Crystallizing Divalent Anion Salts from Brine
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Solution Overview
Problem
Existing methods for removing soluble alkali metal or ammonium salts of divalent anions from concentrated brine solutions are inefficient, leading to contamination and significant salt losses, especially in processes like membrane electrolysis, as they result in small crystal sizes that are difficult to separate and require costly washing steps.
Innovation Solution
A method involving the use of a crystal growth inhibitor during membrane filtration and subsequent crystallization to produce coarse salt crystals with a narrow size distribution, allowing for easy separation and reducing impurity levels, thereby minimizing waste and enabling the isolation of divalent anion-comprising salts for further use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional evaporative crystallization is used to produce solid sodium chloride from brine, then sodium chloride crystals are obtained, but the crystals contain occlusions of mother liquor leading to contamination with divalent anions (SO42−, CO32−)
Solution Approach 1:
The invention extracts and removes divalent anion contaminants (SO42−, CO32−) from the brine solution before the crystallization process through filtration or other separation methods, preventing their incorporation into the sodium chloride crystal lattice and eliminating the need for subsequent washing steps
Solution Approach 2:
The invention performs preliminary removal of divalent anion contaminants from the brine solution before crystallization occurs, thereby preventing contamination at the source rather than addressing it after crystal formation
2Object-affected harmful factors
If additional washing and centrifuge steps are employed to reduce contaminant levels in sodium chloride, then purity is improved, but energy consumption and process complexity increase
Solution Approach 1:
The invention extracts and removes divalent anion contaminants (SO42−, CO32−) from the brine solution before the crystallization process through filtration or other separation methods, preventing their incorporation into the sodium chloride crystal lattice and eliminating the need for subsequent washing steps
Solution Approach 2:
The invention allows the crystallization process to produce inherently pure crystals by preventing contaminant incorporation in the first place, making the system self-sufficient without requiring additional energy-intensive washing or centrifugation operations
3Object-affected harmful factors
If brine containing high concentrations of sulfate or dichromate salts is treated by nanofiltration, then these salts can be removed up to their solubility limits, but the brine must be purged leading to salt losses
Solution Approach 1:
The invention extracts and removes divalent anion contaminants (SO42−, CO32−) from the brine solution before the crystallization process through filtration or other separation methods, preventing their incorporation into the sodium chloride crystal lattice and eliminating the need for subsequent washing steps
Solution Approach 2:
The invention recovers divalent anion contaminants from the brine solution through selective removal processes, converting what would be waste purge streams into recoverable byproducts and minimizing salt losses
4Quantity of substance
If crystallization is attempted without a crystal growth inhibitor, then salts can be removed from supersaturated solution, but very small crystals and aggregates are formed that are difficult to separate from mother liquor
Solution Approach 1:
The invention introduces a crystal growth inhibitor as an intermediary substance that mediates the crystallization process, controlling crystal nucleation and growth to produce larger, well-formed crystals that are easily separable from the mother liquor while maintaining effective salt removal
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 approach effectively reduces the need for additional washing steps, minimizes salt losses, and produces purified brine and isolated divalent anion salts in a single process, with the use of crystal growth inhibitors preventing primary nucleation and allowing for efficient separation of crystals from the mother liquor.
Implementation Method 1
EP 0 821 615, for instance, discloses a nanofiltration process for filtering a brine comprising e.g. sodium sulfate or sodium dichromate by feeding said brine comprising more than 50 g/l of sodium chloride to a nanofiltration membrane module under a positive applied pressure
Implementation Method 2
subjecting the resulting brine solution to a membrane filtration step, thereby separating the brine solution into a brine stream being supersaturated for the divalent anion-comprising salt (concentrate) and a brine stream being undersaturated for the divalent anion-comprising salt (permeate)
Implementation Method 3
concentrating the salts into a supersaturated concentrate e.g. by subjecting the solution to nanofiltration
Implementation Method 4
precipitating crystallizable supersaturated salts, such as calcium sulfate, in the concentrate
Data Source
AI summary
The invention pertains to removing soluble alkali metal or ammonium salt of a divalent anion from brine comprising following steps: obtaining brine with NaCl-concentration between 150g/L and saturation in the presence or absense of a cyrstal growth inhibitor for NaCl(GCI-NaCl),or with NaCl concentration above saturation in the presence of a CGI-NaCl, said brine optionally comprising a crystal growth inhibitor for the alkali metal or ammonium salt of the divalent anion(CGI-DA); if necessary, acidify the solution to pH<11.5; if the concentration of CGI-DA is less than 20 mg/L, adding CGI-DA to obtain at least 20 mg CGI-DA/L; subjecting the solution to a membrane filtration; if the concentration of CGI-DA in the concentration from the separation is less than 20 mg/L, adding CGI-DA to obtain at least 20 mg CGI-DA/L; crystalling the concentration; removing the crystallized alkali metal or ammonium salt of the divalent anion.