Separation, upgrading, and mineralogy of placer magnetite in the black sands, northern coast of Egypt

The black sand magnetite is a raw material to produce iron and steel. High content magnetite in the top meter beach sands of the north-west of El-Burullus Lake of Egypt is separated and mineralogically and geochemically investigated. Magnetite content obtained by laboratory techniques varies between 2.92 and 0.11 wt%, with 1.15 wt% average. It represents about one third of the total economic heavy mineral (31.6 wt%). The western and northern halves of the study area are richer in magnetite content (1.33–1.51 wt%) than the eastern and southern halves (0.80–0.98 wt%). On the other hand, the average value of magnetite obtained by ore dressing techniques is 1.13 wt% with a recovery of 98.3 wt%. About 306 samples at a 1-m depth of a grid pattern 200 m × 200 m nearly parallel and perpendicular to the shoreline were covered the area. Microscopic study shows that the magnetite concentrate occurs as irregular, octahedral, or abnormal spherical grains and represented either by fresh homogeneous black or heterogeneous exsolved grains with ilmenite. XRD data indicate that the sample is composed mainly of magnetite grains. Grain size distribution suggests a very fine sand size modal class of more than 93 wt% of the particles. The fine sand size class contains 5.21 wt% magnetite grains. The abnormal spherical grains are mostly more coarser than the associated magnetite concentrate, so they are easily concentrated by sieving process. The contents of iron oxide and titanium dioxide of octahedral magnetite vary from 73.3 to 91.5 and 2.0 to 16.0 wt%, with 85 and 6.0 wt% averages, respectively. On the other hand, these contents of the abnormal spherical one are variable from 81.4 to 95.6 wt%, with 90.3 wt% averages for iron oxide and from 0.3 to 4.0 wt%, with 1.3 wt% average for titanium dioxide. The tonnage of magnetite using laboratory and ore dressing techniques is 182,850 and 179,670 t, respectively. The chemical data of the investigated magnetite suggest their basic volcanic rock origin of the Blue Nile provenance and can be considered as a good indicator for the volcanic source of the Ethiopian plateau.