High-Alumina Fly Ash Alumina Extraction Process
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Solution Overview
Problem
Current methods for extracting alumina from high-alumina fly ash face challenges such as high energy consumption, large material flow, and significant slag formation, with the soda lime sintering method being unsuitable due to low alumina silica ratio and complex equipment requirements.
Innovation Solution
A method involving pre-desiliconization of high-alumina fly ash with sodium hydroxide, followed by the production of activated calcium silicate through a series of reactions and treatments, including milk of lime addition, dealkalization, and sulfuric acid soaking, to achieve a high alumina silica ratio and reduce slag formation, while recovering sodium hydroxide and producing alumina with low energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If soda lime sintering method is used to extract alumina from high-alumina fly ash, then alumina extraction is achieved, but energy consumption is high and slag formation is large due to low alumina silica ratio
Solution Approach 1:
The patent applies preliminary desiliconization treatment to fly ash before alumina extraction. By removing silicon dioxide in advance through chemical reactions (using sodium hydroxide solution followed by carbonation), the alumina silica ratio is improved before the sintering process, thereby reducing energy consumption and slag formation during alumina extraction
Solution Approach 2:
The patent extracts and removes silicon dioxide from fly ash through a two-step process: first using sodium hydroxide solution to dissolve silicon as sodium silicate, then carbonating to precipitate calcium silicate. This extraction of silicon before alumina extraction resolves the contradiction by improving the alumina silica ratio and reducing subsequent energy consumption
2Productivity
If soda lime sintering method is used to extract alumina from high-alumina fly ash, then alumina extraction is achieved, but large amount of slag is generated requiring high energy consumption
Solution Approach 1:
The patent performs preliminary desiliconization by treating fly ash with sodium hydroxide solution to dissolve silicon, then carbonating to precipitate calcium silicate. This preliminary removal of silicon reduces the amount of slag formed during subsequent alumina extraction, as less silicon remains to form slag with alumina
Solution Approach 2:
The patent extracts silicon dioxide from fly ash through chemical reactions, converting it into calcium silicate precipitate that can be separated. This extraction removes the harmful silicon component before alumina extraction, thereby reducing slag formation and improving overall process efficiency
3Device complexity
If acid method is used to extract alumina from fly ash, then equipment investment is reduced and slag formation is minimized, but equipment corrosion becomes severe
Solution Approach 1:
The patent changes the chemical parameters by using sodium hydroxide solution (alkaline) instead of acid for desiliconization. This parameter change maintains the advantages of low equipment investment and reduced slag formation while avoiding severe equipment corrosion, as the alkaline treatment is less corrosive to typical industrial equipment
4Productivity
If direct use of soda lime sintering method is made on fly ash with low alumina silica ratio, then alumina extraction is attempted, but clinker sintering control becomes difficult and material flow increases
Solution Approach 1:
The patent performs preliminary desiliconization treatment to improve the alumina silica ratio before sintering. By removing silicon dioxide in advance, the sintering process becomes easier to control, as the improved ratio allows for better clinker formation and reduces the narrow sintering range problem
Solution Approach 2:
The patent extracts and removes silicon dioxide from fly ash through chemical reactions before sintering. This extraction improves the alumina silica ratio, making clinker sintering easier to control and reducing material flow requirements, as less silicon interferes with the sintering process
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 effectively reduces material and energy consumption, minimizes slag formation, and enhances the alumina silica ratio, enabling the co-production of high-value activated calcium silicate and alumina with improved properties, such as high surface area and low density, suitable for various industrial applications.
Implementation Method 1
high-alumina fly ash and sodium hydroxide solution are mixed, heated up and introduced into a pressure container for desiliconization reaction
Implementation Method 2
milk of lime is added to the desiliconized solution from step 1) for reaction, to obtain calcium silicate filter cake
Implementation Method 3
calcium silicate obtained from dealkalization reaction is washed with clean water and then added to dilute sulfuric acid solution for soaking; aluminum sulfate is added to decrease the pH to be below 10
Implementation Method 4
the second-stage desiliconized refined solution is subjected to carbonization decomposition to obtain aluminum hydroxide as seed crystal
Implementation Method 5
the second-stage desiliconized refined solution is subjected to carbonization decomposition to obtain aluminum hydroxide as seed crystal
Data Source
AI summary
A method for co-producing alumina and activated calcium silicate from high-alumina fly ash, comprising the steps that: high-alumina fly ash reacts with sodium hydroxide solution to obtain desiliconized solution and desiliconized fly ash; milk of lime is added to the desiliconized solution to obtain activated calcium silicate; limestone and sodium carbonate solution are added to the desiliconized fly ash to blend raw slurry, the raw slurry is baked into clinker, and sodium aluminate crude solution is obtained from dissolution of the clinker; the sodium aluminate crude solution is subjected to the processes of first-stage deep desiliconization, second-stage deep desiliconization, carbonization decomposition, seed precipitation and etc to obtain alumina. According to the invention, less material flow and small amount of slag formation are achieved, the energy consumption, material consumption and production cost are low; the extraction rate of alumina is high, and meanwhile, activated calcium silicate with high added value is co-produced.