Fly Ash Fractionation for Precipitated Calcium Carbonate
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Solution Overview
Problem
The pulp and paper industry faces challenges in using fly ash as a raw material for producing inorganic fillers or pigments due to high levels of harmful elements like arsenic and heavy metals, leading to uneven quality and unprofitable production.
Innovation Solution
A method involving the fractionation of fly ash into coarser and finer fractions, where the coarser fraction is used to produce precipitated calcium carbonate by reacting it with carbon dioxide, reducing the amount of arsenic and heavy metals in the final product, and potentially including magnetic separation to enhance purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fly ash is used as raw material for producing precipitated calcium carbonate, then production cost is reduced and waste utilization is improved, but the filler quality deteriorates due to high amounts of arsenic and heavy metals
Solution Approach 1:
The fly ash is divided into different size fractions through classification. The finer fraction containing harmful elements is separated from the coarser fraction suitable for filler production. This segmentation allows selective use of the coarser fraction for PCC production, reducing contamination while maintaining cost-effectiveness.
Solution Approach 2:
The harmful fine fraction containing arsenic and heavy metals is extracted and removed from the fly ash before the carbonation process. This extraction eliminates the source of contamination, enabling production of quality filler from what would otherwise be waste material.
2Object-affected harmful factors
If fly ash is used as raw material, then environmental friendliness is improved through waste reuse, but the filler exhibits uneven quality and low brightness
Solution Approach 1:
Classification separates fly ash into size-based fractions, removing the problematic fine fraction that causes quality uniformity issues. The coarser fraction provides more consistent particle size and composition for filler production, improving quality uniformity while maintaining environmental benefits.
Solution Approach 2:
Different fractions of fly ash have different properties - the coarser fraction is suitable for filler production while the finer fraction contains contaminants. By applying local quality selection (using only the coarser fraction), the patent achieves both environmental friendliness and consistent filler quality.
3Quantity of substance
If the finer fraction of fly ash is used in carbonation, then complete utilization of raw material is achieved, but the amount of arsenic and heavy metals in the final product increases
Solution Approach 1:
The fly ash is segmented into size fractions before carbonation. Only the coarser fraction is used in the carbonation process, while the finer fraction is discarded or treated separately. This segmentation prevents harmful elements from entering the PCC production stream while still utilizing the coarser fraction effectively.
Solution Approach 2:
The harmful fine fraction is extracted and removed before the carbonation step. This extraction ensures that arsenic and heavy metals do not contaminate the final PCC product, allowing safe and effective use of fly ash as a raw material.
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
This method reduces arsenic and heavy metal content by 20-60% in the filler, resulting in a higher-quality filler with improved brightness, suitable for use in paper and paperboard production.
Implementation Method 1
adding carbon dioxide to said suspension to form precipitated calcium carbonate
Implementation Method 2
fractionating said fly ash in at least one step, whereby a coarser fraction is separated from a finer fraction
Data Source
AI summary
The invention provides a method of producing a filler comprising calcium carbonate (PCC), preferably to be used in paper or paper board production or in fibre based composites. The method of the invention comprises the steps of; —providing fly ash generated in paper or paper board production; —fractionating said fly ash in at least one step, whereby a coarser fraction is separated from a finer fraction; —forming a suspension of said coarser fraction; —adding carbon dioxide to said suspension to form precipitated calcium carbonate. The method of the invention avoids problems with high amounts of arsenic and heavy metals in the production of filler comprising PCC, when using ash generated in paper or paper board production as a raw material. It has been shown that harmful elements, such as arsenic and heavy metals, are primarily accumulated in the finer fractions of the fly ash. Thus, by using the coarser fraction in the step of carbonation, the amount of arsenic and heavy metals in the final product is reduced.