FORC study of the ferromagnetic impurities in Na and K feldspars of “El Realejo” mine

Feldspar is a Na-K-Ca-Al tectosilicate, generally poor in iron or other elements with large magnetic moments. Being the most abundant constituent minerals in Earth’s crust, feldspars are technologically used in a broad variety of applications, which include glass-manufacturing, fabrication of ceramics elements, fillers in paintings, enamels, floors, etc. However, most applications require the absence (or minimization) of Fe inclusions, being this a very relevant factor that controls the price of the mineral. Typically, Fe content in the mineral produced at a mine is determined by chemical analysis, which implies an off-site test and small sampling volume. Separation of magnetic inclusions is usually made by crushing the rocks and applying a magnetic field gradient that, in combination with gravity, guides the magnetic particles out from the production line. In this work we use FORC to determine the content of the magnetic phases and show that the conventional separation methods used in the mine, which indirectly affect the final price of the product, are selective in the extraction of magnetic particles, as evidenced by the different FORC distribution of the natural rock and that of the separated particles.