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Título : | Nickel retention by calcium silicate hydrate phases: Evaluation of the role of the Ca/Si ratio on adsorption and precipitation processes |
Autor : | Missana, Tiziana García-Gutiérrez, Miguel Alonso, Ursula Almendros-Ginestà, Oscar |
Palabras clave : | Adsorption Surface precipitation Surface complexation modelling Radioactive waste |
Fecha de publicación : | ene-2022 |
Editorial : | ELSEVIER |
Citación : | Missana T., García-Gutiérrez M., Alonso U., Almendros-Ginestá O., Nickel retention by calcium silicate hydrate phases: Evaluation of the role of the Ca/Si ratio on adsorption and precipitation processes, Applied Geochemistry 137 (2022) 105197 |
Resumen : | The objective of the present study is to investigate Ni retention processes in Calcium Silicate Hydrate (CSH) phases, as the main cement hydration products, and to describe them in a generalized form for the first time. In particular, the effects of the CSH Ca/Si ratio (from 0.8 to 1.6) on the equilibrium water chemistry, Ni speciation,
adsorption and solubility have been addressed. Nickel adsorption tends to decrease as the Ca/Si ratio increases, especially when Ca/Si is < 1.2, and then Ca/Si becomes less relevant. The “adsorption” region is limited to low final aqueous Ni concentrations (<5⋅10- 9 M), and when the Ni concentration exceeds this limit, an increase in the (apparent) distribution coefficient, Kd, is observed, which is related to precipitation processes. The onset of precipitation depends on Ni solubility but also on the Ca/Si ratio: at the lowest ratio, the lowest Ni concentration
occurs when the apparent Kd starts to increase. The existence of Ni–Si phases as surface precipitates could explain
the observed experimental behaviour, which is not totally explicable assuming Ni(OH)2(s) as the unique phase limiting Ni solubility. Nickel retention on the CSH phases was analysed and interpreted with the help of surface complexation modelling using an electrostatic double layer approach and accounting for the major species
present in solution for each CSH. The uncertainties in the available Ni thermodynamic database under alkaline
conditions and in the presence of Si are underlined. |
URI : | https://doi.org/10.1016/j.apgeochem.2022.105197 http://documenta.ciemat.es/handle/123456789/3245 |
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