Calcification-Carbonation Process for Bayer Red Mud Alkali Recovery
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Solution Overview
Problem
Current methods for treating Bayer red mud result in high alkali content, leading to low product prices and high energy consumption, with limited recovery of valuable elements like aluminum oxide, and often require costly evaporation for alkaline solution concentration.
Innovation Solution
A calcification-carbonation method is employed to recover alkali and aluminum from Bayer red mud, involving calcification dealkalization and carbonation conversion reactions, which recycle high-concentration alkaline solutions and water, allowing for direct reuse and reducing energy consumption by avoiding evaporation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional dealkalization methods using lime are applied to red mud, then alkali content is reduced to cement industry standards, but only sodium oxide can be recovered and the overall benefit is low
Solution Approach 1:
The patent changes the chemical parameters by using calcium aluminate instead of conventional lime for dealkalization. This parameter change enables simultaneous recovery of both sodium oxide and aluminum oxide from red mud, transforming a single-element recovery process into a multi-element recovery process that significantly improves overall benefit
Solution Approach 2:
The patent makes the dealkalization process multi-functional by selecting calcium aluminate as the reagent, which simultaneously achieves: (1) dealkalization of red mud to meet cement standards, (2) recovery of sodium oxide, and (3) recovery of aluminum oxide. This multi-functionality resolves the limitation of conventional single-element recovery
2Quantity of substance
If low-concentration alkaline solutions are produced after dealkalization, then alkali is removed from red mud, but the solutions cannot be directly used and require evaporation concentration, leading to high energy consumption
Solution Approach 1:
The patent changes the concentration parameter of the alkaline solution by using calcium aluminate dealkalization, which produces high-concentration alkaline solutions that can be directly reused without evaporation concentration. This parameter change eliminates the energy-consuming evaporation step while maintaining effective alkali removal
Solution Approach 2:
The patent implements self-service by making the alkaline solution produced during dealkalization directly reusable in subsequent Bayer process operations. The high-concentration solution generated in situ serves the next process step without requiring external energy input for concentration, creating a self-sufficient material cycle
3Quantity of substance
If sintering method or acid leaching method is used to extract valuable elements from red mud, then aluminum oxide can be recovered, but energy consumption and equipment requirements are high
Solution Approach 1:
The patent changes the chemical environment parameters by using calcium aluminate dealkalization followed by carbonation conversion, creating conditions that enable aluminum oxide recovery without the high energy input required by sintering or acid leaching methods. The process operates at lower temperatures and pressures while achieving effective aluminum recovery
Solution Approach 2:
The patent introduces calcium aluminate as an intermediary substance that facilitates aluminum oxide recovery. Instead of directly applying high-energy sintering or acid leaching, the calcium aluminate acts as a mediator that enables aluminum extraction through chemical conversion and carbonation at lower energy levels
4Adaptability or versatility
If red mud is used directly as cement raw material, then utilization is achieved, but high alkali content makes the red mud unusable for cement and other bulk industries
Solution Approach 1:
The patent extracts the harmful alkali (sodium oxide) from red mud through dealkalization with calcium aluminate. The extracted sodium oxide is recovered as a valuable product, while the dealkalized red mud with reduced alkali content becomes suitable for cement industry applications, resolving the conflict between utilization and alkali content
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 enables full utilization of red mud, recovering sodium and aluminum oxides with high yield, reducing energy consumption, and producing tailings that can be used in the cement industry, increasing aluminum oxide extraction efficiency by 15% and reducing ore consumption by 20%.
Implementation Method 1
Mixing the Bayer red mud with lime and calcium aluminate, performing a calcification dealkalization conversion reaction in high-concentration sodium hydroxide mother liquor
Implementation Method 2
mixing clear water with the calcified residues by the liquid-solid ratio of the clear water to the calcified residues being 5 to 1 mL/g in a sealed container, and filling the sealed container with CO2 for pressurizing at first, so that the partial pressure of CO2 gas in the sealed container reaches 1.8MPa; then performing a carbonization conversion reaction for 180min under the condition of 120 DEG C
Implementation Method 3
extracting aluminum hydroxide from carbonization residues with low-temperature aluminum dissolution mother liquor containing sodium hydroxide of which the concentration is 150 g/L under the conditions that aluminum dissolution temperature is 100 DEG C and the aluminum dissolution time is 20min
Implementation Method 4
treating the liquid phase obtained after the low-temperature aluminum dissolution reaction with lime for aluminum precipitation, wherein the mass ratio of the amount of calcium oxide in the lime to aluminium oxide in the solution is 2.5 to 1, and under the conditions that the precipitation temperature is 90 DEG C and the reaction time is 1min, obtaining 38.63t of precipitated calcium aluminate and a sodium hydroxide solution
Implementation Method 5
a liquid phase is a high-concentration sodium hydroxide solution containing aluminium oxide, 3% by volume of the high-concentration sodium hydroxide solution after the conversion reaction is taken out and returned to replenish alkali for the Bayer method
Data Source
AI summary
The present invention relates to the field of environmental protection, in particular to a method for recovering alkali and aluminum in the course of treatment of Bayer red mud by using a calcification-carbonation method. The method comprises the following steps of after mixing the Bayer red mud with calcium aluminate or with the calcium aluminate and lime, performing calcification dealkalization conversion in high-concentration alkaline liquor of which the caustic alkali concentration is 100-300g/L, enabling all of a silicon-containing phase in the red mud to be converted into hydrated garnet to enter calcified residues produced during dealkalization, and carbonizing the calcified residues so as to obtain carbonized residues; and then performing the working procedures including low-temperature aluminum dissolution, aluminum precipitation and the like so as to obtain calcium aluminate products, wherein the calcium aluminate is returned to the course of the calcification dealkalization conversion of the red mud for recycling. Part of an alkali-containing and aluminum-containing liquid phase after calcification dealkalization conversion can be used as supplementary alkali in a Bayer production course for recycling. According to the method disclosed by the present invention, recovering alkali and aluminum from the red mud and harmless treatment of the Bayer red mud can be realized, so that the method is an energy-saving environmentally-friendly utilization method of the red mud.