RESEARCH ARTICLE Adsorption of cadmium, nickel and lead ions: equilibrium, kinetic and selectivity studies on modified clinoptilolites from the USA and RSA Joshua Gorimbo 1 & Blessing Taenzana 2 & Adolph A Muleja 3 & Alex T Kuvarega 3 & Linda L Jewell 4 Received: 15 June 2018 /Accepted: 15 August 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract The performance of modified clinoptilolites (zeolites) from two different sources (South Africa and the USA) for the adsorption of Ni 2+ , Cd 2+ and Pb 2+ from synthetic industrial effluent contaminated with metal concentration levels at 50, 150 and 500 ppm was evaluated. The selectivity of the clinoptilolite for the adsorption of Ni 2+ , Cd 2+ and Pb 2+ was investigated with mixed feed solutions containing all three ions in equal concentrations and single-component concentrations containing only one of the ions. The homoionic forms of the clinoptilolite were made of Na + ,K + and Ca 2+ . Batch experiments were then conducted to measure the uptake of metals by the zeolites. The zeolites were characterised using SEM, XRD and BET. The South African clinoptilolite showed a higher surface area and pore volume (17.52m 2 /g and 0.047cm 3 /g respectively) than the USA zeolite (12.26m 2 /g and 0.028cm 3 /g respectively) for the Na + homoionic form. According to the equilibrium studies, the selectivity sequence was found to be Pb 2+ > Cd 2+ > Ni 2+ , with good fits being obtained using Langmuir and Freundlich adsorption isotherms for low metal concentrations. Examples of equilibrium adsorption capacities for RSA and USA clinoptilolite modified with Na + for Pb were 26.94 mg/g and 27.06 mg/g when RSA-Na + and USA-Na + were used respectively. The adsorption was found to depend on the homoionic form of the zeolite and to a lesser extent the source of the zeolite. The selectivity of a particular zeolite for a particular heavy metal can be altered by the homoionic form of the zeolite. Overall, the adsorption capacity of the USA clinoptilolite was higher than the adsorption capacity of the SA clinoptilolite, revealing the potential of clinoptilolite in metal-polluted industrial effluent treatment. Keywords Modified clinoptilolites . Adsorption . Equilibrium . Kinetic . Selectivity . Heavy metals Introduction The accumulation of heavy metals including nickel, cadmium and lead in the environment is a threat to the health and well- being of humans and the global ecosystem (Alloway and Ayres 1998; Argun 2008; IARC 1997; Silbergeld et al. 2000; Godt et al. 2006; Febrianto et al. 2009, Awual et al. 2014). The discharge of these heavy metals has a direct impact on the receiving waterbodies and has an indirect effect on human beings and ecological systems. Notably, anthropogen- ic sources of nickel, cadmium and lead include mining and metallurgical engineering, electroplating, nuclear power plants, aerospace industries, battery manufacturing industries, production of glass, paints and pigments, as well as municipal waste (Argun 2008). It is therefore warranted that these heavy metals be removed from the environment for the protection of human beings and the environment. Responsible editor: Tito Roberto Cadaval Jr * Joshua Gorimbo joshuagorimbo@gmail.com 1 Institute for the Development of Energy for African Sustainability (IDEAS), University of South Africa (UNISA), Florida Campus, Private Bag X6, Johannesburg 1710, South Africa 2 Department of Chemical and Metallurgical Engineering, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa 3 Nanotechnology and Water Sustainability Research Unit, College of Science, Engineering and Technology, University of South Africa (UNISA), Florida Campus, Private Bag X6, Johannesburg 1710, South Africa 4 Department of Civil and Chemical Engineering, University of South Africa (UNISA), Florida Campus, Private Bag X6, Johannesburg 1710, South Africa Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-2992-0