decarbonate alkali electrolyte

Jul 2016
[FONT=&quot]I have a very strange problem restoring old flooded pocket plate NiCd cells. As I understand it, the new electrolyte would be a solution of 12 grams LiOH and 264 grams KOH in 1 liter water. With exposure to air over time it becomes carbonated. I tried to decarbonate it by reacting it with Calcium hydroxide. This is a slow process because the solubility of the Calcium hydroxide in electrolyte of about 200 ppm but it can be done. I judge it to be complete when injecting a bit of Ca(OH)2 saturated water into the middle of the solution produces no precipitate. (a precipitate is formed briefly because the solution is locally super saturated with calcium hydroxide but it redisolves). I thought I would remove trace sulfate by reacting it with barium hydroxide but found a very heavy precipitate. Ultimately 80 grams of barium hydroxide per liter of electrolyte is required. The precipitate is white, dissolves quickly almost completely with HCl with evolution of a lot of gas. After heating the precipitate to dull red then cooling, the reaction with HCl is unaltered. All this points to the precipitate being mostly barium carbonate, but all the carbonate was supposed to have been removed using calcium hydroxide. So the question is where did this precipitate come from?[/FONT]
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