Where 𝑐 𝑖,𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑,𝐼𝐶 is the measured ion concentration of Ca or Mg by ion chromatography. 𝑐 𝑖,𝑡ℎ𝑒𝑜 𝑚𝑎𝑥 is the calculated concentration of calcium and magnesium, given the composition described in Table and Table , when all calcium and magnesium available is in solution. The calculated maximum concentrations are given in Table for 5 mass percent. Fabric 07-1500-SK 011 from SEFAR AG (Heiden, Switzerland) is used for the experiments. It is made of polyethylene terephthalate (PET) and is therefore suitable for the low pH values of the leaching. The mesh is responsible for the coarse filtration of the solids. The filtrate is then filtered again using a ROTILABO syringe filter with a pore size of 0.45 µm made of cellulose acetate from Carl Roth GmbH + Co KG (Karlsruhe, Germany) for ion chromatography.