at roasting temperatures. In addition, ammonium oxalate is almost non-volatile below 90°C, avoiding expensive and complicated ammonium control operations.
Non-salt roasting ammonium oxalate leaching procedure
· In the process of non-salt roasting, 50 g of vanadium slag was placed in a corundum boat and roasted in a tube furnace. Once the roasting was completed, the slag was cooled with air to room temperature and then crushed using an agate mortar before being sieved to produce fine powders ranging from 48-75 μm.
· The roasted slag underwent leaching in a glass container placed in a temperature-controlled water bath. The setup included a reflux condenser, Teflon-protected mechanical stirring for agitation. The leaching process involved roasted vanadium slag particles sized 48-75 μm, ammonium oxalate concentrations ranging from 5-15% by weight, a solid to liquid ratio of 1:4 (50 g slag and 200 g solution), temperatures between 30-90°C, leaching times from 1-120 min, and stirring at 300 rpm. Following leaching, the slurry was filtered, and the resulting filter cake was rinsed with deionized water.