Fluoride-free, simple, and environmentally friendly extraction of mixed oxides of niobium and tantalum from the Nigerian and Rwandan columbite-tantalite concentrates

Habinshuti, Jean Baptiste; Munganyinka, Jeanne Pauline; Himanshu, Tanvar; Adetunji, Adelina. R.; Mishra, Brajendra; Mukiza, Janvier; Ofori-Sarpong, Grace; Onwualu, Azikiwe P.