Efficient removal of Pb(II) and Cd(II) from aqueous solutions by mango seed biosorbent

•High and rapid uptakes of Pb(II) and Cd(II) were achieved by MS biosorbent.•Multilayer adsorption of Pb(II)/Cd(II) occurred on the heterogeneous MS surface.•MS biosorbent maintained 96–97% of the adsorption capacity after desorption.•The mechanism was elucidated by coupling physicochemical and spectroscopic methods.•Carboxyl, hydroxyl, amine, and ether groups were the binding sites.