Cornwall sea treatment (magnesium hydroxide)

[Mr Gus]

https://www.theguardian.com/uk-news/202 ... chnologies

Does this make sense then?

Mined in china (by heavy industry)
Shipped to America for grinding / milling, (no idea where)
Shipped to the uk to be poured into the sea as a measured dose..

At the rates given (presumably) 1kg of heavily travelled chemical, magnesium hydroxide = a net carbon benefit of 451g being produced.

Seems like a mile heavy solution & get rich scheme on a summer fete favourite "the back to front bike"maybe?

Anyway, your thoughts?

[Countrypaul]

How exactly do they obtain the Magnesium hydoxide. I thought most MgO was made through treatment of MgCl2 or Mg(OH)2 with CaO (lime) obtained by heating CaCO3 to drive the CO2 off. The MgO is then heated to various temperatures depending on wh the final product is intended for use in. Mg(OH)2 is usually produced from seawater by the use of CaO (lime), but also from MgO by adding water, although some is mined.

The article quotes "a net carbon benefit of 451g per 1kg of Mg(OH)2 used" but gives no explanation of how thar figure is derived.

[Paul_F]

Magnesium hydroxide forms Mg²⁺ ions when dissolved, which are pretty common in seawater anyway (Magnesium Hydroxide forms 1 part in 600 of sea water, and is commercially extracted from seawater by treating it with lime).

Chemistry is pretty simple: Mg(OH)₂ + 2 CO₂ => MgCO₃ + H2O
This also means the net carbon benefit is pretty easy to work out:
1 Mole of Mg(OH)₂ has atomic weight 24+(16+1)x2 = 58
1 Mole of CO2 has atomic weight 16*2+12 = 44

Therefore 1kg of Magnesium Hydroxide should absorb 44/58 kg of CO₂ (0.758 kg) - they're claiming about half this value indicating that they're guessing/predicting how much of the additional magnesium hydroxide will eventually react with CO₂ before it precipitates out.

TBH it looks like a bit of a storm in a teacup - I'm pretty sure a bit of extra Magnesium is about the nicest thing coming out of a South West Water sewage outfall at the moment, and the least harmful to sea life. Shipping the minerals about is probably pretty low-carbon as well (it's found naturally as Brucite, although no doubt the trials are using the commercially available stuff extracted from sea water), but given how much of it is in seawater already I'm somewhat sceptical about the prospects of it making much of a difference.

[Krill]

Mg(OH)2 + 1CO2 -> MgCO3 + H2O, only 1 carbon dioxide is in the reaction.

[Countrypaul]

Mg(OH)2 + 1CO2 -> MgCO3 + H2O, only 1 carbon dioxide is in the reaction.

He might have got the equation wrong, but at leat he got the calculation right

[Countrypaul]

2.5Kg of Mg(OH)2 has about 1000g of Magensium. 1kg of magnesium in 18 tonnes of water is about 55ppm. The natural concentration of magnesium in sea water is around 1300 ppm, The discharge would have to be very large to have a significant effect on the magenesium concentration in the whole bay as far as I can see.