The precipitation of transition metal oxalate powders from aqueous solution. Crystal numbers and final sizes

✍ Scribed by Dr. A. Packter

• Publisher: John Wiley and Sons
• Year: 1976
• Tongue: English
• Weight: 371 KB
• Volume: 11
• Category: Article
• ISSN: 0232-1300
• DOI: 10.1002/crat.19760111105

✦ Synopsis

The precipitation of manganous, ferrous, cobalt, nickel and copper oxalate hydrates was studied from equivalent solutions of concentrations from 0.001 to 0.3 M a t p H s 7 to G, by optical microscopy and other methods. Crystal growth started after induction periods : the precipitations were heterogeneously nucleated a t low supersaturations and homogeneously nucleated a t medium to high supersaturations. The crystal numbers of the final precipitates dependcd on thc number of nuclei (and crystallites) formed during the induction periods. At medium to high supersaturations, crystal numbers increased with increasing initial metal oxalate complex ion concentrations according to the relation. N = N,CEoX, where was 5. The N values increased in the order Mn < Fe < Co < < Ni < Cu.

The final crystal lengths, in this range, then decreased with increasing metal oxalate complex ion concentrations according to the relation Zfin = Zl/C&ox, where y was 1.3. For precipitations from solution of any concentration, smaller crystals were generally obtained in the precipitatcs of the metal oxalate of lower solubility; nickel oxalate precipitations were the exception to this.' Fallungen von Mangano-, Ferro-, Kobalt-, wickel-: und Kupferoxalathydraten aus 0.001-0,3 m Losungen bei pH-Werten von 7 -G wurden lichtoptisch und mit anderen Methoden verfolgt. Bei niedrigen tfbersiittigungen erfolgte heterogene, bei mittleren bis hohen homogene Keimbildung. Die Kristallzahl hing ab von dcr Zahl der Keime, die in der Induktionsperiode entstanden. Zunahme der Za.hl der Kristalle erfolgte nach N = = N,Ciox mit / 3 = 5. Die Anzahl nahm in folgender Reihe zu: Mn < Fe < Co < Ni<Cu.

Die KristallgroBe nahm ab nach kin = ZJC&ox mit y = 1,3. Im allgemeinen wurden die kleineren Kristalle unter sonst gleichen Bedingungen in den Fiillungen mit. den leichter loslichen Oxalaten erhalten.