Kinetic study for copper adsorption onto soil minerals in the absence and presence of humic acid Zanaty R. Komy a , Ali M. Shaker a , Said E.M. Heggy b , Mohamed E.A. El-Sayed b,⇑ a Chemistry Department, Faculty of Science, Sohag University, Sohag, Egypt b Soil, Water and Environment Research Institute, Agriculture Research Center, Cairo, Egypt highlights  Humic acid enhanced the rate and amount of adsorbed Cu 2+ onto soil minerals.  Total active sites were calculated for humic acid–soil minerals complex.  Copper adsorption increased with increasing pH and decreasing ionic strength.  K + as background electrolyte enhanced copper adsorption in comparison to Ca 2+ .  Influence of solution cations on the rate of Cu 2+ adsorption is firstly studied. graphical abstract Mechanisms and kinetics study of interaction between soil minerals and heavy metal cation in the absence and presence of humic acid. C C J J C CJ *3+ *4+ *5+ = Cu +2 C = Humic acid J = Cu +2 - HA / Soil Minerals complex CJ = Soil Minerals article info Article history: Received 16 April 2013 Received in revised form 27 August 2013 Accepted 14 October 2013 Available online 19 November 2013 Keywords: Adsorption Copper Humic acid Soil minerals Kinetics abstract Equilibrium and kinetics of Cu 2+ adsorption onto soil minerals (kaolinite and hematite) in the absence and presence of humic acid have been investigated under various conditions. The influences of ionic strength, pH and solution cations on the rate of the adsorption have been studied. The rate and the amount of adsorbed Cu 2+ onto soil minerals in the absence or the presence of humic acid increased with decreasing ionic strength, increasing pH and in the presence of the background electrolyte K + rather than Ca 2+ . Humic acid enhanced the rate and the amount of adsorbed Cu 2+ onto soil minerals. The adsorption equilibrium data showed that adsorption behavior of Cu 2+ could be described more reasonably by Lang- miur adsorption isotherm than Freundlich isotherm in the absence or presence of humic acid. Pseudo first and pseudo second order models were used to evaluate the kinetic data and the rate constants. The results indicated that the adsorption of Cu 2+ onto hematite and kaolinite in the absence and presence of humic acid is more conforming to pseudo second order kinetics. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The intensive use of sewage sludge, municipal compost, mines wastes, phosphates fertilizers and development of industries with- out effective effluent control has resulted in accumulation of heavy metals in soil. Heavy metal cations are the most toxic inorganic pollutants, which occur in soils and can be of natural or of anthro- pogenic origin (Siegel, 2002). Many metal ions are essential as trace elements, but at higher concentrations, they become toxic. Heavy metals are difficult to remove from the environment and are ultimately indestructible, unlike many other pollutants that can be chemically or biologically degraded (Ozaki et al., 2003). Copper is ubiquitous in the environment and an important trace 0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.10.048 ⇑ Corresponding author. Tel.: +20 1224063877; fax: +20 932470031. E-mail address: eid1592003@yahoo.com (M.E.A. El-Sayed). Chemosphere 99 (2014) 117–124 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere