Heavy metals immobilization mechanism

Among the remediation technologies available for soils contaminated with heavy metals, in situ immobilization techniques are of particular interest because of their cost-effectiveness. The use of phosphorus (P) amendments has been identified as a potentially efficient in situ remediation technology. These amendments are available in various forms, and they are environmentally friendly and simple to use. Numerous studies have been conducted to demonstrate the mechanisms and effectiveness of heavy metal immobilization in soils using various P sources (Ma et al., 1993 Chen et al., 1997a Singh et al., 2001 Mavropoulos et al., 2002). 

The Chemical Stabilization Technology (CHEM-STA ) is a proprietary contaminant immobilization mechanism for treating soils, sludges, and ashes contaminated with toxic heavy metals and hydrocarbons. The three-step process can be applied either in situ or ex situ to form stable and insoluble chemical compounds. Treated wastes are usually acceptable for landfill disposal. This technology is commercially available from Environmental Solutions, Inc. (ESI). According to the vendor, CHEM-STA has the following advantages ... 

Sorption, Desorption, and Fixation Rates. A further indication that the basic immobilization mechanism for heavy metals is one of sorption and fixation by the hydrous oxides, is indicated by the slowness with which the heavy metals often become deficient after fertilization. In... 

Biotesting based on photosynthetic material is new and a potentially commercially viable method of pollutant detection. The photosynthetic apparatus including photosystem II (PSII) is particularly sensitive to heavy metals. In this chapter, the mechanisms of heavy metals action on photosystem II are discussed. The characteristics of different biosensors based on immobilized photosynthetic material are compared and the possibility to use immobilized photosystem II sub-membranes fractions as a tool to monitor environmental sample contained the heavy metals (sewage sludge) is demonstrated. 

Cements have been suggested as materials that could be used to immobilize heavy metals produced by various industries. Cadmium and its compounds are highly toxic and can effectively be retained in concrete provided the pH does not fall below 7. The main mechanism of Cd stabilization is related to its precipitation as cadmium hydroxide and physical entrapment. The possibility of Cd substituting Ca " by solid diffusion or dissolution mechanism, forming a precipitate of Ca Cd(OH)4 has been proposed by Goni, et al.,t l based on TG/DTG studies. 

For metal desorption from the biomass certain dilute solutions of mineral acids like hydrochloric acid, sulfuric acid, acetic acid and nitric acid were used [219, 76]. Batch system was carried out to study the desorption of the adsorbed Hg (II) from the biosorbent - immobilized and heat inactivated Trametes versicolor and Pleurotus sajur-caju [8]. Hg (II) ions adsorbed onto the biosorbents were eluted with 10 mmol dm HCl and the results showed that more than 97% of the adsorbed Hg (II) ions were desorbed from the biosorbents. In order to evaluate the feasibility of applying the prepared biosorbents in the heavy metals removal processes, the metal desorption efficiency from loaded biosorbents, and the reusability of the biosorbent in repeated adsorption-desorption operations were determined. The charged species exhibited desorption-resistance fraction whereas the desorption of the neutral form was completely reversible. The difference in sorption and desorption between the neutral and charged species is attributed to the fact that the anionic species sorbs by a more specific exothermic adsorption reaction whereas the neutral form partition by the hydrophobic binding to the soil [206]. Desorption of soil-associated metal ions and possible mechanisms have received considerable attention in literature [148],... 

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