Low-iron quartz sand (Fe2O3≤0.010%) is a crucial material for manufacturing photovoltaic glass, and its scarcity has been evident in recent years. The resources of vein quartz and high-quality quartzite are gradually diminishing. Although it presents challenges in the separation process, bauxite-associated quartz can be purified through ore dressing to meet the specifications for low-iron quartz sand, emerging as a new source for this material.
Bauxite, along with its associated minerals like quartz, feldspar, and mica, among other aluminosilicate minerals, exhibits natural variations in native particle size composition. In production, the physical purification processes applied to bauxite (such as dissociation and classification) also contribute to the enrichment of other aluminosilicate minerals like quartz and feldspar. Bauxite-associated quartz is typically enriched in the tailings of bauxite physical purification. Therefore, research on the particle size separation and ore dressing purification of bauxite-associated quartz often focuses on the original ore containing quartz or the tailings from the physical purification of bauxite.
In the original ore, the SiO2 content in +0.71mm particles is consistently above 95%, with Al2O3 and Fe2O3 contents not exceeding 2.10% and 0.24%, respectively. However, the SiO2 content sharply decreases in particles sized 0.125~0.71mm. As the particle size decreases, the SiO2 content decreases, while the Al2O3 and Fe2O3 contents increase.
The chemical composition of +0.71mm samples is superior to that of -0.71 mm. Quartz is mainly distributed in particles sized +0.045mm. Using this bauxite-associated quartz sand as a raw material for photovoltaic glass quartz sand, particle size separation in ore dressing contributes to improving the quality of quartz sand concentrates.
To prepare low-iron quartz sand for photovoltaic glass, the bauxite-associated quartz sand undergoes particle size separation ore dressing. This process involves separate studies on particle sizes of +2mm, 0.71-2mm, and 0.125-0.71mm, achieving a cascade utilization of bauxite-associated quartz sand.
During the experiments, it was found that the SiO2, Al2O3, and Fe2O3 content of strong magnetic concentrates for different particle sizes did not meet the quality requirements for low-iron quartz sand used in photovoltaic glass manufacturing. This indicates that the sample does not require a re-selection process to reduce TiO2 content.
Subsequently, acid reverse flotation was applied to strong magnetic concentrates. The results showed that, with the same flotation reagent dosage, the SiO2 content of flotation concentrates for +0.125-0.71mm, -2+0.71mm, and +2mm particles significantly increased, while the Al2O3 and Fe2O3 contents decreased significantly.
Leaching experiments were conducted using +2mm flotation concentrates (SiO2, Fe2O3, Al2O3 contents were 99.55%, 0.16%, 0.016%, respectively) as raw materials. Sulfuric acid, hydrofluoric acid, oxalic acid, and mixed acids were used as leaching media. Atmospheric warm acid leaching was performed on +2mm flotation concentrates. The types of leaching media, their quantities, experimental leaching time, and temperature were 1.5 hours and 100°C, respectively.
For different particle sizes, a grinding-classification-magnetic separation-flotation process was employed. The SiO2, Al2O3, and TiO2 contents of +0.71mm quartz concentrates met the chemical composition requirements for photovoltaic glass quartz sand. However, the Fe2O3 content was still higher than 0.010%, not meeting the relevant requirements. The SiO2, Fe2O3, and Al2O3 contents of +2mm particle size were superior to +0.71-2mm; the -0.71mm particle size quartz concentrate did not meet the chemical composition requirements for photovoltaic glass quartz sand.
For +2mm flotation concentrates, leaching with sulfuric acid and oxalic acid as leaching media reduced the Fe2O3 content of quartz concentrate to 0.0091%, meeting the requirements for Fe2O3 content in low-iron quartz sand for photovoltaic glass.
