Can apple trade in my old mini iPad ?

You can verify eligibility for trade-in and obtain an estimate of the potential trade-in value here:

Apple Trade In - Apple

You should be able to trade-in at a physical Apple Store - many choosing this option by preference as the device can be checked, the trade-in value finalised and the process completed while in-store. Be aware that Apple’s in-store trade-in values may differ from the on-line estimate.

If your iPad is too old or otherwise not eligible for trade-in, Apple will still responsibly recycle you iPad without any cost to you.

Before parting with your iPad, whether trading-in or selling privately, ensure that the device is properly prepared:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support