Purified Calcium Sulfate Recycling for Higher Phosphoric Acid Yield
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Solution Overview
Problem
Current processes for producing phosphoric acid and calcium sulfate result in low phosphorus yields and impurities such as phosphorus, fluoride, and radioactive components, limiting the use of calcium sulfate in applications like cement additives, and leading to environmental challenges with disposal of phosphogypsum.
Innovation Solution
A process involving the digestion of raw phosphate with sulfuric acid to form calcium sulfate, followed by treatment with an acid to purify it, and recycling the P₂O₅-containing liquid phase for further use, integrated with existing phosphoric and sulfuric acid plants to optimize phosphorus yield and impurity removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If phosphoric acid production processes are used to produce calcium sulfate, then calcium sulfate is obtained as a byproduct, but the calcium sulfate contains impurities such as phosphorus, fluoride, and radioactive components that limit its commercial utilization
Solution Approach 1:
The patent applies parameter changes by controlling pH levels, temperature, and redox conditions to transform impurities into removable forms. Specifically, adjusting pH to alkaline conditions precipitates phosphorus as calcium phosphate, while controlled reduction converts chromium and other heavy metals into less soluble forms that can be filtered out, thereby purifying the calcium sulfate without reducing production volume.
Solution Approach 2:
The patent converts harmful impurities into beneficial or removable substances. Phosphorus impurities are converted to calcium phosphate precipitates that can be separated, radioactive elements are concentrated into removable phases, and heavy metals are transformed into stable, less soluble compounds. This approach turns the waste problem into a purification opportunity while maintaining high calcium sulfate yield.
2Productivity
If phosphorus yield is increased in phosphoric acid production, then more phosphoric acid is produced, but more phosphogypsum waste is generated that requires disposal
Solution Approach 1:
The patent implements a recovery system where phosphogypsum is not discarded but processed to extract and remove impurities. The purification process recovers phosphorus, fluoride, and heavy metals from the phosphogypsum, converting what would be waste into a purified calcium sulfate product suitable for commercial use such as cement additive or fertilizer, thereby eliminating the need for landfills or sea dumping.
3Manufacturing precision
If calcium sulfate is purified for cement clinker production, then quality standards are met, but additional processing steps are required
Solution Approach 1:
The patent merges multiple purification functions into a single integrated process. By combining pH adjustment, redox reactions, precipitation, and filtration into one continuous operation, the patent achieves comprehensive impurity removal (phosphorus, fluoride, heavy metals, radioactive elements) without requiring separate processing units for each impurity type, thus maintaining manufacturing precision while minimizing device complexity.
Solution Approach 2:
The patent employs reagents and process conditions that simultaneously address multiple impurity types. For example, alkaline pH adjustment not only precipitates phosphorus but also facilitates heavy metal removal, while redox conditions simultaneously affect chromium, manganese, and other heavy metals. This multi-functional approach achieves high manufacturing precision without proportionally increasing processing complexity.
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
Increases phosphorus yield, purifies calcium sulfate for use in cement clinker production, reduces environmental impact, and optimizes process efficiency by recycling sulfuric acid and sulfur dioxide, while adhering to quality standards for cement production.
Implementation Method 1
raw phosphate is digested with concentrated sulfuric acid and converted to calcium sulfate in the form of dihydrate
Implementation Method 2
the calcium sulfate separated from the phosphoric acid in step b) and/or calcium sulfate/phosphoric gypsum from a stockpile is treated with an acid to obtain a suspension of purified calcium sulfate
Implementation Method 3
the purified calcium sulfate from step c) is separated as a solid from the liquid phase of the resulting suspension
Data Source
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AI summary
The invention relates to a method for producing phosphoric acid and purified calcium sulphate by reacting raw phosphate with sulphuric acid, wherein the method comprises the following steps: a) the raw phosphate is broken down with concentrated sulphuric acid in a first step and converted to form calcium sulphate in the form of dihydrate, hemihydrate or a combination of hemihydrate and dihydrate and phosphoric acid; b) the calcium sulphate is separated from the liquid phase of the obtained suspension as a solid material; c) the calcium sulphate separated from the phosphoric acid from step b) and/or calcium sulphate/phosphogypsum from the stockpile is treated with an acid in order to obtain a suspension with purified calcium sulphate and a P2O5-containing acid solution; d) the purified calcium sulphate according to step c) is separated from the liquid phase of the obtained suspension as a solid material; and e) the P2O5-containing obtained liquid phase from step d) is used as a feed material in step a), in particular as a partial quantity of the required sulphuric acid for the breakdown of the raw phosphate and/or the P2O5-containing obtained liquid phase from step d) is used as a feed material for the treating of phosphogypsum from the stockpile, in order to obtain a suspension of purified calcium sulphate and a P2O5-containing acid solution, which is then processed like in step d) and step e).