Removal of Other Metal Contaminants

Traces of calcium can be removed from solutions of sodium salts by precipitation at pH 9.5-10 as the 8-hydroxyquinolinate. The excess 8-hydroxyquinoline acts as a collector. 

In some cases, a simple solvent extraction is sufficient to remove a particular impurity. For example, traces of gallium can be removed from titanous chloride in hydrochloric acid by extraction with diisopropyl ether. 

---

Other procedures for the removal of trace metal contamination from the separation matrix will be discussed under the individual separation technique. 

Metal precipitation and removal may also be used as a pretreatment step prior to a snbseqnent treatment for removal of other contaminants. Examples of their downstream process inclnde ultraviolet oxidation, air stripping, and biological treatment (D16512I, p. 5-6). 

Pool Process electrokinetic remediation (Pool Process) is a patented, commercially available technology for the removal of heavy metals and other ionic contaminants. The technology uses a series of electrodes placed in contaminated media to recover ionic contaminants in situ or ex situ from soils, muds, groundwater, dredgings, and other materials. The Pool Process can also be used to enhance bioremediation of media contaminated with a combination of ionic and nonionic organic contaminants. 

The detachment of molecules with concomitant cross-coupling or allylic substitution is an elegant means of increasing diversity on cleavage. A common drawback of most methods is contamination with transition metal catalysts and organo-metallic by-products, although a variety of methods is available for the sequestering of transition metals from the cleaved products. The same applies to removal of other by-products. 

An increase of the zinc/protein ratio to a constant limiting value is found with increasing protein purity and increasing specific activity, while simultaneously all other metals decrease to absolutely and relatively insignificant concentrations. Contamination with both zinc and other metals is readily detected, and remedial action can be taken when indicated. The removal of extraneous metals often further increases specific activity. 

Coupled with the fact that the proportion of trace metal contaminants detected within continuous flow reaction products is inherently low, due to reduced catalyst degradation, the use of a scavenger cartridge at the end of a reaction sequence represents a relatively long-term solution to this problem. Other examples of the use of solid-supported scavengers have been reported by Ley and co-workers [65], where in one example, two scavenger modules, comprising QuadraPure TU (126) and phosphane resin, were used in the synthesis of 1,4-disubstituted-l,2,3-triazoles [66], and by Watts and co-workers [67], where silica-supported copper sulfate was used for the removal of residual dithiol (ppb) in the synthesis of 1,3-dithiolanes and 1,3-dithianes. 

The electrokinetic remediation of Hg from contaminated soils is notoriously very difficult due to its low solubility, as stated in the previous chapter. Moreover, the electrokinetics of Hg mixed with heavy metals has not been extensively studied. The most efficient removal of Hg in soils was conducted by the oxidation of reduced insoluble Hg(l) to Hg(II) using I2 (Cox, Shoesmith, and Ghosh, 1996). Here, an anionic complex is formed, where Hg(II) ions are available to migrate through the soil toward the anode. In a recent investigation of the decontamination of mixed heavy metals from contaminated field soils, only Hg was observed to have a different removal property from more than the 10 other metal contaminants (Reddy and Ala, 2005). The system where EDTA solution was applied as the electrolyte was... 

In order to insure the sufficient efficiency of electrokinetic removal of multiple heavy metals from porous media, it is essential to understand the main parameters affecting the transport and electrokinetic phenomena. Such parameters can be summarized as (a) the theoretical ionic mobility related to the ionic valance and molecular diffusion coefficient of species, (b) the delaying or retardation effect caused by the affinity of heavy metals in solid matrix, and (c) the chemical forms of metal contaminants initially existing in soils. In addition, some unexpected effects especially brought about in the electrokinetic remediation of mixed metal contaminants should be considered. The electrokinetic remediation for mixed metal contaminants generally shows lower removal efficiency than that for individual metal contaminants. High concentrations of multiple metal contaminants can be related to other parameters, for example, transference number, zeta potential, electroosmotic flow, and so on, which are factors that should be taken into consideration with regard to the removal mechanisms. 

A series of laboratory experiments involving simple, ultrasonic, EK, and EK-ultrasonic flushing tests for the treatment and removal of heavy metals and hydrocarbons from contaminated groundwater in sandy layers under a river bank were also carried out by Chung (2007). The test results showed that the EK-ultrasonic flushing technique is the most effective one for the removal of heavy metals and hydrocarbon from contaminated sandy layers. It was also found that the EK process is the most effective one to enhance the removal efficiency of heavy metals (e.g., Cd) from contaminated sandy soil under the river bank. On the other hand, the ultrasonic technique is the most effective one to enhance the removal efficiency of hydrocarbon contaminants (e.g., diesel fuel) from contaminated soil. 

Electrokinetics involves the application of low-level direct current (DC) between electrodes placed in a contaminated area. Different variations of this process were developed to suit the needs of each case. The processes adopted at each site differ with each other in one or many aspects. Basically, two approaches are defined depending on the type of contaminant. The first approach is the enhanced removal in which the contaminants are transported by electromigration and/or by electro-osmosis toward the electrodes for subsequent removal, and the second approach is the treatment without removal, which involves the electroosmotic transport of contaminants through the treatment zones and may also include the frequent reversal of polarity of electrodes to control the direction of contaminant movement (USEPA, 1997). The first approach is applicable for the removal of heavy metals, whereas the second approach was developed for the removal of organic species from contami-... 

Ciassification Organo-sulfur polymer Uses Precipitant for removal of heavy metals from process wastewater, ground waters, and other polar soivs. stabilizer for detoxification and stabilization of heavy metals in contaminated solids, such as soils, sludges, ash and sediments... 

---