207. URANIUM FROM SEAWATER (PART 1)
Lately, we've been hearing a lot of the "peak uranium" soundbite: "if we turn to uranium, it too will peak in 30 years." This isn't true, and to see why, I'm going to walk you through the most elegant and beautiful mining technique ever invented: recovering uranium from seawater.
This feat has actually been accomplished by Takanobu Sugo and his colleagues at the Japan Atomic Energy Research Institute (JAERI).
To begin, the group fabricates a material called the "adsorbent" which can selectively soak up uranium. This material begins as a nonwoven fabric made primarily of polyethylene. Molecules called amidoxime groups are attached to this fabric by a process called "graft polymerization" (which apparently involves irradiating the polyethylene with a high energy electron beam). Each pair of attached amidoxime groups can "grab" a single heavy metal ion.
This material has an amazing capacity to soak up uranium (as well as other valuable metals like vanadium, cobalt and titanium). Bench tests show it can hold an amazing 500g of heavy metals per kg of absorbent. It can also be washed with alkali, and reused. Here's an abstract of the JAERI group's most recent experiment (2003):
The total amount of uranium dissolved in seawater at a uniform concentration of 3 mg U/m3 in the world's oceans is 4.5 billion tons. An adsorption method using polymeric adsorbents capable of specifically recovering uranium from seawater is reported to be economically feasible. A uranium-specific nonwoven fabric was used as the adsorbent packed in an adsorption cage 16 m2 in cross-sectional area and 16 cm in height. We submerged three adsorption cages in the Pacific Ocean at a depth of 20 m at 7 km offshore of Japan. The three adsorption cages consisted of stacks of 52 000 sheets of the uranium-specific non-woven fabric with a total mass of 350 kg. The total amount of uranium recovered by the nonwoven fabric was >1 kg in terms of yellow cake during a total submersion time of 240 days in the ocean.SourceThis is what one of these adsorption cages looks like:
So if you want to collect tons of yellow cake, instead of just kilograms, you just need to string 300 of the cages together and hang them in the ocean. Sugo illustrates three possibilities (from the top): suspension from a floating platform, dangling under a bridge, or stringing with buoys (like a trot line):
The technique reminds me of Asian seaweed farms:
It's a beautiful low-tech approach... almost agricultural. And it's hard to imagine any cleaner method of "mining". No tailings, no scarring of the landscape. In fact, it would clean the ocean rather than pollute it.
You can even take it a step further. The following shows an idea for synergetic wind farming and aquaculture, but we could just as well imagine hanging adsorbent cages, and hoisting them with wind power (click to enlarge):
*Part 2 of this article is located here: 208. URANIUM FROM SEAWATER (PART 2)
-- by JD