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Abstract

Pure brochantite was prepared at 60° from 0.5M copper(II) sulphate and sodium hydroxide solutions at pH 8.0. The decomposition products arising when it was heated at different temperatures were identified using X-ray diffraction analysis and infrared spectroscopy. Dolerophanite, CuO.CuSO4, which is invariably reported to be formed during the thermal decomposition of brochantite (of both synthetic and mineral origins), was not formed at any stage of the decomposition in the present case. The sequence of decomposition is
$\begin{gathered} CuSO_4 .3Cu(OH)_2 .xH_2 O\xrightarrow{{80 - 170^ \circ }}CuSO_4 .3Cu(OH)_2 + xH_2 O \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,CuSO_4 .3Cu(OH)_2 \xrightarrow{{250 - 400^ \circ }}CuSO_4 .2Cu(OH)_2 + CuO + H_2 O \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,CuSO_4 .2Cu(OH)_2 \xrightarrow{{610 - 700^ \circ }}3CuO + 2H_2 O + SO_2 + {\raise0.5ex\hbox{$\begin{gathered} CuSO_4 .3Cu(OH)_2 .xH_2 O\xrightarrow{{80 - 170^ \circ }}CuSO_4 .3Cu(OH)_2 + xH_2 O \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,CuSO_4 .3Cu(OH)_2 \xrightarrow{{250 - 400^ \circ }}CuSO_4 .2Cu(OH)_2 + CuO + H_2 O \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,CuSO_4 .2Cu(OH)_2 \xrightarrow{{610 - 700^ \circ }}3CuO + 2H_2 O + SO_2 + {\raise0.5ex\hbox{
The higher pH conditions adopted here for the precipitation are probably responsible for the above mechanism of decomposition.
Reines Bronchantit wurde bei 60° und pH 8 aus Lösungen von Kupfer(II)-sulfat (0.5 M) und Natriumhydroxid hergestellt. Die beim Erhitzen auf verschiedene Temperaturen entstehenden Zersetzungsprodukte wurden röntgendiffraktometrisch und infrarotspektroskopisch identifiziert. Dolerophanit, CuO.CuSO4, das bei der thermischen Zersetzung von sowohl synthetischem als auch natürlich vorkommendem Bronchantit gebildet werden soll, konnte nicht als Produkt einer der Zersetzungsstufen nachgewiesen werden. Die Reihenfolge der Zersetzung ist:
.3Cu(OH)_2 .xH_2 OCuSO_4 .3Cu(OH)_2 + xH_2 O CuSO_4 .3Cu(OH)_2 CuSO_4 .2Cu(OH)_2 + CuO + H_2 O CuSO_4 .2Cu(OH)_2 3CuO + 2H_2 O + SO_2 + \begin{gathered} CuSO_4 .3Cu(OH)_2 .xH_2 O\xrightarrow{{80 - 170^ \circ }}CuSO_4 .3Cu(OH)_2 + xH_2 O \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,CuSO_4 .3Cu(OH)_2 \xrightarrow{{250 - 400^ \circ }}CuSO_4 .2Cu(OH)_2 + CuO + H_2 O \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,CuSO_4 .2Cu(OH)_2 \xrightarrow{{610 - 700^ \circ }}3CuO + 2H_2 O + SO_2 + {\raise0.5ex\hbox{
CuSO4 .3Cu(OH)2 .xH2 O\xrightarrow80 - 170° CuSO4 .3Cu(OH)2 + xH2 O                CuSO4 .3Cu(OH)2 \xrightarrow250 - 400° CuSO4 .2Cu(OH)2 + CuO + H2 O               CuSO4 .2Cu(OH)2 \xrightarrow610 - 700° 3CuO + 2H2 O + SO2 + 1/2O2   \begin{gathered} CuSO_4 .3Cu(OH)_2 .xH_2 O\xrightarrow{{80 - 170^ \circ }}CuSO_4 .3Cu(OH)_2 + xH_2 O \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,CuSO_4 .3Cu(OH)_2 \xrightarrow{{250 - 400^ \circ }}CuSO_4 .2Cu(OH)_2 + CuO + H_2 O \hfill \\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,CuSO_4 .2Cu(OH)_2 \xrightarrow{{610 - 700^ \circ }}3CuO + 2H_2 O + SO_2 + 1/2O_2 \, \hfill \\ \end{gathered}

One of the authors (SVS) express his gratitude to the University Grants Commission for the award of a Fellowship under the Faculty Improvement Programme, and to the Director of Higher Education, Andhra Pradesh, Hyderabad, and to the Principal, Government College, Srikakulam, for their kind permission to undertake this work.

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