Scheelite Tungsten Extraction via Mixed Acid Decomposition
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Solution Overview
Problem
Current methods for extracting tungsten from scheelite are inefficient due to high reagent dosages, energy consumption, and environmental concerns such as acid corrosion and volatilization, with residual tungsten impurities and complex impurity interactions leading to incomplete decomposition and high production costs.
Innovation Solution
A method involving a mixed acid solution of sulfuric acid and phosphoric acid at specific concentrations is used to decompose scheelite, forming soluble phosphotungstic acid, which reduces tungstic acid precipitation and corrosion issues, while recycling acids to minimize waste and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If hydrochloric acid is used to decompose scheelite, then the reaction rate is fast, but acid corrosion and volatilization occur causing poor working conditions
Solution Approach 1:
The patent changes the chemical parameters by substituting hydrochloric acid with sulfuric acid and phosphoric acid. This parameter change maintains fast reaction kinetics while eliminating the corrosive and volatile harmful effects of HCl, thereby improving working conditions without sacrificing decomposition speed
Solution Approach 2:
The patent converts the potentially harmful interaction between acid and scheelite into a beneficial process by using phosphoric acid to form soluble phosphotungstic acid complexes. This converts what could be a corrosive attack into a selective complexation reaction that enhances tungsten extraction while minimizing equipment corrosion
2Manufacturing precision
If sodium carbonate is used as a leaching agent, then scheelite decomposition is stable with residual WO3 less than 1%, but reagent dosage requirements are too large (3-6 times theoretical dosage)
Solution Approach 1:
The patent changes the chemical mechanism from carbonate leaching to acid complexation. By using sulfuric-phosphoric mixed acid, the system achieves complete decomposition through a different chemical pathway that forms soluble phosphotungstic acid, eliminating the need for excessive reagent dosages while maintaining low residual WO3 levels
Solution Approach 2:
The patent introduces phosphoric acid as an intermediary that forms soluble phosphotungstic acid complexes with tungsten. This intermediary mechanism allows for efficient tungsten extraction without requiring the large excess of sodium carbonate needed in conventional leaching methods
3Productivity
If NaOH is used for autoclaving scheelite, then more than 80% of APT is produced with residual WO3 at 1-3%, but large amounts of energy are consumed and production costs are high
Solution Approach 1:
The patent changes the physical parameters by conducting the reaction at lower temperatures and pressures compared to autoclaving. The sulfuric-phosphoric acid system achieves effective decomposition under milder conditions, significantly reducing energy consumption while maintaining high APT production efficiency
Solution Approach 2:
The patent employs a cost-effective acid system that can be easily prepared and applied. The sulfuric-phosphoric mixed acid provides an economical alternative to expensive autoclaving processes, achieving comparable or better results at lower operational costs
4Productivity
If sulfuric acid is used for decomposition, then tungsten leaching is achieved, but supersaturated gypsum quickly nucleates forming fine crystals that produce wrapping
Solution Approach 1:
The patent introduces phosphoric acid as a mediating agent that complexes with calcium ions to form soluble calcium phosphates instead of insoluble gypsum. This intermediary chemical pathway prevents gypsum nucleation and wrapping while maintaining efficient tungsten leaching through phosphotungstic acid formation
Solution Approach 2:
The patent converts the harmful gypsum precipitation into a beneficial process by using phosphoric acid to form soluble calcium phosphates. This transforms what would be a problematic wrapping issue into an advantageous soluble complexation reaction that enhances tungsten extraction efficiency
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 method achieves high tungsten extraction efficiency (>99%) with reduced reagent and energy use, minimizing waste and environmental impact, and allows for the recycling of phosphoric and sulfuric acids, making the process more cost-effective and environmentally friendly.
Implementation Method 1
A method involving a mixed acid solution of sulfuric acid and phosphoric acid at specific concentrations is used to decompose scheelite, forming soluble phosphotungstic acid
Implementation Method 2
forming soluble phosphotungstic acid, which reduces tungstic acid precipitation and corrosion issues
Data Source
AI summary
A method for extracting tungsten from scheelite by: 1) adding a mixed acid including H2SO4 and H3PO4 to a decomposition reactor; 2) heating the mixed acid to a temperature of 70-100° C.; adding scheelite while controlling the mixed acid present in an amount of 3-8 L per kg of scheelite; allowing the components in the decomposition reactor to react for 1-6 h, and filtering the resulting mixture to obtain a filtrate; 3) supplementing the filtrate with sulfuric acid consumed in the reaction; 4) crystallizing the filtrate to obtain phosphotungstic acid crystals and mother liquor; 5) dissolving the phosphotungstic acid crystals in water to obtain a phosphotungstic acid solution; 6) transforming the phosphotungstic acid solution into an ammonium tungstate solution for the purpose of preparing ammonium paratungstate; and 7) supplementing the mother liquor with phosphoric acid and water to an initial level and reusing the mother liquor for ore leaching.