Electrifying a Reef

Part 2:  With Biorock mineral accretion, what happens chemically during electrolysis? That’s the question I want to answer, but first, I’m attuned to the seasonal moment.  If you’re in the tropics, you aren’t feeling the darkness of the winter solstice we experience in the upper latitudes.  Up here we celebrate snow and cold, the warming from wool, hot food, and hopefully good insulation.

Electrifying a reef

Dec 19, 2009 Jokimaa, Southern Finland - Courtesy Seppo Ranta. copyright 2009

The beautiful “frost flowers,” as Jeff Bowman refers to them in Robert Krulwich’s NPR piece, are home to millions of bacteria.  These freezing super salty forms remind me of Whoville in Dr. Seuss’ Horton Hears a Who!  You can’t see all the microscopic life, but it IS there.

“No one believes Horton. They think he’s crazy.”

Aggregations of shimmering crystals like these are eye candy.  They conjure up an image of flocked corals.  Not bleached corals, I’m happy to say; something about them is festive and fantastical.  Since they may be a result of warming poles, their beauty is likely a paradox, yet for now, they appear as winter wonderland mysteries.  They are a biological chemical feat.

salty ocean blossoms

photo by Matthias Weitz/ "Suddenly There's a Meadow in the Ocean with Flowers Everywhere"

Which brings me back to the question: What is the chemistry behind the electrolytic process for Biorock mineral accretion?  Now that the power is on, what happens in the seawater?

bit-o-biorock jewelry

Bit-o-Biorock pendants in process. Photo by Clay Connally, 2012

According to a research paper by Wolf Hilbertz and Thomas J. Goreau1, deposition of minerals results from alkaline conditions created at the cathode – negatively charged steel sculpture, in our case – by the reduction reaction: 

2H2O+2e =H2 +2OH                                                                                                        2 water molecules + 2 electrons = 1 hydrogen + 2 hydroxide molecules

which precipitates calcium and magnesium minerals from seawater: A basic natural limestone substrate that continues to “grow” and “heal” if damaged while also preventing rust/corrosion of the metal.

OH + HCO3 + Ca++ = CaCO3 + H2O                                                                  hydroxide + hydrogen carbonate (bicarbonate ion) + calcium = calcium carbonate + water

2OH + Mg++ = Mg(OH)2                                                                                                    2 hydroxide molecules +  magnesium (3rd most abundant mineral in seawater) = brucite (mineral form of magnesium hydroxide: not a very stable mineral for accretion)

In contrast, the anode becomes acidic due to:
2H2O = 4H+ + O2 + 4e                                                                                                        2 water molecules = 4 protons + oxygen + 4 electrons

and highly oxidizing conditions result in:
2Cl = Cl2 + 2e                                                                                                                  2 ionic chlorides/organic chlorides= elemental chlorine + 2 electrons

The sum of the net reactions at both electrodes (the {+} charged titanium mesh anode and the {-} charged steel cathode) should be neutral with regard to hydrogen ion production, and hence with regard to CO2 generation through acid–base equilibrium and carbonic acid hydrolysis:

2HCO3 = CO3−− + CO2 + H2O                                                                                           2 hydrogen carbonates = carbonate + carbon dioxide + water

Samuel Raj

"Flame" by Samuel Raj. CC flickr

As a metalsmith, I learned over the years what a reducing flame, oxidizing flame, and neutral flame do to metal.  Equations were not a critical part of learning this, though; it was through hands-on experience that I saw what happened from varying flames. But for the curious and chemistry buffs, I hope this shines light for you.  I’m still learning what the equations mean through my experiments in tanks and the ocean.  Without my “mistakes” of plating stainless steel with iron, and accidentally creating rust baths as I try to grow pendants, I would not be able to grasp these principles.

Kochi at Hitachi Seaside Park in Japan

And without incredible plants like these in Japan, Dr. Seuss might not have drawn endless fields of clover for Horton to roam, seeking to find…

Photo from Alice’s blog at Extraordinary Travel Destinations Off the Beaten Path

1Thomas J. Goreau and Wolf Hilbertz, 2012. Reef Restoration Using Seawater Electrolysis in Jamaica; Innovative Methods of Marine Ecosystem Restoration 4:  36-37.