Extraction of Halite from El-Bardawil Lake, North Sinai, Egypt: Sedimentological attributes and environmental impacts

doi:10.21203/rs.3.rs-4847993/v1

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Extraction of Halite from El-Bardawil Lake, North Sinai, Egypt: Sedimentological attributes and environmental impacts

https://doi.org/10.21203/rs.3.rs-4847993/v1

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The main goal of the present study is to consider the technology of preparing multi-ecosystem ponds in order to extract pure halite and discuss the sedimentology of this valuable mineral in the shallow modern artificial brine ponds. The lake water passes by three main stages to be prepared and to be ready for extraction of halite from suitable brine solution. The first stage is the concentration stage ponds, where the lake water flows through a series of ponds to increase brine salinity and deposit less soluble salts first (calcium carbonate and calcium sulphate). The other more soluble salts (sodium chloride and magnesium chloride) remain in solution. The second stage is the crystallization stage ponds, where the brine is pumped to solar ponds and left to increase brine density again until most of the halite mineral has crystallized and deposited. The pure halite crystals are crystallized in different sedimentological (e.g., rafts, mounds, cumulates and bottom crusts) and petrographic (e.g., euhedral cubic to subhedral, distorted platy and chevron crystals) forms. Finally, the third stage is the storage ponds, where the residual bittern solution that is left over after recovery of sodium chloride is pumped to storage ponds to precipitate the residual high soluble minerals and salts (magnesium sulphate and magnesium chloride). Saltworks from El-Bardawil Lake don't have economic impact only, but also have environmental impacts through decreasing the salinity of the lake and accordingly kept its ecological systems.

El-Bardawil Lake

Halite

Saltworks

Sinai

Egypt

Artificial evaporation solar ponds or saltworks are anthropogenic supratidal systems formed of multi-stages ecosystem ponds (Taher, 2014), which are progressively concentrated by solar evaporation (Warren, 2016). They represent valuable natural laboratory for studying the mineralogical, sedimentological and biological processes operating under controlled conditions of evaporation, hydrological regime, salinity gradient, …etc. (Taher et al., 2014 and Warren, 2016). These processes provide different salinity levels with an extensive range of environments, from that of seawater to bittern solution level. By the time, evaporation increases salinity of the saline solution or brine, which is subsequently pumped or fed by gravitational flow to the next high concentration pond, so the salinity in each individual concentration pond is preserved steady. Saltworks are not different a lot from natural evaporites. Minimized models of perennially-filled, evaporitic minerals formed in shallow-water basins can introduce important information about depositional environments and fossils (Oren, 2009). In contrast, natural saline lakes studies introduce additional changeable parameters. Saltworks are much more distinct for appointed investigations than the natural saline lakes. The only prerequisite is an arid and dry climate during the evaporation time (Warren, 2006 & 2016). They also interpret the ancient formation of the hydrocarbon from microbial mat degradation (Busson, 1988 and Fathepure, 2014). Saltworks lateral sequence variations explain facies changes in the vertical succession of the evaporitic sequences.

El-Bardawil Lake is a very shallow saline lake situated at the northern coastal plain of Sinai (Mediterranean Plain), where it occupies much of the northern coast of Sinai with a long of 85 km and maximum width of about 20 km (Fig. 1). It shows a maximum depth of about 7.5 m and a mean depth of about 1.5 m. Large areas of the lake with shallow water (less than 1 m) occupy about 20% of the lake, also the areas between 1 and 1.5 m depth form about 65%, and the areas with depth more than 1.5 m don't cover more than 15% only of the lake (Embabi and Moawad, 2014). El-Bardawil Lake bulges into the Mediterranean from east to west with a simple convex coastal barrier. The northern shore of the lake is represented by a smooth sand bar, with scattered salt marshes and mudflats, while its southern shore is irregular due to pre-lake topographical effect of the northern Sinai sand dunes. The El-Bardawil Lake area is characterized by complex and different geomorphologic features. The lake can be divided into two main basins, which include several other trivial inner basins (Embabi and Moawad, 2014). The larger one (Eastern Basin) takes a triangular shape and occupies nearly 66% of the total lake area. The second main basin (Western Basin) shows a stretch of water parallel to the coastal barrier with about 40 km long and average width of about 4 km (Fig. 1). The sand barriers are classified, according to their location and size, into a main El-Bardawil Barrier to the north and a number of small barriers in the lake basins called as "Lake Barriers". Sand dunes are major morphological forms constituting about 40% of the total area of north Sinai Peninsula (Embabi and Moawad, 2014).

Figure (1). Enhanced ETM mosaic shows location of Agret Soliman Saltworks, El-Bardawil Lake, Sinai, Egypt (white arrow refers to Boghaz I, green arrow refers to Boghaz II and red arrow refers to El-Zaranik).

El-Bardawil Lake is considered as a potential economic resource not only based on its fish resources, but also on the beneficiation of about 2 million tons/year from the extraction of pure halite as a clue for the economic importance and sustainable development of the northern Sinai area. The lake is regarded as a natural reservoir for the Mediterranean seawater enriched in mineral salts because of the arid climate (daily temperature in the summer ranges from 30 to 35°C), low precipitation rate (average rainfall 10 cm/year), respectively high evaporation rate (2 meter/year), and the restricted connection between the lake and the Mediterranean Sea. Seawater flows from Boghaz I, Boghaz II and El-Zaranik into the lake by normal gravity (Fig. 1). There is no outflow from the lake, except for that which is withdrawn by the saltwork companies to feed their solar concentration ponds. Many saltwork companies extract pure halite salt from the eastern and southern parts of the lake with a total production reaches to about 2 million ton per year (e.g.; Sebeka Salt, Sinai Salt, El-Ismailia Crystal, International Sinai, El-Roda El-Kafrawy, Egyptian Company for Refining Salt, Agret Soliman for Refining Salt and Malahet El-Katarat…..etc). In the present study, Agret Soliman Saltworks System is chosen as a model for El-Bardawil saltworks systems (Fig. 2). Agret Soliman Saltworks started production by the sixties of the last century. The overall halite salt production is about 100,000 tons per year. This amount of crystallized pure halite salt has magnificent influence in diminishing lake water salinity, which shows an environmental positive effect on the lake. The present work sheds the light on the extraction style, sedimentological aspects and environmental impacts of the halite mineral of the El-Bardawil Lake Saltworks Systems (northern Sinai, Egypt).

Figure (2). Enhanced ETM mosaic shows a general view of Agret Soliman Saltworks Company; concentration ponds 1, 2 & 3, crystallization ponds 1, 2, 3 & 4 and storage ponds 1 & 2.

The concentration, crystallization and storage ponds technology by the influence of solar energy raises the salinity to more than 400 g/l. In general, saltworks production systems consist of three main successive evaporation ponds stages to extract pure halite. The first stage is the concentration ponds stage, where the lake water flows through a series of ponds to increase the brine density and deposit less soluble minerals (e.g., calcite and gypsum). The more soluble salts (sodium chloride and magnesium chloride) stay in solution. The second stage is the crystallization ponds stage, where the brine is pumped to solar ponds and is left to increase the brine density again until most of the sodium chloride has crystallized and deposited. The third and final stage is the storage ponds, where the residual bittern solution that is left over after recovery of sodium chloride, is pumped to storage ponds to precipitate the residual salts (magnesium sulphate and magnesium chloride). Fifteen samples were collected from the three stages ponds of Agret Soliman Saltworks. Each sample was air-dried, chemically analyzed, petrographically inspected and mineralogically investigated and identified. The XRD (X-Ray Diffraction) analysis was used during the present study for the determination of the various types of minerals present in the evaporitic and non-evaporitic sediments. All the solid-phased salts from the studied bittern, as well as those separated experimentally from the studied samples were examined by XRD using Phillips X-ray diffraction unit model PW/1710 with Ni-filter, Cu-radiation ( ג = 1.542) at 40 Kv, 30 MA and scanning speed 0.02/ sec. All XRD analysis was carried out on powdered samples in the Central Metallurgical Research Institute (CMRI). Thin-sections of the solid phases at different intervals of temperature were prepared for identification of minerals and examination of textures, microstructures and revealing the relationships between the identified minerals. Because of water solubility of some minerals and the sensitivity of most of these solid phases toward heat, a special treatment during the preparation of thin sections was carried out. Polarizing microscope and binocular microscope were used for the microscopic study. The analytical chemical methods include the acid-base titration (CO₃²⁻), flame photometer (Na⁺, K⁺), titration complex metrically with Ca²⁺ by using Eriochrom black T (Mg²⁺), titration complex metrically by using muroxide (Ca²⁺), titration with silver nitrate using potassium chromate as indicator for (Cl⁻) and barium sulfate precipitation (SO₄²⁻; Dunk et al., 1969).

The sabkhas occupy the southern area of the El-Bardawil Lake as dispersed irregular closed lowland areas of different sizes. Field study and geographic setting of the southern area of El-Bardawil Lake show that the sabkhas could be classified into two types; the coastal and inland sabkhas. The coastal sabkha speard along the southern stripe coast of the lake. They are active as they are continuously fed by seawater. The second type is inland sabkhas which cut off from the lake by sand dunes and fed mainly by groundwater. The artificial or human-controlling evaporites from which valuable pure halite mineral is extracted are used as raw material for many industries (food, chemicals and deicing).

3.1. First ponds group (concentration ponds)

The first ponds group in Agret Soliman Saltworks includes three concentration ponds (ponds 1, 2 and 3) with a total area of about 2.7 million m² and a depth of about 1.5 m (Fig. 2). These ponds receive water directly from the lake through long channel about 4.7 km (Fig. 3), with an average salinity of 64 g/l. In the concentration ponds group, the lake water salinity reaches up to about 220 gm/l before it is pumped to the second ponds group (halite crystallization ponds). El-Bardawil Lake water enters the first ponds group (concentration ponds) by gravity to precipitate the suspended matter and the least soluble salts (calcium carbonate, calcium bicarbonate and calcium sulphate) together with silica. After precipitation of clay and crystallization of uneconomic evaporitic minerals, the effluent brine rich in sodium chloride is pumped to the secondary ponds group for further evaporation and crystallization to extract the sodium chloride. The brine concentration in each pond is controlled and adjusted before being permitted to flow into the next pond. Gradual evaporation in these primary solar concentration ponds results in decreasing the volume of solution pumped from the lake by about 70% (i.e. the volume of brine in the third pond reaches about 30% of the original water from the lake). The brine and water samples from the lake and the artificial concentration ponds were analyzed for the main anions and cations. They show the abundance of ionic concentration as Cl^-> Na⁺> (SO₄ )^2-> Mg²⁺> Ca²⁺ > (HCO₃ )^2- >(HCO₃)^-.

Figure (3). General view of Agret Soliman saltworks intake.

3.2. Second ponds group (crystallization ponds)

3.2.1 Fieldwork

After precipitation of the uneconomic minerals (e.g. calcite and gypsum) in the concentration ponds group (ponds 1, 2 and 3), the brine reached a certain saturation degree with soluble sodium chloride then it pumps to the second ponds group (i.e. crystallization ponds group). The crystallization ponds include four ponds (1, 2, 3 and 4) feed in parallel from the third concentration pond (Fig. 2). The crystallization ponds are designed to crystallize and precipitate pure halite crystals that act as raw materials to feed sodium chloride plant (washing method). The first crystallization pond (pond 1) (Figs. 2 and 4A) is selected to study the crystallization of halite, because it was ready to harvest during our visiting time. It shows an area of about 260000 m² and a depth of about 1.3 m. It obtains the brine directly from the third concentration pond (in parallel with the rest crystallization ponds). The brine total dissolved solids are allowed to increase to a proper concentration at about average Sp. Gr. of about 1.237.

Five cores (each is about 20–40 cm in length) were taken from the evaporite sediments of the first crystallization pond. X-Ray diffraction pattern from the pond shows that halite is the dominate evaporite mineral, which reflects the high purity of evaporitic halite ore mineral (Fig. 5). The halite shows different forms and sizes (rafts, mounds, hopper, cubic and chevron) reflecting different rates of salt precipitation (i.e. precipitation is not simultaneous in all parts of this pond). Halite rafts are recognized in almost all the crystallization ponds. Because of its high concentration in these ponds, halite rafts could be observed as thin flakes (flat films) at the brine surface (Fig. 4B). They develop later into tightly connected, mostly flattened translucent cubic crystals. The rafts grow laterally outwards along the cubic edges and cover a surface area of many centimeters. In places, where gentle water flow occurs, rafts blown to the edges of the pond, where they aggregate into a larger form (cubic and chevron forms, Fig. 4C). Cumulates are halite crystals that formed firstly at the water-air interface and later settled down on the pond floor due to gravity (Lowenstein and Hardie, 1985 and Warren, 2016). The halite crystals coalesce and because of its continuous growth, they become too heavy and overcome the surface tension resulting in its settling down on the pond bottom. They accumulate to form layers of aligned rafts which form the nucleus for the growth of cubic halite crystals (Fig. 4C). Bottom halite crusts are well observed in the first crystallization pond. Halite crystals, which are nucleated on the bottom, represent the mature stage of precipitation (Fig. 4D). They are responsible for thickening and growth of halite layers and cementation of the cumulus crystal aggregates and rafts. It is observed that the halite crystals at the bottom of the halite crusts have different vertical orientation depending on the attitude of the parent cumulus and rafts crystals. Halite crust showed well-recognized hopper structure (Fig. 4D). The crystals sizes are medium- to coarse-grained (reaches to about 2 cm), badly-sorted and milky white in color reflecting the purity of crystallized halite mineral. At the bottom, halite grows upward into centimeter-scale chevron crystals forming a subaqueous crust (Fig. 4E). When syntaxial overgrowth of halite cubic crystal begins on the edges, the chevron shape is formed with upward pointing cosigns (Fig. 4D, E; Schreiber, 1981 and Lowenstein and Hardie, 1985). Halite mounds are scattered in the crystallization pond 1 showing domal or conical shape, smooth surfaces with elevation reaches about 10 cm and width of few centimeters (Fig. 4F).

Figure (4). A. First crystallization pond, the pink color (black arrows) is attributed to the presence of halophilic bacteria. B. Halite rafts floating over the brine surface (black arrows). C. Cubic halite rafts on the crust (black arrows). D & E. cubic and chevron crystals form hopper structure, which indicates bottom crystallization (black arrows). F. Halite mounds (black arrows).

Figure (5). X-ray diffraction pattern of the analyzed bulk sample from the first crystallization pond shows pure halite crystals with different crystallinity forms (ranges from high to low).

3.2.2 Petrographic analysis

The petrographic examination of the thin-sectioned samples from the first crystallization pond reveals that the crystallized halite is occurred as clusters of euhedral cubic, irregular-subhedral, distorted platy and chevron crystals (Figs. 6 & 7). The petrographic analysis confirms which had been noticed in the halite crystallization ponds (pond 1) about the chevron crystals (Fig. 7). Occasionally, halite spheroids, ooids or halolites could be observed in the high saline crystallization ponds. They are rounded to subrounded spheres ranging between 0.5 to 1 mm in diameter (Figs. 6C and 7C, D). The observation of these halolites showed that the cortex was rich in organic matter with dark fluid inclusions. The petrographic inspection displays that some halite crystals are partially dissolved and subsequently re-precipitated as syntaxial fine halite crystals on the inner margins of the large ones (Fig. 6B, C).

Figure (6). Photomicrographs of halite of crystallization pond 1 with fluid inclusions (dark material). A. Clusters of euhedral cubic crystals (blue arrows). B & C. Irregular-subhedral to distorted platy halite crystals (red arrows) with ooids or halolites (black arrows) and with the partially dissolved halite and recrystallized syntaxial fine halite crystals on the entire large ones (blue arrows). All photos were taken in plane-polarized light.

Figure (7). A-D. Photomicrographs of chevron halite crystals with fluid inclusions (dark material) and ooids or halolites (blue arrows). All photos were taken in plane-polarized light.

3.3. Third ponds group (storage ponds)

After the precipitation of halite in the crystallization ponds, the residual bittern solution is directed to the storage ponds stage, where the highly soluble salts as K-Mg chlorides (carnalite and bloedite) are formed. These salts can be exploited in the future. The bittern solution is reach to high concentration in theses ponds (Sp. Gr. of about 1.340).

4.1 Sedimentological attributes

The halite mineral shows many crystal shapes depending on the variation in salinity (e.g., Aquilano et al., 2016). Geisler-Cussey (1997) suggested three intervals of salinity. The first ranges from 320 to 325 g/l, whereas crusts of halite cubes are precipitated. The second varies from 325 to 370 g/l, whereas crusts of chevron halite are formed. The third shows halite crusts with cubic hopper and skeletal faces at salinity > 370 g/l. The precipitation rate of halite in the crystallization ponds is not the same during the year months. The summer months had high precipitation rate of halite crystals than the winter months. Taher et al. (2014) revealed that the brine solution is passing through two main stages. The first stage is a concentration stage, during which the evaporation causes the reduction of the bittern and the precipitation rate is low, so it produces large halite crystals on the floor of the pond. In the second stage (crystallization stage), the solution is reaching the maximum saturation point, so the evaporation rate is less than in the first stage and the precipitation rate is higher. This produces fine crystals of halite in the form of rafts that accumulated into crusts (Fig. 4B and C). The presence of clustered cubic euhedral halite crystals (Fig. 6A) indicates bottom crystallization and static conditions for the pond solution (Schoenherr et al., 2009 and Filippi et al., 2011). Large halite crystals were also recorded since the evaporation rate is slow and the bittern solution is slightly supersaturated (Palmer, 2007). Halite crystals of more than a half of centimeter in size constitute aggregates of interlocking crystals or consolidated layer at greater depths on the pond floor (e.g., Herut et al., 1998). Hopper and chevron textures contain many primary fluid inclusions (Fig. 7A-D), which indicate that the halite crystals were formed and precipitated in a shallow brine lacking evidences of drying or desiccation, where they are formed as bottom-nucleated precipitate crystals in modern shallow brine ponds (Benison and Bowen, 2013 and Warren, 2016).

The inner zonation in the halite crystals indicates growth in shallow subaqueous conditions; such zonation is most likely attributed to the rapid change in growth rate (Goodall et al., 2000). Chevron and cubic halite crystals (Fig. 4D, E and Fig. 7) indicate the bottom crystallization, low rate of precipitation and static conditions for the pond solution (Warren, 2006; Schubert et al., 2009; Taher et al., 2014; Wang and Lowenstein, 2017 and Ercan, et al., 2019). Chipley and Kyser (1994) revealed that the chevron halite texture is ambiguously distinctive for growth at the surface. El-Shafeiy (2007) revealed that the formation of halite mound (Fig. 4F) could be a result of rapid nucleation of halite crystals or encrusting non-evaporitic materials such as plant roots and wood pieces that present in the end of the crystallizer margin, or as a result of a residue from the pre-existing halite crust of the former season. The existence of irregular subhedral to distorted platy halite crystals (Fig. 6B, C) denotes the dissolution of the halite crystals in the studied crystallization pond 1 and indicates a variation in solution concentration and salinities with the preservation of dark fluid inclusions (Filippi et al., 2011 and Gracia-Veigas et al., 2011). The irregular subhedral to platy halite crystals are most likely formed in shallow parts of the pond as a result of adding and withdrawing of solution from the pond (e.g., Levy et al., 2018). Shearman (1970) revealed that the repeated phases of flooding and desiccation cause the halite crusts to develop the characteristic irregular subhedral to distorted platy halite crystal textures. Pink halite bands were recognized in crystallization pond 1 (Fig. 4A, B). Red and pink color in halite bands and brine solution is most likely attributed to the entrapment of red halophilic bacteria (Dunaliella salina) and microorganisms in the halite crystals (Schubert et al., 2009). Such microorganisms are characterized by their efficiency to save an intracellular sodium chloride concentration lower than the extracellular one (Castanier et al., 1999 and Weinisch et al., 2018). This can be ascribed to the bacterial metabolism that is relying on the ionic pumps which are governed by the pigment activity. This results in raising the total salinity in the proximity of cells and colonies growth, local saturation and as well as supersaturation, if the solution is extremely concentrated. Prescott et al. (1993) attributed the pink or reddish color to be resulted from the existence of patches bacteriorhodopsin and retinal-based pigments in the cell membrane and as patches (purple membrane). These pigments are partially authentic for the coloration of halite depositing brines in saltworks. Prescott et al. (op. cit) added that they are only synthesized under low oxygen existence, which is the case of El-Bardawil Lake crystallization ponds. Castanier et al. (1999) revealed that the halite hopper structures (Fig. 4D) are always formed on active parts of the bacterial colonies, whereas the shape of the external edges of the halite crystals is related to the volumes and shapes of the growing colonies.

Halite crystals that are precipitated in summer as rafts and plates are transported in suspension by aroused supersaturated brine solutions out of the channels and creeks during pumping processes. Later on, these crystals become the nuclei of further halite precipitation forming halolites or halite ooids (Fig. 6B and Fig. 7C, D). The well-rounded shape of these halolites is most probably owed to the wind rolling action which is very common in the study area. Many authors considered that the halolites are produced from the conjugated growth of halite crystals and winding processes in supersaturated stirred saline solutions (e.g., Sonnenfeld and Perthuisot, 1989 and Perthuisot et al., 1993). Similar halolites were recorded by Tekin et al. (2007) from the Tuz Golu (Turkey). They are represented by nucleus (coarse-grained halite) surrounded by cortex of concentric halite lamina with a radial fabric and inner to outer zonation. Each zone refers to different morphological and mineralogical features. Castanier et al. (1999) described spheroids or similar halite bodies in Lake Assal, Republic of Djibouti and solar saltworks in Berre (France) as bacterial biocrystalline build-ups, which are very distinctive for the precocious stages of halite formation in brine solutions attaining saturation, oxygenation and fairly affluent in organic matter. Castanier et al. (op.cit) confirmed that the halophilic bacterial colonies play an essential role in the generation of the halolites through the metabolism process that maintains local saturation. It is highly accepted that only little groups of microbes can live in high salt concentrations in brines. These are Cyanobacteriaceae like Phormidium sp. (Thomas and Geisler, 1982), Halobacteriaceae (Larsen, 1984) and Ectothiorhospira (Imhoff et al., 1989). Additionally, Perthuisot et al. (1990) depicted nanoscopic semispherical bodies within carbonate bacterial strata (huntite) in Sabkhat El-Melah (Tunisia), which are colonies or clusters of carbonated bacteria where halite crystals formed as a type of skeletal mineral adapted to each colony size. Nevertheless, in El-Bardawil Lake crystallization ponds, the halolites could be formed due to agitated conditions during pumping operations combined with biological factors that have a significant influence on the complexity of the cortex.

In the present study, the fluid inclusions are recorded with all the recognized halite textures (Figs. 6 and 7). They act as sealed micro-chambers and preserved their saline content against surroundings external changes as long as they still closed, thus there is no change contamination of their content (e.g., Schubert et al., 2009). Fluid inclusions are classified into primary and secondary types (Benison and Bowen, 2013). The primary inclusions are formed during crystal growth, whereas the secondary ones are formed after the growth of the host crystal (Blamey and Brand, 2019). Two-phased fluid inclusions (gas and liquid) are very rare. The presence of the fluid inclusions was greatly changeable, relying on the biomass type added to primary solution (Schubert et al., 2009).

4.2 Environmental impacts

El-Bardawil Lake belongs to the dry lands of the southern Mediterranean coastal zone with a low winter rainfall of about 200 mm/year (Khalil and Shaltout, 2006) and evaporation rate of about 2000 mm/year (Levy, 1980). The increase in salinity is owed to the absence of the outflow from the lake except for the withdrawal implemented by the saltworks companies. The main factor causing the salinity increase in water is the evaporation through the total surface area of the lake. This directly results in raising the concentration of soluble salts and hence increases the salinity. The water surface depends on the variation of water levels which accordingly affects the salinity (Warren, 2016).

The estimated annual volume of water lost by evaporation from the El-Bardawil Lake can be calculated using the formula:

V1 = (E*A)/1000….………… (1)

Where: V1 is the annual volume of water lost by evaporation (million cubic meters/year), E is the evaporation rate by mm/year and A is the total area of El-Bardawil Lake (629 km²; Embabi and Moawad, 2014). Using the above equation, substituting the evaporation rate (E) by 2000 mm/year, the annual volume of water lost by evaporation from El-Bardawil Lake is about 1258 x 10⁶ m³/year.

The estimated annual volume of rainfall water to El-Bardawil Lake can be calculated using the formula as follows:

V2 = (F*A)/1000….………… (2)

Where: V2 is the annual volume of rainfall (million cubic meters/year), F is the rainfall rate by mm/year and A is the total area of El-Bardawil Lake (629 km²). Using the above equation, substituting the rainfall rate by 200 mm/year, the annual volume of waterfalls rains to El-Bardawil Lake is about 125.8 x 10⁶ m³/year.

The estimated annual volume of seawater makeups to El-Bardawil Lake can be calculated using the formula as:

V3 = V1-V2….………… (3)

Where: V1 is the annual volume of water lost by evaporation (million cubic meters/ year) and V2 is the annual volume of rainfall (million cubic meters/year). Using the above equation, the total seawater should be entering the lake to maintain its level in is about 1132 x 10⁶ m³/year.

The estimated annual total dissolved solids enter from the Sea to El-Bardawil Lake can be calculated using the formula:

T1 = V3* T2/1000….………… (4)

Where: T1 is the total dissolved solids enter the lake in ton per year, T2 is the Mediterranean seawater total dissolved solids (kilograms per cubic meter) which is about 38 kg/m³ and V3 is the annual volume of seawater makeups the lake (million cubic meters/year). Using the above equation, the total dissolved solids enters the lake from the seawater is about 43 x 10⁶ ton /year. Accordingly, El-Bardawil lake acts as nature reservoir for marine salts with high potentiality for extraction and crystallization of high pure halite mineral which can be acted as raw material in numerous industries (food, pharmaceuticals, glass-making, waste and water treatment and textiles).

The extraction of pure halite from El-Bardawil Lake demands three stages of ponds. These are the "concentration ponds" to precipitate the uneconomic minerals (calcite and gypsum) and to prepare the suitable brine to feed the next stage, which is called as "halite crystallization ponds", in addition to the third stage "storage ponds", which receives the residual bittern solution after crystallization of halite salt. The fieldwork reveals that the halite crystallization inside the ponds shows various textures (e.g., rafts, cumulates, hopper, bottom crusts, cubic, chevron and mounds) demonstrating variable precipitation rates. In addition, the halophilic bacteria pigment the brine with pink color. The petrographic analysis manifests that the halite is formed as clusters of large euhedral cubic crystals indicating crystallization at the bottom of the ponds, steady circumstances of the pond solutions, slow rate of evaporation and a bit supersaturated bittern solution. Chevron and irregular subhedral to distorted platy textures with abundant primary fluid inclusions are also observed denoting precipitation in the shallow zones of the ponds. Rounded to subrounded halite ooids or halolites were recorded in high saline crystallization ponds as a result of the wind rolling action. The partial to complete dissolution of the halite crystals designates a significant change in the concentration of the solutions. The economic importance of the saltworks in El-Bardawil Lake lies in their great potential for crystallizing and extracting the pure halite mineral, which is used in many important industries and for several purposes. Moreover, these saltworks play a conspicuous role in stabilizing the water salinity and hence preserving the lake ecosystem.

Author Contribution

Ahmed Waheed1,2, Mohamed S. Abu El Ghar1 and Ahmed W. Hussein11 Geology Department, Faculty of Science, Fayoum University, Fayoum, Egypt2 Egyptian Salts & Minerals Company (EMISAL)

Acknowledgements

The authors would like to acknowledge and give thanks and gratitude to all workers in Agret Soliman Saltworks, especially Mr. Sallem Atallah for supporting during the field study. Deepest gratitude is due to Prof. Amany G. Taher (Professors of Sedimentology, Geology Department, Cairo University) for her kind and continuous help and guidance.

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Extraction of Halite from El-Bardawil Lake, North Sinai, Egypt: Sedimentological attributes and environmental impacts

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Abstract

Figures

1. Introduction and geologic setting

2. Methods

3. Results: Agret Soliman Saltworks Production Systems

3.1. First ponds group (concentration ponds)

3.2. Second ponds group (crystallization ponds)

3.2.1 Fieldwork

3.2.2 Petrographic analysis

3.3. Third ponds group (storage ponds)

4. Discussion

4.1 Sedimentological attributes

4.2 Environmental impacts

5. Conclusions

Declarations

Author Contribution

Acknowledgements

References

Additional Declarations

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