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CalciTech has developed a new and patented process for the upcycling of industrial waste lime into Synthetic Calcium Carbonate (SCC), a valuable product with a multitude of applications. SCC is the next generation mineral for the paper industry and is a revolutionary improvement on precipitated calcium carbonate (PCC), which constitutes the third generation.
In order to appreciate the revolutionary character of CalciTech's technology, it is useful to look at the conventional way of producing PCC.
Conventional Carbonation Process for PCC Production
In the conventional process, carefully selected high-grade limestone is calcined in a kiln to produce quicklime (calcium oxide/CaO) and carbon dioxide (CO2). The quicklime is slaked with water into calcium hydroxide (Ca (OH) 2.), which is sparsely soluble hence resulting in milk-of-lime, a suspension of solid calcium hydroxide particles in water. A milk of lime with a typical lime concentration of 150 g/l will have 1.6 g/l of lime in solution and 148.4 g/l in suspension.
The carbonation process then involves sparging the cooled and purified carbon dioxide-bearing kiln gas through the milk-of-lime in a batch reactor known as a carbonator. Carbon dioxide reacts with calcium hydroxide in solution forming calcium carbonate which, being insoluble, precipitates out. The rate-determining step is the steady dissolution of lime in replenishment of the lime precipitated out of solution as carbonate. As calcium hydroxide is sparsely soluble (1.6 g/l), the total reaction time is very long and gassing typically continues for several hours until all calcium hydroxide (Ca(OH)2) has been converted to the carbonate.
Following the carbonation process, the PCC slurry is classified by screening or hydrocloning to remove impurity-containing grit. Most commercial grades of PCC have a minimum purity of 98%, the major contaminants being magnesium carbonate, silica and unconverted lime. The purity of the finished PCC is directly related to the purity of the original limestone.
Following classification, the PCC is de-watered, dried and de-agglomerated. The finished material is then stored for shipment in bulk or loaded into bags for sale as merchant product.
The CalciTech Process for SCC Production
The CalciTech process can utilize any grade of lime including low quality limestone or industrial waste lime like for example carbide lime. In the CalciTech process the carbide lime is mixed in a digester with a solution of water and a proprietary solution promoter, which selectively dissolves the calcium and leaves the impurities behind as insolubles, which are readily removed by subsequent flocculation and decantation. The clear calcium solution is then pumped into a reactor into which carbon dioxide is also sparged, to precipitate calcium carbonate. After the reactor, the PCC product is filtered off, and the filtrate of barren promoter solution is reconditioned and recycled back to the digester for re-use.
CalciTech's Small-Scale Production Plant in Leuna, Germany
The filtered PCC product can then be supplied directly as high solids content slurry, or dried and bagged for the merchant market.
SCC vs PCC Production
The CalciTech process is described in the figure below and differs from the conventional process in the following ways.
- The CalciTech process does not require lime slaking and classification steps. This gives the company significant advantages in both quality and cost effectiveness.
- The CalciTech process includes a digester circuit that facilitates the use of any waste lime, such as carbide lime, thereby removing the need to purchase lime as is required in the conventional process.
- The CalciTech process includes a promoter recycle loop to enhance the process economics.
- Any impurities in the lime feed are rejected as insolubles in the digester resulting in a final SCC product of the highest purity. The purity of CalciTech SCC is independent of the purity of the starting material and is always superior to that of the starting material.
- In the CalciTech process, the total lime content is present in solution whereas in the conventional process the lime is present in suspension (milk-of-lime). The reaction times in the CalciTech process are therefore much shorter than in the conventional process as the CalciTech process eliminates the slow lime dissolution step. This advantage allows for the use of smaller equipment as well as providing a much higher degree of control over the process.
- A solution is always homogeneous, a suspension never is. The CalciTech solution process is therefore more flexible and easier controlled than the conventional suspension process enabling a narrower particle size distribution. Additionally, the higher level of control enables CalciTech to tailor make products in a wide range of crystal sizes, from nano-sized product (< 0.1micron) up to 20micron, so that various markets can be served.
Conventional PCC Production
The CalciTech Process
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