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Tuesday, 20 August 2019
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Raw materials & technologies, Raw materials, Coatings binders

Evaluating a novel slag binder for the immobilisation of lead and zinc

Wednesday, 20 August 2014

In a study, a novel binder, reactive MgO activated slag, is compared with hydrated lime activated slag in the immobilisation of lead and zinc.

Slag-based binders have gained significant attention for construction materials
Source: Luna - Fotolia.com

Slag-based binders have gained significant attention for construction materials
Source: Luna - Fotolia.com

Although Portland cement is the most widely used binder in the stabilisation/solidification (S/S) processes, slag-based binders have gained significant attention recently due to their economic and environmental merits.

Reactive MgO-slag was proposed as a novel binder

A series of lead or zinc-doped pastes and mortars were prepared with metal to binder ratio from 0.25% to 1%. The hydration products and microstructure were studied by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The major hydration products were calcium silicate hydrate and hydrotalcite-like phases. The unconfined compressive strength was measured up to 160d. Findings show that lead had a slight influence on the strength of MgO-slag paste while zinc reduced the strength significantly as its concentration increased. Leachate results using the TCLP tests revealed that the immobilisation degree was dependent on the pH and reactive MgO activated slag showed an increased pH buffering capacity, and thus improved the immobilisation efficiency compared to lime activated slag. It was proposed that zinc was mainly immobilised within the structure of the hydrotalcite-like phases or in the form of calcium zincate, while lead was primarily precipitated as the hydroxide. It is concluded, therefore, that reactive MgO activated slag can serve as clinker-free alternative binder in the S/S process.

The study is published in: Chemosphere, Volume 117, December 2014, Pages 285-294.

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