Abstract: A start-up process of making aluminum using a single carbothermic reactor/furnace (11) having a single hollow reactor compartment with bottom resistance heating electrodes (16) (13) in the side of the reactor, involves adding Al2O3 and C (carbon) for start-up and melting the mixture to provide a (Al2O3—Al4C3) slag having a temperature between about 1875° C. and 2000° C.; and then adding Al4C3 to the slag and raising the temperature of the furnace (11) to form a top Al phase with 6 to 8 wt % C (21) and a bottom slag phase (22); and then adding Al2O3 is added to the Al—C/slag (21, 22) to produce an Al2O3 rich slag lower the reactant temperature and produce a decarbonization reaction (step 30) providing a top Al phase with less than 5 wt % C (23) which is then tapped after step (40). The remaining slag is the starting material.