Metal cations, uptake efficiencies

Metal cation Uptake efficiency ((fmol/cell)/v,M)/h) ... 

Table 9.9 Uptake efficiencies of metal cations by fibroblasts (Wataha et al, 1993)...

Equilibrium uptakes of metallic cations, dyes, and even gold and anionic adsorbates are largely governed by electrostatic attraction or repulsion. It is suggested that further studies of the role of the carbon surface are needed to show whether this is indeed the case. If not, only then does the role of specific interactions (e.g. complex formation), or even nonspecific van der Waals interactions, become a reasonable alternative or complementary argument. Indeed, in the adsorption of inorganic solutes, the main fundamental challenge remains how to activate the entire carbon surface in order to achieve maximum removal efficiencies. The solution conditions, at which maximum uptake can be achieved, depend on the surface chemistry of the adsorbent. 

Other factors influencing the rate of metal-ion transport across artificial membranes have been identified. As might be expected, such transport is dependent on the interplay of several factors. For example, as briefly mentioned already in Chapter 4, it is clear that the strength of complex-ation of the cation by the carrier must be neither too high nor too low if efficient transport is to be achieved. If the stability is low, then uptake of the metal ion from the source phase will be inhibited. Conversely, for those cases where highly stable complexes are formed, there will be a reluctance by the carrier to release the cation into the receiving phase. 

It is reasonable to assume that the surface of metal sulfides show amphoteric behavior and it has been shown that uptake of bivalent cations is pH-dependent. Metal sulfide precipitates are efficient scavengers for heavy metal ions. 

Interactions of metal ions with solid particles suspended in aqueous solutions have been a subject of countless studies. Intuitively, one may expect cations to adsorb on negatively charged surfaces, and the efficiency of the uptake to increase with higher charge of the solute species. However, this assumption is not supported... 

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