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CDE Group delivers ManSand washing with no loose ends

CDE Group

Australia has seen bursts of activity in the space of washing crusher fines as a replacement for natural sand led in part by the efforts of CDE Group. 

Almost 20 years ago, Cement Concrete and Aggregates Australia commissioned a report that highlighted the potential of beneficiated crusher fines, or more commonly known as manufactured sand (ManSand).

However, even as natural reserves of sand near exhaustion around the country’s capital cities, ManSand has not begun to replace it to a huge extent.

There are several potential reasons for this:

A quarry’s ability to put a fines beneficiation plant in retrospectively. Constraints being development application amendments, access to space, water and power.

Crusher fines are bimodal with a lot of coarse grains and then a lot of bottom end (-75 micron) but do not contain enough medium/fine material to make a viable/high percentage sand alternative, or it adversely affects concrete mix (strength/slump/admix requirements).

Available solutions can tackle only part of the problem but can create more headaches for the operation and site downstream.

The quarry can already find a home for its fines and then buy in the sand it needs without a capital investment.

CDE has continued to develop systems to better tackle the beneficiation of manufactured sand, addressing all four of the above-recognised pain points. It comes after the success of CDE’s compact systems across large parts of Asia and the Middle East, which was designed in response to a sand mining moratorium established by many countries.

CDE washed ManSand almost eliminates organic and soluble impurities such as clay and silt that adversely affect the setting, slump, shrinkage and strength properties of a concrete mix.

In the Australian context, the industry typical AS:1141.33 sand test does not hold back the use of manufactured sand, as quality fine sand (even sub 75 micron) will settle out and not make a sample fail the typical <5 per cent silt by volume test.
An efficient washing system needs to:

Extract problems fines (actual silts and clays or excess ultra-fines causing mix issues)

Look to increase percentage of medium/fine sand.

Maximise productivity through water recovery, power and land availability.

CDE’s latest generation of EvoWash sand wash system, rinses and cyclone washes ultrafine sand, minimising overall water by reducing cyclone diameter. Water demand is a large contributor to the use of sand-screws in ManSand applications. Sand screws are not as efficient as they commonly lose sand up to and over 200micron which is precisely the sand crusher dust is usually missing. Equally, with screws, waste becomes higher and tailings management can worsen. Sand screws also often require additional equipment post-commissioning to retain the fines and increase dewatering.

After washing the rest of the downstream, a CDE system remains compact with an AquaCycle thickener, which can be as small as 4m. This would be placed alongside a containerised water and buffer tank that supports a decanter centrifuge or filter press. ManSand plants are now capable of treating up to 100tph taking up less than a 200m2 (excluding sand stockpiles) and using less than 15m3/hr. Reject fines being presented as a spadable cake is ideal in most instances.

Regarding gradation control, CDE can utilise tight tolerance fine screens to cut down to 400 Microns for blending. At the same time, vertical shaft impactors (and more recently rolls crushers) have been integrated to turn fine aggregate/grit into medium/fine sand in a more controlled manner. By only imparting a few breaks on stone, the company can create the sand missing from the particle size distribution (PSD) without creating ultrafines that go to waste.

CDE already has several installations in the Australasian region processing crusher fines to make quality manufactured sands. From landmark projects like Walker Quarries in NSW and the 300tph plant with TPI in Thailand, to early adopters such as Jungs Quarry in Coffs Harbour and more compact systems.

As natural resources continue to dwindle and with cartage costs continuing to rise, it is expected that quarries will once again look to crusher fines to make up a larger proportion of their concrete sand blend. While some quarries can move this material for bedding or in asphalt already, the industry is likely approaching a tipping point where the bottom line supports investment to offset more natural sand in construction/concrete sand. CDE is developing systems that make this possible without requiring space and water that doesn’t exist, and without undesirable trade-offs around yield or dry dust tailings.

With an installation base across Australasia, CDE is also happy to arrange live site demonstration visits. •

For more information, visit cdegroup.com

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