As a pollutant, nickel release to soil and water sources is of great concern. Clay minerals and calcite are widely recommended to remove excess amounts of heavy metals form soil and water environments. This study deals with assessing and characterizing fibrous clay minerals (palygorskite and sepiolite) and calcite based on their ability for nickel sorption and studying the effects of temperature, presence of other metals, organic ligands on nickel sorption to the minerals as well. Our results showed that sepiolite and calcite have the greatest and lowest abilities for sorption of nickel, respectively. Simultaneous presence of Cd, Zn and Cu decreased sorption of Ni to palygorskite and sepiolite, considerably. Decrease in nickel sorption to minerals mainly caused by Cu competition. Temperature had an increasing effect on sorption of nickel to the minerals. Sorption of Ni to palygorskite and sepiolite was an endothermic reaction. Sorption of nickel to sepiolite was more spontaneous than to palygorskite. Our results indicate that different ligands affect sorption of Ni to the minerals in different ways. Generally, citrate and DTPA decreased sorption of nickel to all minerals. Contrarily, arginine increased sorption of Ni to all minerals. DFOB increased sorption of Ni to calcite but decreased that to palygorskite and sepiolite. Overally, sepiolite could be a suitable option for nickel removal from water systems. Key words Organic ligands, competitive sorption, metal sorption, thermodynamic
