Removal of Cr(VI) from aqueous solution by nano-carbonate hydroxylapatite of different Ca/P molar ratios

► Cr(VI) adsorption performance by nano-CHAPs was evaluated. ► Increasing the Ca/P molar ratio enhanced the adsorption capacity of nano-CHAPs. ► Characteristics of nano-CHAP was preliminarily investigated. ► The main removal mechanism was physical adsorption.