Cationic Agents

Although all of the metal ions might be considered to be resurfacing agents, only a few are commonly used as such. These are shown in Table 4. Copper, one of the most important, finds use in the flotation of sphalerite (zinc sulfide) which is unaffected by xanthate. Cooper ions are added to the pulp as copper sulfate (Cuso₄). The copper adsorbed on the sphalerite surfaces replaces the zinc in the mineral lattice, forming a copper sulfide film on the sphalerite. The sphalerite, therefore, behaves as a copper mineral which can be floated with xanthate.

The electromotive used to determine the suitability of any metal as a resurfacing agent for any particular mineral. Any metal in the series will displace from solution those metals appearing below it. Copper salts would thus be expected to be suitable for resurfacing nickel, cobalt, iron, and zinc sulfides prior to xanthate flotation and, in fact, are utilized for that purpose.

Electromotive Series of Metals

K, Na, Li Cd Hg (H)
Ba, Sr, Ca Fe Ag Cu
Mg, Al Co Pd As
Mn  Ni Pt Bi
Zn  Sn Au Sb
Cr  Pb

Calcium, which is usually added as CaO (quicklime) or Ca(OH)₂ (slaked lime), is the most common depressant for pyrite and other iron sulfide minerals when xanthate collectors are used. The mechanism of the calcium adsorption (resurfacing action) differs form that discussed previously, and is subject of much controversy. An important contribution to the knowledge of such adsorption was made by Gaudin and Charles who showed that the presence of oxygen and high Ph increases calcium adsorption in preference to the collector adsorption.

Calcium or barium ions also are used for the resurfacing of silica and other acidic minerals to make them floatable with fatty-acid-type collectors.