Application of carbonated calcium silicate materials in metal sorption processes

The current work proposes a novel approach to the production of sorbent materials, which integrates recycling of calcium silicate-based industrial residues and sequestration of carbon dioxide in the process of accelerated carbonation. The concept was tested on model substrates of suitable mineralogy, namely Portland cement and dicalcium silicate, which were carbonated, and examined by nitrogen adsorption, XRD, NMR, SEM, TG-DTA analytical techniques. The carbonated materials were evaluated in batch sorption studies with the solutions of cadmium, lead, nickel, cobalt, zinc, strontium and cesium. The findings of the structural examination indicated the transformation of nesosilicate-type calcium silicates during carbonation into polymerized Ca-silicate frameworks, aragonite (in carbonated cement only) and calcite. The NMR investigation, for the first time, described in detail the nature of polymerized silicates (predominantly Q3 and Q4 silicon environment) in carbonated cement and dicalcium silicate. The carbon dioxide uptake measured by thermogravimetric analysis was equivalent to 480 kg/t and 370 kg/t of CO2 reacted with dicalcium silicate and Portland cement, respectively. Batch sorption experiments demonstrated better metal removal efficiencies by carbonated cement, particularly for cadmium and cesium. It was concluded that the metal removal mechanisms ranged from adsorption (e.g. ion-exchange, complexation, isomorphic substitution) to surface and bulk precipitation. The main solubility-limiting phases identified for cadmium, lead, strontium and zinc were otavite CdCO3 (only detected in carbonated cement), (hydro-)cerussite, strontianite, and hydrozincite. Cobalt, nickel, cesium were selectively sorbed within the Si-rich phase of both carbonated cement and dicalcium silicate. The leach study demonstrated an adequate containment of sorbed/precipitated metals within carbonated cement (= 2.5% leached) and carbonated dicalcium silicate (= 12% leached) in water. Metal mobility, however, increased during the exposure to acidic conditions, with = 5% of cadmium, lead, cobalt, nickel and 15- 75% of zinc, cesium, strontium being mobilized into leachates.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Greenwich

Year dc:date.issued

2007

Author dc:creator

• Shtepenko, Olga L.

• QD Chemistry
• TN Mining engineering. Metallurgy