Metal fixation

Guy R. D., Chakrabarti C. L., and Schraumm L. L. (1975). The application of a simple chemical model of natural waters to metal fixation in particulate matter. Canadian Jour. Chem., 53 661-669. 

Zevenbergen, C., Bradley, J. P van Reeuwijk, L. P., Shyam, A. K., Hjelmar, O. Comans, R. N. 19996. Clay formation and metal fixation during weathering of coal fly ash. Environmental Science and Technology, 33, 3405-3409. 

N (5) is a very weak basic site in FloX (pK < 0), a moderately strong one in FI" (pK 8.5) and again very weak in Flred. In both HFl red (pK 6.5) and FIoX (pK 0.5), N(l) is the preferred protonation site. This explains why enforced blockade of the N(5)-lone pair favors the radical, i.e., le"-transfer, while enforced N( 1)-blockade favors Flox and Flred and, therefore, 2e"-transfer. If, however, the blockade is achieved by metal instead of protons, the attachment site at Flox is switched from N (1) towards N (5) because of the 4 ,5-bidentate mode of metal fixation. Hence, metal complexation as such is sufficient to shift the 2e -transfer system into a le"-transfer system. For redox-active metal,... 

Ideally, bone substitute materials should be replaced by mature bone without transient loss of mechanical support. Unfortunately, at present there is no material available fulfilling these requirements. Consequently, mechanically unstable bone defects ought to be stabilised with a non-resorbable metallic fixation made from stainless steel or titanium and the bone defect filled with a bone graft substitute. While the mechanical properties of the bone graft substitute are of minor importance, much more important it is to optimise the resorption rate of the bone graft substitute to minimise the time required for bone healing (Bohner, 2010). To control the resorption rate several strategies such as modification of the... 

Nitrogen fixation, denitrification, soil weathering, phosphate fixation, clay mineral degradation, and potassium and transition metal fixation are problems for which the reaction rates are usually as, or more, important than equilibrium. Most soil chemical applications of kinetics have been in soil microbiology and soil biochemistry, where the lack of equilibrium is more obvious. The use of kinetics in inorganic soil chemistry will undoubtedly broaden in the future. It can even be argued that kinetics is basic to thermodynamics, because equilibrium is the condition where opposing reaction rates are equal. 

There appears to be little point in a detailed evaluation of the more ambiguous hypotheses of heavy metal fixation. However, it may be noted that a number of investigators have considered the possibility of either the sorption of complex ions on clay mineral surfaces or reaction of heavy metal cations with clay surfaces in some manner other than simple electrostatic sorption (31, 66, 67, 156, 157, 217), However, the solubility products of Cu(OH)2 and Zn(OH)2 in aqueous suspensions of montmorillonite (19) have been found to be quite similar to those previously found for solutions in contact with only the pure hydroxides. This would indicate that metal ion-clay mineral surface complex formation is not important otherwise the apparent solubility would have been greater in the presence of montmorillonite. 

Some intriguing variations in the nature of the humate ligands have also recently come to light. Studies of metal fixation in sedimentary organic matter recently deposited in the form of algal mats have been carried out. " The material was originally derived from cyanobacteria and the humic substances are characterized by a very low aromatic content balanced by the incorporation of large amounts of carbohydrates and amino acids. Similarities between cation coordination... 

Bone fixation devices The metal fixation in fractured bone is the most popular and successful painless treatment. Mechanical properties are very different for critical bone and steel. The elasticity constant of the steel and the bone differ completely. The elasticity of bone is 110 whereas for the steel it was 10 times lesser. Thus, removal of metal implants can lead to weakened bones with the danger of re-fracture. 

Although metal fixation is an efficient method for undisturbed bone treatment, bone and metal have completely different mechanical properties. The elasticity constant of bone is only a tenth that of implanted steel, whereas its tensile strength is 10 times lower. Because of this, removal of metal implants can bring about bone weakness and refractures. 

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