Episode #9 – Process foundations: Understanding primary grinding and rougher-scavenger flotation circuits

The starting point is modal analysis, which identifies the minerals present in the ore and indicates the most appropriate process route.

For example, in a gold ore, it is important to know what minerals occur in the ore and how the gold is deported within those minerals.

• If free, it may be treated via grinding, gravity concentration, and cyanide leaching.
• If associated with sulphides such as pyrite, arsenopyrite, or chalcopyrite, a grind, gravity concentration, flotation, regrind, leach circuit is probably required.

Once the route is defined, liberation studies determine the grind size needed for effective mineral separation.

 In primary grinding for flotation, achieving 50–60% liberation of the valuable mineral is typically targeted. The modal analysis also informs the energy requirements: quartz-rich ores demand higher energy and lead to greater wear through abrasion, whereas softer mineral assemblages require less energy.

Wear mechanisms further depend on ore type:

• Quartz-rich ores : high abrasion of liners, media, and equipment.
• High-sulphide ores : lower abrasion but increased risk of corrosive wear.

The mineral assemblage also provides indications about pulp and surface chemistry. For instance, pyrite, being the most noble sulphide, will galvanically couple with other sulphides and grinding media. As its proportion increases, this galvanic effect may result in lower concentrate grades and recoveries.