Other Inorganic Ligands

As the pH increases to between 6 to 8.5, the removal of cobalt from solution by adsorption on the silica particles increases dramatically. In the pH range from 6 to 8,5 the free Co , ion decreases from 100 percent of the total cobalt to zero, and the predominant cobalt species become the adsorbabie hydroxocobaltfll) complexes, CoOH and Co(OH)2°. 

Reference to Table 1-5 shows that the predominant metal cations in typical fresh and ocean waters are Na, Ca, and Mg the major ligands are HCO3 , Cl , and SO/ . At the typical natural water pH values of between 6.5 to 8.5, these metals are not strong complex formers in comparison with metals such as Al and Fe +. 

For complicated systems such as natural waters it is necessary to use a computer to determine the degree of complexation of the various cations with the ligands available. To illustrate this technique, we determine the degree of complexation of the various cations present in the ocean and in average river water.  

Assume the following compositions for ocean and river water at 25 C  

We neglect interactions with the atmosphere and consider the following species  

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Complexes with Other Inorganic Ligands 219 Tables S-3 to 5-6 are the results of the solution of these equations. 

Other Inorganics. Inorganic species in solution have been studied very effectively by Raman spectroscopy. Work in this area includes the investigation of coordination compounds (qv) of fluorine (qv) (40), the characterization of low dimensional materials (41) and coordinated ligands (42), and single-crystal studies (43). Several compilations of characteristic vibrational frequencies of main-group elements have been pubflshed to aid in the identification of these species (44,45). 

A number of other metal atom-matrix studies have appeared in the literature, with such typical inorganic ligands as NO and H. In the following Section, we shall briefly summarize some of these results. 

Although buffer components are often present at the highest concentration in a medium, metals can also bind to inorganic ligands in solution. Ligands such as CL, OHand SO can form soluble complexes with many metals.127 These complexes remain in solution, but are considered to be less bioavailable than the free, ionic species under most conditions.97 Even though other soluble metal species are considered less bioavailable, they may play roles in metal toxicity. 

The effect of other inorganic anions (sulfate, molybdate, silicate), low molecular mass organic ligands (LMMOLs, such as oxalate, malate, citrate, tartrate and succinate), and fulvic or humic acid on the sorption of arsenate and arsenite onto variable charge minerals and soils has been studied (Roy et al. 1986 Grafe et al. 2001 Liu et al. 2001 Violante et al. 2005a,b). 

Few inorganic ligands form stable complexes with the beryllium ion in aqueous solution. This is a reflection of the fact that on the one hand Be2+ shows a strong preference for oxygen donor ligands such as water and the hydroxide ion, and on the other hand reacts with the more basic ligands such as ammonia to give the insoluble hydroxide. Reported equilibrium constants are in Table V. 

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