The particle-to-acid concentration ratios vary between 0 and 1.0 with 𝑆𝑡 = 0 for the experiment without acid. It is not the objective to achieve a stoichiometric ratio 𝑆𝑡 above 1, given that the particles are present in large quantities in tailings, and the use of acid represents an additional expense. Accordingly, the acid utilized in the experiments is restricted to 𝑆𝑡 = 1.