190 • Marine Minerals: Exploring Our New Ocean Frontier 



Conducting minerals may be separated from 

 nonconductors using electrostatic separation. Only 

 a few minerals are concentrated using this method, 

 but electrostatic separation is used very successfully 

 to separate heavy mineral beach sands, such as ru- 

 tile and ilmenite from zircon and monazite.'* Fig- 

 ure 5-15 illustrates how conducting and noncon- 

 ducting minerals and "middlings" are split from 

 each other using an electro-dynamic separator. 

 During processing, the feed particles acquire an 

 electrical charge from an ionizing electrode. Con- 

 ducting minerals lose their charge to the grounded 

 rotor and are thrown from the rotor's surface. A 

 non-ionizing electrode is then used to attract con- 

 ducting minerals further away from the rotor. Non- 

 conductors do not lose their charge as rapidly and 

 so adhere to the grounded rotor until they do lose 

 their charge or are brushed off. Middlings may be 

 run through the electrostatic separator again. '^ 

 Electrostatic separation is usually combined with 

 gravity and magnetic separation methods when sep- 

 arating minerals from each other. 



Many of these technologies require adjustments, 

 depending in part on the volume and grade of ore 

 passing through the plant and on the ratio of in- 

 put ore to output concentrate or final product. The 

 ratios of valuable mineral to ore mined are shown 

 in table 5-3 for some typical heavy minerals. The 

 amount of primary concentrate produced by jigs 

 on a dredge mining 30,000 cubic yards of gold ore 

 per day would be on the order of a few tons (de- 

 pending on the other heavy minerals present); ini- 

 tial processing of 30,000 cubic yards per day of 

 ilmenite ore would yield a few hundred tons of pri- 

 mary concentrate. 



The amount of machinery, space, and power 

 needed for producing a final concentrate or prod- 

 uct varies widely for different minerals. Final sep- 

 aration and recovery of ilmenite, rutile, zircon, and 



'Ibid. 



nhid. 



Table 5-3.— Ratio of Valuable Mineral to Ore 



In ore mined In primary concentrate 



Diamonds 1:5,000,000 1:1,000 



Gold, platinum. .. 1:2,000,000 1:1,000 



Tin 1:1,000 1:100 



I lmenite, etc 1:100 1^10 



SOURCE: Office of Technology Assessment, 1987. 



monazite require elaborate plants that occupy large 

 spaces and consume large amounts of energy. 

 These heavy minerals are first dried in long kilns, 

 then passed through batteries of magnetic and elec- 

 trostatic separators. Experience using these tech- 

 nologies is mostly on land, and there do not ap- 

 pear to be any economic advantages to undertaking 

 final separation and recovery of these minerals off- 

 shore. Conversely, technologies for final recovery 

 of diamonds, gold, and tin occupy little space and 

 consume litde power. Some techniques (e.g., shak- 

 ing tables) require flat, level platforms. Final re- 

 covery of gold by amalgamation with mercury can 

 be easily done at sea if the mercury is safely con- 

 tained. Final separation of diamonds from concen- 

 trates is done using X-rays. 



Processing Unconsolidated or Semi- 

 Consolidated Deposits of Chemically 

 Active Minerals 



Examples of unconsolidated or semi-consolidated 

 deposits of chemically active minerals include min- 

 erals found in such deposits as the Red Sea brines 

 and sulfide-bearing sediments on the Outer Con- 

 tinental Shelf. In general, the minerals of economic 

 interest in ore deposits of this type are complex sul- 

 fides of base metals such as copper and zinc, and 

 minor quantities of precious metals (mainly silver). 



This type of mineral is generally concentrated 

 on land using flotation technology (figure 5-16). 

 Flotation concentration is based on the surface 

 chemistry of mineral particles in solution. Meth- 

 ods vary, but all employ chemical reagents that in- 

 teract with finely crushed sulfide particles to make 

 them selectively hydrophobic. The solution is aer- 

 ated, and the hydrophobic minerals adhere to the 

 air bubbles and float to the surface (other mineral 

 particles sink to the bottom). A froth containing the 

 floated minerals is formed at the surface of the so- 

 lution and is drawn off.'® Flotation concentrates are 

 collected on filters and dried prior to further pyro- 

 metallurgical processing (e.g., smelting) to sepa- 

 rate individual metals. 



Experimental flotation of metalliferous muds at 

 a pilot-scale plant in the Red Sea is the only ex- 

 perience using this process offshore. Since wind. 



'Ibid. 



