PQ silicates are inorganic water-based solutions of silica. These products feature large concentrations of dissolved alkali and silicate polymers. The hydrolysis of alkaline silicate solutions gives rise to polyvalent polymeric species which have useful multifunctional wetting and dispersing properties. Those species are highly charged and very reactive with the polyvalent cations at the mineral surfaces and in solution.
The depressant action results from density modulation of the process stream and action of the alkali and silica to modulate pH and surface charge. In flotation operations, sodium silicate keeps the undesirable gangue particles in the water phase while the desirable value particles are carried to the surface by air bubbles. In flotation, the mild dispersion due to sodium silicate can increase both the rates of collection and gangue drainage. Increased collection and drainage rates translate to higher flotation selectivity, thus concentrate grades and recoveries are improved. Silicates can also enhance the adsorption of polysaccharide depressant reagents (e.g., CMC, guar gum, starch, etc.) on the surfaces of floatable silicate minerals, hence allowing for better selectivity.
Silicate also serves to disperse and aid grinding again due to the dissolved anionic silicate polymers. Those highly charged anionic polymers can create large forces on mineral surfaces, resulting in rapid charge reversal, surface ionization, and zeta potential modification, thus leading to effective mineral slurry dispersion. Likewise, silicates improve separation leading to higher grade and improved recovery.
For titanium dioxide pigment applications, adding silicate to an acidic slurry of titanium dioxide results in the formation of silica gel on the particle surfaces. This precipitated coating protects the titanium dioxide from UV light that would otherwise discolor it.
In the mining applications, silicate can act as a binder of other components of the formulation, e.g. cemented backfill. Silicate has an alkali value, which in turn neutralizes acidic mine waste. Likewise, neutralization of silicate leads to polymerization of the dissolved silica, as in grouting (soil stabilization) applications.