What if I told you that the “lime” in “limestone” does not refer to the citrus fruit but scientifically denotes the mineral calcium carbonate?
So let’s unpack with the definition. Limestone is a sedimentary rock composed of calcium carbonate – CaCO3. The original limestone is formed from the accumulation of the remains of marine organisms like shells, corals, plankton, fish scales and teeth, that are composed mainly of calcium carbonate and compacted over millions of years on the ocean floor.
It is extracted from quarries like the one in Ernstbrunn-Dörfles, Dürnbach in Waldegg, in Karbach or many other places. Austria has rich deposits of natural stones, there are around 350 quarries, and around 950 sand and gravel pits across the country. Austria can cover its needs for mineral building raw materials from its own production, these deposits allow for short transport routes, the average transport distance from the quarry to the place of use is around 25 kilometers.
One of the oldest quarries in Austria is the Sankt Margarethen quarry. The limestone extracted there was used for example in the construction of the Roman city of Carnuntum more than 2000 years ago, or later in the middle ages for construction of cathedrals and majestic historical buildings in Vienna. Today it serves as a museum and a well known open-air theater.
Now back to the subject: after extraction from the quarry, the limestone is roughly chopped in the processing plant and heated in a kiln to high temperatures (around 900–1000°C). This process, known as calcination, causes the limestone to undergo a chemical reaction, releasing carbon dioxide – CO2 and converts to a white crystalline solid called quicklime, or calcium oxide – CaO. Quicklime is highly reactive and with water can produce slaked lime – calcium hydroxide – Ca(OH)2. This process (slaking) results in a chemical reaction that produces heat and transforms quicklime into less reactive and more user-friendly form.
There are two types of emissions resulting from the processing in this case, the CO2 emitted by combustion of the fossil fuels to obtain the needed heat, and the CO2 released from the limestone that was embedded inside, in both cases the kiln technology is key for reduction of these emissions.
As the process of heating limestone in kilns emits a high amount of emissions, the lime industry accounts for an average 1% of global CO2 emissions (the estimated global production of lime in 2022 was 430 million metric tonnes), and that’s the reason why there are a lot of international engineering initiatives to reduce emissions, and decarbonise the kiln operations. Some of the leading initiatives in Europe are the Swiss Maerz Eco Kiln projects, or the partnership of Nordkalk with Aqualung Carbon Capture AS, but also commitment from important lime producers like the CRH, Carmeuse Group, or Holcim is a sign that the industry is heading towards carbon capture and utilization. Nevertheless the one who will manage to decarbonise first, will not only be the technology leader and first mover, but also gain a lot of new market share. It is quite an exciting contest, and that should help to speed up the developments.
Once the lime is ready for use, the material is appreciated in multiple industries, in construction industry for mortars and plasters, in agriculture to provide calcium and neutralize soil acidity, in the food industry for processing, in the chemical industry for the production of calcium stearate and other chemicals, in the dental industry for the components of dental cements, in the paints and coatings industry it is used as an extender or a filler in pigments, in the sugar industry for the purification process, in the paper industry for the pulp bleaching, or in the pharma industry for the preparation of specific medications. It is widely used indeed, and plays a crucial role in many important processes.
In our case, in Hempstatic we use the slaked lime in our production processes by mixing it with the biobased part: the hemp hurd (or called also ”shives”), water and occasionally earth pigments, to create novel biocomposites with great material properties and functionality. When the biocomposites are formed, the mixture undergoes a hardening process, where the lime reacts with carbon dioxide from the air, forming calcium carbonate again. This process is known as carbonatization. Ca(OH)2 (s)+CO2 (g)→CaCO3 (s)+H2O(l)
Gathering deep detail on all topics relevant to our startup, we have been partnering up for studying the carbonatization process with the competence center Wood K Plus last year, and this year within our participation in the New European Bauhaus Booster programme we conducted a conservative calculation to approximate the CO2 intake of this process with the Climate Impact Forecast Tool and concluded a capture of 0,57 kgCO2eq. per functional unit. To further support our claims and assumptions, subsequent research projects are awaiting us in the 2024 pipeline, and we are excited and looking forward to it.
Hempstatic was born into the circular economy seed phase, it’s the time when the seeds of circularity are sawn in the fields of our industries, our upbringing in the startup ecosystem revolves around new principles of understanding the real negative impact externalities that our systems cause to the natural environment and we therefore cannot think linearly, we consider the life cycle of all our inputs and outputs from the get go, and are working hard to support our advocacy and passion for bioeconomy with scientific knowledge and empirical research.
Over time, the carbonatization process continues, and the calcium hydroxide in the biocomposite gradually turns back into calcium carbonate. This means that over an extended period, the biocomposite product allows the lime to turn to limestone again and thus regain its original form. Isn’t that mind-blowing and cool? We love the innate circularity of it! Well, we consider the lime to be a static component of our biocomposites, it’s the “static” in Hempstatic, but if you think about that, it’s still quite a dynamic one.
To wrap this up within an anecdotal line, limelight refers to a type of theater stage lighting used in the 19th century, where a flame was directed at a cylinder of lime. The strong light produced by the heated lime was used to illuminate stages before the advent of electric lighting. That’s why the term “in the limelight” means being in the center of attention,
and so keep staying in the limelight with your endeavors! 😉