Ettringite

About: Ettringite is a research topic. Over the lifetime, 2702 publications have been published within this topic receiving 67056 citations. The topic is also known as: woodfordite.

Ettringite and oxyanion-substituted ettringites -- their characterization and applications in the fixation of heavy metals: a synthesis of the literature

Abstract: This report constitutes a synthesis of the literature relating to the formation, structure, analysis, and characterization of ettringite from a variety of sources including hydration of portland cement, calcium aluminates, expansive cements, rapid-set cements, hydration of fly ash and coal combustion by-products, and laboratory synthetic processes. The major focus of the review is on the formation and properties of oxyanion-substituted ettringites. Substituted ettringite structures generally contain oxyanions of amphoteric heavy metals such as chromium, boron, arsenic, and selenium. Such amphoteric metals, under the elevated pH conditions of hydrating portland cement, usually will form water-soluble oxyanion species such as chromate. However, it has been established that the ettringite structure can accommodate many such heavy metals oxyanions in place of the usual sulfate anion, and will thus exhibit a very high degree of insolubility at those pH values where heavy metal water-soluble oxyanions will readily be subjected to water leaching.

Hydro-mechanical evaluation of stabilized mine tailings

Abstract: In this study, mine tailings waste was stabilized using a combination of lime, fly ash type "C", and aluminum. Treated samples were subjected to mineral identification for evaluating the formation of ettringite and gypsum. Also, unconfined compression, hydraulic conductivity, and cyclic freeze and thaw tests were performed to evaluate the hydro-mechanical properties of the stabilized samples. Experimental results have shown that the application of lime and fly ash type "C" to high sulfate content tailings has improved its plasticity, workability, and volume stability. Moreover, upon addition of aluminum to lime and fly ash in a sulfate-rich environment, ettringite and calcium sulfo-aluminate hydrate are formed in these samples. Application of 5% lime, 10% fly ash type "C", in combination with 110 ppm aluminum, resulted in the formation of a solid monolith capable of producing more than 1,000 kPa of unconfined compressive strength, and reduced tailings permeability to 1.96×10–6 cm s–1, which is less than the recommended permeability of 10–5 cm s–1 by most environmental protection agencies for reusability of solidified/stabilized samples. The permeability of the treated tailings samples remained below the recommended permeability, even after exposing the treated samples to 12 freeze and thaw cycles. Therefore, based on the experimental results, it is concluded that treatment of high sulfate-content tailings with lime and fly ash, combined with the availability of aluminum for reactions, is a successful method of solidifying highly reactive mine tailings.