Brine selective dissolving

Selective Dissolving. Brine quality improves if NaCl can be dissolved selectively, leaving some of the impurities behind. Selective dissolving techniques usually are aimed at partial rejection of calcium sulfate, the major impurity in salt. These techniques can be divided into three categories ... 

Concentration of Seawater by ED. In terms of membrane area, concentration of seawater is the second largest use. Warm seawater is concentrated by ED to 18 to 20% dissolved soHds using membranes with monovalent-ion-selective skins. The EDR process is not used. The osmotic pressure difference between about 19% NaCl solution and partially depleted seawater is about 20,000 kPa (200 atm) at 25°C, which is well beyond the range of reverse osmosis. Salt is produced from the brine by evaporation and crystallisa tion at seven plants in Japan and one each in South Korea, Taiwan, and Kuwait. A second plant is soon to be built in South Korea. None of the plants are justified on economic grounds compared to imported solar or mined salt. 

Theory. Conventional anion and cation exchange resins appear to be of limited use for concentrating trace metals from saline solutions such as sea water. The introduction of chelating resins, particularly those based on iminodiacetic acid, makes it possible to concentrate trace metals from brine solutions and separate them from the major components of the solution. Thus the elements cadmium, copper, cobalt, nickel and zinc are selectively retained by the resin Chelex-100 and can be recovered subsequently for determination by atomic absorption spectrophotometry.45 To enhance the sensitivity of the AAS procedure the eluate is evaporated to dryness and the residue dissolved in 90 per cent aqueous acetone. The use of the chelating resin offers the advantage over concentration by solvent extraction that, in principle, there is no limit to the volume of sample which can be used. 

To establish the well drainage boundaries and fluid flow patterns within the TFSA-waterflood pilot, an interwell chemical tracer study was conducted. Sodium thiocyanate was selected as the tracer on the basis of its low adsorption characteristics on reservoir rocks (36-38), its low and constant background concentration (0.9 mg/kg) in produced fluids and its ease and accuracy of analysis(39). On July 8, 1986, 500 lb (227 kg) of sodium thiocyanate dissolved in 500 gal (1.89 m3> of injection brine (76700 mg/kg of thiocyanate ion) were injected into Well TU-120. For the next five months, samples of produced fluids were obtained three times per week from each production well. The thiocyanate concentration in the produced brine samples were analyzed in duplicate by the standard ferric nitrate method(39) and in all cases, the precision of the thiocyanate determinations were within 0.3 mg/kg. The concentration of the ion in the produced brine returned to background levels when the sampling and analysis was concluded. 

Figure 19.16. Basic designs of electrolytic cells, (a) Basic type of two-compartment cell used when mixing of anolyte and catholyte is to be minimized the partition may be a porous diaphragm or an ion exchange membrane that allows only selected ions to pass, (b) Mercury cell for brine electrolysis. The released Na dissolves in the Hg and is withdrawn to another zone where it forms salt-free NaOH with water, (c) Monopolar electrical connections each cell is connected separately to the power supply so they are in parallel at low voltage, (d) Bipolar electrical connections 50 or more cells may be series and may require supply at several hundred volts, (e) Bipolar-connected cells for the Monsanto adiponitrile process. Spacings between electrodes and membrane are 0.8-3.2 mm. (f) New type of cell for the Monsanto adiponitrile process, without partitions the stack consists of 50-200 steel plates with 0.0-0.2 ram coating of Cd. Electrolyte velocity of l-2 m/sec sweeps out generated Oz.

Several inorganic ion exchangers like the zirconium salts of phosphates, silicate phosphates, molybdate phosphates, and tungstate phosphates showed selective sorption properties for potassium dissolved in sea water and brines. The potassium capacity of zirconium phosphate was found to be 25 mg K+/g. The selectivity for potassium increased with higher drying temperatures of the exchangers. The potassium ion sorption rate exceeded that of other cations40). 

Norphlet formation waters produced from three Fairway Field wells were analysed for major components and for selected minor cations as part of normal production operations (Table 1). The samples were taken from platform separators during production. Multiple samples from individual wells taken over a period of several years show only minor variations in composition. The waters are extremely saline brines with total dissolved solids between 300 and 373 g/1. Chlorine is the dominant anion in these brines, and sodium (71.6-89.8 g/1), calcium (33.0-41.6 g/1) and potassium (12.9-17.6 g/1) are the major cations. Norphlet formation waters at Fairway are also characterized by relatively high concentrations of Mg, Ba, Sr, Fe, Mn, Li and Pb. Brines of similar composition are produced from deep Norphlet reservoirs and other Mesozoic strata of onshore Mississippi (Carpenter et al. 1974 Kharaka et al. 1987). 

The langbeinite ore is separated from sylvite and halite by selective washing, froth flotation, or heavy media separation. The commercial langbeinite used in the process must be pulverized in ball mills, and fine powder is mixed with a solution of the muriate of potash. The muriate of potash is dissolved and clarified in a separate unit. The reaction in the presence of water yields potassium sulfate in a crystalline form and brine. Crystals are centrifuged or filtered, dried in a rotary dryer, sized, and finished. The finishing methods either produce coarse material or granulated product. The brine is evaporated, crystallized, and filtered. The mixed salts are added to the sulfate reactor. The liquor is discarded as a wasted... 

Small particles, with their high surface/volume ratio, pick up water more readily and are especially liable to caking. Vacuum salts and potash, as suggested by Fig. 7.13, are therefore the most sensitive. They are frequently treated with an anticaking additive before shipping. The one most widely used is sodium ferrocyanide, or yellow prussiate of soda (YPS). By the nature of the addition process, YPS also tends to concentrate at the surfaces of the particles. Therefore, when a batch of treated salt is dissolved, the first brine formed has a high concentration of YPS. Rain also selectively removes YPS from the salt, and this is one reason not to store such salts in the open. 

I. Silica. Silica is one of the secondary impurities, but it has synergistic effects in membrane cells when present along with calcium and aluminum [80]. It is difficult to remove silica from brine. The operator s best defense is prevention. Selection of salt, choice of dissolving conditions in order to reject as much silica as possible, and prevention of contamination by foreign substances are all important toward this end. 

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