Calera - Calcium Carbonate
Calera’s Calcium Carbonate, made from CO2, can be used in a variety of applications. The material is produced as a fine free-flowing white powder. It can function as a supplementary cementitous material (SCM) in traditional concrete mixes where the environmentally sustainable calcium carbonate can replace a portion of portland cement, helping reduce the overall carbon footprint of traditional concrete. The Calera calcium carbonate can also be used as the sole cement or binder system in concrete products. Calera developed wallboard and cement board products where the unique binder can be used instead of gypsum, magnesium oxide, calcium silicate or portland cement.
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Calera Calcium Carbonate was used as a supplementa...
Calera Calcium Carbonate was used as a supplementary cementitous material in several projects including sidewalks in a local municipality and flatwork in a commercial office building where it replaced approximately 15% of portland cement in the concrete mixture.
The unique calcium carbonate cement made in the Calera process can be used without any other cement or binder system to make concrete products. Calera demonstrated the ability to make a variety of decorative concrete products such as countertops, plant holders and benches. The products contain traditional sand and aggregate all held together in a concrete mix by the calcium carbonate cement. Calera also produced full fiber cement board sheets on a commercial line, exceeding strength requirements with formulations that are lighter weight than many existing cement board products.
The Process
Calera’s process for CO2 reduction involves the capture of CO2 gas from industrial emitting sources and converting the CO2 into a novel calcium carbonate cement system that’s used to make a variety of valuable products. Calera concentrates on the manufacture of building materials, particularly focusing on innovative board products from Calera’s novel cement system. Calera’s process removes CO2 from emitting sources by converting the gas into a solid form of calcium carbonate thereby permanently sequestering the CO2. The Calera process is unique with a CO2 capture and conversion technology that transforms CO2 into a profitable feedstock. Calera’s CO2 solution couples environmental sustainability with economic sustainability.
The conversion of CO2 to calcium carbonate requires a source of alkalinity and calcium. One option is the use of industrial waste streams that contain both alkalinity and calcium, like calcium hydroxide (Ca(OH) 2). Another option is separate streams – an alkalinity source, such as caustic soda (NaOH), which can be supplied from the conventional industrial manufacturing process and a calcium source, like calcium chloride, which can be naturally occurring or found in the waste streams of existing chemical processes. Both methods result in the capture and conversion of CO2 to the special calcium carbonate cement which can be used to form board products.
The Science
The Calera process for the capture and conversion of CO2 takes its lead from nature. The earth’s atmosphere has had higher concentrations of CO2 in the past and nature dealt with these high levels of CO2 by a mineralization process whereby marine organisms use CO2 to form calcium carbonate structures that deposit on the ocean floor over time. It is estimated that up to 100 million billion tonnes of CO2 is stored in the geological record in the form of calcium carbonate.
The special form of calcium carbonate that Calera produces in its process mimics the form of calcium carbonate that marine organisms use to make their shells and other structures. The special form of calcium carbonate is a binder that creates structures with high strength and toughness.
Calcium carbonate exists in nature in different forms or polymorphs. The Calera process results in the production of the vaterite polymorph which is stable when stored in the absence of water. When water and other proprietary additives are added to the vaterite polymorph, a cement reaction occurs in which the vaterite transforms via a dissolution and reprecipitation reaction to form another polymorph of calcium carbonate known as aragonite. This conversion of vaterite to aragonite results in a material with high strength, just as natural systems like nacre (mother of pearl) are also constructed from the aragonite polymorph of calcium carbonate.
Scale-Up
Calera’s CO2 capture and conversion pilot plants produced up to 2 tonnes of CO2 containing calcium carbonate product per day using raw flue gas with no concentration of CO2 needed.
Calera designed, constructed and operated two pilot plants to develop the CO2 capture and conversion technologies. These demonstrations included flue gas from power plants and burning coal, without concentrating the CO2. The flue gas is contacted in a scrubber with an aqueous alkaline solution that effectively removes the CO2 and a calcium source that results in the formation of the special calcium carbonate product that is then dried to a free flowing powder. This powder can then be used to make products, like boards, because of the special cementing nature of the calcium carbonate.
Calera also installed a commercial fiber cement board line to refine formulations to produce full size fiber cement board sheets that are lighter than conventional board products with equivalent performance properties.
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