Characterization for Disposal of the Residues Produced by Materials Used as Solid Oxygen Carriers in an Advanced Chemical Looping Combustion Process

Featured Application: (1) The residues of six low-cost materials found in Colombia were characterized with CH4 and H-2 used as fuels in a chemical looping combustion (CLC) system. (2) The residues of the low-cost materials evaluated would not have a negative impact on the environment when disposed of in a landfill. (3) The residues are not considered toxic waste or dangerous according to current Colombian legislation or European regulations, respectively. Chemical looping combustion (CLC) is a technology that is part of the capture and storage of CO2 through the combustion with solid oxygen carriers (OCs). It is considered an energy-efficient alternative to other methods, since it is a technology that inherently separates CO2 and has the advantage of not requiring additional energy for this separation. The key to the performance of CLC systems is the OC material. Low-cost materials, i.e., natural minerals rich in metal oxides (chromite, ilmenite, iron, and manganese oxides) were used in this investigation. These may contain traces of toxic elements, making the carrier residues hazardous. Therefore, the oxidized and reduced-phase residues of six OCs, evaluated in a discontinuous batch fluidized bed reactor (bFB) using methane and hydrogen as the reducing gas, were characterized by several techniques (crushing strength, SEM, XRD, and XRF). The researchers found that, in general terms, the residues present a composition very similar to that reported in the fresh samples, and although they contain traces of Ba, Cu, Cr, Ni or Zn, these compounds do not migrate to the leachate. It was mainly found that, according to the current regulations, none of the residues are classified as toxic, as they do not exceed the permissible limits of metals (100 and 5 mg/L for Ba and Cr, respectively), with 3.5 mg/L the highest value found for Ba. Thus, they would not have a negative impact on the environment when disposed of in a landfill.