Precipitation sequence

The Special Issue of Resource Geology on the Hishikari deposits (Shikazono et al., 1993) includes various aspects of the Hishikari deposits (oxygen isotopes of gangue minerals, hydrothermal alteration, precipitation sequence, fluid inclusions, vertical electric profiling and electric sounding surveys, structural geological analysis, opaque minerals. 

Nagayama, T. (1992) The precipitation sequence of the Hishikari vein deposits, Kyushu, Japan. Unpub. Masters Thesis, U. Tokyo. 

Nagayama, T. (1993a) Precipitation sequence of veins at the Hishikari deposits, Kyushu Japan. Resource Geology Special Issue, 14, 13-28. 

The Ostwald Step Rule, or the rule of stages postulates that the precipitate with the highest solubility, i.e., the least stable solid phase will form first in a consecutive precipitation reaction. This rule is very well documented mineral formation via precursors and intermediates can be explained by the kinetics of the nucleation process. The precipitation sequence results because the nucleation of a more soluble... 

Other research groups have also made significant contributions to the themes described above. Fiuorous catalysts that have been recovered from homogeneous reactions in organic solvents at elevated temperatures by simple precipitations (sequence A-I, Fig. 1) are summarized in Fig. 10 (20-25). A representative application for each is given in Scheme 4. 

The precipitation sequence presented in Figure 17.1 is a function of temperature and the extent to which equilibriiun is maintained with the increasingly saltier brine. Each of these precipitations alters the ion ratios in the remaining seawater. Since the rule of constant proportions is violated, density, rather than salinity, is used to monitor the increasing saltiness of the brine. 

Chapter 10 provides an exhaustive description of how these techniques can be applied to a large number of industrial alloys and other materials. This includes a discussion of solution and substance databases and step-by-step examples of multi-component calculations. Validation of calculated equilibria in multi-component alloys is given by a detailed comparison with experimental results for a variety of steels, titanium- and nickel-base alloys. Further selected examples include the formation of deleterious phases, complex precipitation sequences, sensitivity factor analysis, intermetallic alloys, alloy design, slag, slag-metal and other complex chemical equilibria and nuclear applications. 

The solute and salt sequence for the final stages of seawater evaporation has been determined computationally (Eugster et a/., 1980), and in commercial solar salt ponds (Hermann et al., 1973). The only equivalent information on a saline lake system of considerable size has been provided for the Great Salt Lake (GSL) area, also from evaporation ponds (Jones et ah, 1997) and by direct computation. Kohler (2002), utilized the computer model of Moller et al. (1997), allowing for the dominance of halite in the GSL system, and worked out a precipitation sequence essentially of Ca-sulfate to Mg-sulfate to MgCl2,... 

The Ostwald step rule, or the mle of stages, postulates that the precipitate with the highest solubility (i.e., the least stable solid phase) will form first in a consecutive precipitation reaction. This mle is very well documented mineral formation via precursors and intermediates can be explained by the kinetics of the nucleation process. The precipitation sequence results because the nucleation of a more soluble phase is kinetically favored over that of a less soluble phase because the more soluble phase has the lower solid-solution interfacial tension (7cw) than the less soluble phase (equation 50). In other words, a supersaturated solution will nucleate first the least stable phase (often an amorphous solid phase) because its nucleation rate is larger than that of the more stable phase (Figure 13.26). While the Ostwald step mle can be explained on the basis of nucleation kinetics, there is no thermodynamic contradiction in the initial formation of a finely divided precursor. 

Figure 9.7 Simplified chart showing the evaporite precipitation sequence from waters of various compositions. Alkaline and neutral pathways are shown. The alkaline pathway is common in salinas, playas and apolyhaline lakes. The neutral pathway can be divided into two different sequences according to the ratio of the concentrations of HC03 to (Ca2+ + Mg2+). The main ions still in solution in the residual brines are given at the end of the sequence (grey frames). On the right-hand side, the average salinity of the water is provided as an indicator of total ion concentration (g L-1).

G) Palustrine micritic limestone infilled by a dark secondary micrite associated with gypsum crystals. Simplified chart showing the evaporite precipitation sequence from waters of various compositions. 

Calculations demonstrating the actual limits on changes in the major ion chemistry of seawater imposed by the evaporite precipitation sequence are beyond the scope of this book. However, some simple... 

Precipitation Sequence. It should be concluded that the ions from the more noble metals are changed into atoms and crystallized from the solution. Simultaneously, due to electron transfer, the atoms of the active metal go into solution through the formation of ions. This hypothesis can systematically be tested with other metal pairs (see E8.4) the observations are noted by the precipitation sequence of the metals. 

TABLE 3.3 Precipitation Sequence of Seawater Evaporitic Salts... 

S. Jogan, and T. Hashimoto, Precipitation Sequence in Friction Stir Weld of 6063 Aluminum During Aging, Metall. Mater. Trans. A, Vol 30, Dec 1991, p 3125-3130... 

No hydrothermal solution (except fluid inclusions in minerals) is preserved in the ores of Kuroko deposits in Japan because they formed at past (ca.l5 million years ago) and hydrothermal solution responsible for the ore deposits moved away from the depositional site. The calculations on the precipitation of minerals due to the mixing of seawater and hydrothermal solution is useful to know the precipitation sequence and temperature of mineralization. 

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