Phosphate Digestion with Mixed Acids to Reduce Calcium Sulphate Co-precipitation

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Solution Overview

Problem

Existing processes for extracting phosphates from phosphate sources often result in the co-precipitation of calcium sulphates with phosphates, leading to decreased yield and efficiency, particularly when using sulphuric acid which introduces sulphate ions and requires additional steps to manage.

Innovation Solution

A process involving the digestion of a phosphate source with a digestion liquor composed of an aqueous solution of sulphuric acid and one or more mineral acids, such as hydrochloric acid, at controlled ratios and concentrations, to precipitate calcium sulphates while maintaining phosphate solubility, thereby enhancing filtration efficiency and reducing P2O5 losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If sulphuric acid is used to digest phosphate source, then calcium sulphates are precipitated, but co-precipitation with phosphates occurs leading to decreased yield

Engineering Contradiction:

Improvephosphate recovery yieldVSAvoidP2O5 loss in calcium sulphate cake

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The digestion process is divided into two sequential steps: first digestion with phosphoric acid to solubilize phosphates, then a second digestion with sulphuric acid to precipitate calcium sulphates. This segmentation allows selective precipitation of calcium while keeping phosphates in solution, resolving the co-precipitation problem.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first digestion step with phosphoric acid is performed as a preliminary action before the second digestion with sulphuric acid. This preliminary solubilization of phosphates ensures they remain in solution during the subsequent calcium sulphate precipitation, preventing co-precipitation losses.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If strong acid (HCl or H2SO4) is used for digestion, then phosphates are solubilized, but equipment cost increases due to corrosion resistance requirements

Engineering Contradiction:

Improvedigestion efficiencyVSAvoidequipment material cost

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent changes the chemical parameter of the digestion liquor from strong mineral acids (HCl, H2SO4) to phosphoric acid, which has sufficient acidity for phosphate solubilization but much lower corrosion potential. This parameter change maintains digestion efficiency while reducing equipment material requirements and costs.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If HCl is used for digestion, then phosphates are solubilized, but chlorine is introduced into the system which is banned from many applications

Engineering Contradiction:

Improvedigestion efficiencyVSAvoidchlorine contamination

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the harmful strong acid HCl with phosphoric acid, which achieves the same digestive function without introducing banned chlorine. Phosphoric acid itself is a phosphate source, so it contributes to the desired product rather than creating harmful byproducts.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

4Device complexity

If phosphoric acid alone is used for digestion, then equipment corrosion is reduced, but phosphate solubilization may be insufficient

Engineering Contradiction:

Improveequipment material costVSAvoidphosphate solubilization efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The patent merges two digestion steps: first with phosphoric acid for gentle solubilization and corrosion protection, then with sulphuric acid for complete phosphate extraction and calcium precipitation. The combination of these two acids achieves superior overall performance compared to either acid alone.

Inventive Principle:

Principle #5Merging (Combining)

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 effectively precipitates calcium sulphates, facilitating efficient filtration and maintaining high phosphate recovery, thus improving the overall efficiency and reducing operational costs compared to traditional methods.

Implementation Method 1

Undesired calcium can be precipitated as calcium sulphates (=CaSO4·nH2O) by addition of sulphuric acid (=H2SO4)

Methodology Applied

Scientific EffectPrecipitation: Precipitation

Implementation Method 2

raw material issued from the phosphate source can be digested in a first step in a digestion liquor to solubilize the phosphate ions

Methodology Applied

Scientific EffectSolubilization: Solvation

Data Source

PatentUS20250042742A1Process for producing a phosphate containing product from a phosphate source

Publication Date: 2025.02.06 PRAYON SA

AI summary

A process for producing a phosphate containing product from a phosphate source is provided. a reactor is fed with a raw material including phosphate in amounts of at least 5 wt. % P2O5, and calcium in amounts of at least 0.7 wt. % CaO. The raw material is digested with a digestion liquor (L) of an aqueous solution of sulphuric acid (H2SO4) and a mineral acids (HX), in a ratio (H+(SA)/H+(L) of between 2 and 75%, where H+(SA) and H+(L) are the mole content of H+issued from the sulphuric acid and the digestion liquor (L), respectively. The in amounts such that the molar ratio H+(L)/Ca is between 0.8 and 1.95, wherein Ca is the mole content of calcium. The digested suspension is separated into an aqueous phosphate rich solution and a first solid phase.