After an acid variation, hydrochloric acid shows the largest leaching quantity when used on calcium containing feeds, which is why all further tests are carried out with hydrochloric acid. In addition to anhydrite as a calcium source, talc is present in the mixture as a magnesium source. Figure shows the progression of the Ca 2+ and Mg 2+ ion concentration over the leaching time. The stoichiometric ratios 𝑆𝑡 of hydrochloric acid to the particles are again 0.2, 0.5 and 1.0. The comparison of the calcium leaching of the two minerals anhydrite and talc shows no acid dependence for talc. The calcium value is identical for each acid addition. One explanation for this is that the particle only contains calcium in the impurities, and these are all dissolved with the smallest amount of acid. An increased amount of acid therefore does not change the ion concentration.