Technology
Process makes pure metals from ocean nodules Manganese, nickel, copper, and cobalt in 95% yields are made in pilot plant using continuous flow hydrometallurgical process Sheets of pure manganese, nickel, copper, and cobalt are being prepared from deep ocean floor manganese nodules by a chemical hydrometallurgical process now undergoing pilotplant testing at Deepsea Ventures, Inc., Gloucester Point, Va. Developed over several years by a team led by Deepsea's research director, Dr. Paul H. Cardwell, the continuous flow process yields 95% recoveries of the four metals and offers favorable economics, the Virginia firm says. Deepsea Ventures' progress in nodule-processing technology is a step toward the Tenneco subsidiary's goal of full production of metals from nodules by 1975-76. Last July and August the company successfully tested in 2500 feet of water off Florida its hydraulic dredge system for collecting nodules from the ocean floor (C&EN, Aug. 31, 1970, page 13). Deepsea has already spent about $20 million on exploration and development, and anticipates outlays of $200 million to achieve production, according to its president, John E. Flipse. Competition. The vast commercial potential of the nodules (C&EN, July 6, 1970, page 15) has also attracted some 18 other organizations, commercial and governmental, in five countries to engage actively in development of nodule recovery and process technology, notes Dr. Vincent McKelvey, senior research geologist, U.S. Geological Survey. Deepsea appears to hold an overall lead over other companies, despite increasing competition. Deepsea's hydrometallurgical process was chosen after investigation of more than 100 different processes. The nodules are chemically reactive and contain more than 30 metals in high enough concentration to interfere with process separations. Nodules used in the pilot plant were dredged 56
C&EN MAY 10, 1971
from a prime candidate mine site at 18,000 foot depths in the Pacific by Deepsea, and contain 26 to 27% manganese, 1.3% nickel, 1.0% copper, and 0.2% cobalt. Hydrochlorination. The pilot plant can process 1 dry ton a day of nodules. In the process, the nodules are first crushed and dried. They are then reacted with hydrogen chloride gas at temperatures above 120° C. in a multihearth furnace, reducing manganese dioxide from Mn4+ to Mn 2 +, and also converting the other metals to their water-soluble chlorides. Dr. Cardwell terms this reduction a novel commercial use of an old textbook reaction of HC1. He also notes that HC1 for the reduction could be obtained readily as a by-product from chlorinated hydrocarbon production, and the chlorine produced could be returned to chemical industry. The soluble chlorides of manganese, nickel, copper, cobalt, and other metals are leached out with water and filtered off. The solid residue contains
inert silicates, sulfates, and oxides, and could be used for landfill. Ion exchange. The heart of Deepsea's metal extraction lies in the next step. The leach liquor undergoes a liquid ion exchange separation process to produce four streams. Aqueous solutions of first copper, then nickel, and then cobalt are separated out, leaving a fourth stream containing manganese and other metal chlorides. The reagent for the ion exchange separation process is kerosine containing one or more proprietary ion-selective organic compounds. The three metals are extracted in succession by countercurrent flow from the aqueous leach liquor into the organic phase. Deepsea will not reveal the nature of the reagent. It is possible that the reagent is a complexing or chelating agent which selectively complexes first copper, then nickel, and then cobalt through variation in the conditions—such as pH. However, the reagent might instead consist of two or three different complexing agents,
Hydrometallurgical process prepares pure metals from nodules r*CI Crushing, drying
Nodules-
Filtration
Leaching
t
Solid residue silicates and iron oxides)
H O
HCI Aqueous phase
Organic phase (Copper) Liquid ion exchange separation
(Nickel)
Copper Electrolytic cells
Stripping
(Cobalt)
Nickel Cobalt
Ion-selective organic compounds in kerosine
• Manganese
Crystallization
T
Other metal Chlorides
Metal
each selective for one or two ions. Dr. Cardwell believes that this is the first successful use of liquid ion exchange separation for nickel and cobalt ions. The three metal ions are then stripped from the organic phase back into aqueous solutions and the kerosine solution recycled to pick up more metal ions. The three aqueous metal solutions are directed to electrolytic cells for deposition of the pure metals. For efficiency, electrolysis is not carried to the end, and solutions containing low concentrations of the metals are recycled to strip more metal ions from the organic phase. The stream containing manganese and other metals after separation of copper, nickel, and cobalt is concentrated and manganese chloride crystallized out. The other metal chlorides can then be recovered from the mother liquor, Dr. Cardwell says. (Precipitation of insoluble sulfides would be a possible path here.) Of particular interest are silver and molybdenum, and Deepsea Ventures is examining the economics of recovering these two metals and others. Meanwhile, the crystallized manganese chloride is dried and converted to metallic manganese by a metal reduction process which involves heating manganese chloride with another metal in a furnace. The chloride of the other metal is formed. Deepsea will not identify the metal used. (Sodium, for example, is used in a similar way to prepare pure titanium and zirconium from their chlorides.) Alternatives. Deepsea has applied for U.S. and foreign patents on a number of steps in the process. However, the present pilot-plant process is not the last word on Deepsea's technology. The final commercial process chosen will depend on plant location, availability of reagents, and on which metals are to be recovered (and hence on market conditions). Other laboratories are developing alternative processes. For example, Dr. D. W. Furstenau, University of California, Berkeley, is working on methods of differential leaching of nickel, copper, and cobalt from nodules without dissolving manganese. Current Deepsea plans call for scaling up to a 75 ton-per-day pilot plant, and then to a 750 ton-per-day pilot plant, before building a full-scale plant processing 3000 tons a day. The firm bases its calculations on processing of 1 million tons of nodules per year, supplying 12,600 tons of nickel, 10,000 tons of copper, 2,400 tons of cobalt, and 260,000 tons of manganese. However, Mr. Flipse says, this would still be only a small percentage of the world market for these metals.
England plans first freeze desalting Flash evaporation and distillation processes predominate in the numerous sea water desalination plants that have been built around the world. But various other processes that may in time prove more economical are under development—membrane separation and hydrate formation, for example. One of these developmental processes, freezing, will now be used in England in the first large-scale plant based on the technique. The plant, which will likely be on stream in 1973, will t u r n out 1 million gallons of purified water per day and will augment the water supplies of the east coast town of Ipswich, Suffolk. Simon-Carves, Ltd., of Stockport, England, will build the plant for the nation's Water Resources Board and the U.K. Atomic Energy Authority (UKAEA). The plant will incorporate technology for secondary-refrigerant freezing developed jointly over a period of five years by Simon-Carves and UKAEA at a total cost of more than $2 million. Starting with about 2 million gallons of estuary water at high tide (in effect sea water with a salt content of about 3.5%), the plant will produce water with a salinity of about 100 p.p.m. and a content of n-butane—the refrigerant used—of 0.1 p.p.m., according to project coordinator William R. Burton of UKAEA's Risley facility. Butane. Butane will be used as the evaporating liquid to freeze water from the brine, Dr. Burton explains. n-Butane is a gas at room temperature and atmospheric pressure. Concentration of butane in product water from the freeze desalination plant is well below levels considered toxic by U.K. government toxicologists, Dr. Burton says. In the U.S., work on freezing processes has slowed down. The Office of Saline Water has carried out pilot plant studies of vacuum freezing and secondary-refrigerant processes, but at present only bench-scale studies of some new crystallizer and wash colu m n developments are being carried out. These developments may reach pilot plant operation in a year. Basically, the freeze desalination process is aimed at industrially developed areas in the world's temperate zones, according to Paul Richards, director of Simon-Carves' power plant division. The Ipswich plant is a prototype from which data will be collected for building commercially viable plants, he emphasizes. Such plants would probably have a capacity of 5 or more million gallons per day, Mr. Richards adds. Simon Engineer-
ing, Simon-Carves' parent company, currently operates a 10,000 gallon-perday pilot plant at Cheadle, near Stockport, as part of its nine-year R&D program in freeze desalination. Brine. Operating a plant in temperate zones derives from the temperature requirement of the plant's brine feed, which should be at 35° to 70° F. The freeze process gets less attractive as the inlet temperature approaches 90° F., Dr. Burton says. At about 50° F., the average temperature of U.K. coastal waters, fuel costs are only one third to one half those for other desalination processes, such as flash evaporation and vertical tube evaporation, he notes. Higher temperatures reduce the fuel cost advantage, however. Another advantage of freeze desalination is that in plants larger than about 3 million gallons per day the process achieves economies in scale. Also, the process can operate up to the 4% salt content encountered in the oceans. Economics of freezing improve at lower concentrations of salts, compared to distillation. But at very low salt concentrations (about 0.1%) membrane processes, such as reverse osmosis and electrodialysis, begin to compete, he says. In the Ipswich plant's operation, 30 metric tons of n-butane are used to freeze water from the brine feed. Butane at 24° F. bubbles through the sea water, forming ice as it evaporates. n-Butane's vapor pressure of about 1 atm. at water's freezing point (32° F.) obviates the need for pressure
Simon Engineering operates, this 10,000 gallon-per-day pilot plant at Stockport MAY 10, 1971 C&EN 57
