Natal Portland Cement (NPC) have announcedmajor productivity and efficiency improvementsat their Sterkspuit Quarry in KwaZulu-Natal,

South Africa, following the introduction of a newwashing plant from CDE Global.The loss of high-quality fines during the sand-

processing phase of production has been eliminatedfollowing the introduction of the CDE EvoWash plantto replace the bucket-wheel dewaterer previouslyemployed at the site.NPC have also reported an industry first with the

introduction of a CDE AquaCycle high-rate thickener,which permits the recycling of 90% of the water usedin the washing of their crushed material. Whilethickener systems are used throughout the miningsector in South Africa, the CDE AquaCycle is believedto the first of its kind in a crushed rock or sand andgravel application in the country.NPC are a subsidiary of global construction

materials producer Cimpor of Portugal and operate11 facilities in South Africa with total production of 1.7million tonnes. These include seven ready-mixedconcrete plants, three aggregate production plants (ofwhich Sterkspuit is one), two grinding plants and onecement plant.

TThhee wwaasshhiinngg pprroocceessssSterkspuit Quarry is located in the Cliffdale area, some30km from Durban, on the eastern coast of SouthAfrica. The CDE washing plant is used to process tillitefrom the existing blasting and crushing operations, andthe washed material is sold by NPC for use in theproduction of various asphalt mixes and as areplacement for river sand in their own concrete plants.From the crushing plant the –9.5mm material is first

sent to a CDE ProGrade P2-75 double-deck rinsingscreen fitted with modular Isenmann polyurethanepanels on both decks. The ProGrade unit produces–9.5mm +6.7mm and –6.7mm +5mm aggregates, withthe –5mm material being delivered to the sand-washing phase.According to CDE, the design and construction of

the ProGrade rinsing screen, which features a fullyindependent spray bar assembly, offers majoradvantages compared to many other screens on themarket. ‘The spray bar assembly is not rigidlyconnected to the screenbox as is the case on manyother rinsing screens,’ explained Des Crawford, CDEsales manager in South Africa. ‘This eliminatesvibration and the associated risk of plant failure. �

New Approach for NPCNatal Portland Cement’s new CDE plant set to change the face ofaggregate washing in South Africa

The new CDE washing plant at NPC’s Sterkspuit Quarry in KwaZulu-Natal, South Africa

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‘There is also a major focus on reducing the loss ofboth material and water during screening through theuse of splash prevention over decks and specialistspray bar seals, which results in a safer, cleaner andmore productive site.’ The advantages of polyurethane screen media on

the ProGrade also became immediately clear atSterkspuit. On the previous washing plant the wiremeshes had been lasting only a few weeks owing tothe abrasive nature of the material being processed,whereas the polyurethane screen decks on theProGrade have shown enhanced performance in thefirst few months of operation, which has resulted ina reduction in the cost of maintenance both in termsof spare parts and man hours. An additional advantagefrom a health and safety perspective is the ease offitting of the modules compared with side-tensionedwire meshes.

IInnccrreeaassiinngg ssaanndd wwaasshhiinngg eeffffiicciieennccyyPrior to the introduction of the new washing plant, thesand-washing process was the biggest area ofconcern for NPC at Sterkspuit Quarry. The bucketwheel was losing up to a third of the fine sand thatNPC needed for the production of asphalt, and the verycoarse sand from the wheel meant the company washaving to buy in large quantities of natural finesand to blend with it, leading to significantly increasedproduction costs.‘Sand production was very inefficient with the

bucket wheel,’ explained Dave Kendall, generalmanager at the site. We had to buy in between 70%and 80% of the fine sand we needed as a result of theseinefficiencies.’

The new CDE washing plant employs an EvoWash71 system, which has been used in many similarapplications throughout the world. ‘I visited Ireland andthe UK and saw the EvoWash in action in manysimilar crushed rock applications,’ said Mr Kendall.‘These visits backed up the manufacturer’s claimsregarding the capability of the EvoWash to eliminatethe loss of quality sand during the sand-washingphase. This offered us an opportunity to greatlyincrease the efficiency of our Sterkspuit operation andthe new washing plant now installed is delivering onthis.’As a result of their increased capability to recover

the fine-sand material, NPC have seen the quality ofthe washed sand improve and they have been able todramatically reduce the need to purchase natural finesand from external suppliers as the washed sandproduct now meets the specifications they require forasphalt mixes.‘The move towards self-sufficiency that this new

plant has given us makes a huge difference to ouroperations,’ explained Mr Kendall. ‘Higher-qualitysand, increased volumes of sand and the effectiveelimination of the costs of buying in natural fine sandwill help us deliver significant efficiency improvementsin the months and years to come.’

WWaatteerr rreeccyycclliinngg ssyysstteemmFollowing the sand-washing phase, the waste waterfrom the EvoWash is delivered to an AquaCyclethickener, which allows for the recycling of 90% of thewater used in the washing process.The AquaCycle has been extensively used in recent

years and provides operators with a means of reducing

The washed sand stockpilefollowing the introduction ofthe EvoWash system

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Washing Plant

the environmental impact of their operations while alsooffering other advantages, such as improved healthand safety on site and a significant reduction in theamount of space required to accommodate settlingponds.‘We believe that the introduction of the AquaCycle

to our operation is a first for sand and aggregateproducers in South Africa,’ said Mr Kendall. ‘But withthe environmental benefits and health and safetyimprovements that it offers, I’m sure it will beadopted by others in the not too distant future.’Wash water containing –75 micron material from

the EvoWash first enters the AquaCycle thickener viaa de-aeration chamber located on the side of thethickener tank. The location of the waste dischargepoint at the top of the EvoWash allows for a gravity feedof this material, thereby eliminating the additionalsumps and pumps that are often required with othersimilar systems.In the de-aeration chamber the material is dosed

with a small amount of flocculant, which is preparedin a FlocStation poly-dosing plant. Material is thendelivered to the centre of the circular AquaCycle tankbefore being released. The flocculant that has beenmixed with the waste material forces the –75 micronparticles to bind together whereupon their cumulativeweight causes them to descend to the bottom of thetank where a set of rotating rakes maintains an evenconsistency within the settled sludge. When thesludge reaches an appropriate density the rakesreport back to the PLC control panel which activatesthe sludge pump. The settled sludge is then deliveredto nearby settling ponds.Meanwhile, the clean water overflows an integrated

weir at the edge of the AquaCycle thickener and is sentto the AquaStore collection tank for recirculation tothe washing plant. ‘The advantages of the AquaCycle thickener to our

operation are two-fold,’ said Mr Kendall. ‘First, wehave significantly reduced our use of naturalresources through the water-recycling capability wenow have, and secondly, the space required toaccommodate our settling ponds has been massivelyreduced.’The settling ponds at Sterkspuit previously required

a substantial area due to a lack of water recyclingcoupled with the loss of large volumes of material tothe ponds. The reduction in area that was possiblefollowing the introduction of the AquaCycle has givenNPC additional security in relation to the safe storageof waste material from their operations.‘Our settling ponds are located adjacent to a river

so the introduction of the AquaCycle thickener is anexample of our focus on environmental protection andsustainable production,’ said Mr Kendall.

SSoouutthh AAffrriiccaann ssuucccceessssThis new washing plant represents the first installationfor CDE in South Africa and the company hopes tosecure further installations as a result of its success.‘We have spent a lot of time in South Africa recently,and we know that we can offer operators greatlyincreased efficiencies based on the existing washingplants we have seen,’ commented Des Crawford. ‘Theplant at Sterkspuit gives us a reference where ourclaims regarding plant performance are provenbeyond question.’For further information visit: www.cdeglobal.com

The AquaCycle systemrecycles 90% of the waterused in the washing process

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