Nickel system, goethite

For the nickel-citrate-goethite system (Figure 7), the oxide becomes more competitive with increasing pH because of the greater coulombic attraction predicted by the Nernst equation. Unlike silica. Nr is the... 

For the case of nickel-ligand-goethite systems, the results for sulfate, citrate, and NTA could be accounted for by the model used, although some small degree of specific adsorption appeared to take place for citrate and NTA complexes. The evidence for this is not conclusive. However, for both nickel glycine and nickel cyanide, specific energies of adsorption of —3 and —7 kcal/mol, respectively, were calculated. 

Figure 18. Three-dimensional depiction of the nickel-cyanide-goethite system (conditions as given in Figure 17)...

The dissolution of goethite in acidic media and the reprecipitation of the Fe as hematite, is a crucial process in the high-temperature leaching of nickel laterite ores. At 250 °C the rate of transformation increased as the Eh of the system was lowered... 

Nitrilotriacetate. Nitrilotriacetic acid (NTA) is a triprotic weak acid which is a well known sequestering agent. It forms a quadradentate chelate with Ni of the form Ni-NTA which is very stable (log K = 13.1). If sufficient NTA is added to solution, virtually complete ( 100%) chelation of Ni takes place in the neutral and alkaline pH range. Results of the nickel-NTA-oxide systems are shown in Figures 8 and 9 for silica and goethite, respectively. 

The results of the specific adsorption of nickel onto silica and goethite are in basic agreement with similar work reported for other metals (2, 18), The James and Healy model is capable of describing the interactions well. Similarly, when complexing ligands are added to nickel-silica systems the results can be adequately explained by a competition model in... 

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