Halite-saturated brine

Predicting the Ca/Na ratio of the resultant brine accurately is difficult, and depends on the availability and reactivity of plagioclase and whether or not the brine remains in contact with halite -1- quartz -I- plagioclase. If a halite-saturated (or near-halite-saturated) brine flowed into a clastic section lacking halite as a phase, Na removed from the brine by albitization would cause undersaturation with respect to halite but Na could not be replaced by continued halite dissolution. 

But three facts suggest that Edwards brines today should contain less dissolved silica than when they initially formed (1) the most saline brines we sampled are only saturated with halite, and thus have probably been diluted since they formed (2) cooling to 160°C, the present bottom-hole temperature of the wells, may have caused precipitation of about half the original silica in the deep aquifer and (3) the solubility of silica in near-halite-saturated brines may be lowered significantly because of the reduced activity of water. Clearly the SiO2 values obtained today do not preclude quartz-saturation at the time the brine originally formed. 

Halite (NaCl) can be selectively floated using n-alkyl carboxylates (collector), heavy metal ions (activator), and a non polar oil (additional collector). This yields a concentrated dispersion of the potash. Alternatively, the potash can be selectively floated from a saturated brine solution, using n-alkyl amine as the collectors, leaving the other salts behind. The flotation steps may involve a sequence of rougher, cleaner, and re-deaner stages. Either way the collected potash would be centrifuge de watered, dried, then sized by screening. The final potassium concentrate would probably be at least about 60%,... 

Attempts to calculate actual brine compositions using existing algorithms (WATEQ — Truesdell and Jones, 1973 SOLMNEQ — Kharaka and Barnes, 1973 EQ3/6 — Wolrey, 1979) have not been very successful at present writing, owing to lack of reliable thermochemical parameters in aqueous solutions near halite saturation and in excess of 150°C. Even so, values not too different from the Edwards brine ion ratios are obtained when halite, quartz, albite, anorthite, calcite, anhydrite, celestite and fluorite are reacted to saturation, and K-feldspar and dolomite held below saturation. 

Oklahoma is remarkably close to 0.64, regardless of whether the water is a low-salinity or a saturated brine (Leonard and Ward, 1962). This is because salt (and very little else) is being dissolved from the nearby salt deposits, and the combining ratio of Na and Cl in pure crystals of halite is 0.65. Oil-field brines consistently have Na/Cl ratios of 0.55 or less, and the ratio decreases well below 0.50 as the salinity increases. 

Since the deposit contains halite and anhydrite, the brines should be saturated with respect to these minerals and hence provide a good test of the activity models. Table 8.8 shows analyses of brine samples from the deposit. Note that the reported pH values are almost certainly incorrect because pH electrodes do not respond accurately in concentrated solutions. Hence, there is little to be gained by calculating dolomite saturation. 

Figure 8.8 shows the resulting saturation indices for halite and anhydrite, calculated for the first four samples in Table 8.8. The Debye-Hiickel (B-dot) method, which of course is not intended to be used to model saline fluids, predicts that the minerals are significantly undersaturated in the brine samples. The Harvie-Mpller-Weare model, on the other hand, predicts that halite and anhydrite are near equilibrium with the brine, as we would expect. As usual, we cannot determine whether the remaining discrepancies result from the analytical error, error in the activity model, or error from other sources. 

Fig. 8.8. Saturation indices of Sebkhat El Melah brine samples with respect to halite (left) and anhydrite (right), calculated using the B-dot (modified Debye-Huckel) and Harvie-Mpller-Weare models.

Vodrias E. A. and Means J. L. (1993) Sorption of uranium by brine-saturated halite, mudstone, and carbonate minerals. Chemosphere 26(10), 1753—1765. 

Salt (halite) is highly soluble, more soluble than any other rock in the Permian sequence of western Oklahoma and nearby areas. Groundwater in contact with salt will dissolve some of the salt, providing the water is not already saturated with NaCl. For extensive dissolution to occur, it is necessary for the brine thus formed to be removed from the salt deposit otherwise the brine becomes saturated, and the process of dissolution stops. 

Eogenetic magnesite cement in sandstones is relatively rare because its formation requires pore waters to be enriched in Mg " " and depleted in Ca " ", S04 and Cl". These conditions may occur in arid climates in which marine pore waters evaporate and become successively saturated with respect to calcium carbonates, calcium sulphates and halite, such as in sabkha settings (Kinsman, 1969 Morad et al., 1995). Continental brines enriched in Mg + are also suitable for the formation of eogenetic magnesite due to the low sulphate and chloride ion concentrations. Most recent magnesite cements form in the fine-grained sediments of alkaline/saline lakes (Last, 1992 Warren, 1990) and, less commonly, in freshwater lacustrine sediments (Zachmann, 1989). 

When the brine in the halite ponds became saturated with potassium chloride it was pumped to 100,000 sylvinite ponds where it was joined by brine from a few wells that were already saturated with potash. The sylvinite ponds were also periodically taken out of service, drained and harvested, and their salts sent to the potash plant storage-drainage piles (Fig. 1.61). In 2002 the total of the potash plant s capacity was 650,000 mt/yr, and the KCl was hauled to Coya Sur in covered... 

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