As the mining industry matures, so too does the need for high level, technologically advanced equipment. ‘Easy-to-process’ PGM ores are largely depleted and the need for energy generation from low quality fine coal is becoming urgent. Suppliers that can offer solutions to either or both of these industry challenges will thrive, writes Laura Cornish.

Fine vibrating screen specialist Derrick Corporation and its six-year old South African subsidiary are offering such technology, equipment and methodologies to both these market sectors. As a result, its South African company is performing extremely well locally and in neighbouring countries.

Regional manager, Nic Barkhuysen believes the company’s growing success is attributable to its patented technology and cost-saving production enhancing screening equipment. “We can screen very efficiently down to 45 micron apertures with polyurethane surfaces and down to 35 microns with wire deck technology. I don’t believe any competitor can screen so finely at high capacity, very high frequencies and very low amplitudes,” he says.

The benefits of machines capable of handling and screening fine material at high feed rates, on small footprints (with capacities of between 40 and 500 tph), for both wet and dry applications, are obvious. Because the platinum’s increasingly high UG2/chrome material has smaller sized PGM minerals and increasingly higher dissociation of PGM minerals from the larger and hence more easily floatable sulphide minerals, its processing capabilitieswill still prosper with fine screening equipment.

The coal sector, which is frantically evaluating technology that can viably extract fines for upgrading, will also benefit from screening technology that can handle very fine material.

“It is easy to see why our patented Stack Sizer – a high capacity, efficient, fine wet screening machine – has become our local flagship product. It provides solutions to our local industry’s immediate needs. The fact that there are over 1 800 installed and operating across various international mining operations is sufficient proof of its market attraction.

Thanks to their process performance enhancements, Barkhuysen says the Derrick machines have a payback period no longer than a year, in some cases as low as a couple of weeks!

Taking on the Southern African coal sector

While the local gold and platinum sectorsare already reaping the benefits of the Derrick Stack Sizer, Southern Africa’s coal sector will soon realise the benefits it has to offer.

Derrick Corporation South Africa recently secured its first major coal contract – to supply 12 x 5 deck 200 tph Stack Sizer machines to a major coal operation in Mozambique. “The screens will be manufactured at our parent company’s highly automated facility in the US and shipped directly to site. We will send a commissioning team to site to ensure they are assembled, installed and commissioned properly when delivery starts in November this year,” Barkhuysen explains.

Replacing cyclones in a closed circuit

TheStack Sizer screens arepopularly used to ‘close the mill circuit’– an application that Derrick Corporation promotes to clients, Barkhuysen continues. “Our Stack Sizers can replace cyclones within the milling circuit, significantly increasing their throughput by reducing the circulating load inherent in closed circuit milling. It further reduces flotation reagent consumption, overall mill power consumption and decreases the volume of slimes material, thereby offering environmental advantages as well.”

For UG2 operations, Barkhuysen adds that the combination of cyclones and screens can deliver optimal results. The company has two five-deck Stack Sizersinstalled and operating at a tailings stream overflow for one of the major local platinum company’s UG2 operations.

Reducing ash content

TheStack Sizeralso offers the advantage of significant ash reduction in clean coal spiral circuits. Fitted with Derrick 100 micron urethane screen panels and months of continuous production, the Stack Sizer has confirmed its ability to consistently produce a clean coal fraction that typically halves the ash content.

A typical example of a five-deck Stack Sizer operating today produces approximately 33 short tonnes per hour of clean coal containing about 9% ash. This represents a clean coal yield of about 75%and an ash reduction of about 50% from the feed slurry. “Ultimately, this means that what has been considered a tailings product up until now can be converted into a saleable product – the financial benefits and increasing demand for coal makes this particular application extremely attractive.”

Dewatering ultra-fines

Next to the Stack Sizer, Barkhuysen is achieving considerable success with its dewatering screens aimed at recovering ultra-fines out of slimes. “We can recover around 85% of fines coarser than 38 microns in slurries. The screen oversize is always stackable and conveyable, meaning it can be conveyed or handled mechanically.”

Where Derrick screens can be found

Derrick screens are suited to any processing plant, including iron ore, gold, platinum, gold, chrome, base metals, phosphates, silica and mineral sands.

  • PGM, gold and diamond mines in South Africa and Namibia
  • Gold mines in Namibia and Ghana
  • Mineral sand operations across Africa
  • Base metals (copper) mines in the Democratic Republic of the Congo
  • Fluorspar mine in Namibia (Okorusu)
  • Iron ore mines – Derrick Corporation South Africa has 60 dry screens installed at an iron ore mine in Mauritania
  • Uranium mine in Namibia

The foundations of Derrick Corporation

Derrick Corporation is an American family-owned business, which was established 60 years ago.

Its head office and manufacturing facility are situated in Buffalo, New York, and it has another office in Huston, Texas.

Its South African company is the only office established outside of the US and will focus on the African mining markets.