The release of critical ash-forming elements during the pyrolysis and combustion of corn stover has been investigated through controlled lab-scale experiments supported by multicomponent and multiphase thermodynamic equilibrium calculations. Fuel samples were treated under isothermal conditions ranging from 500 to 1150 degrees C, under both pyrolysis and combustion atmospheres. The volatilized material was quantified by means of mass balances based on char and ash elemental analysis, compared to a corresponding feedstock fuel analysis. Close relations between the observed K and Cl release are found, suggesting that Cl is the main facilitator for K release through sublimation of KCl, determined to begin as the reaction temperature approaches 700-800 degrees C. K is present in abundance relative to Cl, and the K release is found to cease as the fuel reaches complete dechlorination. In addition, around 50 wt % of the Cl is released at temperatures below 500 degrees C, presumably as HCl formed through ion-exchange reactions with functional groups in the organic matrix. Complete dechlorination was achieved under combustion conditions as the temperature exceeded 800 degrees C. Approximately 50 wt % of the feedstock S is released at temperatures below 500 degrees C. This low-temperature release is related to the decomposition of the organic matrix, releasing the organically associated S. Under combustion conditions, the S release increases gradually at temperatures exceeding 800 degrees C, eventually reaching complete desulfurization at 1150 degrees C. The silicate/alumina chemistry is found to play a significant role in the alkali retention. The Si-rich sample is capable of retaining all excess K not released as KCl.