is removed from the solution by filtration the final concentration of cd in the solution is then less than 3 ppm weight of cadmium per weight of solution 10 g of an aqueous solution comprising an amount of cobalt salt cocl 2 to be removed corresponding to 2000 ppm weight of cobalt per weight of solution are brought into contact with a amount of raney nickel acros corresponding to 0 1 g g of solution after reacting for 24 hours the solid is removed from the solution by filtration the final concentration of co in the solution is then only 4 ppm weight of cobalt per weight of solution 10 g of an aqueous solution comprising an amount of cobalt salt cocl 2 to be removed corresponding to 100 ppm weight of cobalt per weight of solution are brought into contact with an amount of raney nickel acros corresponding to 0 1 g g of solution after reacting for 24 hours the solid is removed from the solution by filtration the final concentration of co in the solution is then only 0 5 ppm weight of cobalt per weight of solution 10 g of an aqueous solution comprising an amount of cerium salt ce no 3 3 to be removed corresponding to 4760 ppm weight of cerium per weight of solution are brought into contact with 1 g of a solid composed of nickel supported on alumina comprising 23 by weight of nickel after reacting for 24 hours the solid is removed.