Waelz Oxide Pressurized Alkali Washing for Halide Removal
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Solution Overview
Problem
Existing methods for removing halides, particularly insoluble fluorides, from Waelz oxide are inefficient, leading to high residual halide content and the generation of excessive by-products like gypsum, which increases costs and hampers valuable metal recovery processes.
Innovation Solution
A pressurized alkali washing technique using an autoclave to heat Waelz oxide with alkali under controlled conditions, followed by a repulping step with water, effectively removes insoluble fluorides and soluble chlorides, reducing the need for additional processing steps and by-product generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If atmospheric alkali washing process is used to remove halides from Waelz oxide, then chlorine removal rate is over 99%, but fluorine removal rate is only about 69% and a large amount of gypsum is generated
Solution Approach 1:
The patent applies parameter changes by transitioning from atmospheric pressure to pressurized conditions (autoclave at 2-3 atm). This pressure parameter change enables the conversion of insoluble CaF2 into soluble forms that can be washed away with alkali, thereby dramatically improving fluorine removal rate to over 90% while eliminating the need for additional chemicals that would generate gypsum by-products
Solution Approach 2:
The patent converts the harmful effect of insoluble CaF2 (which is difficult to remove and generates gypsum waste) into a beneficial process. Under pressurized alkali washing conditions, the insoluble CaF2 is transformed into soluble fluorosoda compounds that can be easily washed away, turning a waste-generating problem into an effective purification process with minimal by-products
2Manufacturing precision
If selective fluorine precipitation process is used to remove fluoride, then fluoride can be removed up to about 56 mg/L, but a large amount of gypsum is generated due to introduction of CaCO3, Ca(OH)2, and aluminum sulfate
Solution Approach 1:
The patent fundamentally changes the process parameters by using pressurized alkali washing instead of atmospheric precipitation. This parameter change eliminates the need for adding CaCO3, Ca(OH)2, and aluminum sulfate, thereby preventing gypsum formation while achieving superior fluoride removal through the conversion of CaF2 into washable soluble forms under pressure
Solution Approach 2:
The patent extracts fluoride from the system in a different manner - instead of precipitating it as gypsum through chemical addition, the pressurized alkali washing extracts fluoride by converting it into soluble fluorosoda compounds that are washed away with the alkali solution, thereby removing fluoride without generating gypsum waste
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 method achieves a significant increase in halide removal rates, up to 90% for fluorine and 99% for chlorine, minimizing the need for additional processing and reducing costs associated with by-product management.
Implementation Method 1
a pressurized alkali washing step of removing halide by heating a Waelz oxide cake containing Waelz oxide together with alkali under pressurized conditions
Implementation Method 2
a repulping step of removing halide by agitating a cake obtained from the pressurized alkali washing step together with water
Data Source
Figure 1
AI summary
The present disclosure relates to a method for removing halide from halide-containing Waelz oxide. According to the method, it is possible to effectively remove halide contained in Waelz oxide, especially insoluble fluoride such as CaF2, which are difficult to remove under atmospheric pressure conditions and present as insoluble substances. Accordingly, in the process of recovering valuable metals, an additional process for adjusting the concentration of fluorine or chlorine present in the electrolyte can be omitted, and costs can be reduced.