The precipitation of sparingly-soluble metal salts from aqueous solution: Heterogeneous nucleus numbers at low to intermediate supersaturation

✍ Scribed by Dr. A. Packter; A. Alleem; P. Chauhan; S. C. Uppaladini

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 295 KB
• Volume: 16
• Category: Article
• ISSN: 0232-1300
• DOI: 10.1002/crat.19810161219

✦ Synopsis

The precipitation of series of alkaline-earth metal and transition hydroxides, sulphates, chromates and molybdates, hydrogen phosphate carbonates, oxalates and 'oxinates' were studied in aqueous solution of low to intermediate supersaturation. Heterogeneous nucleation probably occurred onto micro-crystalline particles of some siliceous mineral (of the trigonal, hexagonal or cubic system), dispersed in the solution. The heterogeneous nucleus numbers for these precipitations then depended on the rates of the heterogeneous nucleation onto these substrates and the rates of the mononulcear growth of nuclei to crystallites (during the induction periods). Generally, Nhet values in polypropylene and glass beakers, at low supersaturation, varied from lo4 to lo1* dm-s : the Nhet values then increased slightly with concentration and supersaturation according to the relation Nhet = KS, where K N is a function of the metal salt surface energy and an 'epitaxy' factor; B = 0.4-0.5. In turn, at any supersaturation, log Nhet = log Nhetm + Pa, where Nheto and F were constants for any precipitation: Nhet values then increased from lo4 to lo8 times for increase in u from 50 to 150 m J m-a.

At any supersaturation and surface energy, Nhet values increased in the order monoclinic < orthorhombic < tetragonal < trigonal crystals.