Valorisation of Ca and Mg by‐products from mining and seawater desalination brines for water treatment applications

Abstract

BACKGROUNDBrines from the drainage of potash mine tailings and from seawater reverse osmosis (SWRO) desalination were previously evaluated as sources of NaCl for the chlor-alkali industry. Valorisation of NaCl as raw material is required to meet the membrane electrolysis specifications of NaCl saturation and control of interferences (Ca, Mg and sulphate). Brines concentration in NaCl was previously achieved for SWRO brines using electrodialysis (ED). In this work, valorisation of Ca and Mg by-products via selective recovery was evaluated.; RESULTSRecovery of Ca(II) and Mg(II) using chemical precipitation with Na2CO3 and NaOH was evaluated at 25 degrees C and 65 degrees C using one single reagent and mixtures of reagents. The excess of reactants needed to achieve the maximum removal efficiency ranged from 0.35 to 14 g L-1 Na2CO3 and 0.85 g L-1 NaOH. Selective concentration of SWRO brines by ED benefited the purification, as it slightly diluted the antiscalants. The increase of temperatures also benefited their removal process.; CONCLUSIONSTotal chemical analysis of Ca and Mg by-products showed the presence of mixed salts of Ca and Mg when Na2CO3 was used and more pure precipitates of Mg when NaOH was used. In both cases, small amounts of minor traces initially present in the brines were found. (c) 2014 Society of Chemical Industry.Peer ReviewedPostprint (published version

Determination of optimal conditions for magnesium recovery process from seawater desalination brine using paper sludge ash, sulfuric acid, and ethanol

“…When the ratio was 1:40, the concentration of Mg was 46 mg/L, which was close to zero compared with the initial Mg concentration of 2,340 mg/L, and the pH was 10.8. This was because the Mg ion in the brine precipitated in the form of Mg(OH) 2 [5,7,21]. Therefore, the optimum ratio of PSA to brine required for precipitating the Mg of the brine was decided to be 1:40 (g:mL; PSA:brine), and the Mg precipitation efficiency was 98%.…”

“…Many resources that are dissolved in seawater desalination brine have been the targets of extraction, such as Mg [5][6][7][8][9][10][11][12][13], Li [14][15][16], Ca [17], K [18], and Cl [19]. An evaluation of the profitability of each element recovered from seawater desalination brine via its concentration and market price implies that Mg is worth extracting from seawater desalination brine because of economic aspects, which highly depend on the purity of the final Mg product (Fig.…”

“…Many novel methods for recovering Mg from seawater desalination brine have been presented, including membrane separation [10], ion exchange [11], biocrystallization [5], and chemical processes [5][6][7]21]. Zahedi and Mohamad Ghasemi [10] recovered 97% of the Mg contained in seawater desalination brine using a bulk liquid membrane in 2.5 h. Pérez-González et al [11] used an ion-exchange resin to extract Mg from seawater desalination brine along with Ca.…”

“…However, currently commercialized methods for recovering Mg from brine or seawater are simple chemical precipitation methods that use lime or dolomite [20]. Alkali precipitants, such as sodium hydroxide (NaOH), ammonium hydroxide (NH 4 OH), or sodium carbonate (Na 2 CO 3 ), have been used in many studies [5][6][7]21]. The form of recovered Mg salts depends on the components of the precipitant, and its purity is determined either by the amount of impurities derived from the brine (such as Ca or B) or precipitant.…”

“…The form of recovered Mg salts depends on the components of the precipitant, and its purity is determined either by the amount of impurities derived from the brine (such as Ca or B) or precipitant. Casas et al [5] obtained magnesium hydroxide (Mg(OH) 2 ) by using NaOH as a precipitant, which has a purity of approximately 52%-57% and contains approximately 3%-26% calcium carbonate (CaCO 3 ) along with a small amount of K and B. Sorour et al [6] recovered Mg in the form of magnesium carbonates and magnesium phosphates using Na 2 CO 3 and Na 3 PO 4 •12H 2 O as Mg precipitants in seawater desalination brine, but large amounts of Ca was also precipitated in the process. Dong et al [7] added NH 4 OH to brine for precipitating Mg(OH) 2 with a purity of approximately 75.6%-98%.…”