Iron Hydroxide Filter Granules Freeze-Thaw Stability
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Solution Overview
Problem
Existing methods for producing iron-containing filter materials result in materials that are either prone to disintegration in water or produce small, high-pressure granules, both of which compromise filtration effectiveness and stability.
Innovation Solution
A method involving the reaction of a trivalent iron compound with a base, followed by washing and partial water removal using ceramic membranes, and subsequent freeze-thawing in a refrigerated chamber at atmospheric pressure to produce mechanically stable granules with controlled particle size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the colloid is dried at ambient temperature or above to remove more than 50% of water, then the product forms dry or hard lumps that can be granulated, but the drying operation closes the material pores and reduces the specific surface area, resulting in low contaminant removal capacity
Solution Approach 1:
The invention uses freeze-drying (lyophilization) which involves freezing the colloidal suspension and then sublimating the ice directly to vapor under vacuum, bypassing the liquid phase. This phase transition removes water without closing pores or reducing specific surface area, unlike thermal drying. The frozen water crystals create a porous structure that is maintained during sublimation, preserving the high surface area needed for contaminant removal while achieving low water content in the final granulated product.
2Stability of the object's composition
If freeze-thawing is used to concentrate and compact the material while maintaining high porosity, then the material forms highly porous compact granules, but the granules are of very small dimensions causing high pressure drops on water passage
Solution Approach 1:
The invention performs preliminary concentration and partial drying of the colloidal suspension before freeze-drying, adjusting the solids content to an optimal range. This preliminary action ensures that during subsequent freeze-drying and granulation, sufficiently large granules form with appropriate dimensions. The pre-adjusted concentration allows ice crystals to grow to sizes that, upon sublimation, leave behind granules of adequate size (avoiding the high pressure drop issue) while maintaining the porous structure needed for high contaminant removal capacity.
3Length of moving object
If freezing under high pressure is used to achieve large-dimension granules, then large granules are obtained, but vessels able to withstand pressures of 800-1000 atm are required
Solution Approach 1:
The invention replaces the mechanical high-pressure freezing system with a vacuum-based freeze-drying system. Instead of applying 800-1000 atm pressure to achieve large granules, the process uses vacuum (reducing pressure) to enable sublimation of ice at low temperatures. The large granule formation is achieved through controlled freezing and sublimation dynamics in vacuum, eliminating the need for complex high-pressure vessels while still producing sufficiently large granules with appropriate dimensions for filtration applications.
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 yields granules with enhanced mechanical stability and filtration performance, maintaining high contaminant removal capacity while minimizing material loss during back-washing and reducing pressure drops in water passage.
Implementation Method 1
reacting ferric chloride with sodium hydroxide. The reaction product is an iron hydroxide in colloidal form, together with sodium chloride
Implementation Method 2
The iron hydroxide suspension is then fed to a membrane filter press where part of the water is removed
Implementation Method 3
freezing the product resulting from the filtration. The effect of this freezing is that the water contained in the material is removed from it by the growth of ice crystals
Implementation Method 4
During growth, the crystal subtracts pure water from the product which in this manner is concentrated and compacted, but maintains a high porosity determined precisely by the canaliculi through which the freezing has drawn out the water
Implementation Method 5
After this freezing, the material is thawed, the ice is converted into water and the iron hydroxide remains in the form of highly porous compact granules
Data Source
AI summary
A method for producing an iron-containing filter material for water treatment includes the steps of reacting a trivalent iron compound and a base inside a vessel until the trivalent iron is completely neutralized, to obtain an iron hydroxide and a salt consisting of the anion of the trivalent iron compound and the cation of the base; feeding the iron hydroxide and the salt into ceramic membranes to wash the iron hydroxide from the salt in cross-flow; feeding the iron hydroxide suspension to a membrane filter press where part of the water is removed, to obtain a panel having a moisture content of less than 77% by weight; inserting the panel into containers; and positioning the containers inside a refrigeration chamber operating at atmospheric pressure and at temperatures less than 0° C. for a time between 24 and 240 hours.