Analyzing the Role of Fe<sup>0</sup> and Fe<sup>3+</sup> in the Formation of Expanded Clay Aggregates
José Manuel Moreno-Maroto,
Beatriz González-Corrochano,
Ana M. Martínez-Rodríguez,
Antonio Conde-Sánchez,
Carlos Javier Cobo-Ceacero,
Jacinto Alonso-Azcárate,
Manuel Uceda-Rodríguez,
Ana B. López,
Carmen Martínez-García,
Teresa Cotes-Palomino
Affiliations
José Manuel Moreno-Maroto
Department of Geology and Geochemistry, Faculty of Sciences, Autonomous University of Madrid, Cantoblanco, 28049 Madrid, Spain
Beatriz González-Corrochano
Department of Chemical, Environmental and Materials Engineering, Higher Polytechnic School of Linares, Scientific and Technological Campus of Linares, University of Jaén, 23700 Linares, Spain
Ana M. Martínez-Rodríguez
Department of Statistics and Operations Research, Campus of Las Lagunillas, University of Jaén, 23071 Jaén, Spain
Antonio Conde-Sánchez
Department of Statistics and Operations Research, Campus of Las Lagunillas, University of Jaén, 23071 Jaén, Spain
Carlos Javier Cobo-Ceacero
Department of Chemical, Environmental and Materials Engineering, Higher Polytechnic School of Linares, Scientific and Technological Campus of Linares, University of Jaén, 23700 Linares, Spain
Jacinto Alonso-Azcárate
Department of Physical Chemistry, Faculty of Environmental Sciences and Biochemistry, University of Castilla-La Mancha, Avenida Carlos III, s/n, 45071 Toledo, Spain
Manuel Uceda-Rodríguez
Department of Chemical, Environmental and Materials Engineering, Higher Polytechnic School of Linares, Scientific and Technological Campus of Linares, University of Jaén, 23700 Linares, Spain
Ana B. López
Department of Chemical, Environmental and Materials Engineering, Higher Polytechnic School of Linares, Scientific and Technological Campus of Linares, University of Jaén, 23700 Linares, Spain
Carmen Martínez-García
Department of Chemical, Environmental and Materials Engineering, Higher Polytechnic School of Linares, Scientific and Technological Campus of Linares, University of Jaén, 23700 Linares, Spain
Teresa Cotes-Palomino
Department of Chemical, Environmental and Materials Engineering, Higher Polytechnic School of Linares, Scientific and Technological Campus of Linares, University of Jaén, 23700 Linares, Spain
The effect of the addition of Fe0 and Fe3+ on the formation of expanded clay aggregates was studied using iron-free kaolin as an aluminosilicates source. Likewise, the incorporation of cork powder as a source of organic carbon and Na2CO3 as a flux in the mixtures was investigated in order to assess its effect in combination with the iron phases. An experimental protocol, statistically supported by a mixture experiments/design of experiments approach, was applied to model and optimize the bloating index, density, absorption capacity, and mechanical strength. The process of expansion and pore generation and the associated decrease in density required the addition of iron, such that the optimum mixtures of these properties presented between 25 and 40 wt.% of Fe0 or Fe3+, as well as the incorporation of 3.5–5 wt.% of organic carbon. The addition of Fe3+ produced a greater volumetric expansion (max. 53%) than Fe0 (max. 8%), suggesting that the formation of the FeO leading to this phenomenon would require reducing and oxidizing conditions in the former and the latter, respectively. The experimental and model-estimated results are in good agreement, especially in the aggregates containing Fe0. This reinforces the application of statistical methods for future investigations.
