MAGNESIUM EXTRACTED FROM SEA WATER

New Zealand Herald, Volume 81, Issue 25030, 21 October 1944, Page 10

MAGNESIUM EXTRACTED FROM SEA WATER

AN IMPORTANT WARTIME INDUSTRY

By PROFESSOR A. M. LOW, Britain during the present war discovered that, if the sea lapping her boundaries on every side was no longer in itself an impregnable bulwark against invasion, it contains a material vital to her defence. It is from the sea that Britain has teen obtaining the magnesium which is so important a part in those strong, but light, alloys which are built into aircraft. The R.A.E. ones a great deal magnesium extracted from the sea. To the ordinary man sea-water is simply "salt" water, but there are many chemicals dissolved in sea-water besides sodium chloride. One substance very valuable to Britain during wartime is magnesium chloride, which is present in sea-water to the extent of one part in eight hundred. This may seem a trifling amount, but the sea is vast, and even one cubic mile of seawater contains many tons of metal. With Germanv possessing most of the in the world from which magnesium is obtained, Britain decided to turn to the sea, and in greatest secrecy built two plants for magnesium extraction— these "factories" handled over 11 million gallons daily. The chemical process for turning 'the magnesium chloride dissolved in sea-water into the white_ metal so largely used _ for munitions is fairly simple. Magnesium is precipitated _ from the solution by adding lime which forms an insoluble hvdrox-

British Scientist and Inventor. ide. This powder is segregated by filters, and the metal is developed from the powder in the usual way. Although the chemical processes are simple, the engineering difficulties are considerable, because of the great scale on which the operations must be carried out —the war-time erection of these plants within months was a remarkable feat of chemical engineering. Various considerations had to be taken into account when choosing the site for operations. The sea's magnesium content varies, and after choosing a locality where the content was greatest, it was nccessarv to ensure that currents and tides would carry off the used water some distance from the intake. The pumped-in water, filtered for the removal of the finest insoluble particles, passes out of the filters to further huge tanks, where the powdered lime is added to assist precipitation. When the precipitated hydroxide is settled, the water is drained off, and the precipitate scraped up and dried in rotarv kilns ready for conversion to magnesium.

When demand for aircraft falls the magnesium surplus will undoubtedly be used for making light alloys for hundreds of commercial and domestic purposes. Shining metal sheets will probably provide bright kitchen utensils. bathroom fittings, and toys, and will give lightness with' strength t.o motor-car eoaehwork The exact amount of magnesium at present taken from the sen cannot be

divulged, but, measured in tons, it runs into six figures yearly. Magnesium isn't the onlv valuable chemical dissolved in sea-water. In the future, greater use will be made of the sea as a source of bromine, potassium and phosphorus. Bromine, present to the extent of one pound to every four thousand gallons, has already been extensively obtained from the sea in the United States, for the manufacture of "anti-knock" fuel whereof the key substance is a lead compound dissolved in ethylene bromide. Extraction calls for the most exact chemical measurements, and it is remarkable that these have been maintained in a plant dealing with sixty million gallons of sea-water daily. Potash extraction from the sea is possible also. It is estimated that there are two million tons in the Dead Sea alone, and it is easily obtained bv evaporation. Copper, arsenic, iodine and gold are some of the other elements present in sea-water in minute quantities. lodine used to be extracted from seaweed, but other sources now make this uneconomical.

Although gold is present only to the extent of one part in one thousand millions, the ocean's gold greatly exceeds that taken from the earth during man's whole history. At present, there is no practical process discovered for its extraction, though numbers have been tried. Tt is possible that electrical methods mav succeed, and that a ship of the future towing a gold-extracting device will litera'lv be able to "pay its way." Tlte onlv diffieiiHv seems to he that once this is accomplished, gold would lose, all value as a monetary svmhol —but perhaps this would eaiisp no regrets among (he scientists of the future.