 In the "direct conversion" or double-decomposition method, a mixture of celesite and sodium carbonate is treated with steam to form strontium carbonate with substantial amounts of undissolved other solids.This material is mixed with hydrochloric acid, which dissolves the strontium carbonate to form a solution of strontium chloride.Carbon dioxide or sodium carbonate is then used to re-precipitate strontium carbonate, as in the black-ash process.