Geochemical, Mineralogical and Isotopic Fracturing during the Progressive Evaporation of Chott Djerid Brine (Southern Tunisia)

Djerid Chott, in southwestern Tunisia, is one of the biggest salt lakes in the world. This work follows the specific precipitation of evaporites through progressive evaporation of Chott Djerid brines using geochemical, isotopic and mineralogical approaches, to explain the intricacy of the working of saline frameworks controlled basically by climatic driving and the underlying geochemical structure acquired from the geographical system. Toward the finish of every evaporation step, solid and liquid samples went through analyses. Djerid brine is remarkably saline (427.7 g/l) and it is supersaturated contrasted with halite. The outcomes indicated that the Chott Djerid brines shaped fundamentally Cl--Na+-SO4- type geochemistry. Added to halite and gypsum as significant minerals, other minor minerals including carnallite, hexahydrite and sylvite were recognized in various phases of progressive evaporation of Djerid brine. Regardless of their low costs, significant minerals are of geo-economic interest because of their high amounts of production. Then, minor valuable minerals secure their geo-economic interest from their excessive costs. In this work, we find the window of precipitation of these valuable minerals' at the evaporation paces of 80% and 100%.

Screening of halotolerant microfungi isolated from hypersaline soils of Algerian Sahara for production of hydrolytic enzymes

The Algerian Sahara contains numerous hypersaline ecosystems including salt lakes in which the fungal diversity has not been characterized. The abundance and diversity of soil microofungi in three salt lakes in southeastern Algeria was investigated together with their profiles of hydrolytic enzyme. Fungal population size and relative abundance were determined in about 75 soil samples by plate count. From 69 fungal isolates, 46.38% were Aspergillus, 20.29% were Penicillium and 11.59% belonging to Cladosporium genus. The sixty-nine isolates have been studied at different constant temperatures and salinities. All fungal isolates are halotolerant or halophiles with the ability to grow at 50°C. The screening for extracellular halophilic enzymes at 40°C showed that 69.57% of the isolates were able to produce at least two types of the screened enzymes. Protease was the most abundant enzyme detected in 60.87% of the total isolates. The results obtained of all the growth tests indicate the adaptability of fungal isolates tested to the extreme conditions and their possible utilisation as producers of halophilic-active hydrolytic enzymes.

Salsolaius gen. nov. a new genus of Apalochrini (Coleoptera, Melyridae, Malachiinae) from the salt Lake Way of Western Australia

Apalochrini comprises nearly half of the genera of Australian Melyridae, which are all recognized by male specific characters, and are commonly found on grasses, flowers and riverside or seashore rocks. Here we describe a new genus Salsolaius gen. nov. from Lake Way of Western Australia, representing the first known genus of Australian Melyridae inhabitating in salt lakes. The new genus can be easily distinguished by asymmetrically biserrate antennae and exposed apical abdomen from above in both male and female, the former characters is firstly found in Melyridae. Consequently, Salsolaius biserratus sp. nov. was described as the type species of this genus. An updated key to genera of Australian Apalochrini is provided.

Research and Engineering Application of Salt Erosion Resistance of Magnesium Oxychloride Cement Concrete

Aiming at the problem that ordinary cement concrete is subjected to damage in heavy saline soil areas in China, a new type of magnesium oxychloride cement concrete is prepared by using the gelling properties of magnesium oxychloride cement in this study, and the erosion resistance of the synthesized magnesium oxychloride cement concrete in concentrated brine of salt lakes is studied through the full immersion test. The effects of concentrated brine of salt lakes on the macroscopic, microscopic morphology, phase composition and mechanical properties of magnesium oxychloride cement concrete are investigated by means of macro-morphology, erosion depth, SEM, XRD and strength changes. The salt erosion resistance mechanism of magnesium oxychloride cement concrete is revealed. The results demonstrate that under the environment of full immersion in concentrated brine of salt lakes, there is no macroscopic phenomenon of concrete damage due to salt crystallization, and the main phase composition is basically unchanged. The microscopic morphology mostly changes from needle-rod-like to gel-like. Due to the formation of a new 5·1·8 phase on the surface layer and the increase in compactness, its compressive strength has a gradual increase trend. Based on the engineering application of magnesium oxychloride cement concrete, it is further confirmed that magnesium oxychloride cement concrete has excellent salt erosion resistance and good weather resistance, which provides theoretical support for future popularization and application.

Distribution characteristics, source identification, and risk assessment of heavy metals in surface sediments of the salt lakes in the Ordos Plateau, China

Salt lakes have a significant effect on the regional climate, environment, and ecology in semi-arid regions characterized by lower rainfall and high evaporation. However, under the stresses of global change and human disturbance, anthropogenic pollution is the main factor threatening the lake ecological environment. Surface sediment samples collected from four salt lakes in the Ordos Plateau were used to investigate the salinity, concentration, pollution status, potential sources of heavy metals, and influencing factors. The surface sediments of Beida Pond and Gouchi Pond were weakly alkaline (pH < 9) owing to Na2SO4, whereas those of Chaigannaoer and Hongjiannao were strongly alkaline (pH > 9) owing to Na2CO3. The concentration range of Cr, Ni, Cu, Zn, As, Cd, and Pb in the sediment samples collected from the salt lake in the Ordos followed the order of Cr > Zn > Ni > Pb > Cu > As > Cd. The Cr values were higher in Chagannaoer and Hongjiannao, but the Ni, Cu, and Zn values were higher in Beida Pond and Gouchi Pond. The geoaccumulation index (Igeo) and enrichment factor (EF) consistently indicated that Cr posed the greatest potential ecological risk and that Ni, Cu, and Zn pollution was more severe in Beida Pond and Gouchi Pond than in Chagannaoer or Hongjiannao. However, Er and RI indicated these heavy metals were a low risk to the environment. Risk assessment code (RAC) revealed that Pb and Cr exhibited no mobility and had low potential bioavailability risk, although Zn, Ni, and As were categorized as medium risk. Cu had the highest mobility and high risk. Principal component analysis for Beida Pond and Gouchi Pond revealed that the source of Ni, Cu, Zn, Cd, and Pb might be associated with water - soluble elements in aqueous migration, and the source of Cr, Pb, and As might be lithospheric minerals carried by dust storms. Ni, Cu, Zn, Cd, Cr, and Pb in Chagannaoer and Hongjiannao may be derived from surface runoff, and chemicals from these sources may eventually accumulate in sediments. Pearson’s correlation analysis indicated that pH was the main environmental factor controlling the distribution of heavy metals in Chagannaoer and Hongjiannao.

Polyacrylonitrile/Crown Ether Composite Nanofibres With High Efficiency for Adsorbing Li(I): Experiments and Theoretical Calculations

Lithium, as the lightest alkali metal, is widely used in military and new energy applications. With the rapid growth in demand for lithium resources, it has become necessary to improve the effectiveness of extraction thereof. By using chemical grafting and electrospinning techniques, nanofibres containing crown ether were developed for adsorbing Li(I) from the brine in salt lakes, so as to selectively adsorb Li(I) on the premise of retaining specific vacancies of epoxy groups in crown ether. In lithium-containing solution, the adsorbing materials can reach adsorption equilibrium within three hours, and the maximum adsorption capacity is 4.8 mg g−1. The adsorption mechanisms of the adsorbing materials for Li(I) were revealed by combining Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) with density functional theory (DFT) calculation. The results indicated that in crown ether, O in epoxy groups was coordinated with Li(I) to form Li–O and four O atoms in the epoxy groups were used as electron donors. After coordination, two O atoms protruded from the plane and formed a tetrahedral structure with Li(I), realising the specific capture of Li(I). By desorbing fibres that adsorbed Li(I) with 0.5-M HCl, the adsorption capacity only decreased by 10.4% after five cycles, proving ability to regenerate such materials. The nanofibres containing crown ether synthesised by chemical grafting and electrospinning have the potential to be used in extracting lithium resources from the brine in salt lakes.