silver extraction from ores

Extracting silver from ores involves several steps, depending on the type of ore and the silver content. Here’s a general overview of the most common methods:

1. Ore Preparation
– Crushing & Grinding: The ore is crushed and ground into fine particles to liberate silver minerals from the gangue (waste material).
– Concentration: If silver is present as sulfide minerals (e.g., argentite – Ag₂S), froth flotation may be used to concentrate the silver-bearing fraction.

2. Extraction Methods
# (A) Cyanidation (Most Common for Silver Ores)
– Used for ores where silver is finely disseminated or associated with gold.
– Process:
1. The crushed ore is leached with a dilute sodium cyanide (NaCN) solution (~0.1–0.5%).
2. Silver dissolves as a cyanide complex:
\[
\text{Ag}_2\text{S} + 4\text{NaCN} + \text{O}_2 + 2\text{H}_2\text{O} → 2\text{Na}[Ag(CN)_2] + \text{NaOH} + \text{S}
\]
3. The solution is filtered, and silver is recovered by:
– Zinc Precipitation (Merrill-Crowe Process):
\[
2\text{Na}[Ag(CN)_2] + \text{Zn} → 2\text{Ag}↓ + \text{Na}_2[\text{Zn(CN)}_4]
\]
– Electrowinning: Passing an electric current through the solution to deposit pure silver.

# (B) Smelting (For Sulfide or Lead-Rich Ores)
– Used when silver is present in galena (PbS) or other sulfide ores.
– The ore is roasted to remove sulfur, then smelted with fluxes (e.g., silica, limestone) in a blast furnace.
– Silver reports to lead bullion, which is then refined via:
– Parkes Process: Zinc is added to molten lead; zinc-silver dross forms and is skimmed off.
– Cupellation: The zinc-silver dross is heaten air; zinc oxidizes, leaving behind impure silver.

# (C) Patio Process & Amalgamation (Historical Methods)
– Pat