Investigation on NiO solubility in binary and ternary molten alkali metal carbonates containing additives

The solubility of NiO in molten alkali metal carbonates has been investigated in different conditions such as electrolyte composition, gas atmosphere and temperature. Two types of binary eutectic melts have been chosen, namely the state-of-the-art electrolyte (Li-K)2CO3 for molten carbonate fuel cell (MCFC) and (52+48) and (67+33) mol% (Li-Na)2CO3 eutectic mixtures. One type of ternary eutectic melt, namely (43.5+31.5+25.0) mol% (Li-Na-K)2CO3, has been also studied. The NiO solubility value in Li-rich mixtures of the Li-Na system has been found to be the lowest, which followed an acidic dissolution mechanism. The addition of 3 mol% of MgO to the molten carbonates in order to vary the acid/basic character of the electrolyte has been confirmed to reduce further the NiO dissolution. Meanwhile the NiO solubility in ternary eutectic (Li-Na-K)2CO3+MgO melt approaches the value obtained in binary eutectic (52+48) mol% (Li-Na)2CO3 melt without additive. Two types of additives, such as SrCO3 and BaCO3, have been simultaneously added to (52+48) mol% Li-Na carbonate mixture, which are found to be effective in reducing to half the NiO solubility value obtained in Li-Na electrolyte without additives.