This study used untreated Anadara inaequivalvis shells as a biosorbent for Cu(II) and Pb(II) ion removal from aqueous solutions. The biosorbent was characterized using SEM, XRD, BET, and FT-IR. Results showed that the main seashell structure was aragonite with a heterogenic surface. Batch experiments were performed to determine the effects of contact time, initial pH, and biosorbent amount on biosorption efficiency and the isotherms were examined. The biosorption thermodynamics and kinetics also were determined using equilibrium data. The maximum biosorption capacities of Cu(II) and Pb(II) were 330.2 and 621.1 mg/g, respectively (seashell particle size 250 mu m, 100 mg/L metal ion solution, 2.5 mg biosorbent, 25 degrees C). Langmuir isotherm fitted the equilibrium data better than the Freundlich and Temkin isotherms; biosorption was spontaneous and exothermic. The kinetic parameters were pseudo-second order. This low cost and natural biosorbent successfully removed heavy metal ions from water and could be used to treat wastewater. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.