Metal Sorption on Mineral Surfaces: an Overview with Examples Relating to Mineral Deposits

Sorption reactions, involving both inorganic and organic particulates, are an important control on the transport and fate of many trace elements in natural systems. Understanding the controls on trace-element concentrations in waters is critical for a number of applications including the transport of contaminants and nutrients, geochemical prospecting, agriculture, municipal and industrial water treatment, and bioavailability to name a few. This chapter provides an overview of metal sorption on mineral surfaces and gives examples of predictive modeling of metalsorption reactions in mine-drainage systems. The word “sorption” is a general term that describes removal of a solute from solution to a contiguous solid phase and is used when the specific removal mechanism is not known. “Sorbate” or “adsorbate” refers to the solute that sorbs on the solid phase. “Sorbent” or “adsorbent” is the solid phase or substrate onto which the sorbate sorbs. “Adsorption” refers to the two-dimensional accumulation of an adsorbate at a solid surface. In the case of “surface precipitation,” there is a three-dimensional accumulation of sorbate at the solid surface. The term “absorption” is used when there is diffusion of the sorbate into the solid phase. Absorption processes usually show a significant time dependency. Sposito (1986) and Jenne (1998) provide a more detailed description of these terms. In this chapter, the term adsorption is used when describing laboratory studies with simple, well-characterized systems, and when discussing models that have been developed to describe adsorption phenomena.