Question

Describe the role of the following :

(i) $Si{O}_2$ in the extraction of copper from copper matte.

(ii) NaCN in froth floatation process.

Answer 1

(i) Function of silica is to remove $FeS$ present in the matte as $FeSi{O}_3$ slag.

$2CuFe{S}_2+O_2\stackrel{\Delta }{\to }C{u}_{2}S+2FeS+S{O}_2$

$2FeS+3O_2\to 2FeO+2S{O}_2$

$FeO+\underset{\left(Flux\right)}{Si{O}_2}\to \underset{\left(Slag\right)}{FeSi{O}_3}$

(ii) It acts as depressant to prevent one type of sulphide ore particles from forming froth. e.g., when $NaCN$ is added to a mixture of $ZnS$ and $PbS$, it prevents ZnS from forming froth by forming complex, $N{a}_2\left[Zn\right(CN{)}_4]$. Only $PbS$ forms froth.

$4NaCN+ZnS\to N{a}_2\left[Zn\right(CN{)}_4]+N{a}_{2}S$