Potassium perrhenate KReO

Rhenium. The element rhenium, atomic number 75, was fliscovered by the Gennan chemists Walter Noddack and Ida Tacke in 1925. The principal compound of rhenium is potassium perrhenate, KReO. a colorless substance. In other compounds all oxidation numbers from -f-7 to —1 are represented examples are RCgOj, ReOg, ReClg, Re02, Re20g, Re(OH)2. 

For calibration, the melting point of indium were measured, which has a temperature of fusion (MP) = 156.4°C and a heat of fusion Hj= 28.46 J/g (Fig. 2-8). Because reactions at higher temperatures occur in experiments with petroleum refinery residues, additional calibration runs were performed using pewter (MP = 231.84°C, Ffj= 59.61 J/g) and lead (MP = 327.40°C, H = 26.47 J/g). If a calibration at higher temperatures is necessary, potassium perrhenate KReO (MP = 550°C, Hf= 294.8 J/g) can be used. 

Using this method the annual production of potassium perrhenate KReO, at the beginning of the 1930s increased to ca. 120 kg. The metal rhenium had ceased to be the Noddack family s small private element. 

After filtering the solution contained the rhenium originally present in the complex sludge. Potassium chloride was added and impure potassium perrhenate was precipitated. Very pure KReO was obtained by recrystallization. 

---