Polyhalite KNO3 Production via Calcium Hydroxide Precipitation
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Solution Overview
Problem
Current methods for producing potassium nitrate (KNO3) from polyhalite result in complex product mixtures and require neutralization with ammonia, lacking a process for producing essentially pure KNO3 without these complications.
Innovation Solution
A process involving the reaction of polyhalite with HNO3, followed by precipitation of Mg(OH)2 and separation of NaCl based on solubility differences, allowing for the production of commercially usable KNO3 without preliminary thermal treatment or washing out NaCl, and including steps for concentrating and purifying the KNO3.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polyhalite is reacted with strong acid to produce KNO3, then potassium nitrate is obtained, but complex product mixtures are formed requiring ammonia neutralization
Solution Approach 1:
The patent changes the pH parameter of the reaction system by using calcium carbonate neutralization instead of ammonia, achieving pure KNO3 product while avoiding the formation of ammonium salts. This parameter change in the neutralization agent eliminates the need for complex separation processes.
Solution Approach 2:
The patent extracts and removes impurities (CaSO4, Mg(OH)2, NaCl) from the reaction mixture through systematic filtration and precipitation steps, isolating pure KNO3. This extraction approach separates the desired product from complex mixtures without requiring ammonia neutralization.
2Manufacturing precision
If polyhalite is washed to remove NaCl before reaction, then product purity is improved, but process time and water consumption increase
Solution Approach 1:
The patent converts the harmful effect of NaCl impurity into a beneficial separation opportunity by utilizing the large solubility difference between NaCl and KNO3 at different temperatures. The NaCl remains in the mother liquor during cooling crystallization, automatically separating impurities without requiring preliminary washing steps.
3Productivity
If polyhalite undergoes thermal treatment before reaction, then reaction efficiency is improved, but energy consumption increases
Solution Approach 1:
The patent performs preliminary action by finely grinding the polyhalite ore to increase surface area and reactivity, achieving efficient reaction without thermal treatment. This mechanical preparation replaces energy-intensive heating while maintaining high reaction efficiency.
4Manufacturing precision
If complete separation of all impurities is performed, then product purity is maximized, but process complexity and cost increase
Solution Approach 1:
The patent utilizes parameter changes in solubility with temperature to achieve automatic separation. By cooling the reaction mixture, KNO3 crystallizes while NaCl remains dissolved, providing high purity product through a simple temperature-dependent separation mechanism.
Solution Approach 2:
The system performs self-service separation where the crystallization process automatically purifies the product. The KNO3 crystals form pure phases while impurities remain in the mother liquor, eliminating the need for additional purification equipment or complex separation procedures.
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 process achieves almost total recovery of KNO3 with high purity (>98.5%) and efficient separation of by-products, eliminating the need for ammonia neutralization and simplifying the production process.
Implementation Method 1
Reaction of polyhalite with acids (e.g. HNO3) is known in the literature as a means of producing crude salt mixtures
Implementation Method 2
adding at least one inorganic base to the solution obtained in the step of contacting polyhalite with HNO3, thereby precipitating as a solid at least part of the sulfate present in said solution
Implementation Method 3
precipitating as Mg(OH)2 at least part of the Mg2+ remaining in said solution by adding at least one basic compound to the remaining solution
Implementation Method 4
concentrating the solution obtained after said step of precipitating at least part of the Mg2+ remaining in said solution
Implementation Method 5
separating as solid KNO3 at least part of the K+ and NO3− contained in the solution remaining after the step of precipitating at least part of the NaCl
Data Source
AI summary
A process for producing KNO3 from polyhalite to is disclosed. In a preferred embodiment, the process comprises steps of (a) contacting polyhalite with HNO3; (b) adding Ca(OH)2 to the solution, thereby precipitating as CaSO4 at least part of the sulfate present in said solution; (c) precipitating as Mg(OH)2 at least part of the Mg2+ remaining in said solution by further addition of Ca(OH)2 to the remaining solution; (d) concentrating the solution, thereby precipitating as a sulfate compound at least part of the sulfate remaining in solution; (e) separating at least part of the NaCl from the solution remaining; and (f) crystallizing as solid KNO3 at least part of the K+ and NO3-contained in the solution. The process enables direct conversion of polyhalite to KNO3 of purity exceeding 98.5% and that is essentially free of magnesium and sulfate impurities.