Composition of black shale from Quseir, Red sea, Egypt with emphasis on the sequential extraction of some metals

ABSTRACT

The black shales Duwi Formation, within Gabel El-Atshan in Quseir area are rich in sonic trace elements. Petrogaphically, the studied shales are dark colored mudstone enriched in phosphatic elastics and are highly fossiliferous. The presence of framboidal pyrite revealed that the studied black shales were deposited under reducing conditions. Mineralogically, XRD revealed that the studied samples consist of smectite, kaolinite, mixed layer [smectite/illite], illite in addition to minor chlorite. Such heterogeneous composition indicates recycling from pre-exiting clay sediments. The studied shales are relatively enriched in some heavy metals such as zinc and nickel. The SEM and EDX studies indicate that these metals are concentrated in the clayey materials but do not form minerals of their own. The present work provides new data on the speciation of such enriched metals. The sequential extraction proves that the heavy metals are largely bound to the residual phase [57% Zn, 51% Fe, 50% Cu. 18% Ni and 10% Mn]. However, the metals; Ni, Cu and Zn have mostly been extracted into the first three fractions