Brines supersaturated

This mixture is prepared by dissolving the sodium hydroxide in the brine at ambient temperature and then cooling the total to 3°C. The resultant cloudy, supersaturated suspension is used in toto. The use of this reagent ensures complete extraction (vide Infra) of the somewhat water-soluble product. In addition, it minimizes contact of this material with the aqueous... 

The model predicts equilibrium concentrations for metals in concentrated electrolyte solutions which are in contact with a precipitated solid phase. An application of the model to a Great Salt Lake brine showed that predicted cadmium, zinc, and copper solubilities were in good agreement with measured dissolved cadmium, zinc, and copper levels in these same brines. Lead was supersaturated with respect to its basic carbonate in the Great Salt Lake brine according to the model prediction. 

In the course of evaporative evolution, it is usually valuable to compare individual solute concentrations to a conservative solute. In general, this is chloride in less concentrated brines, and bromide in waters supersaturated with respect to halite (Eugster and Jones, 1979). Solute behavior plotted this way takes one of the several diagnostic routes as shown in Figure 7. In the later stages of chemical evolution, the ratios with respect to the alkalies and sulfo-chloride become important, and it is advantageous to consider associations within the entire major solute matrix. A useful tool for this purpose is normative analysis (Jones and Bodine, 1987). The computer program SNORM (Bodine and Jones, 1986) calculates the... 

At approximately optimum salinity, spontaneous emulsification of brine drops in the oil phase began in both systems. This phenomenon resulted from local supersaturation of the oil phase, as explained in the discussion section below. The amount of emulsification tended to increase with increasing salinity. As a result, the cloud of emulsion drops began to obscure the interface between the microemulsion and oil, making interface position measurements difficult. These observations of spontaneous emulsification confirm the results of the earlier contacting experiments performed in the horizontal configuration ( 4). 

To calculate gas solubility in natural geochemical systems, basic thermodynamic properties such as the Henry s law constant and, in the case of weak electrolytes the dissociation constant, must be combined with a thermodynamic model of aqueous solution behavior. An analogous approach has been used to predict mineral solubilities in concentrated brines (1). Such systems are also relevant to the atmosphere where very concentrated solutions occur as micrometer sized aerosol particles and droplets, which contain very small amounts of water relative to the surrounding gas phase. The ambient relative humidity (RH) controls solute concentrations in the droplets, which will be very dilute near 1(X)% RH, but become supersaturated with respect to soluble constituents (such as NaCl) below about 75% RH. The chemistry of the aerosol is complicated by the non-ideality inherent in concentrated electrolyte solutions. 

With the experimentally determined solubility data the maximum obtainable magma densities (AfT,max) were calculated for the crystallization of sodium chloride from its saturated solution with DMiPA as antisolvent. Mr,max is defined as the total mass of solids divided by the mass of the suspension times one hundred, if the supersaturation in the crystallizer is zero. In Figure 7 MT,max is displayed as a function of the amine to brine feed ratio. It can be seen that the maximum obtainable magma densities are generally low, which will probably give rise to high supersaturations during crystallization. 

FIGURE 6.24 (a) Diffusion path at optimal salinity in a model oil-surfactant-brine system, (b) Enlargement of an oil corner showing local supersaturation leading to spontaneous emulsification. Reprinted with permission from Raney and Miller (1985). Copyright (1985) American Chemical Society. 

The use of concentrated acid can present another problem. Addition of 30% HCl to nearly saturated brine can result in supersaturation. Potter and Clyime [136] studied the solubility of HCl in NaCl solution. Figure 7.80 shows some of their data at temperatures from 20°C to 100°C, as plotted by Rodermund [137]. Any tie line between two points on a curve will lie entirely within the insoluble region, and so mixing of any two solutions mutually saturated in NaCl and HCl results in some precipitation. If the brine being acidified is fully saturated and the acid is at full strength, one can expect solids to collect at the acid addition point. Some technologists recommend the use of more dilute acid for this reason. The simplest method then is to add a stream of pure water along with the acid. The heat of dilution will increase the temperature of the acid about 10°C but will have little effect on the mixed brine temperature. Most membrane-cell suppUers specify feed brine concentrations below saturation, and in that case the problem is relieved. 

Calcium sulfate also tends to form supersaturated solutions, and its precipitates thus have a strong tendency to form scale. Pribidevic [157] described a reactor into which the reagents were injected into a contact bed of gypsum crystals. This bed was held in the lower conical section of the reactor. The ujqter cylindrical section served as a final reactor and clarifier. Crystals of precipitated CaS04 fell from the upper zone into a small-diameter standpipe that carried them into a bottom leg for dischaige. Cool brine... 

Larger continuous crystallizers often achieve crystal formation by cooling a supersaturated solution in a reactor-type vessel with brine or cooling water circulated through its jacket. The crystal slurry is pumped to a filter and the filtrate returned to a dissolver. In some cases crystallization is helped by cooling under conditions of vacuum. 

Definitive data on nucleation of colloidal silica particles in brine solutions at pH 4.5-5.5 and 95°C have been obtained by Makrides and associates in a study related to the deposition of silica from hot geothermal waters (106d). Their work showed conclusively that a solution of monosilicic acid requires an induction period for the formation of nuclei that strongly depends on the degree of supersaturation. Under these conditions appreciable time is required for the early stages of polymerization to produce three-dimensional polymer particles of the type that can function as nuclei. With a supersaturation ratio of 2-3. the nucleation time ranged from a few minutes to several hours. 

Some of the analyses were run through an ion-association model computer program to determine the susceptibility of the brine to halite precipitation. If a halite precipitation problem was predicted, the ion-association model was run in a "mixing" mode to determine if mixing the connate water with boiler feedwater would prevent the problem. This approach has been used successfully to control salt deposition in the well with the composition outlined in Table 8.18. The ion-assodation model evaluation of the bottom-hole chemistry indicated that the water was slightly supersaturated with sodium chloride under the bottom-hole conditions of pressure and temperature. As the fluids cooled in the well bore, the production of copious amounts of halite was predicted. 

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