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

Abstract

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) 2CO 3 for molten carbonate fuel cell (MCFC) and (52+48) and (67+33) mol% (Li–Na) 2CO 3 eutectic mixtures. One type of ternary eutectic melt, namely (43.5+31.5+25.0) mol% (Li–Na–K) 2CO 3, 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) 2CO 3+MgO melt approaches the value obtained in binary eutectic (52+48) mol% (Li–Na) 2CO 3 melt without additive. Two types of additives, such as SrCO 3 and BaCO 3, 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.