In the corundum industry, high-alumina bauxite is actually in a rather "awkward" position.
Looking at it from the perspective of the final product, it's not considered a finished product; however, it determines whether many subsequent processes can be completed.
Many people only know about brown fused alumina and white aluminum oxide, but they overlook a crucial fact:
The upper limit of corundum's quality is largely determined before it even enters the furnace.
The transformation of high-alumina bauxite from refractory raw material to fused alumina is not a simple upgrade, but a thorough selection process.
Let's start with the most obvious change.
High-alumina bauxite is a mineral aggregate with a complex structure and dispersed impurities;
while corundum is essentially high-purity alumina crystals.
To transform from "ore" to "crystal," a complete "break-down and rebuild" process is necessary.
This "rebuild" process takes place in the electric furnace.
Before entering the electric furnace, high-alumina bauxite has already undergone many rounds of selection. Not all high-alumina bauxite is suitable for making corundum. Aluminum content, impurity structure, iron content, and alkali metal content are all repeatedly weighed. Many seemingly decent bauxite materials end up remaining in the refractory system because once they enter the furnace, the problems caused by impurities are amplified.
When producing brown fused alumina, high-alumina bauxite is not fed into the furnace alone.
It is usually mixed with reducing materials such as carbon and iron filings to remove impurities at high temperatures. This process is essentially a reduction smelting process. Iron is reduced, silicon is removed, and what remains is a melt primarily composed of alumina.
This step has a relatively higher tolerance for raw materials, which is why brown fused alumina can absorb more types of bauxite. However, "absorbing" and "absorbing well" are two different things. Poor quality raw materials will affect the color, toughness, and crystal structure of the resulting brown fused alumina, and the differences in its performance in the mold are already predetermined.
The path to producing white aluminum oxide is even more demanding.
Strictly speaking, white aluminum oxide no longer uses high-alumina bauxite directly, but rather alumina powder "purified" from bauxite. However, going back further, the root is still the bauxite itself. Higher impurity levels in the ore source increase the cost and difficulty of producing chemical alumina, and whether stable white aluminum oxide production can be achieved is already evident upstream.
The electrofusion process of white aluminum oxide is more like a "purity test." There's no room to reduce impurities; more impurities result in more disordered crystals and a darker color. Ultimately, this manifests in the product as unstable particle size, insufficient toughness, and an unsatisfactory lifespan. This is why white aluminum oxide, despite its "whiteness," can vary greatly in usability.
What comes out of the electric furnace is merely the "prototype" of corundum.
Following this are a series of processes including cooling, crushing, shaping, screening, magnetic separation, and acid washing. Many people focus on post-processing, but in reality, the true framework of corundum is determined by that one furnace smelting. If the initial steps are done incorrectly, subsequent steps can only be patched up, rarely fundamentally altering the process.
Therefore, looking back at this process, you'll find something: high-alumina bauxite isn't simply "upgraded" into corundum; it undergoes a complete reconstruction. The quality of the raw materials doesn't disappear; it simply remains in the product in a different form.
This is precisely why the real difference in the corundum industry isn't just the size of the electric furnace or the age of the equipment, but rather the depth of understanding of the upstream raw materials. Whoever understands better which bauxite is suitable for which path is more likely to successfully produce corundum.
