Iron Oxide Separation from Phosphate Slag via Controlled Magnetite Crystallization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods fail to effectively separate iron oxide and phosphate from slag melts, resulting in low plant availability of phosphates due to their strong affinity, making phosphate from sewage sludge unsuitable for fertilizer production.
Innovation Solution
A controlled cooling process in a melting pan forms magnetite from iron oxide and optionally chromium oxide in slag melts, allowing phase separation and recovery of iron-free, chromate-free phosphate slag suitable for fertilizer production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iron oxide and phosphate are kept together in slag melt, then the phosphate can be recovered, but the plant availability of phosphate is extremely low due to strong affinity between iron oxide and phosphate
Solution Approach 1:
The slag melt is divided into two separate phases: an iron-rich magnetite phase and a phosphate-rich slag phase. By controlling cooling conditions, the system segments the mixed iron-phosphate melt into distinct phases, separating iron oxide from phosphate to eliminate their harmful affinity and improve phosphate plant availability.
Solution Approach 2:
The invention changes the temperature parameter during cooling to control phase separation. By cooling the slag melt through a specific temperature range (1600°C to 1420°C) at a controlled rate, the system transitions from a homogeneous liquid phase to a separated solid-liquid phase system, enabling iron oxide to crystallize as magnetite while phosphate remains in the slag phase.
2Manufacturing precision
If iron oxide is crystallized as magnetite from slag melt, then iron can be separated from phosphate, but this requires precise control of cooling rate through specific temperature range
Solution Approach 1:
The invention exploits the phase transition of iron oxide from liquid to solid magnetite crystalline phase during controlled cooling. By utilizing this phase transition at specific temperature ranges, the system achieves automatic separation of iron oxide as solid magnetite particles from the liquid phosphate-containing slag, simplifying the separation process despite the need for controlled cooling.
Solution Approach 2:
The invention replaces complex mechanical separation systems with a thermally-driven phase separation process. Instead of using mechanical filters or separators, the system uses controlled cooling to induce spontaneous phase separation based on temperature-dependent solubility and crystallization behavior, reducing mechanical complexity.
3Productivity
If rapid cooling is applied to slag melt, then cooling time is reduced, but magnetite crystallization does not occur and iron oxide-phosphate modifications form with low plant availability
Solution Approach 1:
The invention applies dynamic cooling control where the cooling rate is adjusted according to the temperature range. During the critical temperature range (1600°C to 1420°C), the cooling rate is controlled to allow magnetite crystallization, while outside this range, cooling can be faster. This dynamic approach balances productivity with reliable magnetite formation.
Solution Approach 2:
The invention performs preliminary heating or holding of the slag melt at temperatures above 1600°C to ensure complete melting and homogenization before entering the controlled cooling phase. This preliminary action ensures that the subsequent controlled cooling through the magnetite formation range produces consistent and reliable crystallization results.
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 enables the production of high-quality phosphate fertilizer with improved plant availability by selectively crystallizing iron and chromium as magnetite, facilitating efficient separation and recovery of phosphates.
Implementation Method 1
cooling the iron oxide-containing and phosphate-containing slag melt under oxidizing conditions to form solid magnetite, in particular magnetite in spinel configuration
Implementation Method 2
the cooling is controlled such that a temperature range of 1600°C to 1420°C is traversed over a period of 5 minutes to 25 minutes
Data Source
AI summary
A process for separating iron oxide from iron oxide-containing and phosphate-containing slag melts comprises the steps of: providing an iron oxide-containing and phosphate-containing slag melt in a crucible, cooling the hydroxide-containing and phosphate-containing slag melt under oxidizing conditions to form solid magnetite, in particular magnetite in the spinel configuration, wherein the cooling is controlled such that a temperature range of 1600°C to 1420°C is traversed over a period of 5 minutes to 25 minutes, preferably 10 minutes to 20 minutes, and particularly preferably 15 minutes, and separating the solid magnetite formed during the cooling step from the phosphate-containing slag.