## 2 Materials and Methods
### Experimental Procedure  
The six materials selected as OCs were evaluated in a discontinuous batch fluidized bed (bFB) prototype (Figure 1). The heart of the system is a discontinuous batch fluidized bed reactor (2) in which each of the oxygen carriers are charged and undergo purge-reduction-purge-oxidation cycles. The furnace (1) provides the heat necessary to reach the operating temperature and the heating is performed through electric resistors. The gas supply system (3) regulates nitrogen, air, fuel gas, and/or the mixtures required according to the needs of the process. At the outlet line of the reactor gases, there are two filters (4) for retaining the particulate matter (fines) entrained by the gases. The collection of the fines in these filters permits the calculation of the attrition rate, A (%/h), according to Equation (1), where p\({}_{\text{f}}\) is the weight of elutriated particles <40 \(\upmu\)m during \(\Delta\)t, p\({}_{\text{t}}\) is the total weight of the solids inventory, and \(\Delta\)t is the period of time during which the particles are collected [51].  
\[A=\frac{p_{f}}{p_{t}\Delta t}*100 \tag{1}\]The gas conditioner (5) enables the particulate matter and moisture to be removed from the gases from the reactor prior to entering the gas analysis system (6), which enables the composition of the reactor outlet stream to be quantified.  
The residues studied were collected from the reactor core in the last reduction and oxidation cycle. This operation was performed under the conditions summarized in Table 2.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**OC** & **CRS1003** & **FEMA004** & **FEMA011** & **ILME007** & **OXMN009** & **OXMN010A** \\ \hline
**Origin** & **Chromite Ore, Antioquia** & **Iron Ore, Antioquia** & **Iron Ore, Cuuca** & **Ilmenite Ore, Antioquia** & **Manganese Ore, Valle** & **Manganese Waste, Naríno** \\ \hline Element & & & & Composition (\%) a & & \\ Si & 0.8 & 0.0 & 1.6 & 2.4 & 1.8 & 13.0 \\ Al & 3.5 & 0.9 & 0.4 & 0.5 & 0.2 & 2.5 \\ Fe & 27.2 & 41.5 & 65.9 & 30.7 & 1.0 & 3.5 \\ Ca & 0.2 & 0.3 & 0.8 & 0.9 & 0.5 & 1.9 \\ Mg & 2.8 & 1.3 & 0.1 & 0.3 & 0.1 & 0.8 \\ Na & - & - & - & 0.1 & - & 0.4 \\ K & - & - & - & - & - & 0.2 \\ Cu & - & - & - & - & - & 0.1 \\ Zn & 0.2 & 0.1 & - & - & - & - \\ Ti & 2.6 & 12.9 & - & 24.5 & - & 0.2 \\ V & 0.2 & 0.2 & - & 0.2 & 0.1 & - \\ Cr & 28.7 & 7.0 & - & - & - & - \\ Ni & - & - & - & - & - & - \\ P & - & - & - & - & 0.1 & 0.1 \\ Mn & 0.5 & - & - & 2.5 & 53.4 & 35.7 \\ Ba & - & - & - & - & - & 0.4 \\ O & 33.1 & 31.8 & 31.0 & 34.2 & 18.7 & 30.7 \\ LOI b & 0.0 & 0.6 & 0.0 & 3.5 & 23.1 & 10.3 \\ \hline Total & 100.0 & 96.6 & 100.0 & 99.9 & 99.1 & 99.7 \\ \hline Crushing strength (N) & 7.3 & 5.0 & 5.8 & 5.9 & 5.6 & 2.3 \\ \hline Crystalline phases & FeCr\({}_{2}\)O\({}_{4}\) & FeCrO\({}_{3}\), FeCrO\({}_{4}\) & Fe\({}_{2}\)O\({}_{3}\) & FeTiO\({}_{3}\) & \({}^{\rm a}\) & FeTiO\({}_{3}\), FeCO \\ \hline Density (kg/m\({}^{3}\)) & 4964 & 4943 & 3116 & 4639 & 3286 & 3009 \\ \hline \end{tabular}  
* Percentage in \(\%\) w/w. Values less than 0.1 are negligible. b LOI: Loss on ignition.  
\end{table}
Table 1: Characterization of low-cost oxygen carriers (OCs).  
Figure 1: Diagram of the discontinuous chemical looping combustion (CLC) system.  
All oxygen transporters were evaluated using hydrogen as the reducing gas in the proportions described in Table 2; in addition, the materials FEMA011 and OXMN010A were evaluated using methane. Thirty cycles were performed for each experiment. The material was heated in an air atmosphere until 950 \({}^{\circ}\)C; between reduction and oxidation periods, a purge was carried out with N\({}_{2}\) for 2 min to prevent contact between the fuel and the air.