Solar Salt Purity via pH Control and Alum Treatment
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Solution Overview
Problem
Current methods for producing solar salt from sea and sub-soil brines fail to achieve both high purity and the desired Ca2+ to Mg2+ ratio, which are essential for industrial applications like chlor-alkali and soda ash industries, often resulting in costly processes or low purity levels.
Innovation Solution
A process involving alum treatment of brine followed by controlled pH adjustment in the crystallizer to prevent the formation of insoluble magnesium compounds, optimizing the pH to 6.5±0.1 to achieve high purity and the desired Ca2+ to Mg2+ ratio of 2:1 to 3:1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional solar salt production from brines is used, then cost-effectiveness is maintained, but salt purity and Ca2+ to Mg2+ ratio are insufficient for industrial applications
Solution Approach 1:
The brine is treated with alum before charging into crystallizers to pre-precipitate magnesium impurities. This preliminary treatment removes magnesium oxy compounds that would otherwise co-precipitate with salt during crystallization, ensuring high purity salt with controlled Ca2+ to Mg2+ ratio while maintaining the simplicity of solar salt production
Solution Approach 2:
The pH of the brine is controlled and maintained between 6.0-6.5 during the alum treatment process. This specific pH range optimization prevents the formation of insoluble magnesium compounds that could contaminate the salt crystals, thereby achieving the desired Ca2+ to Mg2+ ratio of 2:1 to 3:1 without requiring complex additional processing steps
2Manufacturing precision
If alum treatment is applied to brine before crystallization, then salt purity is improved, but magnesium impurities increase unless pH is controlled
Solution Approach 1:
The pH of the brine is precisely controlled and maintained between 6.0-6.5 during alum treatment. This parameter control prevents the formation of insoluble magnesium oxy compounds that would otherwise co-precipitate with salt crystals, thereby achieving both high salt purity and low magnesium impurity content simultaneously
Solution Approach 2:
Alum acts as an intermediary substance that selectively precipitates magnesium impurities from the brine before salt crystallization. By controlling the pH during this intermediary treatment step, the process prevents magnesium compounds from contaminating the final salt product while maintaining high purity levels
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 produces solar salt with >99.5% purity and the desired Ca2+ to Mg2+ ratio, reducing magnesium impurities and maintaining high absolute purity levels, making it suitable for industrial use while being cost-effective.
Implementation Method 1
it is treated with alum to yield high purity salt
Implementation Method 2
subjecting the brine to solar evaporation to crystallize out carbonate, salt and gypsum
Implementation Method 3
controlled adjustment of pH to also effect the desired ratio of Ca2+ to Mg2+ in the salt
Data Source
AI summary
The process of the invention is an improvement over the existing process of producing salt of high purity from alum-treated brine disclosed recently in the prior art. More particularly, the invention rectifies the ratio of Ca2+ to Mg2+ from a value <1 to a value in the range of 2-3 desired by chlor-alkali and soda ash industries. The improved process involves the adjustment of pH of clarified brine with aqueous HCl so as to carry out salt crystallization at a pH of 6.5 instead of at the natural pH of 7. The pH adjustment reduces the Mg2+ impurity in salt while slightly raising the Ca2+ impurity in the salt and thereby achieving the desired ratio.