By removing the ash and adding an appropriate proportion of fresh sand, it can be reused. This only applies to cast iron sand. I have only used it once here and replace it every day. How can the black sand produced be reused to produce what kind of casting? If it is a steel casting, it is used for backing sand.
If it is a cast iron component, remove the ash content and add an appropriate proportion of fresh sand, it can be reused. This requires sand treatment. If you say it is a waste sand that has already been eliminated, the treatment cost may be greater than adding new sand, so most people choose to add new sand regularly in proportion instead of reusing these old sand.
There are many chemical substances such as binders in the waste sand, which generally require regeneration before reuse. Direct use can cause pollution. Complete sets of recycling equipment are relatively expensive, so some small factories' sand is disposable because buying new sand is cheaper than buying equipment.