Abstract
Removal of Mg 2+ , K + , and SO 4 -2 ions in seawater has been successfully done by precipitation in a mixing tank method. This study aims to remove the content of magnesium ions (Mg + ), potassium (K + ) and sulfate (SO 4 -2 ) in sea water with the addition of chemicals disodium phosphate (1.2 % volume), calcium chloride (2 % volume) and sodium hydroxide (2% volume). Stirring is performed at 100 rpm and the pH solution is adjusted to 9. Disodium phosphate serves to bind magnesium ions and potassium, CaCl 2 serves to bind the sulfate ion, while sodium hydroxide is used to adjust the pH of the solution mixture and also reacted with magnesium ions. In total, the removal efficiencies of Mg 2+ , K + and SO 4 -2 ions in seawater were 97%, 96%, and 92%, respectively. The precipitated solids contains component of PO 4 - (14.5%), Mg 2+ (13.8%), SO 4 -2 (28.2%), Ca 2+ (24.1%) and K + (1.9%) ions.
Highlights
The average waters of the world’s oceans contain 3.5%dissolved salts, 96.5% water and average salinity is about 35 g/kg
Six major ions make up > 99% of the salts dissolved in seawater: four cations sodium (Na+), magnesium (Mg2+), calcium (Ca2+), and potassium (K+); and two anions: chloride (Cl-) and sulphate (SO42-)
The molar concentration of magnesium in sea water is about five times higher than calcium. Both magnesium and calcium are in a delicate equilibrium where slight charge in alkalinity and carbon dioxide tension may cause precipitation (Irving, 1926)
Summary
Dissolved salts, 96.5% water and average salinity is about 35 g/kg. When salts dissolve in water they usually react with water and dissociate (break apart) into ions, positively and negatively charged atoms or groups of atoms. Six major ions make up > 99% of the salts dissolved in seawater: four cations sodium (Na+), magnesium (Mg2+), calcium (Ca2+), and potassium (K+); and two anions: chloride (Cl-) and sulphate (SO42-). The molar concentration of magnesium in sea water is about five times higher than calcium. This study developed a purification of salt through the removal of ions in sea water by precipitation method. For the second stage: 1000 ml sea water was entered in stirred tank added with Na2HPO4 solution in the range of 8-16 ml, stirred for 10 minutes added CaCl2 solution in the range of 10-30 ml; stirred for 10 minutes added with NaOH solution until the mixture reaches a pH 9 stirred until a specified time. EDAX and X-ray fluorescence (XRF) were used for component analysis in the precipitated solid product
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