Sounds like a bonzer idea to me:
The company, Marine Minerals, said the project would only go ahead if the tin could be \”extracted\” – it rejects the idea that it will be \”dredging\” – in an environmentally and socially responsible way.
Its proposal is to suck the sand up from the seabed — between 200m and 1km out – to a depth of up to around 2m and sift it at sea. The portion containing tin, estimated at around 5%, would be taken back to shore and milled, while the other 95% would be returned to the seabed at once.
Marine Minerals is aiming to sift 2m tonnes of sand a year and says there is roughly a billion tonnes of sand in total in the area it wants to work in.
Not entirely sure how they\’ll \”sift\” that sand at sea though. The ore they\’re after is cassiterite and you usually use gravity to separate that out from the other pieces of the sand. It\’s not magnetic, so you can\’t use magnetic separation.
Hmm. Well, the gravity separation you use is usually in water…..think those troughs to separate out the gold you see in every western movie. I suppose that could be done in sea water, on site. Mebbe.
The company argues that the project, which would not begin before 2015, will create skilled jobs, help meet a growing global demand for tin and could help develop a technology that could be used in other parts of the world, including south-east Asia, where much more intrusive methods of extraction cause damage to marine habitats.
And that last is most definitely true. If they can get the technology to work then it would indeed be a good one.
Reckon some sort of centrifuge’d do that. Denser particles would take a different path & be separated.
Tim adds: Yup, usually a “hydrocyclone”. But how that would work under water I’m not sure.
There’s a programme on Discovery about various groups of Americans setting up Heath Robinson contraptions which hoover up sand from the seabed off Alaska, which is then passed over the various sieves set up on deck with the rocks and gold falling to the bottom. So the equipment and methods exist, it’s just a question of whether it will work with tin (don’t know if it is heavy enough).
The company plans to alter 1/500 of the seabed by reducing its level by 10cm, according to my calculation. That doesn’t look like an environmental or surfing disaster to me.
The word is “sieve”. The tin will be in sand-size and finer particles. Pump up the sediment, screen it through sieves and return the larger size fraction directly to the sea bed. Further process the fine fraction onshore. Processing placers isn’t rocket science.
Tim adds: Should have thought of that. For of course, they’re not claiming that it’s 5% cassiterite, are they?
““hydrocyclone”. But how that would work under water I’m not sure.”
Quite well one would imagine. Create a vortex to separate densities then pump up the required stream. There’s a lot of natural process sort like this. Chesil bBach? The word ‘tosheroon’ also rings a bell
The process was described in a Wilbur Smith novel wrt diamonds. “The Diamond Hunters”, I think.
“At sea” doesn’t mean “in the water”, though, does it?
if they have sense and want access to things that might break down, they’ll be hoovering up at the seabed, pumping slurry up to a barge for cyclone separation then depositing back down near the dredging head
the greenies are right in that this will cause disturbance to the sea bed and there will be fine particles released into the water that may not settle that quickly though, and the operation won’t be allowed to use flocculants to accelerate the process. Scarcely the end of the world though
is the seabed barren? or will they be hoovering up and killing plaice, oysters, kelp and whatnot?
To try to answer Ambrose Murphy, if the rig is anything like the ones used in Alaska, the sucking hose is about 4″ wide and hand-held by a diver who moves it around like a Hoover. Note that this all takes place in very shallow water, 2m according to the article. I don’t think it will be some enormous industrial operation.
@Tim Newman: I too watch Bering Sea Gold, and suspect that any operation capable of shifting 2 million tonnes of sand per year is going to be significantly more industrial in scale that that portrayed on that show. They are after a few ounces of gold, not hundreds of tonnes of tin.
Been pondering this.
I think you could do this with a vortex. The fringe could push the lighter organic material out of harms way before the sand itself gets spun up. Which would placate the lugworm hugger community. If the depth is only a couple metres, wouldn’t me much more stress on the bios that a mild storm. At that depth, you’d have surf stirring the shit out of it.
Depends on the nature of the sand itself & some nifty hydrodynamics design. It’s not really the same as gold & diamonds. There’s no real requirement to extract all the tin, is there? It’s a balance between shifting the minimum amount of material to extract the maximum yield. Could be a lot more cost effective than processing all of the sand for 100% recovery.
I can remember something about panning rivers for alluvial gold. It’s not evenly spread. Tends to concentrate where natural eddies in the river flow deposit it.
@Jim: true, but let’s see. It’s a £15m project, which sounds like chump change to me. But maybe £15m still gets you something outside the oil business.
Tim & Jim
I think you’re talking about air lift. This shifts a lot of silt and we used to dig trenches with them. They get progressively less effective as depth increases as they depend on the relative not barometric pressure.
And you won’t need any divers. We’re not uncovering sunken treasure here, just hoovering silt.
And given that an air lift works best with about 4m of pipe at the top the whole primary separation process might best be done underwater, below the barge.