G-Vault interstage screens process golden results

Operational inefficiencies are a common occurrence in dry and wet processing. Jim Colgrove reveals what truly sets Derrick’s G-Vault interstage screen apart when it comes to avoiding these issues.

The development of Derrick’s G-Vault interstage screens in the gold processing sector has challenged the perception of what was previously too difficult or even impossible to screen.

The G-Vault addresses the shortcomings presented by stainless steel wedge wire screens in carbon-in leach (CIL)/carbon-in-pulp (CIP) and resin-in-leach processes.

The secret to overcoming these shortcomings lies in the development of Derrick’s polyurethane screen surface technology that has been refined incrementally over the past 35 years.

This refinement has resulted in a screening technology that addresses the common issues of blinding and pegging in processing plant screens. As Derrick senior vice president and director of new business development Jim Colgrove puts it, angular materials are “very prone” to blinding or pegging when using woven wire mesh or wedge wire screens.

“Blinding and pegging are different concepts,” he says. “Blinding occurs when particles become trapped in the ‘hourglass’ shape of a square wire mesh screen aperture (see figure 1).

“Pegging occurs mainly in a slotted wire mesh or wedge wire screen surface, whereby a particle wedges in a slot that becomes unstable along its length, or the particle is wedged or pegged in a worn and rounded wedge wire slot opening.”

While the relief angle of a wire mesh and wedge wire opening can be adjusted to help reduce material blinding, the result from a small amount of wear is eventually a blinded screen. This reduces the available screening area, therefore lowering its capacity and efficiency.

“Derrick has been designing and manufacturing polyurethane screens since 1984,” Colgrove says.

“We are the world leader in the technology of urethane screen surfaces. We manufacture them from six millimetres down to 38 micrometres – all with superior performing open area and cut points.

“While all urethane screen panels are well known for their abrasion resistance, only Derrick screens combine long life with high open area, capacity and performance rivalling that of conventional woven wire screens.”

Derrick was committed to developing proprietary technology in designing and building the intricate moulds needed for producing these novel screens, while its research and development department focussed on their application.

“There have been many long weeks at customer sites developing the right type of screen surface for a particular application,” Colgrove reveals.

These screens were developed without the Derrick team taking its eyes off of the equipment they would be used on.

According to Colgrove, the urethane surfaces and equipment have a symbiotic relationship. In 2003, Derrick developed its Stack Sizer – a “revolutionary design” for the mining industry – specifically to complement the company’s urethane screen technology.

“The next evolution in Derrick’s development occurred when we made the jump to thermoplastics,” Colgrove says.

“It gave us the ability to make small screens via an intricate moulding process. This lets us build screens of smaller sizes to achieve fine openings and high open areas.

“These smaller screens can be attached to one another via a support structure to achieve the size and shape of a larger screen.”

This technology led to many new developments in the company, one of which is a modular screening surface for use as an interstage screen in gold leaching circuits, called G-Vault. It is a bolt in replacement to existing interstage screening units.

The result of that collaboration is a long-life, high open area (G-Vault) interstage screen, which can last for six to 12 months – 10–15 times longer than some conventional wedge wire panels. Due of its high open area, it offers higher capacity (see figure 2).

The G-Vault interstage screen utilises urethane screens, with a very sharp flat surface opening with excellent abrasion, cut resistance and a high relief angle (see figure 1).

By making the screens in a replaceable cartridge format, users can easily replace an individual section when it is worn or damaged instead of the entire interstage basket.

They are lightweight and easy to install, removing many barriers and safety hazards involved in screen maintenance.

This commitment sees its value in the more consistent processing and less interruption enjoyed by many companies as a result of the flexibility, long-life and high open area characteristics (35–45 per cent).

“Traditionally, Derrick has only made urethane surfaces for use on its own equipment,” Colgrove says.

“But these principles affect the bottom line of any operation. Better screening efficiencies make a more efficient operation which lowers costs. So now we have branched out to other markets and equipment that can benefit from our technology.”

Colgrove says that nowadays, Derrick is able to make custom sizes with custom materials easily using its technology.

“Derrick engineers enjoy working closely with each application to determine the appropriate technology and to address all customer process issues,” he says.

The growth in G-Vault technology and applications demonstrates Derrick’s commitment to exploring new opportunities to improve and increase the company’s value to the mining industry.

This feature also appears in the October edition of Australian Mining.

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