Modern Quarrying Q3 2022

construction companies and sister establishments within AfriSam. A closed circuit for washing “All the products produced by the quarry are washed. The plant was originally designed for the asphalt market. In road building the aggre gate must be devoid of any parti cles,” says Du Preez. Dust on the aggregate surface adversely affects bituminous hot mix pavement performance and decreases the long-term performance of roads. “In order to produce the various products for the road building industry, a washing process is needed to meet the requirements and specification of the saleable products. During this process those fines that are by-products of the washing process are discarded.” The tailings produced as a result of the washing of aggregates is pumped to the unused dolomite pit that is used as a tailings dam and its rehabilitation facility. “We have a closed circuit regarding water within the operation itself,” explains Du Preez as environmental regulations prohibit the release of untreated contaminated water into the stream that runs alongside the site, and it is economically feasible to recover and reuse the same process water again. Rooikraal Quarry does not make use of municipal water as this will be uneconomical given the volume of water needed for washing. Instead, the quarry is dependent on rainwater that is collected in both the dolerite and dolomite pits. “The last time the facility used municipal water was in 2014. Since then seasonal rain has provided us with enough water to run the closed circuit. On the dolerite side there is a sump too and we collect water there and pump the water to the dolomite side,” says Sterley. There is an HDPE pipeline running underground from the unused pit (which functions as a tailings dam) to the primary, secondary and tertiary sites of the plant and a pipeline taking slime away from the plant to the pit. “We supply water to all the screens and cyclone. Including the dewatering screen, there are

AfriSam’s Rooikraal Quarry is located near Brakpan, Gauteng and mines competent dolerite rock.

The tertiary plant produces a coarser and a finer sand.

KEY TAKEAWAYS

Rooikraal Quarry does not make use of municipal water as this would be uneconomical given the volume of water needed for washing. Instead, the quarry is dependent on rainwater that is collected in both the dolerite and dolomite pits.

The tailings produced as a result of the washing of aggregates is pumped to the unused dolomite pit that is used as a tailings dam and its rehabilitation facility.

The biggest challenge is sales demand. It is a cut throat market. Road projects are scarce and there are many competitors.

The fairly square shape of the shallow pit allows for big blasts.

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MODERN QUARRYING QUARTER 3 | 2022