A method for removing calcium in a lithium battery recycling process includes recovering acidic lithium liquid including calcium; adding an oxalate aqueous solution to the acidic lithium liquid as a first calcium removal process; raising the pH of the acidic lithium liquid to prepare an alkaline lithium liquid; and adding ammonium oxalate to the alkaline lithium liquid as a second calcium removal process.

Divalent ions are extracted from solids by leaching to form a divalent ion-containing solution. The divalent ion-containing solution is subjected to concentration to form a concentrated divalent ion-containing solution. Precipitation of a divalent ion hydroxide salt is induced from the concentrated divalent ion-containing solution. In other cases, the concentrated divalent ion-containing solution is exposed to carbon dioxide to induce precipitation of a divalent ion carbonate salt.