Why need acid pickling white corundum

Regardless of white corundum or brown corundum, there will be a certain amount of impurities after smelting, and the main components of these impurities are iron-containing oxides or magnetic substances. How to remove these impurities can be said to be a problem that many people have to face.
The main method used at present is magnetic separation. Magnetic separation mainly utilizes the difference in magnetic force of different magnetic substances, so that they form different movement routes, and then remove these iron-containing or other magnetic substances.
Many people will ask questions about this. I always heard that pickling removes impurities before, so under what circumstances would white corundum be pickled?
When white corundum needs to be pickled, we can think that the customer has put forward a request similar to this: the iron content of white corundum is lower than a certain value or as low as possible. Because at this time, it means that the objects they process cannot come into contact with iron ions, and once they come into contact, they will react chemically, so the content of iron ions is required to be lowered and lowered.
Pickling is mainly to use acid to remove iron ions in white corundum through chemical reaction, and the content of iron ions in white corundum after pickling is indeed low. However, it should be noted that pickling is easy to cause environmental pollution, so large-scale sewage treatment equipment is required, and the acid used for pickling is not easily available, so the price of pickling white corundum is also very high.