In addition to the individual particles, two tailings are examined and compared as a function of leaching time and acid amount. Since an explicit reaction equation cannot be written for tailings, the same acid amounts are used as for anhydrite. At 5 mass percent, the equivalent for 𝑆𝑡 = 1 is 0.75 M HCl. Figure shows the fraction of dissolved ions from the particles. According to Figure , a steady state for calcium determination is reached after 30 minutes, so the measuring intervals are reduced to one measuring point per minute. After one minute, the anhydrite has already reached 85 % of the steady-state value, while the copper tailing has only reached 75 %, even though both use the same mineral as a source of calcium. Furthermore, only 25 % of the calcium contained in the mineral can be dissolved in anhydrite, while 38 % can be dissolved in copper tailings. This can be explained by the chemical equilibrium, as is the case with anhydrite, see Figure . However, this value is not reached in copper tailings. Here, after 10 minutes, only 360 mg L -1 dissolve, which is one tenth of the 3700 mg L -1 reached in anhydrite. Therefore, other minerals are interfering with the process. There is no significant difference in the speed of the leaching process, which can be attributed to the identical minerals.