3.1. The addition of activators
Both of the addition of activators and alternative collectors to
replace xanthate has been considered by researchers to mitigate
the depression effect of cyanide on minerals flotation. These
available mitigation methods were developed on the basis of the
depression mechanisms of cyanide on mineral flotation which
has been described previously in this paper. Cyanide may prevent
the chemisorption of xanthate on minerals surface due to its higher
affinity with metals in the sulphide minerals. Agent that can
decompose the strong complexion of metal cyanide, detaching
cyanide from minerals surface thus providing available sites for
xanthate adsorption may be considered to mitigate the depression
of cyanide. It is reported by Reddy et al. (1991) that nickel sulphate
is used as an activator for sphalerite flotation in the presence of
cyanide since Ni(CN)4
2 forms with higher stability than zinc
cyanide, staying in the solution preventing the adsorption of cyanide
onto sphalerite surfaces. Besides, the use of formaldehyde
(HCHO) improves the cyanide depressed sphalerite flotation due
to the decomposition of zinc cyanide complexes by formaldehyde
(Reddy et al., 1991). Because formaldehyde is much cheaper than
copper sulphate, it is suggested to be an alternative activator to
replace a large amount of copper sulphate, and then a small
amount of copper sulphate is used to finalize the activation
process. However, the depression effect of cyanide on pyrite flotation
is unlikely to be affected by either nickel ions or formaldehyde
because cyanide has a stronger affinity with iron than nickel as can