Advancing flotation process technologies to maximise gold extraction

Warren Taylor, Product Specialist for Weir Minerals, looks at the flotation process of extracting gold, and explains the complexities of froth flotation.

The process used to extract gold is largely dependent upon the ore deposit and the mineralogy of the ore.

A flotation process is one method used throughout the industry to recover gold. It’s a very cost-effective method for concentrating gold, and is a desirable process used for the upgrading of low-sulphide and refractory ore for further gold recovery treatment.

Froth flotation is a process used to selectively separate hydrophobic materials from hydrophilic materials. Air bubbles can only stick to the desired mineral particles if they can displace water from the mineral surface, and can only continue to support the mineral particles at the surface if they can form a stable froth achieved by using floatation reagents.

As the characteristics of froth can vary from day to day, a thorough understanding of froth transfer applications is critical when designing and selecting froth pumps. Insufficient froth volume factor (FVF) knowledge can often contribute to incorrect froth pump selections and hopper designs.

Pumping Mineral Froths

Pumping mineral froths using standard slurry pumps often leads to problems for operators, especially when treating mixed ores. Furthermore, froths can easily vary from brittle froth - generally large bubbles that are easily broken down, to very tenacious froth - generally fine, tightly bound air bubbles that remain in a froth state for many hours.

In high FVF conditions such as medium to tenacious froths, air separation from the liquid contributes to air-binding within the eye of the impeller. This may create the expectation of cavitation, but rather than the collapse of vapour pockets, the entrained air bubbles rapidly expand in areas of low pressure within the pump impeller to decrease both head and efficiency, causing air-binding.

As a result, poor froth pumping performance normally leads to overflowing hoppers and the loss of valuable concentrate.

As flotation performance is greatly influenced through the on-going development of new and improved reagents, companies producing mining chemicals are continually striving to develop “super performing chemicals”. Collectors are being developed to further increase the separability of the hydrophobic and hydrophilic particles, while froth advancements aim to create more stable froths to increase flotation kinetics and allow for improved drainage of entrapped gangue material.

Warman® AHFC froth pumps with CARS technology 

To meet the demands of flotation plants that exhibit complex and tenacious froth conditions, Weir Minerals has developed the heavy duty Warman® AHFC froth pump with Continuous Air Removal System (CARS) technology.

Our Warman® AHFC froth pump technology is purposely designed for flotation processes that produce medium froths, and very tough froth concentrate transfer applications that produce long lasting, tenacious froth conditions. 

The Warman® AHFC froth pump has open inducer vanes that protrude into the large intake throat area, designed to create a strong swirling air core, while drawing the froth air bubbles into the impeller-eye. This process separates the valuable concentrate from the tenacious froth bubbles. Our CARS technology is then able to expel a vast amount of air into the atmosphere, enabling more efficient froth concentrate pumping.

Our enhanced froth pump technology, CARS, is expertly designed for heavy duty slurry froth pumps and is successfully operating in a number of Gold, Phosphate, Potash, Coppr, Molybdenum, Silver, Zinc, Lead, Coal and Oil Sands applications around the world.

To support optimum froth pump performance, froth hopper design and geometry is absolutely critical.

Every one of our froth hoppers are uniquely designed to suit both the application and the chosen Warman® AHFC froth pump. Froth hoppers must be designed to enhance the efficiency of the froth transfer system by reducing ‘froth generation’ turbulence inside the hopper, while ensuring that the froth slurry concentrate is effortlessly induced into the AHFC inlet. 

As some degree of flotation plant instability is always to be expected, especially during plant start-up, it is likely that under extreme, adverse conditions the froth hopper may overflow. Anticipating this instability, we have innovatively designed large overflow launders with a large down-pipe feeding directly into the spillage handling system to minimise the loss of valuable froth concentrate.

Successful froth concentrate transfer projects are only achievable through detailed process plant reviews, involving a team of process engineers and froth pump application engineering consultants. We always partner with our customers to deliver an autonomous flotation process. 

To find out more about about our Warman AHF froth pump with CARS technology visit our product page or contact our Warman team.