Rare Earth Extraction from Low-Grade Ores via Sulfate Conversion
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Solution Overview
Problem
Conventional rare earth extraction processes are ineffective for low-grade ores with high levels of iron and aluminum, as they require excessive acid consumption and high temperatures, leading to difficulties in solid-liquid separation and increased costs due to high impurity levels.
Innovation Solution
A method involving the reduction of ore particle size, formation of iron and aluminum sulfates with sub-stoichiometric sulfuric acid, and high-temperature treatment to convert rare earth minerals into soluble sulfates, allowing for selective solubilization and subsequent separation using known methods like solvent extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional acid or caustic attack processes are applied to low-grade rare earth ores with high iron and aluminum content, then rare earth extraction can be achieved, but acid or caustic consumption increases significantly and solid-liquid separation becomes difficult
Solution Approach 1:
The patent introduces an intermediary step of converting iron and aluminum to sulfates using sulfuric acid, which then act as mediators to react with rare earth minerals at high temperature. This indirect approach through sulfate formation allows selective leaching of rare earths while leaving iron and aluminum as insoluble residues, solving both the high reagent consumption and separation difficulty problems
Solution Approach 2:
The patent changes the temperature parameter to high temperature conditions (above 780°C) during the sulfate reaction step, which fundamentally alters the solubility characteristics of different metal sulfates. At this temperature, rare earth sulfates become soluble while iron and aluminum sulfates remain insoluble, enabling effective separation without excessive acid or caustic consumption
2Productivity
If high levels of concentrated sulfuric acid are used to attack monazite concentrates, then rare earth sulfates are formed, but acid consumption increases and solution purification becomes more difficult and costly
Solution Approach 1:
The patent applies partial action by using sulfuric acid only to convert iron and aluminum to sulfates in sub-stoichiometric amounts, rather than using excessive acid to attack all minerals. This controlled partial conversion creates the necessary conditions for selective leaching without the high acid consumption and purification difficulties associated with conventional methods
3Productivity
If caustic soda is used to attack rare earth phosphates, then rare earth hydroxides are produced, but aluminum and silicon leaching increases reagent consumption and solution viscosity
Solution Approach 1:
The patent converts the harmful effect of iron and aluminum presence into a beneficial separation mechanism. By converting these impurities to sulfates that remain insoluble at high temperature, they become part of the insoluble residue rather than contaminating the solution. This transforms the problem of high impurity content into an advantage for selective separation, avoiding the reagent consumption and viscosity issues of caustic attack
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 effectively recovers rare earth elements from low-grade ores by reducing acid consumption and impurity issues, producing a clear solution that simplifies downstream processing and enhances the extraction rate of rare earths.
Implementation Method 1
adding sulfuric acid in a sub-stoichiometric amount to obtain sulfates of iron and/or aluminum, submitting the mixture to a high temperature operation, where iron and/or aluminum sulfates react with rare earth minerals, forming soluble rare earth sulfates
Implementation Method 2
Adding this mix of rare earth sulfates and impurities to water in order to solubilize such compounds selectively
Data Source
AI summary
It is described a method for recovering rare earth elements from low grade ores including a first metal selected group containing at least one of iron and aluminum and a second metal selected from the group consisting of at least of the rare earth elements (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium and scandium), the method comprising the steps of: (i) contacting the ore with sulfuric acid to obtain sulfates of the first group of metals, (ii) subjecting the mixture to high temperatures in order to convert the first group of sulfates into phosphates or other stable species and the second group into sulfates, (iii) adding water to the cool mixture, selectively dissolving the rare earth elements and (iv) subjecting the rare earth solution to a purification process.