Metal fuel production through the solar carbothermal reduction of magnesia: effect of the reducing agent

The use of metallic powders as alternative combustion fuels for transportation attracts much interest due to their high energy value, the absence of greenhouse gas emissions, and the ability to regenerate them. Herein, we studied their production through the carbothermal reduction (CTR) of magnesia in a Sol@rmet reactor, at low pressure, using concentrated solar power (CSP) and different charcoal reducing agents as sustainable sources. Previous kinetic studies suggested that the C/MgO phase boundary reaction is the dominant phase at the initial stage of reduction. Additionally, one of the main problems encountered at high temperatures is the sintering of MgO particles, which reduces their contact with carbon and in consequence the reduction rate. Thus, we investigated the effect of the charcoal reducing agent properties (source, pyrolysis conditions, C-content…) and bentonite binder on the metallic conversion. Experimental results proved the catalytic-like role of bentonite binder giving values up to 95% Mg yield and purity during the gradual increase of the temperature using charcoal with a high fixed carbon content of 94%.