Abstract
It is feared that heavy metals contained in sea water become obstacles to the manufacturing of salt, and besides those contained in common salt are no good for the reasons of food sanitation. There, forethe author conducted a study as to how to remove copper, zinc and lead from sea water and salt by means of filtration and coprecipitation, and obtained to following results:
(1) Judging from the results obtained by measuring the solubilities of these heavy metals in sea water, it is difficult to remove them by filtration. However, when common salt is made from the sea water saturated by these metals, the content of these impurities is supposed to amount to less than 10 pp. The salt containing a great amount of these metals can be refined to the extent of less than 15 ppm by disolution, filtration and recrystalization at pH 9.
(2) Those metals contained in sea water can be removed by coprecipitating them at the pH of over 7 with the floc of ferric hydroxide, aluminium hydroxide or magnesium hydroxide. To any concentration of heavy metals in sea water, the treatment with the floc amounting to less than 12mg/l of ferric ion or aluminium ion was sufficient for coprecipitation. As to the treatment with magnesium hydroxide, addition of 5 ml/l sodium hydroxide solution (1 N) was sufficient for the coprecipitation. In all cases, the velocity of coprecipitation was quick, and the effects of temperature were insignificant.
(3) The coprecipitation method with ferric hydroside, aluminium hydroxide or magnesium hydroxide was also effective for the removal of copper, zinc and lead in the common salt solution of high concentration.
