Brine Process

FIGURE 3.8. Brine processing scheme for mercury-cell operations. 

Brine is treated in a reactor with sodium carbonate and caustic soda to precipitate calcium carbonate and magnesium hydroxide, as shown in Eqs. (1) and (2). 

The depleted brine from the membrane and mercury cell processes carries dissolved chlorine. This brine is acidified to reduce the chlorine solubility, and then dechlorinated in a vacuum brine dechlorinator. The dechlorinated brine is returned to the brine wells for solution mining, or to the salt dissolver. If the membrane and diaphragm processes coexist at a given location, the dechlorinated brine is sent for re-saturation before being fed to the diaphragm cells. 

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Brines. About 65% of the iodine consumed in the world comes from brines processed in Japan, the United States, and the former Soviet Union (see Chemicals frombrine). The predorninant production process for iodine from brines is the blow-out process, which was first used in Japan. Iodine is present in brines as iodide, and its concentration varies from about 10 to 150 ppm. As shown in Figure 3, the recovery process can be divided into brine clean-up, iodide oxidation to iodine followed by air blowing out and recovery, and iodine finishing. 

The key difference between the brine process and seawater process is the precipitation step. In the latter process (Fig. 6) the seawater is first softened by a dding small amounts of lime to remove bicarbonate and sulfates, present as MgSO. Bicarbonate must be removed prior to the precipitation step to prevent formation of insoluble calcium carbonate. Removal of sulfates prevents formation of gypsum, CaS02 2H20. Once formed, calcium carbonate and gypsum cannot be separated from the product. 

Dead Seas Periclase Ltd., on the Dead Sea in Israel, uses yet another process to produce magnesium oxide. A concentrated magnesium chloride brine processed from the Dead Sea is sprayed into a reactor at about 1700°C (127,128). The brine is thermally decomposed into magnesium oxide and hydrochloric acid. To further process the magnesia, the product is slaked to form magnesium hydroxide which is then washed, filtered, and calcined under controlled conditions to produce a variety of MgO reactivity grades. A summary of MgO purities, for the various processes is given in Table 20. 

A wide range of operating conditions and design philosophies affect mercury cell efficiency. For example, the fundamental distinction between a resaturation and a waste brine process influences the temperature and brine strength profile along the length of the cell and hence the overall efficiency. Another important factor is the quality of the brine. Impurities in the brine can cause base-plate deposits, which tend to reduce the anode/cathode gap. This gradual reduction in gap requires either manual or automatic adjustment and, eventually, the cell must be taken off-line and the thick mercury removed. 

Table 20.1 summarises the model errors from the validation trials and shows that the model is successful in predicting the steady-state condition of the plant. Errors in waste brine strength and temperature must be compared with the total change across the cell which is about 13% for brine strength and 40°C for temperature. This is because the plant is a waste brine process changes in brine temperature and strength are much smaller for a resaturation process. 

As previously mentioned, the mercury cellroom at Runcorn is operated as a waste brine process with some of the brine recycled through the cells. This process involves a trade-off between electricity and brine costs since with increased brine flow the cells operate at a higher average concentration, which saves power. 

Brine processing will inhibit the destruction of chemical agent or chemical agent munitions/bulk items ... 

Phenolic epoxy lining 55 75-150 12 h For sweet and sour crude, brine, processed petroleum products, C02— and H2S-containing C02... 

Brine processing is carried out at a bromine concentration of 1 g/L and higher by steam stripping after preliminary acidification and by oxidative chlorination in a countercurrent mode. In this case, the raw bromide is obtained in one stage and then further reftned. 

Brining and fermentation include preservation by the use of acids. Acids are added in the brining process. In fermentation, however, the process can be self-driven (natmal) or acids can be added to drive the process towards optimal conditions. 

Figure 6.10 shows the anolyte balance. The sulfate flow into and out of the electrolyzers is an arbitrary but reasonable number chosen to suit a typical membrane supplier s specification. The balance ignores any flow of sulfate out of the anolyte. Sulfate in some form is known to penetrate the membrane (therefore the need to limit its concentration). The rate of penetration is so small, however, that the assumption of zero flux is the basis for one method of estimating current efficiency [3]. The chlorate flows are in the same category as the sulfate flows. There is a small difference between the flows out and in, representing the rate of chlorate production in the cells. This amount would be removed by purging or by deliberate destruction in the brine process. 

The temperature of the saturated brine is variable when salt is dissolved outdoors. When depleted brine at the process temperature is part of the fluid used to dissolve the salt, heat loss can be a serious matter, upsetting the balance in the brine process. A steam plume from the dissolving area can be a hazard as well as a nuisance. 

Conservation of heat becomes more important as the operating temperature increases. Operators of hot brine processes may use fluidized salt resaturators in which an internal cone holds a recirculating salt slurry. Fresh undersaturated brine enters the cone, and saturated brine overflows to flie bottom section of the vessel for removal. The supply of salt is replenished by addition of flesh slurry near the circulating pump. 

Construction is of rubber-lined steel or other standard materials for the brine process. The small size of the dissolver often makes FRP (reinforced with PVC or CPVC) a good choice for the vessel, and the same resins can be used for internal piping. The saltsupporting grid can be carbon steel, but the thin screen should be of a more resistant material such as Monel. 

I. Primary Filtration. Classically, sand has been used as the medium in bed filters. While it is acceptable in most diaphragm and mercury brine processes, the possibility of dissolving small quantities of silica usually disqualifies sand from use in membrane plants. Other media such as garnet and anthracite are used instead. These have little effect on filter design, and plant conversions usually continue with the same vessels on line but the new fill substituted for sand, lypical particle sizes for both sand and anthracite are about 1 mm, but sand is, on the average, a bit smaller and contains more fines. Regardless of the fill, the apparatus still is frequently referred to as a sand filter. 

At least conceptually, the potential of these filters goes far beyond replacement of the polishing filters. The ultimate achievement in the chlor-alkali brine process would be to take treated brine from the precipitation reactors and filter it directly in a single step to produce clear filtrate. This would combine the functions of the clarifier, the primary filters, and the polishing filters in a single step. Further discussion is in Section 17.3.1. 

The filtrate, after polishing in a filter press, passed on to the brine process. The filter cake dropped into a second agitated slurry reactor, the desorber. Addition of caustic there raised the pH and reversed the reaction of the zirconium. This slurry was transferred to a second vacuum filter. The filtrate in this case, after polishing, became the purge stream. The cake from the second vacuum filter dropped into the first reactor to begin another cycle. 

IB. Inventory Control. The membrane-cell brine process loses water with the waste streams, by transport through the membranes into the cell catholyte, and through evaporation into the chlorine produced in the ceUs. Even with minimization of the waste streams, there is a constant need for makeup water. This can be added to the saturator feed or directly to the pump tank. The choice of the addition point will determine the size of the bypass flow requited to maintain the brine density. Addition to the pump tank is feasible only when its dilution of the brine is not excessive. One method for controlling the makeup water flow is to measure the total brine volume continuously and add water to maintain the desired amount This is easily done because there are usually only two or... 

They are characterized as hazardous wastes and are regulated substances. Their use in the brine process forms BaS04. This material forms because of its extremely low solubility, and process wastes may therefore contain less than the allowable level of soluble barium [44,45]. Disposal then becomes a matter of good practice and local regulation. 

In any of these cases, prior removal of dissolved chlorine from the spent acid is desirable, and this is the subject of Section 9.1.4.4E. Method (4) appears on the list above as well as method (1) because the amount of acid generated may exceed the local demand for neutralization of alkaline waste. This situation depends on a plantwide balance and is not constrained to the battery limits of the chlor-alkali unit. Use of the acid as a dechlorinating agent, as in number (2), is limited to situations in which the treated condensate is not returned to the brine process (e.g., diaphragm-cell plants). The presence of sulfates in the stripped product makes it unsuitable for recycling. Many producers favor option number (3), when it is available. The supplier s ability to handle the material may dictate the concentration of the spent acid. 

Parti Lithium Brine Processing Solar Ponds... 

Kotsupalo, N. P., Menzheres, L. T., and Ryabtsev, A. D. (1999). Choice of Complex Technology for Calcium Chloride Brine Processing. Khim. Interesakh Ustoych. Razvit. 7(1), 157-167. 

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