Coordination Chemistry Reviews 256 (2012) 212–221 Contents lists available at SciVerse ScienceDirect Coordination Chemistry Reviews journa l h o me page: www.elsevier.com/locate/ccr Review Sorption of toxic metal ions by solid sorbents: A predictive speciation approach based on complex formation constants in aqueous solution Valeria Marina Nurchi a,∗ , Isabel Villaescusa b a Dipartimento di Scienze Chimiche, Università di Cagliari, Cittadella Universitaria, 09042 Monserrato Cagliari, Italy b Departament de Enginyeria Quimica Agraria i Tecnologia Agroalimentaria, Universitat de Girona, Av. Lluis Santalo s/n, 17071 Girona, Spain Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 2. Removal of polluting metal ions .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 3. Chemical features of biosorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 4. Mechanisms of sorption .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 4.1. Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 a r t i c l e i n f o Article history: Received 1 May 2011 Accepted 2 September 2011 Available online 8 September 2011 Keywords: Biomass Sorption Functional groups Waste water Heavy/toxic metal Metal speciation Isotherm pH effect a b s t r a c t Heavy metal pollution constitutes one of the more compelling environmental problems. The use of biomass sorption has been proposed as an alternative to conventional methods for metal ion removal from wastewater, and the research on this topic has become very important. In this paper, after an overview on the conventional methods a brief survey of the chemical features of biosorbents is presented. Following the speciation studies briefly outlined in the previous literature we present here a speciation and simu- lation study of the behaviour of sorbing materials toward metal ions. This simulation is based on simple assumptions, which link solution complex formation equilibria to the two-phase sorption phenomena. Using a sorbent characterized by different surface groups as a model and lead as representative of toxic metal ions, this simulation allows us to draw some particular aspect of data collection and data treat- ment. Several aspects are presented which can be of great utility in designing rational data acquisition procedures and in drawing a correct interpretation of the results, but most of all a method is presented that can be profitably employed by people working in sorption research on their own systems. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Industrial effluents are nowadays very often polluted by high levels of toxic metal ions due to the increasing use of metals in such different fields as mining and smelting of metalliferous ores, surface finishing industry, energy and fuel production, industry and application of fertilizers and pesticides, iron and steel metal- lurgy, electroplating, electrolysis, electro-osmosis, leatherworking, photography, metal surface treating, aerospace and atomic energy plants [1]. According to Volesky [2] the more polluting wastes are: ∗ Corresponding author. Tel.: +39 0706754476; fax: +39 0706754478. E-mail addresses: nurchi@unica.it (V.M. Nurchi), isabel.villaescusa@udg.es (I. Villaescusa). • those associated with mining operations, specified as acid mine drainage (AMD); • solutions derived from electroplating industry; • those derived from metal processing; • those generated from power plants; • special wastes from nuclear power plants. Since metal ions are non-degradable and persistent, they cause serious trouble in the environment. Three classes of heavy metals can be envisaged: toxic metals (Hg, Cr, Pb, Zn, Cu, Ni, Cd, As, Co, Sn, etc.), radionuclides (U, Th, Ra, Am, etc.), and precious metals (Pd, Pt, Ag, Au, Ru, etc.) [1]. Different processes are used in order to remove these kinds of pollution or to recover the precious metals. These include chemical precipitation, ion exchange, reverse osmosis, as well 0010-8545/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ccr.2011.09.002