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Volume 33, Number 5September/October 1982

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Silver from the Sea

Written by Glyn Ford and Jonathan Simnett

In the Red Sea three years ago, Saudi Arabia and The Sudan jointly launched an experiment that, in the Middle Ages, might have been called alchemy: the transmutation of a common, worthless substance - mud - into a rare and valuable substance: silver. In the Red Sea, however, the process depends on technology rather than magic, and is extraction rather than transmutation.

The experiment - carried out by a German mining company on behalf of the Saudi-Sudanese Red Sea Joint Commission - is one of the most exciting projects underway in the world today: undersea mining of metal-rich mud. If it succeeds, the technology involved might provide a way of tapping the mineral resources of the world's oceans. Not insignificantly, it might also point the way toward a more rational form of sharing such wealth among competing regions and countries.

What the commission is investigating are thick layers of mud - up to 30 meters (98 feet) - that have been collecting over the last 10,000 years in the deep depressions along the center of the Red Sea 90 kilometers from land (56 miles). Found beneath pools of dense, extremely hot brines-60°C (140°F)-that have formed in depressions two kilometers deep, these muds are rich in zinc and copper, smaller amounts of other metals, including gold, and — the main target-silver.

Since the 1880s, oceanographers have suspected that the Red Sea had hidden secrets. It was not until 1948, however, as the post-war boom in ocean research got underway, that the strange, high-temperature brines were found and recorded by the Swedish vessel Albatross. And it was not until about 1963 that scientists, in a burst of exploratory activity, obtained samples of the metalliferous muds.

Since then, 18 brine pools and associated mud deposits have been discovered. But from a commercial viewpoint only one of these is important: the Atlantis II Deep. The largest found so far, the Atlantis II Deep, named after the survey ship which discovered it, has a surface area of 60 square kilometers (23 square miles) and vast deposits of multi-colored muds, the consistency of soft toothpaste, containing, in the southwest basin, six percent zinc, one percent copper and 100 parts per million of silver.

The formation of these deposits came about, partially, as a result of the split in the earth's crust between Africa and Arabia - the continuation of which may eventually turn the Red Sea into a full fledged ocean; it widens at the rate of 10 kilometers (six miles) every million years. When this thin ocean crust cracked, sea water poured onto the molten rocks below and formed salt solutions rich in metallic compounds. Carried upwards by convection currents, these solutions mingled with the colder water closer to the surface, where -since solubility is temperature dependent - the salts with the metallic components were precipitated - i.e. forced out of the solution - within the muds.

To be of commercial interest these deposits must, of course, be recovered economically. To determine costs, therefore, the governments of Saudi Arabia and The Sudan, in September 1975, established the Saudi-Sudanese Red Sea Commission to sponsor research into, and development of, these resources (See Aramco World, July-August 1981), and engaged Preussag to carry out a $28 million, five-year feasibility study.

Preparations for the study took time, of course, but by March, 1979, Preussag had readied the Sedco 445, a large mining ship equipped with a 2,200-meter steel drill-string (7,200 foot) with a suction head attached to the end of a standard oil drilling pipe. Lowered into the deeps, the suction head, with a motorized vibrating attachment, broke up the mud and pumped it to the surface; between March and June 1979, 15,000 cubic meters (68,190 cubic feet) of muds and brines were pumped to the surface for processing.

On land, this processing — which extracts a mineral-rich concentrate from the slurry and which is called "froth flotation" - is fairly common. First, the particles of mud are separated from the brine by adding chemicals to the liquefied mixture -causing the particles to repel water. Then the mixture is put into agitation tanks in which air, bubbling through the mixtures, picks up the particles and forms a mineral-rich froth, which is carried to the surface of the tank and scraped off at intervals.

At sea, of course, such processing is more difficult. Preussag engineers estimate that commercially viable recovery of silver and other metals from the mud will require at least 400,000 metric tons of slurry - brine and seawater - per day, no simple task at a minesite 90 kilometers (56 miles) from shore. Because the mud particles are tiny -80 percent are less than 1/500th of a millimeter in diameter — it is impossible to filter particles out of such massive quantities of brine without froth flotation, or a similar technique.

Engineers, therefore, had to be sure that the process could function in the Red Sea's frequently rough weather. This was assured by tests run by the Warren Spring Laboratory in Britain, in which a ship's motion simulator reproduced Red Sea conditions on land-so successfully that the commission's pre-pilot test achieved concentration factors of eight to10 times, with an overall recovery rate of up to 70 percent and a final product containing 32 percent zinc, 5 percent copper and 0.07 percent silver.

Onshore, still further processing is necessary - to isolate the individual metals by either smelting the concentrate or working it in solution. Smelting, known as pyrometallurgy is not used, however, because a salt-free feed is essential and that can only be achieved if large quantities of fresh water are available for washing. Instead, Preussag has chosen the hydrometallurgical route, specifically "metal-chloride leaching" and "pressure oxygen leaching," both of which have achieved recovery rates of more than 90 percent in tests. Yanbu', Saudi Arabia's new industrial city on the west coast, may be the site for this operation.

The technology, then, seems promising - though one major problem will be corrosion on a massive scale, the result of hot brines and muds - and the next stage is to run a pilot operation in 1984 which will produce dry, salt-free concentrate at one seventieth the scale of commercial operations.

Technical optimism aside, Saudi Arabia and The Sudan must also consider the economics - and they are as tricky as the technology. To be sure, the latest estimates of Atlantis II Deep suggest a tremendous potential: 1.95 million metric tons of zinc, 400,000 metric tons of copper, 4,000 metric tons of silver and 60 tons of gold worth some $4 billion at current prices. But metal markets are highly volatile. At today's prices, for example, almost half the revenue would come from zinc - which has recently been steadily rising in price - while copper revenues would be much smaller.

As for silver, the target metal, commission experts have to keep in mind such upsets as the 1980 fiasco when prices gyrated wildly during an attempt to corner the market - and then crashed. On the other hand, the silver market is usually less vulnerable than other metals and now seems assured of a long-term upward trend.

In addition to the monetary value of silver and other metals, this project could make an important contribution to Saudi-Sudanese development; in the long term, it would provide not only minerals, but jobs -2,000 skilled and semi-skilled jobs - plus experience that may prove invaluable later. As Zuhair A. Nawwab, Deputy Secretary General of the commission, put it: "In terms of profit, mining the Red Sea cannot, of course, compare with the return from oil, but in relation to land-based mining, it does compare favorably"

"And even if the project does not go all the way to the commercial phase, we will have achieved something. We have, for instance, modified equipment that can be utilized for ocean mining - and are now filing for international patents. We are gaining a huge amount of valuable Red Sea data, both mineralogical and environmental. And we are providing practical training, which would not otherwise be available, to a lot of nationals from Saudi Arabia and The Sudan"

Mining the Red Sea has also produced an interesting side-effect: cooperation between Saudi Arabia and The Sudan - in favorable contrast to the negotiations at the United Nations Law of the Sea Conference, which after eight years, have produced no agreements and which, as a consequence, have delayed investigations into ocean mining. This is particularly interesting because The Sudan has limited financial resources; thus the whole project is funded by Saudi Arabia. Yet, in pursuing their mutual interests, the two countries have avoided all legal disputes over the ownership of the resources.

Early on - in May 1975 - they signed an agreement limiting their respective exclusive economic zones in the Red Sea to the sea bed less than 1,000 meters deep (3,280 feet) measured from their respective coastlines. The remainder of the seabed below this depth was defined as a common economic zone where joint exploration and exploitation would take place. Happily, continued exploration has confirmed that all 18 muddeposits lie in this common zone.

One serious obstacle is the environmental impact of such mining on what is a fragile ecology. Because commercial mining would produce up to 400,000 metric tons of tailings - the waste mud - per day, the Red Sea Commission's Dr. Zaki Mustafa, secretary general, has already gone on record as saying that if the mining activity has any severe adverse impact on marine life, the whole program would be phased out. The commission, in fact, has spent more on environmental studies than on its mining work.

The environmental problem could be serious primarily because the waste mud is composed of extremely fine particles - with long settling times - and hot brines contaminated with the chemicals used in froth flotation, and must, logically, be pumped back into the sea since the purpose of "at sea" operations is to avoid the inordinate costs of moving the slurry ashore.

So far, fortunately, detailed environmental monitoring has shown little adverse reaction. During the tests, the German research vessel Valdivia tracked the tailings plume as they were pumped down to 400 meters (1,300 feet) through a steel sewage pipe attached to Sedco 445's bow anchor line - to be sure the tailings neither contaminated the water nor reduced light penetration, an important factor in the biology of the sea. In addition, LANDSAT satellite-sensors that have been monitoring the tailings (See Aramco World, March-April 1982) and post-test investigations showed that so far neither the coral reefs nor the fauna within the surface layers have been affected. Recently, the commission also received a report - from a Saudi doctoral candidate studying in San Francisco - saying that fine zinc particles discarded in the Red Sea develop a thin layer of oxide that makes them sink faster than originally thought-virtually eliminating danger to marine life from this source.

The way seems clear, therefore, for the pilot phase of the project and there is every possibility that it will go commercial eventually. "On the evidence we have now," Dr. Nawwab said, "we think it will be commercially viable. We hope that prlot mining operation will begin by the end of 1983 and once completed - in about a year-we will have a large amount of data to determine the likely problems and requirements for commercial mining. We hope that by the end of the decade we will be the first to put minerals produced from the sea into the marketplace."

If so, Saudi Arabia and The Sudan, along with participating companies, technical consultants and agencies, will have helped remove the technological and political barriers against well-reasoned exploitation of the world's last great untapped resource - its seas and oceans.

Glyn Ford and Jonathan Simnett are members of a research group at Manchester University in England, now studying the future usages of oceans.

This article appeared on pages 22-25 of the September/October 1982 print edition of Saudi Aramco World.


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