Bromine recovery from seawater

None of the numerous technological solutions available for bromine recovery from seawater wholly satisfy modem ecological standards. At present, the closest to acceptable methods exclude the use of aggressive... 

Figure 8 Concentration profiles illustrating the principle of the dual-temperature multistage scheme for bromine recovery from seawater (T2>T ).

Figure 9 Scheme of dual-temperature multistage unit for bromine recovery from seawater. Storage tanks for bromine concentrates (cone. 1-3) are supplied with hicilities for cooling/heating the solution under treatment (T2>Ti). 

The flowsheet of the air-stripping process for bromine recovery from brines (including seawater brines) is shown in Fig. 5 [60]. The stock brine from a reservoir, mbted with H2SO4 and Clj, is directed to the top of the desorber. The bromine-free brine is collected at the bottom of the desorber, neutralized with thiosulfate and lime milk prior to disposal. Release of the chlorine/bromine air mixture from the top of the desorber is directed to the dechlorinating tower (1) where the mixture is treated with diluted FeBrj solution. The halogen exchange is described by the reaction... 

Continuously increasing demand for bromine and its compounds provides the stimuli for further development of new methods for its recovery from seawater [80]. 

Dissolved Minerals. The most significant source of minerals for sustainable recovery may be ocean waters which contain nearly all the known elements in some degree of solution. Production of dissolved minerals from seawater is limited to fresh water, magnesium, magnesium compounds (qv), salt, bromine, and heavy water, ie, deuterium oxide. Considerable development of techniques for recovery of copper, gold, and uranium by solution or bacterial methods has been carried out in several countries for appHcation onshore. These methods are expected to be fully transferable to the marine environment (5). The potential for extraction of dissolved materials from naturally enriched sources, such as hydrothermal vents, may be high. 

Seawater is unfit for drinking or agriculture because each kilogram contains about 35 g of dissolved salts. The most abundant salt in seawater is sodium chloride, but more than 60 different elements are present in small amounts. Table 14.3 lists the ions that account for more than 99% of the mass of the dissolved salts. Although the oceans represent an almost unlimited source of chemicals, ion concentrations are so low that recovery costs are high. Only three substances are obtained from seawater commercially sodium chloride, magnesium, and bromine. 

The world s oceans hold 1.37x10 of water (97.2% of the total amount of water of the hydrosphere). They cover 71% of the earth s surface, are actually the biggest reservoir on our planet, and contain many important minerals. The overall content of mineral matter in the oceans is estimated to be about 5 x 10 tons [1,2]. The seas contain virtually all of the naturally occurring elements and are the only universal source of mineral wealth that is available to most nations. For some of them it is the only source. Yet, most of the elements, the microelements, are available in very low concentrations, i.e., in parts per billion (ppb). The products being extracted from seawater with economic profit at present are sodium chloride, magnesium compounds, and bromine [2-4]. During the last two decades there has been growing interest in the possibility of commercial recovery of additional minerals from seawater [5] and brines [6]. 

According to the latest estimates of Skinner [18], elements potentially recoverable from seawater are sodium, potassium, magnesium, calcium, strontium, chlorine, bromine, boron, and phosphorus because of their practically unlimited presence in the ocean. After improving respective technologies, recovery of the following elements is expected to become profitable as well lithium, rubidium, uranium, vanadium, and molybdenum. Additional profit can be gained since desalinated water will probably be obtained as a by-product. This could be important for countries with a very limited number of freshwater sources (e.g., Israel, Saudi Arabia). 

Figure 6 Schematic diagram of double-chamber apparatus for electrosorption recovery of bromine from seawater 1. activated carbon 2. titanium current carriers 3. hydrophilic diaphragm.

Figure 7 Schematic diagram of two-sectional countercurrent ion-exchange column operating at different temperatures to provide recovery of waste-free bromine from seawater.

The halogens are so reactive that they are found naturally only as compounds. The first mineral found to contain bromine (bro-margyrite, AgBr) was discovered in Mexico in 1841, and industrial production of bromides followed the discovery of the giant Stassfurt potash deposits in Germany in 1858. All methods of bromine production depend on the oxidation of bromide ions. There are no naturally occurring oxygen salts of bromine that would act as a source of the element. Commercial recovery of bromine from brines and from seawater involves the oxidation of the bromide ions in solution with CI2 to free elemental bro-... 

In addition to freshwater, seawater is also a source for sodium, magnesium, chlorides, iodine, bromine, and magnesium metal (see Sodium coLD>ouNDS Magnesium coLD>ouNDS Iodine Bromine Magnesiumand magnesium alloys). Many other elements are certain to be economically obtained from the ocean as technology for the recovery improves. 

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