From slag to cement

When talking about resource extraction the words which spring to mind aren’t usually particularly eco-friendly.  Although extraction businesses across the globe are working to reverse this image, in the minds of many people resource extraction is synonymous with slag heaps and the destruction of the natural habitat.

One global business which is working hard to erase this image is Hindustan Zinc Ltd (HZL).  Its threefold mission statement is to “enhance stakeholders value through exploration, innovation, operational excellence and sustainability” to “be a globally lowest cost producer” and to “maintain market leadership and customer delight”.  In pursuance of these aims HZL believes that every waste is a resource which can be gainfully utilised by exploring suitable applications.

HZL is the world’s largest integrated producer of zinc.  Its mine in Rampura Agucha already operated on a zero discharge basis but that still resulted in an accumulation of slag which after fifteen years of operation covered 20ha.  With no proven uses for Zinc Slag HZL set out to explore whether the material could be used in road construction or cement manufacturing.

Although detailed R&D studies showed that slag could be used in place of sand in road construction the project concentrated on cement production as being a more environmentally favourable option.  Research proved that Zinc slag, as an inert material, could be used as a component of both ordinary Portland Cement and Portland Slag Cements and as a performance improver in Cement Mill.  Following the research, local cement manufacturers incorporated the slag into their products and this has resulted in the clearance of slag heaps from some 18ha of land.

Apart from the environmental impact of reducing slag heaps and reusing waste, the use of zinc slag in cement production has resulted in a reduction in the carbon emissions traditionally associated with cement manufacturing.  With the slag replacing limestone and dolomite and with a consequent reduction in the need to heat these materials to produce the cement, it is estimated that every 100MT slag used results in a reduction in emissions of 23.04MT Co2.  In addition some 40MT of limestone and 83MT of Red Ochre are saved.

Following the success of this experiment, HZL are exploring potential uses for other by-products.  HZL has already won numerous awards for their environmental work and we were happy to add a Green Apple Award to their collection.