Control of size and morphology of calcium carbonate crystals made by the reaction of CO2 gas with Calcium Chloride solution.

Lead Research Organisation: University of Leeds
Department Name: Chemical and Process Engineering


Calcium carbonate has many uses in industry and consumer products. The highest value material tends to be in the micron size range which is usually produced through grinding of larger material, which is very energy inefficient as well as producing a wide size distribution. Since users want a narrow size range a lot of material is recycled or lost. This project aims at controlling the size and morphology by controlling its growth from the bottom up and, at the same time investigating what sort of shapes can be produced.
The method to be used will be bubbling CO2 gas through a solution of Calcium chloride solution to form the carbonate. An additional benefit is that this is a means of capturing CO2 and turning it from a negative environmental material, due to greenhouse gas, to a valuable material with lots of uses.
There is a lot of publications for this reaction reporting a wide variety of results, often appearing to contradict each other. This project takes the view that a broader, more in depth study will help understand why different results are obtained and how it can be more predictable. So far no one has studied it from an engineering perspective with the view point of turning it into an industrial process and so there are no information available on the impact of bubble size, raw material concentrations nor temperatures and additives. Work has been qualitative rather than quantitative. Thus a great deal needs to be learnt around mechanisms and control variables to turn this from academic papers into a process whereby consistent product quality can be produced.
The project will be aided by the use of well-defined membranes to control bubble size and well controlled flowrates and will build on work done in previous bubble reactors, ending up with a model of the process.
Simple models will elucidate what is happening in the process, through mass balances over a bubble as it rises and reacts to the interactions of many bubbles inside a reactor. From early data, as an MSc project it appears that the hydrodynamics is playing a role in control of the shape and size of the crystal and that amine based additives can have a significant impact on the rate of reaction as well as the crystal morphology.
It is hoped that this mechanistic understanding will provide the basis for further work in producing other speciality crystals whose properties are highly dependent on size and shape, such as zinc carbonate.
The project will investigate many of the characterisation tools available across the university from cryo slicing and Xray diffraction ( to build up an understanding as to how the larger crystals are formed) to testing novel ultrasonic techniques to track reaction rates and assess if onset of crystallisation can be controlled to the benefit of tailoring size and morphology.
As part of the modelling work we are working closely with an expert in modelling bubble reactors. Mariano Martin is an assistant professor at the University of Salamanca, Spain and he has already visited once on an Erasmus scholarship.
Currently the process is a batch one, whereby the Calcium chloride is depleted over time. Once the understanding of the main reactions are understood in a way that can be controlled the next step of the project will be to develop this into a continuous process.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509681/1 01/10/2016 30/09/2021
2037457 Studentship EP/N509681/1 01/02/2018 31/07/2021 Christopher James Grimes
Description The work so far has centered around the production of calcium carbonate particles formed within a bubble reactor. Whilst there has been some work reported previously in literature, these are often contradictory when trying to explain the influence of bubble size on the resultant particle size. This has been the primary focus of the study. It was found when probing the particle formation mechanism that the nano-particles are mostly formed within the vicinity of the bubble which are then pulled into the wadke of the bubble. These nano-particles then sinter/agglomerate to form the final larger spherical/cubic particles. Another finding is that the final internal particle structure can be altered depending on the final pH achieved within the reactor.
We have also tested how to achieve control over particles size and size distribution by studying: gas flowrate, stirrer speed, concentration of calcium salts, concentration of additives used, process temperature and gas introduction method. The motivation for this study was partially due to conflicting literature and wanting clarity on the impact of these process conditions. In additionit could also be used to understand the influence of membrane properties on the final particle size/size distribution. We found in most causes the particle size produced fluctuated when changing a variable but in some causes it was controllable. One example is by changing the stirrer speed and gas flowrate the particle size was seen to decrease whilst still achieving good control on the size distribution.
To futher probe the conditions the next step will be to investigate the impact of the additive used to influence the particle size, shape and morphology. It will be centered around the use of amines to capture CO2 (a mature research area) but little is known about how the chemistry translates in to producing CaCO3.
During the 2 years, several skills have been acquired both in experimental design and analytical techniques to probe the particle formation as well as controlling size. These analytical skills include: using a malvern G3 (particle size and distribution) and mastersizer (particle size and distribution) , Bruker XRD (crystallography), acoustic/ultrasound equipment (determine onset of crystallisation and gas fraction changes), SEM and Focused ion beam milling (particle structure/size and size distribution). In terms of experimental design; stagnant bubble to understand the kinetics and formation of particle due to reaction between gas and liquid, single bubble to simplify the reactive system( includes effect of continuous phase viscosity), membrane properties (pore size, size distribution), it is anticipated that the learnings from this work will enable investigation of translating to a continuous reactor.
Exploitation Route The ability to control the particle characteristics will allow for the production of a higher quality product, which will be useful in a high variety of industries such as : paper, cement, rubber, plastics, dyes, drug delivery and roads. This is because current manufacturing techniques of such particles are inefficient and highly energy intensive. The impact from this work will allow particles that fit high specification formulations within paints, pigments and dyes resulting in improved optical properties. The ability to change the internal structure means that you can control the particle density, porosity which will have significant impact in pharmaceutical/food applications. If this process could be made continuous it would result in a cheaper product price whilst still maintaining the desired particle characteristics. An added benefit would be that the process would utilize CO2 as a feedstock and hence would lead to a carbon neutral process.
Sectors Agriculture, Food and Drink,Chemicals,Construction,Energy,Environment,Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology

Title Batch Production of controlled calcium carbonate particles 
Description Investigation of membrane properties Process conditions and its affect on particle properties. Use of analytical techniques to characterize particle properties. 
Type Of Material Improvements to research infrastructure 
Year Produced 2020 
Provided To Others? No  
Impact Better control of particle size by using a highly controlled membrane pore size. 
Description Using Acoustics as a non-invasive characterisation technique 
Organisation University of Leeds
Department School of Food Science and Nutrition Leeds
Country United Kingdom 
Sector Academic/University 
PI Contribution Experimental set up Designing systems to investigate. Data Analysis.
Collaborator Contribution The partners are internationally renowned in the area of acoustic techniques to probe particle characteristics. Therefore, this expertise was sought to aid characterisation of the process used in this study to produce calcium carbonate. The partners contributed resources and space to allow for a research methodology to be investigated. They also helped with day to day operations as well as providing analysis of obtained data. Further work is being carried out to hopefully achieve publication in this area.
Impact Initial work has allowed the quantification of the gas fraction as well as the onset of crystal formation.
Start Year 2018