Tantalum oxide has been electro-deoxidised in a bath of CaCl2-1wt%CaO to form tantalum. It was found that the reaction between the calcium oxide in the melt and the tantalum oxide takes precedence over any reduction process so that until the calcium tantalum oxide Ca-3(CaTa2O9) (equivalent to 4CaO center dot Ta2O5 or Ca4Ta2O10) is formed, calcium ions are reduced to either form calcium metal or reduced calcium species. This eventually results in high electronic conductivity in the melt which means that, compared to the electro-deoxidation of oxides of similar stability to Ta2O5, the energy and current efficiencies are low. In addition, the vast changes in microstructure result in a structure that is extremely fragile so that the resulting tantalum can only be harvested as a fine powder.