The coprecipitation of zinc aluminium hydroxides (refractory‐, absorbent‐, and catalyst precursors) from aqueous solution with ammonium hydroxide: Precipitate compositions and coprecipitation mechanisms

Abstract

Zinc aluminium hydroxide hydrates were coprecipitated from different mixed cation solutions at Zn/Al, ratios from 1/2 to 4/1. The coprecipitations were monitored by potentiometric titrations and the final coprecipitate compositions were examined by chemical analysis and atomic absorption spectrophotometry, X-ray diffraction and preliminary thermal analysis. The product from Zn/Al, = 1/2 solution was amorphous : at Zn/Al, = 1/1.5, the main phase (after drying at 95 "C) was a zinc hydroxoaluminate Zn[AI(OH),], together with some gibbsite: at Zn/Al, = 1, the main phase was probably a solid solution (of Zn[AI(OH),], with Zn, [Al,(OH),,]) together with Zn2[AI,(OH),,] : at Zn/Al, = 2, the main phase was a mixture of Zn, [Al,(OH),,] with (ZnOH), [Al,(OH),,] and some gibbsite:at Zn/Al, = 4, the main phase was (ZnOH), [Al,(OH),,] with some zinc hydroxide.

Thermal analysis

“…In the hydrothermal and decomposition of ground gibbsite the prehistory was important (129). A similar result was obtained by Doherty et al (130). The same general comments apply to Ti02 (131), Fe203 (132), and Ag20 (133).…”