Precipitated Calcium Carbonate Aragonitic Content via Segmented Seed Process
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Solution Overview
Problem
Existing methods for producing precipitated calcium carbonate (PCC) with increased aragonitic crystal content are unable to achieve more than 60% aragonitic content, which is insufficient for various industrial applications.
Innovation Solution
A two-stage process involving the formation of an aqueous suspension of precipitated calcium carbonate seeds with strontium hydroxide, followed by carbonation of a slurry of calcium hydroxide in the presence of these seeds, to produce a PCC product with greater than 60% aragonitic polymorph content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If strontium salts or aragonite seed crystals are added to promote aragonite crystal formation, then the aragonitic content increases marginally, but the total aragonitic content remains below 60%
Solution Approach 1:
The process is divided into two distinct stages: first, formation of aragonite-rich seed crystals with high aragonitic content (≥80%); second, carbonation of calcium hydroxide slurry using these seeds. This segmentation allows optimization of seed crystal composition separately from the final product formation, enabling the seeds to achieve high aragonitic content without being constrained by the overall process limitations of single-stage methods.
Solution Approach 2:
Aragonite-rich seed crystals are prepared in advance through a preliminary carbonation process with controlled strontium addition (0.01-0.05 moles Sr per mole Ca). These pre-formed seeds with high aragonitic content (≥80%) are then used in the second stage to inoculate the calcium hydroxide slurry, ensuring that aragonite crystal formation begins with a favorable nucleation environment rather than attempting to form aragonite de novo in a single stage.
2Manufacturing precision
If strontium compounds are added during carbonation, then aragonite crystal formation is promoted, but the manufacturing cost increases
Solution Approach 1:
The process optimizes the strontium addition parameter to a specific range (0.01-0.05 moles Sr per mole Ca, corresponding to 0.005-0.030 moles Sr per mole Ca(OH)2). This parameter optimization ensures sufficient strontium for aragonite crystal formation while avoiding excessive costs. The strontium is added only in the first stage for seed crystal formation, not throughout the entire process, further controlling costs while maintaining aragonitic content ≥60%.
3Device complexity
If a single-stage carbonation process is used, then the process is simple, but the aragonitic content cannot exceed 60%
Solution Approach 1:
The process is divided into two distinct stages: first, formation of aragonite-rich seed crystals with high aragonitic content (≥80%); second, carbonation of calcium hydroxide slurry using these seeds. This segmentation allows optimization of seed crystal composition separately from the final product formation, enabling the seeds to achieve high aragonitic content without being constrained by the overall process limitations of single-stage methods.
Solution Approach 2:
Aragonite-rich seed crystals serve as an intermediary substance that transfers the aragonite formation capability to the main carbonation process. These seeds act as a mediator between the strontium addition step and the final calcium carbonate precipitation, carrying the aragonite formation template into the bulk slurry carbonation, thereby enabling high aragonitic content in the final product.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process effectively increases the aragonitic content of PCC to greater than 70%, enhancing its suitability for applications such as paper, paints, and pharmaceuticals, while reducing manufacturing costs compared to prior methods.
Implementation Method 1
carbonating a suspension of Ca(OH)2 in the presence of 0.005 to 0.030, or more preferably, 0.01 to 0.02, moles of strontium, in the form of Sr(OH)2, per mole of Ca(OH)2 prior to carbonation
Implementation Method 2
carbon dioxide is reintroduced into this slurry to precipitate the calcium carbonate
Data Source
AI summary
The present invention provides a process for preparing a precipitated calcium carbonate product. The process comprises the steps of preparing an aqueous suspension of precipitated calcium carbonate seeds by carbonating a suspension of Ca(OH)2 in the presence of 0.005 to 0.030 moles of Sr, in the form of Sr(OH)2, based upon moles of Ca(OH)2 prior to or during carbonation; forming an aqueous suspension of a precipitated calcium carbonate product by carbonating a slurry of Ca(OH)2 in the presence of 0.5 to 5% by dry weight of the precipitated calcium carbonate seeds, wherein the precipitated calcium carbonate seeds have a D50 that is less than the D50 of the precipitated calcium carbonate product and the precipitated calcium carbonate seeds have an aragonitic polymorph content greater than or equal to the precipitated calcium carbonate product.