Apatite Recovery Process for High-Purity Gypsum and Phosphate Extraction
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Solution Overview
Problem
Existing technologies face challenges in efficiently processing apatite minerals due to high arsenic content, corrosion issues, and poor recovery of rare earth elements, leading to costly disposal of hazardous by-products and inefficient production of phosphoric acid and gypsum.
Innovation Solution
A method involving the dissolution of apatite in hydrochloric acid, followed by gypsum precipitation using concentrated sulfuric acid to produce high-quality gypsum, combined with solvent extraction to recover phosphoric acid and rare earth elements, while maintaining a balanced water cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulfuric acid digestion is used to process apatite, then phosphoric acid can be produced and calcium separated as gypsum, but the phosphoric acid concentration is limited to maximum 5 M due to difficulty in filtering gypsum from viscous acid at high concentrations
Solution Approach 1:
The patent changes the chemical parameters of the digestion process by using hydrochloric acid instead of sulfuric acid, and controlling the liquid-to-solid ratio and acid concentration to produce phosphoric acid at concentrations exceeding 10 M, thereby overcoming the concentration limit of conventional sulfuric acid processes
Solution Approach 2:
The patent uses a disposable filtration medium (celite) to create a filterable gypsum product that can be easily separated from high-concentration phosphoric acid, solving the filtration difficulty without requiring complex continuous filtration systems
2Quantity of substance
If sulfuric acid is used for apatite digestion, then calcium can be separated as gypsum, but the residual gypsum is of low quality and not suitable for valorization in the gypsum industry
Solution Approach 1:
The patent changes the chemical composition parameters by using hydrochloric acid digestion instead of sulfuric acid, producing high-quality anhydrite gypsum with low phosphorus content that meets commercial specifications and can be valorized in the gypsum industry, eliminating disposal costs
Solution Approach 2:
The patent converts the harmful phosphorus-containing waste gypsum into a beneficial commercial product by using hydrochloric acid digestion that produces low-phosphorus anhydrite gypsum suitable for construction and industrial applications
3Quantity of substance
If sulfuric acid digestion is used, then phosphoric acid can be produced, but about 80% of rare earth elements are incorporated into the gypsum lattice, which does not enable recovery of rare earth elements
Solution Approach 1:
The patent changes the chemical parameters by using hydrochloric acid instead of sulfuric acid for digestion, which prevents rare earth elements from being incorporated into the gypsum lattice, allowing them to remain in solution and be recovered through solvent extraction
Solution Approach 2:
The patent uses solvent extraction to separate and recover rare earth elements from the hydrochloric acid digestion solution, extracting them into an organic phase that can be processed to obtain pure rare earth products
4Quantity of substance
If conventional sulfuric acid process is used, then phosphoric acid production is enabled, but large amounts of water must be evaporated due to low acid concentration and strict water balance
Solution Approach 1:
The patent changes the concentration parameters by using hydrochloric acid digestion and controlling the liquid-to-solid ratio to produce phosphoric acid at concentrations exceeding 10 M directly, eliminating the need for energy-intensive evaporation processes
5Quantity of substance
If nitric acid is used for apatite processing, then calcium nitrate can be produced as a sellable product, but the total amount of nitric acid required is more than double the amount of sulfuric acid required
Solution Approach 1:
The patent changes the chemical parameters by using hydrochloric acid instead of nitric acid, achieving efficient calcium removal with hydrochloric acid consumption comparable to or less than sulfuric acid, while producing high-value anhydrite gypsum and avoiding the transportation and storage issues of large amounts of nitric acid
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 enables the production of high-value phosphoric acid and gypsum, reduces chemical consumption, minimizes environmental impact, and recovers rare earth elements effectively, making the process economically viable.
Implementation Method 1
dissolving of apatite mineral in an acid comprising hydrochloride
Implementation Method 2
extracting of a major part of the phosphate ions with an organic solvent
Implementation Method 3
Solid gypsum comprising at least 70% in a di-hydrate crystal form is precipitated from the second solution
Implementation Method 4
adding the second solution and sulfuric acid simultaneously into a continuous-stirred reactor in the presence of gypsum crystals
Data Source
AI summary
A method for recovery of commercial substances from apatite mineral comprises dissolving of apatite mineral in an acid comprising hydrochloride. The dissolution gives a first liquid solution comprising phosphate, calcium and chloride ions. The first liquid solution is treated into a second liquid solution comprising calcium and chloride ions. This treatment in turn comprises extracting of a major part of the phosphate ions with an organic solvent. A bleed solution is removed from the second solution. Solid gypsum comprising at least 70% in a di-hydrate crystal form is precipitated from the second solution. This precipitation of solid gypsum comprises adding the second solution and sulfuric acid simultaneously into a continuous-stirred reactor in the presence of gypsum crystals. Thereby, the precipitation of solid gypsum gives a third liquid solution comprising hydrochloride. An arrangement for recovery of commercial substances from apatite mineral is also presented.