Bauxite serves as the primary raw material for global metallic aluminum production, accounting for over 90% of total usage. Based on its core composition, bauxite is classified into three main types: high-alumina,high-iron, and high-silica varieties. Among these, high-silica bauxite presents unique technical hurdles due to its elevated reactive silica content—typically exceeding 8% of the ore's total weight.
Countries such as China, India, and Indonesia, which boast substantial reserves of high-silica bauxite, face significant challenges when applying the traditional Bayer process. This method not only demands excessive caustic soda consumption but also triggers the formation of insoluble by-products like sodium garnet. Such compounds severely impair alumina recovery rates, leading to substantial resource losses.
So, how to extract aluminum from high-silica bauxite? This article breaks down three optimized beneficiation methods, detailing their operational steps and ideal applications.
3 Efficient Bauxite Ore Beneficiation Processes
The key to efficient bauxite ore beneficiation lies in the removal of excess silicon dioxide (SiO₂) and the selection of an appropriate extraction route. Depending on the SiO₂ content in the ore, the following three bauxite ore processing flowsheets are widely adopted.
(Ideal For medium-to-low iron, high-silica bauxite ores)
Applicable Ore Conditions:
Al₂O₃≥45%
SiO₂≥ 8%
A/S (Al₂O₃/SiO₂) < 6
Dominant minerals: diaspore with minor boehmite, quartz, illite, and sericite
Bauxite Ore Beneficiation Process:
(1) Ore Preparation: The bauxite ore is crushed and ground using a ball mill machine to 80% passing 0.074 mm, freeing the aluminum-bearing phases.
(2) Alkaline Desilication (Pretreatment): The slurry reacts with NaOH (100–120 g/L) at 95-110°C for 12 hours. Reactive silica dissolves into Na₂SiO₃, achieving silica removal from bauxite ore.
(3) Solid-Liquid Separation: Filtration removes the desilicated residue, improving leach solution quality.
(4) High-Temperature Bayer Leaching:Using concentrated NaOH (180-220 g/L), leach at 140-160°C under 0.6-1.0 MPa for 2-4 hours to form sodium aluminate.
(5) Red Mud Settling: Add flocculant powder (PAM) to settle impurities. Red mud is dewatered and may be repurposed.
(6) Al(OH)₃ Precipitation: Cool solution to 60-80°C and seed with Al(OH)₃ for precipitation.
(7) Calcination: Dry and calcine the Al(OH)₃ at 1050-1100°C for 12 hours to obtain alumina (Al₂O₃).
This modified Bayer process for high-silica bauxite minimizes the drawbacks of traditional routes, enabling more efficient aluminum extraction from bauxite.
(Suitable for refractory high-iron, high-silica bauxite ores)
Applicable Ore Conditions:
Al2O3≥50%
SiO2= 10-15%
Fe2O3> 15%
High contents of illite, chlorite; uneconomical via Bayer process
Bauxite Ore Processing Steps:
(1) Crushing & Mixing: Grind ore to≤0.5 mm and mix with lime and soda ash. Adjust Na2O/Al2O3 molar ratio to 1.1-1.3.
(2) Sintering: Roast in a rotary kiln at 1250-1350℃for 1.5 hours. This forms soluble sodium aluminate and insoluble calcium silicate.
(3) Cooling & Grinding: Cool and grind sintered blocks to 90% passing 0.074 mm.
(4) Alkaline Leaching: Leach in hot water (90–100℃) for 2-3 hours to extract sodium aluminate.
(5) Separation, Precipitation & Calcination: Perform filtration, Al(OH)3precipitation, and final calcination—mirroring steps in the Bayer process.
This bauxite ore beneficiation process is particularly useful when dealing with high-iron, high-silica ores that cannot be treated economically by conventional means.
(Recommended for medium-grade, high-silica bauxite ores with by-product value)
Applicable Ore Conditions:
Al2O3≥40%
SiO2≥10%
Potential to recover by-products (e.g., silica gel, iron salts)
High-Silica Bauxite Beneficiation Process:
(1) Ore Grinding: Crush and grind to D90 < 0.074 mm (200 mesh). Slurry is prepared for leaching.
(2) Acid Leaching: React with 10-15% HCl or H2SO4 at 95℃for 2-4 hours. Al dissolves as Al3+; silica precipitates as gel.
(3) Solid-Liquid Separation: Cool and dilute the solution. Add PAM flocculant and filter using press or ceramic vacuum filters.
(4) Al(OH)3 Recovery & Calcination: Precipitate and calcine Al(OH)3 at 1050-1100℃for 2 hours to yield high-purity alumina.
(5) Acid Recovery: Neutralize and recycle acid via multi-effect evaporation or ion exchange, enabling a closed-loop system.
Conclusion
The above three processes are all applicable to the aluminum extraction treatment of high silica bauxite, but in actual operation, it is necessary to combine with the specific composition of the raw ore, geographic environment, and the project objectives of a comprehensive analysis, to develop a scientific and feasible solution. Xinhai Mining always insists that "there is no identical mine in the world", and we believe that every mine should have its own customized process and equipment configuration. If you are looking for a more suitable solution for your mine, or want to know about related mineral processing equipment, welcome to contact us. Xinhai is willing to work with you to promote the efficient and green development of the project.
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