Submitted on April 4th, 2009 by gwashtracker (not verified)
A quick analysis of Calera’s seawater process:
Assuming Calera captures calcium and magnesium from seawater as carbonates, one ton of carbonate cement would require at least 500 tons of seawater (> 80% capture efficiency) - or about 300 tons of desalination brine. So, to supply just US cement demand (over 120 million Mt per year), you would need to process 50 billion cubic meters of seawater! The most economic method would be to piggyback the process onto desalination plants, but even with desalination capacity increases, desalination brines could supply at most 6% of US cement demand. And, processing seawater for cement production alone is neither economic (Portland cement sells at $100-120 per Mt in the US) nor environmentally friendly.
Also, such a process will generate a calcium/magnesium-stripped brine rich in sodium/potassium. Many, many studies have shown that such brines have severe environmental impacts when discharged into the ocean - the high salinity kills flora and fauna in the brine plume - so much so that regulations now dictate that such brines have to be diluted with seawater prior to discharge, or have to be landfilled. Also, processing seawater produces large amounts of a toxic sludge containing copper, nickel and chromium (leached from metal piping and processing tanks) as well as cleaning agents and disinfectants (used in daily cleaning operations) – this sludge is highly hazardous and has to be landfilled.
It is puzzling that Calera does not appear to be talking about a biological process, and in fact their patent is a pure chemical process that essentially reprocesses natural limestone to make artificial limestone.
Originally, Calera was talking about making calcium/magnesium carbonates via a biological path - ie. use carbonate-forming marine organisms to form magnesian calcite, and collect/process the resulting biomass/skeletons (the precursor to limestone). Of course, the chemistry is such that this product could never be a cement (it does not undergo a hydraulic reacting with water and does not set) – this would explain why Calera has now given up on making a cement (as they had initially claimed). Similarly, this product would be a poor mineral admixture for cement due to its biomass content and the crystalline form of the magnesian calcite – this would explain the poor results reported in the Calera patent application.
Now, presumably as a last-ditch effort to salvage something, Calera is talking about making an aggregate. Well, if you want a strong, resilient and time-tested carbonate aggregate, you simply use limestone. You do not set up a limestone-to-calcined limestone-to artificial limestone process that is dirty and polluting and carries huge environmental consequences, makes a much inferior product to the natural material, and then claim it is Green!
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Calera is Greenwash - Continued
Submitted on April 4th, 2009 by gwashtracker (not verified)A quick analysis of Calera’s seawater process:
Assuming Calera captures calcium and magnesium from seawater as carbonates, one ton of carbonate cement would require at least 500 tons of seawater (> 80% capture efficiency) - or about 300 tons of desalination brine. So, to supply just US cement demand (over 120 million Mt per year), you would need to process 50 billion cubic meters of seawater! The most economic method would be to piggyback the process onto desalination plants, but even with desalination capacity increases, desalination brines could supply at most 6% of US cement demand. And, processing seawater for cement production alone is neither economic (Portland cement sells at $100-120 per Mt in the US) nor environmentally friendly.
Also, such a process will generate a calcium/magnesium-stripped brine rich in sodium/potassium. Many, many studies have shown that such brines have severe environmental impacts when discharged into the ocean - the high salinity kills flora and fauna in the brine plume - so much so that regulations now dictate that such brines have to be diluted with seawater prior to discharge, or have to be landfilled. Also, processing seawater produces large amounts of a toxic sludge containing copper, nickel and chromium (leached from metal piping and processing tanks) as well as cleaning agents and disinfectants (used in daily cleaning operations) – this sludge is highly hazardous and has to be landfilled.
It is puzzling that Calera does not appear to be talking about a biological process, and in fact their patent is a pure chemical process that essentially reprocesses natural limestone to make artificial limestone.
Originally, Calera was talking about making calcium/magnesium carbonates via a biological path - ie. use carbonate-forming marine organisms to form magnesian calcite, and collect/process the resulting biomass/skeletons (the precursor to limestone). Of course, the chemistry is such that this product could never be a cement (it does not undergo a hydraulic reacting with water and does not set) – this would explain why Calera has now given up on making a cement (as they had initially claimed). Similarly, this product would be a poor mineral admixture for cement due to its biomass content and the crystalline form of the magnesian calcite – this would explain the poor results reported in the Calera patent application.
Now, presumably as a last-ditch effort to salvage something, Calera is talking about making an aggregate. Well, if you want a strong, resilient and time-tested carbonate aggregate, you simply use limestone. You do not set up a limestone-to-calcined limestone-to artificial limestone process that is dirty and polluting and carries huge environmental consequences, makes a much inferior product to the natural material, and then claim it is Green!
More Greenwash!