Recent Progress in Research on the Adsorption of Lead in Soil

The adsorption of lead by soils is strongly influenced by temperature and various soil characteristics. Soil pH is one of the most important parameters influencing lead-solution and soil-surface chemistry since it affects lead speciation and the charge of soil surface groups. In general, lead adsorption is small at low pH values, and it increases with the increase in soil pH. Some investigations supported that the adsorption capacity of the soils for the removal of lead increased with an increase in temperature of the solution, and the adsorption reaction of lead is endothermic, while others supported that adsorption of lead on the soils and other minerals (such as hydroxyapatite) was a decrease in temperature favored the reaction, and the adsorption reaction of lead is exothermic. Generally, the adsorption capacity of lead increases with increasing reaction time and becomes constant after the equilibrium time is reached, and the kinetic process is a two-step process: a rapid adsorption of metal ions on the external surface followed by possible slow intraparticle diffusion. Soil type and constituents also plays an important role for the adsorption of lead on soils. In general, fine-grained soils exhibit higher adsorption capacity for lead adsorption than coarse-grained soils. In addition, ionic strength and competitive adsorption also influence the adsorption of lead on soils. Generally, the adsorption of lead decreased with the increase of ionic strength, and the adsorption of lead on soils and minerals decreased with the coexistence of other metals.