Using regression according to equation ( ), the initial range cannot be represented in a way comparable to the individual particles. However, the initial range can be described by a linear function up to 1 h. By comparing the rates 𝑘 𝑀𝑔,𝑖 , a common characteristic can be determined, see Table . The values for all measured particles and particle-acid mixtures are between 0.1 and 0.2, which describes a similar reaction character independent of the particle system. A similar behavior is observed when comparing the rates 𝑘 𝐶𝑎,𝑖 . The reaction is very fast for all measured particle systems, which is reflected in the values in the same size range of 𝑘 𝐶𝑎,𝑖 = 5 h -1 . Therefore, no predictions about the reaction rate can be made by measuring individual particle systems. The situation is different for the amount of ions in solution. The coefficient 𝐶 ∞,𝐶𝑎,𝑖 shows the amount of calcium dissolved in the two tailings, which does not change regardless of the acid concentration used. This is in contrast to anhydrite, although the copper tailings contain the identical mineral gypsum. The fact that the calcium is independent of the acid concentration indicates that there is calcium in the particles that cannot be extracted. The same is the case for the iron tailings. The extractable ion concentration does not change with the amount of acid. This is shown graphically in Figure (left). The amount of calcium with increasing acid amount changes only for anhydrite. For the two tailings and talc, smaller amounts of acid are more effective. With regard to magnesium leaching (Figure , right), a different behavior between the individual particles and the tailings is shown. For the individual particles, there is no increase in rate with increasing amounts of acid. For the tailings, however, the leaching rate increases. This is not apparent from the regression parameters shown in Table due to the small number of data points. The regression for magnesium is therefore less precise, especially for the initial range.