Improve Precious Metals Recovery with Slag Quality

One must try to produce an ideal slag because it will help with the recovery of the precious metals. The best slags are a balance between acidic and basic properties. Slags are classified according to the proportion of oxygen in the acid to the oxygen in the base. A mono-silicate slag has equal amounts of oxygen in each whereas bi-silicate slags have twice as much oxygen in the acid as in the base. The best slags are those that range between a subsilicate and a bisilicate. The different fluxing reagents all have a role in producing an ideal slag. The fluxing and fusion procedures require that the fluxes balanced each other. It should be glassy and homogeneous in colour and texture. Streaky slags are a sign of an imperfect fusion. A sample that indicates high S, As, Sb, Cu or any other base metals requires a knowledge of how to proceed with the fluxes that is gain by experience and asking question from those assayer whose do have the experience.

Here is a list of some common slags.
Various Greens = Ferrous Silicates
Brick red = Copper
Opaque Milky White = Ca, Mg, Al, Zn, Ba - Limestone sample will produce a greenish, opaque and/or streaked slag.
Black = Fe & Mn
Blue = Co
Purple to light Pink = Mn
Greenish white = very high sulphide.

Fusion tips.: Place crucibles in sequence after pouring. A rack should be set aside to dispose the hot crucibles.

Set aside crucibles with unusual pours or lead buttons. A history of difficult or problematic samples should be kept.

Lead button size.: The size of button to aim for is a range from 20 to 35 grams