Desalination Research Paper

Desalination is a common solution to supply fresh water in many regions of the world where face with water scarcity [1]. Water scarcity is one of the most important problems in many parts of Iran and desalination of saline water (sea and brackish water) is the monopolized solution to provide water for drinking, agricultural and industrial purposes [2]. The majority of water resource does not satisfy to the desirable levels of chemical properties, such as hardness, nitrate contamination, heavy metals, etc [3]. Due to the high solubility of magnesium ion in water, it is the third-most-abundant element and second-most-abundant cation dissolved in seawater [4], as well as, magnesium is one of the dominant elements in brackish water and groundwater

However, discharge of the brine produced by the RO desalination process results in many environmental adverse effects, due to the high concentrations of metals and salts. Recovery and removal of elements from RO brine would decrease environmental benefits and have economic gains in the production of valuable metals [8]. Le Dirach et al. [9] are listed magnesium as element that potentially economically for extraction.

3) Extraction of lithium from salt lake brine and seawater is one of the main sources of lithium production. Lithium has similar ionic size as magnesium; making is difficult to separate lithium from magnesium. Magnesium ions prohibit lithium chloride formation, which is the first step in production of lithium carbonate desired product. Removal of magnesium decreases the Mg/Li ratio in brine and facilitates lithium extraction and makes it economical

In precipitation process, large volumes of sludge are generated which can present dewatering and disposal problems [11], as well as re-carbonation of the softened water are needed [3]. Ion-exchange resin have been widely used to remove calcium and magnesium ions due to their many advantages, such as high capacity and fast kinetics [12-14]. However, ion-exchange resins must be regenerated by chemical reagents when they are saturated and the regeneration can cause serious secondary pollution. In large scale, application of resin is expensive [11]. In recent years, various method such as nanofiltration [15, 16], capacitive deionization [17], electrodialysis [18], electrochemical treatment [19] and, adsorption [20, 21] have been widely studied for ions removal from aqueous solution, especially water softening. Several adsorbent are qualified for this purpose. Activated carbon is the most popular adsorbent which used for water softening but it cost remains its main drawback [22]. A large number of low-cost adsorbents have been utilized for ions removal [23]. Recently, natural clay minerals (e.g. bentonite) [24, 25] and zeolite [21, 26] have been widely used as adsorbents for adsorption of ionic and molecular species from various water streams. Utilization of clays has many advantages such as less environmental issues, low cost and abundance in most soils. Bentonite is one