Reagent

Toxicity

Advantages

Disadvantages

Cyanide

Very high

High dissolution rate

Environmental issues

Agua Regia

High

High dissolution rate

No feasible large scale applications

Chlorination

Medium

Proven technology

No feasible large scale applications

Good efficiency

High temperatures required

Bromine & Iodine

Low

High dissolution rate

High reagent costs

Thiocyanate

Medium

Recyclable

No feasible large scale applications

Limited availability

Thiosulfate

Medium

Cheap reagent

Detoxification costs

High reagent consumption

Thiourea

Medium

Proven technology

Dissolution of heavy metals besides gold

High dissolution rate and speed

Bacteria

Low

Reduction of reagent consumption

Slow reaction

Higher leaching yield

Difficult process control