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The Dead Sea-A Live Pool of Chemicals

The Dead Sea-A Live Pool of Chemicals

Indian Journal of Chemical Technology Vol. 9, January 2002, pp. 79-87

EDUCATOR

The Dead -A live pool of chemicals

Jaime Wisniak* Department of Chemical Engineering, Ben-Gurion University of the , Beer-Sheva, 84 105

The Dead Sea has been a source of chemicals since ancient times. Large scale production of by solar evaporation started in 1931 and today the Dead Sea is intensively exploited by Israel and as a major source of potash, , and , for agriculture and the chemical and automotive industries. A smart coupling of solar evaporation and knowledge of the complex phase diagram allows a one-to-one easy separation of the principal present in the brine. A description of the properties of the Dead Sea is provided together with a chemical engineering analysis of the processes used to realize its commercial potential.

Of the several hypersaline bodies present on the trading commodity for the people of the area. surface of the , the Dead Sea is the one that has According to Diodorius Siculus (ca. 50 CE) the attracted and attracts the most attention. The most Nabateans took the to and sold it for probable reasons for this unusual fact are possibly the dead. religious. Interest was renewed strongly after exten­ Christians of the Middle Ages also knew it as the sive geochemical that suggested the Devil's Sea, and their Arab contemporaries referred commercial potential of the composition of the occasionally to the Stinking , presumably because brine and after discovery of the . of the smell of sulphur emitted from several places The Dead Sea is mentioned in several books of the along the shore. Bible as a landmark for several historical events (for Sir Walter Scott (1771-1832) used the Dead Sea example, the destruction of ), as the setting for his novel The Talisman. In geographical pointers, and battles. It appears for the the opening page he wrote: " ... was placing slowly first time in the (Genesis 14:3) as along the sandy deserts which lie in the vicinity of the Yam-Hamelach (the Salt Sea). The peculiar properties Dead Sea, or as it is called, the Lake Asphaltites, were of its brine were noted by many writers, for example, the waves of the Jordan pour themselves into an (384-322 B.C.E.) in hi s treatise Meteoro­ inland sea, from which there is no discharge of 3 logica1, book II, part III, he wrote: "If there were any " . truth in the stories they tell about the lake in The Dead Sea was first mentioned in the scientific it would further bear out what l say. For they say that literature during the first half of the nineteenth if you bind a man or beast and throw him into it he century when Angelot discussed the nature of several floals and does not sink beneath the surface; and that brackish bodies located in the Mediterranean area and the lake is so bitter and salty that there are no fish in proposed that all had originated from an old sea that 4 it, and if you wet clothes in it and shake them out it was centered where the three meet • cleans them' '. Antoine Laurent de Lavoisier (1743-1794) made The Greeks called it Lacus Asphaltitis (Lake the first chemical analysis of seawater5 and also the 6 Asphaltites) because of the lumps of asphalt that were first quantitative analysis of Dead Sea . Gay-Lussac periodically thrown out from its depths, particularly also analyzed the water of the Dead Sea; one of his after earthquakes. This asphalt was used by the early objectives was to check the presence of small animals. 7 inhabitants of the area for waterproofing baskets. for No "microscopic animals" were found . Nissenbaum decorative purposes, and to glue flint implements to has discussed in detail the results of all the papers 2 wooden handles . Later, it became an important published between 1778 and 1830, related to the chemical analysis of Dead Sea water and made an *For correspondence (E-mail: wisniak @bgumail.bgu.ac.il; estimate of the corresponding salts. Some of his 8 9 Fax: 972-8-6472916) results are summarized in Table 1 · . 80 INDIAN J. CHEM. TECHNOL., JANUARY 2002

Table !-Analysis of Dead Sea water (g/100 g)8 6 11 7 12 Macquer Marcet 10 Klaporth Gay-Lussac Gmelin DSW* MgCI2 10.2 10.1 11.3 15.3 11.8 14.8 CaCI2 8.3 3.8 5.4 4.0 3.1 4.1 NaCI 6.3 10.7 7.8 7.0 7.1 7.4 KCI 1.7 1.2 MgBr2 0.4 0.5 Total salts 24.8 24.6 24.5 26.3 24. 1 28.0 Densi ty 1.241 1.211 1.245 1.228 1.2 11 1.233

* Ltd.

It is the purpose of this paper to review the The area is highly arid; it has 300 cloudless days characteristics of the Dead Sea and describe how the during the whole year and an average rainfall of about industrial chemical potential of its waters is being 50-mm. Average air vary between I rc realized for the large-scale production of in January to 34°C in August, with maximum day commodities. temperatures II °C and 30°C, respectively. Average relative during the daytime in April to Geochemistry September are 30 to 40%. The Dead Sea is a located at the Since the Dead Sea has no outlets the balance deepest part of the Jordan-Arava rift, in the East between , runoff, and evaporation African . It forms part of a long fault determines its level and size. The major supply of trench that extends from over the Arava water comes from the . Additional Valley to the Dead Sea. amounts of water are supplied by the Arnon River and The Dead Sea is the world's saltiest natural lake, by a large number of fresh water springs and runoff with an average of 280 g/kg compared with and floods during the rainy winter. The annual flow of the 's average of 35 g. Both the lake's salinity the Jordan River varies considerably; until the late and its low location make it a valuable natural 1950s its annual discharge into the Dead Sea was resource for the production of chemicals and about 1,200x l06 m3 while the total average annual electricity. Israel and Jordan are already exploiting it 6 3 for the large-scale production of commodities such as intake of the Dead Sea was about 1,600x I 0 m . More than one percent of the Dead Sea water was renewed potash and bromine. Both countries have proposed 13 plans to build a canal connecting one of the annually . Increased use of the waters of the Jordan surrounding to the Dead Sea, to realize the lake's River by Israel and Jordan for agricultural purposes potential as a sink for the generation of electric has resulted in a substantial decrease of the input into power. the Dead Sea, and hence, a decrease in its level. Since The Dead Sea presents some unusual geochemical the 1960s, the level has decreased continuously from features . Its surface, today at 412 m below the -397m to --412 min 1999 and would have resulted in Mediterranean , is the lowest surface on the the disappearance of the southern portion, where it not 2 for the artificial evaporation pans built by Dead Sea face of the earth. It covers an area of about 970 km , has a volume of 135 km3 (nine times that of the Great Works. , ), and length 80 km. The lake is The large amount of water lost annually by evapo­ 6 3 divided into two parts, very different in character and ration ( -1 ,600x 10 m ) has resulted in a natural almost separated one from the other by the Lisan increase of deuterium; in the surface of the southern Peninsula protruding from its eastern shore. The Dead Sea basin it reaches 0.01626 mole% in the southern part covers 244 km2 and is very shallow, hydrogen. rarely exceeding 10 m in depth. The north basin As seen in Table 1, the water of the Dead Sea is covers an area of 757 km2 and reaches a depth of characterized by a very high salinity, higher than that 40I m. of any large lake known. The water is of the EDUCATOR 8 1 type, with unusually high content of magnesium and been sometimes communicated with the open sea, as bromine, and unusually low sulphate and carbonate suggested by the presence of Mugil priscus Ag, in the content (bicarbonate probably less than I 00 mg/L). In upper tertiary Sodom formati on of Mount Sodom and terms of total cation content, the amount of calcium of marine micro fauna of age. 15.75%, is again, unusually hi gh. The Dead Sea is In the late Pliocene, or in the early , an currently saturated with respect to (NaCI), extended inland lake, the first of the three that which is being precipitated in the lake and raising its occupied the Jordan-Sea area during this period, bottom. The composition of the Jordan water alone rapidly filled the inland . This first lake would adequately explain the presence and quantities (Lake Samara) was full with fresh water that of most of the salt contained in the Dead Sea, with the eventually turned salty and was replaced by the Li san exception of bromine of which only traces can be Lake. After several hundred thousand years the Lisan found in the river. Lake started to shrink and the present Dead Sea An additional characteristic of the Dead Sea is the became established in late Pleistocene times in the presence of a definite chemical stratification; the lowest part of the area originally occupied by the 13 composition of the water varying with depth . lakes. The most prominent cations present in the Dead According to Bentor13 the geological history of the Sea are Na+ and Mg2+, a common characteristic of area suggests that Lisan Lake contributed only a small lakes in a late stage of development. The Dead Sea is part of the total amount of salts in present-day Dead unique in the nature and amount of the ions it Sea. The salts must, therefore, have been carried into contains. It is very concentrated in cr and also the Lake mainly by rivers, floods, and springs. contains an abnormally hi gh amount of B(. The CI :Br It has been mentioned above that one of the most ratio is 35:1, only about one third that of the characteristic geochemical features of the Dead Sea is springs and rivers, and only one eighth that of the its high concentration of bromine. The total amount of 13 ocean . bromine now present in the Dead Sea is about 900 An interesting comparison is between the Dead Sea million tons. Its di stribution over a large area and brines and the nitrate fields (caliche) present in the almost constant association with , in the North of Chile. The Dead Sea make a common origin almost certain. According to 13 is rich in magnesium, , and bromides, and Bentor , the following facts may explain the origin of has a very large to bromine ratio. The these salts: Chilean deposits are very rich in sodium nitrate and a number of other unusual salts such as iodates, (a) Volcanic activity has been present in the near perchlorates, chromates, and dichromate, and have an past of the area. The corresponding emanations from exceptionally hi gh iodine/bromine ratio of greater th at the interior of the earth may have carried HCI. This I 0 to I, which is the reverse of the rel ati ve abundance acid could have reacted with the limestone layers that of these elements in other saline deposits and in rock, form a large part of the geological secti on on both water, and air. The origin of the salt composition of sides of the , and formed CaCI2. both sites is unclear, particularly, the reason for their (b) Existence of organic material may lead to unusual ratios CI:Br and I:Br. bromine enrichment. It is well-known that most oil waters carry considerable amount of bromine and Origin iodine. Since the Br:I ratio in the Dead Sea water is 5 It is generall y accepted th at the Dead Sea fo rmerly larger than 10 , it is almost certain that the origin of occupied a much larger area and that its volume was 4 the bromine is not organic . Consequently, it is most to 5 times th e present one. Similar to the Atacama likely th at bromine in the Dead Sea originated from Desert, the origin of the unique salt concentration and the concentration of fossil residual salt brines, which compositi on of the Dead Sea has been the subject of formed during the Tertiary. This assumption is many specul ations. Bentor13 has given a very detailed supported by the actual operation of the solar account of the geological history of the Dead Sea: evaporation pans of Dead Sea Works. The residual Towards the end of the Mesozoic times tectonic brines are very rich in bromine. Specifically, mother distmbances and fault formation resulted in the brine having a specific gravity of 1.192 contains about sinking of part of the Jordan-Arava rift, followed by 4.0 ppm bromine. After precipitation of halite and lacustrine deposition. These Neogene lakes must have (MgCh"KCI· 6H 20) the residual brine has a 82 INDIAN J. CHEM. TECHNOL.. JANUARY 2002 specifi c gravity of 1.341 and contains 8,750 ppm Br. species of the halo-obligatory bacteria. According to It is conceivable that the most soluble salts contained Nissenbaum20 the number of recorded species is very in these lakes never crystallized, and that these low but the total biomass is reasonably high (about 13 solutions were trapped at depth . 105 bacteria/mL and 104 algal cells/mL). The indi­ Under th e present conditions rains from the genous flora is comprised mainly of obligate halo­ Medit@rranean deposit at least about 75,000 tons of phylic bacteria, such as the pink, pleomorphic Halo­ chloride ions in the Dead Sea area; ground waters and bacterium sp., a Sarcina-like coccus, and the floods carry thi s deposition into th e closed basin of facultative halophilic green alga, . These the Rift Valley. The almost entire absence of iodine in organisms possess unusual properties. The Halo­ the Dead Sea is a characteristic feature of air borne bacteriwn sp. has extremely high intercellular K+ salts. It has been calculated that to balance the concentration (up to 4.8 m) and extraordinary speci­ quantities of bromide in the Dead Sea at least 200x I 09 ficity for K+ over Na+. The biota microorgani sms 15 tons of NaCI mu st be buried in the Rift Yalley • exert a critical influence on some biogeochemical processes occurring in the lake. For example, bacteria Some researchers have postulated that the main reduce the precipitated sulphate to sulphide and source of chloride in the Dead Sea area is ancient generate bicarbonate. The bicarbonate causes precipi­ th at penetrated th e Dead Sea rift in the tation of calcium carbonate. lt is also possible that Neogene and after evaporation gave ri se to the large bacteria feed on the glycerol liberated by lysing algal amount of salt which exists in the area. Yechieli 16 cells. et a!. have rejected this claim on the basis that such 20 source would have very little 36CI as the 36CI/CI ratio N issenbaum has discussed in particular the fact in seawater is very low due to the very long residence that and Dunaniella have found two time of chloride in the sea. Moreover, since the half­ distinct means of adjusting to their hostile 6 36 environment. Haiobacterium is an obligate life of :1 CI is 301,000 years th e CI would eventually have decayed to zero during the ensuing millions of that represents a complete adaptation to the Dead Sea. years. Its cytoplasmic ionic content is very different from the external composition but has about the same Another interesting phenomenon that took place osmotic pressure and similar ionic strength. The green recently in the Dead Sea is water inversion. alga Dunaliella, is an excellent example of biological Hi stori call y, the fresh water that flowed into the Dead flexibility; it is capable of standing wide ranges of salt Sea mi xed to a small extent with the much saltier lake concentration, and it is not an obligate halophile. water and formed less saline layers fl oating over a According to Ni ssenbaum Dunaliella has solved the dense column of fossil water. Increased use of Jordan problem of differences in osmotic pressure by River water for agricultural purposes stopped this developing a unique metabolic pathway of producing process and started making the surface water saltier large amounts of intracellular glycerol as a response and denser. Eventually, in I 979, the age-old gradient 20 17 to the changes in the external environment . disappeared and the water column turned over .

Life in the Dead Sea Thermodynamic properties of the solutions Arguments about the existence of living organisms The reader interested in the thermodynamic 18 in the Dead Sea have taken place for many years • lt analysis of complex aqueous inorganic solutions has already been mentioned th at in 1819 Gay-Lussac should read the very detailed papers written by 21 22 23 24 looked for and did not find microscopic animals. lt Lenm.n , Marcus · , and Krumgalz et a/. on the took more than one-hundred years until it was proven subject. th at lower organisms could exist and proliferate in the It has already been mentioned that th e salinity of hypersaline environment; Wilkansk/9 showed that the Dead Sea is some eight times that of ocean water bacterial organisms could grow in water taken from and that is the saltiest large on the the sea at depth up to seven meters and that micro­ surface of the earth. A balance among solar radiation scopic examination revealed the presence of phyto­ absorption, surface water evaporation, replenishing by flagell ates. Further investigations have shown that the the Jordan River, and surface mixing by wind and bi ota of th e sea is very limited in variety and is waves, results in a nearly constant surface tempera­ composed of the chlorophyton Dunaliella and a few ture of 25°C, both of the lake and of the pans. EDUCATOR 83

The ionic composttiOn of the Dead Sea is also Table 2-Dead Sea mineral compositi on and rcserves 14 different from that of ocean water, the main Composi ti on Reserves differences being deficiencies in sulphate and bicar­ (g/L) (106 ton ) bonate and in excess of bromide ions. Lerman2 1 calculated the mean activity coefficients 190.2 23,000 of NaCI, KCI , and MgCh and the of halite 91.8 12,650 and carnallite in the Dead Sea brine, and from these Calcium ch loride 52.4 6.1 20 parameters he determined the dissociation constants chloride 15 .9 2.050 Bromide 5 975 of carnallite and bi schofite at 25°C as log Kca ,.,.=4.00 and log Kb;.,ch=4.445. From these values he concluded Table 3-Quantities of minerals produced presentl y that the ground brines from the Dead Sea coastal areas were close to saturation with respect to halite but Israel Jordan un saturated with respect to sylvite (KCI) and Potash (potassium ch loride) 3,000.000 1.800,000 carnallite. ln addition, hi s results indicated that the Sodium chloride 500,000 300.000 Dead Sea had not evolved through a stage of brines Bromine 250,000 50,000* more concentrated than the present. Magnesium ox ide 100,000 60.000* In a first publication, Marcus22 suggested that the Magnesium chloride 1,000 multistage crystallization process presently used for Hydrochloric acid 10.000 separating several of the components of the brine Magnesium 35,000 could theoretically be replaced by another based on a membrane semipermeable only to KCI and water. To *Under construction analyze this possibility he recalculated the activities of KCI and water in Dead Sea water using several As mentioned already, Dead Sea water is approaches dealing with multicomponent electrolyte unsaturated with respect to its chloride salt solutions, and obtained values substantially higher components. Concentrated by partial evaporation in 21 the solar salt pans, it reaches a point where halite than those of Lerman . Anyhow, Marcus came to the conclusion that the Dead Sea brine could not be starts to precipitate, the halite point. According to simultaneously in equilibrium with respect to both Marcus, it was possible to use the calculated activities water and KCI. That is, a hypothetically perfect semi­ to establish how much water would have to be permeable membrane could not lead to a state of evaporated isothermally from a given amount of equilibrium between the brine anD aqueous KCI of solution, in order to reach the halite point. For the any concentration. model composition, evaporation of 192 g of water Since Dead Sea water was composed mostly of from an amount of solution containing 1000 g of chlorides Marcus assumed23 it to be a quinquenary water was enough to reach the solubility product of common ion aq ueous electrolyte solution, composed sodium chloride. More evaporation resulted in halite of the chlorides of sodium, potassium, magnesium, precipitation. Similarly, it was possible to calculate and calcium. In particular, the surface water of the sea how much halite would precipitate when given could be assumed to be equi valent to an aqueous amounts of water were removed by evaporation, as solution of 1.752 m NaCI, 0. I 74 m KCI , 1.555 m well as to follow the change of activity of th e different components as a function of the weight of MgCh, and 0.427 m CaCI2 at 25°C. This concentrated solution had an ionic strength 7. 874 m, osmolality of water evaporated. According to Marcus' model the "end brine" would 9.799 m, and a total chloride concentration of 5.891 m. be a solution constituted mainly of magnesium Marcus then used different models to calculate the (4.24 m) and calcium (1.30 m) chlorides, with small activi ty of the different species present in this model amounts of sodium (0.42 m) and potassium (0.06 m) surface water and arrived at the values chlorides, having an ionic strength of 17.0 m, a water activity of only 0.371, and a densi ty of 1.342 kg/L. aH ,o =0.7514, log a Nac 1 =1.198, log aKCI =-0.102, It has already been mentioned that nowadays water evaporation from the Dead Sea exceeds the input fog aMgCI,.6 H,O = 1.591, fog ac,1o ,.6 H,o =0.788, and from precipitation and runoff. Evaporation increases fog aKM gCI .6H ,O = 1.489. 3 the ionic strength of water and decreases its activity in 84 INDIAN J. CHEM. TECI-INOL., JANUARY 2002 the liquid phase. This process will end when the An interesting historical fact is that Palestine chemical potential of water in the sea's surface and on Potash Ltd., the forerunner of Dead Sea Works Ltd., the adjacent air layer will become equal. Different was practically the only source of potash and bromine approaches have been used to investigate how long for the British Commonwealth during the Second will it take to achieve thi s equilibrium state. Klein25 World War. Production level was 110,000 ton/yr. performed a water budget balance and concluded that Basically, the process consisted in piping sea water thi s state would be reached at the end of 360 years, into a series of shallow evaporation pans where each when the water level had dropped to -680 m. Gavrieli of the various salts precipitated as its concentration 2 and Yechieli (' built a model for water depletion based reached the saturation point. Gypsum crystallized on climate, water input, and diminishing evaporation, first, followed by sodium chloride and then carnallite and calculated a final level of -500 m to be reached in when the brine reached a specific gravity of 4 3 about 400 years. Krumgalz et al? used a thermo­ 1.3 g/cm . The carnallite was then broken into its dynamic approach, based on Pitzer's ion interaction components by water treatment and the potassium parameters, to develop a model that allowed chloride further refined. A small fraction of . the calculation of th e amount of water removed from the remaining "end brine" was treated wi th chlorine gas 29 brine and the amount of precipitated minerals and to extract bromine . ionic concentrations. Under the present climate The northern facility was destroyed during Israel's conditions, the model predicted that equilibrium War of Independence (1947-1948) and the southern would be reached when th e level dropped to - 500 m. facility was reactivated in 1952 under the ownership At that time, the volume and surface of the sea would of the new company, Dead Sea Works Ltd. 3 have decreased from 146 to 88 km and from 815 to Production began again in 1955 at a level of 200,000 2 526 km , respectively . ton/yr and a series of expansions in the later years T he phase diagram of different secti o ns of the brine brought the level of production up to the present level system has been determined, for example, Shestakov of 2.8 million ton/year. 27 28 and Pelsh and Zdanovskii have published data for The Jordanian facility, Jordan Dead Sea Industries, the quaternary system H20-KCl-NaCl-MgC1 2. was established in 1999 on the eastern shore of the sea. Exploitation The quantities of minerals (tons/year) produced at In the 19th and 20th century, The Dead Sea present are as shown in Table 3. attracted many explorers and scientists. The first Derivative products, processed from th e above expedition to study the chemical aspects of the Sea minerals, include potassium nitrate, phosphoric acid, was probably that of C. Costigan, an Iri shman. In chlorine, caustic soda, potassium carbonate and 1853 he descended in a boat fro m the Lake Kinneret sulphate, and bromine compounds. T he Dead Sea is (Sea of ) to the Dead Sea. There he was caught thus the central mineral source of Israel and Jordan, in a storm, thrown up on the Li san Peninsul a and died supporting a considerable export trade and supplying of hunger and thirst before he could be rescued. raw materials for a large variety of local manufac­ 30 Further explorati ons were by E. Robinson ( 1832), W . turing plants . F. Lynch (1 848), L. Lartet (1848), and M. A short descriptio n of the production process of the Blanckenhorn ( 1894 to 1930). different commodities is presented below. In 1911 began the practical chemical investigation 3 31 and experimental work o f th e Dead Sea resources that Potash production "· in 1930 would lead to formati on of the concern Potash producti on begi ns with a firs t stage of solar Palestin e Potash Limited. O n the initiative of Moshe evaporati on. The waters of the sea are pumped into A. Novomeysky ( 1873-1961), a mining engineer from large evaporation pans, which cover an area of about 2 Siberi a who received a concession from the British 130 km . A lmost all of this area is separated from the mandate administration, the first potash and bromine sea by dikes bui ld into the shallow southern part. works were built in 1930 ·at Ramat Ashlag in the Evaporati on is enhanced by the climatic conditions northwest corner of the Dead Sea. Novomeysky' s prevalent in the area. process of selective precipitation is still the basis of The fi rst salt that crystal lizes out is calcium production by the Dead Sea Potash Works. sulphate. Water evaporation continues until the salt EDUCATOR 85 concentration in the pans reaches about 17 % (350 g/L contains very little slimes and sulphates, and the of total dissolved salts). At this point (halite point) content is relatively high. sodium chloride begins to crystallize and continues The carnallite slurry (10-20% solids) is now until the volume of the water has diminished to about pumped to thickeners, where it is concentrated to 40- half of its original value. At the beginning of the 50% solids, and then to filters to yield a cake crystallization stage a typical brine contains (g/L) containing 85-88% solids. Separation of carnallite MgCl2, 165; CaC1 2, 48, NaCI, 105, KCl 14.5, and into its components and impurities (mainly NaCl), is CaS04 1.0. At the end of this step about 90% of the carried by partial crystallization/solution, taking into sodium chloride and more than 95% of the calcium advantage of the different of the salts. suiphate is crystallized. Sodium chloride accumulates Addition of water causes solution of all the at the bottom of the pond and causes an increase of its magnesium chloride and most of the potassium height. chloride. The solid phase is a mixture of sodium and Concentration of the brine by solar evaporation is potassium chloride (sylvinite), containing 50-65% can·ied on a second series of pans. When the specific potassium chloride on a dry basis . gravity of the brines reaches a value of 1.300, The major portion of the potash produced at the corresponding to a total salt content of about 32% at Dead Sea Works is by hot leaching of sylvinite. This 35°C (carnallite point), a new solid phase (in addition process utilizes the fact that KCI is much more to NaCI), consisting of carnallite (KCI.MgCJz.6H20), soluble at high than at low temperatures, while NaCl begins to separate. A typical brine composition at this has an almost constant solubility over a wide point is (g/L): MgCiz, 295; CaC]z, 85, NaCl, 20, KCI . range. Sylvinite is now contacted with

27, Br" 9, and CaS04 less than 0.1. The pans are used hot (I 05°C) recycle brine that is unsaturated with as storage for the carnallite. An important techno­ respect to KCl but saturated in NaCI. Potassium logical feature is that carnallite tends to crystallize in chloride is dissolved and separated by centrifugation separate crystals rather than in continuous layers as from the residua! solid phase (NaCI). The hot brine is sodium chloride, forming a loose layer amenable to fed to vacuum crystallizers to generate a solid phase slun·y pumping from the bottom of the pans. having a typical composition (g/L) of KCl, 19-20%, NaCl, 11-15%, MgCiz, 28-30%, CaCI2, 0.5-1.0%, and When the specific gravity of the brines reaches H20, 37-40%. 1.350, the ratio between evaporation and crystalli­ After centrifugation and washing, the product zation becomes unfavourable; the evaporation process is terminated and the end brine returned to the sea. A contains only some 2% NaCI, it is dried in rotary kilns typical composition of the end brine is MgCJz, 360; and separated on vibrating screens to different grades: coarse, standard, and fine. CaC12, 110, NaCI, 7, KCI 5, and Br" 12 g/L. A small amount of it is used for the production of bromine and Another alternative to produce KCl is flotation. hydrochloric acid. Here sylvinite is slurried in a suitable brine, long Further evaporation of such brines, possible only chain fatty amines are added as flotation reagents, and during 2-3 months every summer, to a specific gravity the mixture pumped to flotation cells. The froth of of 1.365, brings about the crystallization of bischofite these cells is enriched with KCI but may still contain (MgCI2.6 H20). appreciable amounts of sodium chloride. The KCI Analysis of the above figures indicates that crystals are small and tend to stick together and evaporation by solar energy has increased the agglomerate with NaCI crystals, probably by concentration of KCI of about I% weight in the electrostatic attraction. As a result the flotation tops original brine to about 20% as carnallite. contain only 65-75% KCI and require extensive Carnallite ores are found in other parts of the world washing to remove NaCI and obtain a 95% KCI and are normally associated with salt, kieserite product. Agglomeration is reduced by additi on of (MgS04.H 20) and insoluble clays. The carnallite substances that are habit modifiers for sodium deposits are processed for potash only in areas where chloride, e.g., sodium ferrocyanide and nitrilotri­ the sylv inite resources are limited. The carnallite acetamide. The fi nal product is centrifuged and dried obtained by solar evaporation of Dead Sea brines is in rotary kilns giving a very fi ne grade of potassium different in several aspects from the mined variety: it chloride. 86 INDIAN J. CHEM. TECHNOL.. JANUARY 2002

30 1 By products of potash production .J cement, ceramics, textiles, paper, water purification, Sodium chloride and sewage treatment chemicals. Sodium chloride separated from the sylvinite is MgCh is also converted into aqueous magnesium used for producing chlorine and caustic soda by chlorate that is sold as a defoliant agent and desiccant. electroly sis and for other industrial uses. Table salt is produced by a salting-out process. Magnesium oxide by thermal hydrolysis On heating solid MgCh.6H20 it melts and begins dissolving in its own water of crystallization. This Bromine makes heat transfer difficult and completion of the The process depends on the oxidation of bromide hydrolysis process not economical. The problem was to bromine and consists of simultaneous chlorination resolved by the Aman process in which the thermal and steam blowing. The end brine from the carnallite hydrolysis is performed in a spray reactor. The Aman pans contains 11-12 g/L of bromine in the form of process allows production of high purity magnesia bromide salts. This is the highest concentration of (99.3%) and hydrochloric acid. Thermal hydrolysis bromine found in the world and compares favourably takes place in a relatively short residence time. with other sources of bromine such as salt brines in the U.S. (3-4 g/L) and sea water (70 ppm). The end brine is sent to the top of the blowing-out packed tower where it flows counter current to live The raw magnesium oxide is separated from the steam and chlorine. The chemical reaction taking accompanying salts by hydration to magnesium place is: hydroxide followed by water washing. High purity magnesium oxide is then produced by calcination. The main outlet for this highly pure periclase is in the production of high grade refractory bricks for the The brine is usually heated to near-boiling point to basic furnaces used by the steel industry. reduce the partial pressure of bromine to nearly zero. The exit top stream contains excess steam and Magnesium metal by electrolysis impure bromine. After cooling it separates into two Dead Sea Magnesium, a joint venture between the phases, the bromine phase is distilled to remove the Magnesium Division of Dead Sea Works, and dissolved chlorine and then dried with concentrated Volkswagen AG of Germany, inaugurated production sulphuric acid. The water content must be less than 30 of magnesium metal in 1997 at the Plant, ppm to prevent corrosion of metal transportation and near Sodom. Magnesium is considered a critical storage containers. material because of its extensive use in industrial and The Dead Sea Bromine Co. and its subsidiary military applications. Its low has encouraged Bromine Compounds produce a series of bromine its use in structural applications and motor vehicles, derivatives from the bromine produced at the Dead where it competes with aluminium. Sea. The main uses of bromine are in flame retar­ The process is based on the electrolysis of molten dants, drilling fluids, brominated pesticides (mainly anhydrous MgCh prepared under controlled operating methyl bromide), water treatment chemicals, conditions to minimize its decomposition into MgO photographic chemicals, and rubber additives. and HCI. The carnallite is first fed to a chlorinator An important growing application of bromine is in operating at 700°C where it melts and the traces of the manufacture of fire retardants either of the MgO are converted to MgCh. Afterwards, it flows to additive- or reactive-type. an electrolytic cell provided with a graphite anode and

113 1 iron plate cathode. Magnesium deposits on the Magnesium and magnesium derivativei cathode and by it's being lighter than that of the Magnesium chloride electrolyte, it floats. Chlorine is produced in the anode Bischofite brine is used for the production of and proper cell partitions prevent its reaction with the

MgCI2.6H20, magnesia and HCI. The purified MgCh molten metal. Although it is possible to electrolyze liquor is sent to evaporators to yield the solid salt, MgCh pure, it is not done because of technological which is then purified by repeat crystallization. The drawbacks such as the high fusion temperature of the final product finds application in the manufacture of salt (7l2°C), instability in contact with air, low EDUCATOR 87 electrical conductivity, and density similar to that of 4 Angelot V F, Bull Soc Geologie, Ser I, 14 ( 1843) 356. pure magnesium. To improve the process chlorides of 5 Lavoisier A L, Mem Acad Roy Sci Paris. 2 ( 1776) 555. 6 Macquer P J, Lavosier A L & Sage B G, Mem Acad Roy Sci calcium, potassium, and sodium are added to the Paris. (1781 ) 69. electrolyte bath. These salts, in proper concentration, 7 Gay-Lussac J L, Ann Chim Phys, II ( 1817) 195. lower the fusion temperature of MgCb to about 8 Ni ssenbaum A, Israel 1 Chem, 8 (1970) 281. 500°C. A typical electrolyte contains between 10 to 9 Ni ssenbaum A, 1 Chem Educ, 63 ( 19R6) 297. I0 Marcel, Phil Trans, I ( 1807) 296. 15 % MgCb. II Kl apro th M, Ann Phil, I ( 1809) 36. The spent electrolyte is solidified and sent back to 12 Gmelin C S, Ann Physik Chemie. 85 ( 1827) 9. the potash plant where it is processed into . 13 Bentor Y K. Geochim Cosmochim Acta, 25 (1961) 239. The molten crude magnesium is delivered to the 14 Lin I J & Schorr M. Kim Handasa Kim , 31 ( 1997) 46. 15 Loewengart S, Bull Res Council of Israel, IOG ( 196 1) 183. foundry for further refining and casting into ingots. 16 Yechieli Y, Rosen D & Kaufman A, Geochim Cosmochim Acta. 60 (1996) 1909. Lithium 17 Steinhorn I & Gat J R, Sci Am. 299 ( 1983) I 02, 170. The Dead Sea contains approximately 2 million 18 Ni ssenbaum A. Bioscience. 29 ( 1979) 153. tons of lithium with a concentration of 14 to 15 mg/L. 19 Wilkansky B, Nature, 138 ( 1936) 467. This concentration increases to over 30 mg/L during 20 Ni ssenbaum A, Microbiol Ecol, 2 (1975) 139. the evaporation process of the brine to produce the 2 1 Lerman A, Geochem Cosmochim Acta, 3 1 ( 1967) 2309. 22 Marcus Y, Geochem Cosmochim Acta, 41 ( 1977) 1739. main chemicals. Under present conditions about 3,000 23 Marcus Y, Dead Sea Brines: Natural Hi ghl y Concentrated tons of lithium pass annually through the pond Salt Solutions. in Ioni c Liquids, edited by lmman D (Plenum system. Tandy and Canfy32 have described a pilot Press, New York) 198 1, 97. pl ant scale process developed by Dead Sea Works to 24 Krumgalz B S. Hecht A, Starinsky A & Katz A. Chem Geol, 165 (2000) I. extract most of lithium present, based on its selective 25 Klein C, Is 1 Earth Sci, 3 1 ( 1990) 67. precipitation as lithium phosphate, using a hi ghl y 26 Gavrielim I & Yechieli Y, Th e Annual Meeting of the Israel concentrated solution of sodium diphosphate. Geological Society, Ap ril 1997. 27 Shestakov N E & Pelsh A 0 , l.uled Solevyskh Vodn Sisr. 3 References (1977). Ari stotle, Mereorologica. tra nslated by Lee. H D P (Harvard 28 Zdanovskii A B, Zh Neorg Khim. 26 (1981) 456. Universi ty Press, Cambridge) 1952, 159. 29 Novomeysky M A, Trans In st Chem Eng, 14 ( 1936) 60. 2 Ni ssenbaum A, Hydrobiologia, 267 ( 1993) 127. 30 Epstein J A. Hydrametallurgy. 2 ( 1976) I. 3 Scott W, Th e Talisman (J M Dent and Company, London) 3 1 Epstein J A. Chem & lnd, ( 1977) 572. 1906. 32 Tandy S & Canfy Z, Rev Chem Eng, 9 (1993) 293.

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