Gold Plant Unit Process

Comminution: Comminution of gold ores and concentrates is primarily required to liberate gold, gold bearing minerals and other metals of economic value to make them amenable to gold extraction. However, this preparatory may also be necessary to facilitate materials handling stage. The degree of comminution required depends on many factors, including the liberation size of gold, the size and nature of the host minerals and the method, or methods, to be applied for gold recovery. The optimum particle size is dictated by the economics; a balance between gold recovery, processing costs (i.e. reaction kinetics and reagent consumptions) and comminution costs.

The major uses of comminution in gold extraction flowsheets are for the following:

• Gold liberation before leaching.
• Sulphide liberation before flotation.
• Gold liberation before flotation and gravity concentration.
• Regrinding of flotation/gravity concentrates or tailings for gold liberation.
• Ultra fine grinding of gold bearing sulphide concentrate before leaching

Mineral Surface Preparation: Gold particles tend to stay in grinding circuits longer than gangue minerals due to their density. As a result, and because gold is soft and malleable, particles become flattened and hard mineral particles (quartz) may become embedded in gold surfaces. This reduces particles density and hydrophobicity which hinders response to gravity concentration and flotation, respectively. The problem is usually limited to ores with coarse gold (> 50 µm) and may overcome by the early removal of gold by gravity concentration or flotation, if necessary within the grinding circuit.

Grinding circuits typically consume between 0.5 and 2.5 kg/t iron as grinding media. A portion of this corrodes in the slurry, depending on solutions conditions (pH, free cyanide) as a result, gold particles exposed to grinding solutions may become coated with iron oxides, hindering leaching and surface chemical processes. Clay minerals are also known to preferentially coat gold surfaces. In other cases the mineral surfaces may actually be cleaned and fresh surface exposed by grinding action, improving their response to subsequent extraction processes

Classification: The most important application of classification in gold extraction flowsheet is the use of cyclones and screens within grinding circuits for optimizing grinding efficiency and obtaining the desire particle size for subsequent processing. However classification may also perform other functions:

• Material may be separated on size for separate treatment in subsequent processes.
• Separation of absorbents (carbon, resins) from slurries and solutions by screening.
• Underground mine backfill preparation.
• Tailing separation for dam construction