The used iPhone without Apple ID is valuable for recycle.
How to remove Apple ID?
1. Remove Find My iPhone: the first thing you have to do is remove Find My iPhone from your device. This is the one that triggers the Activation Lock so you have to get this out of the way. If you have enabled Find My iPhone, here’s how you can remove it: Settings → iCloud → turn off the switch for Find My iPhone.
2. Remove Your Device from iCloud: Now, follow this tutorial here to remove this device from your iCloud Find My iPhone account too. If you are selling/giving away the iPhone/iPad, it is going to be setup as new on another Apple ID. It makes sense to remove the device from your account.
3. Sign Out Everywhere: Go to Settings → iTunes & App Store and tap on the Apple ID field. Then, tap on Sign Out. Next up, go to Settings → iCloud and repeat the process. These are the two usual places where you have signed in with your Apple ID.
4. Reset: Finally, don’t forget to reset. Erase all content and settings from Settings → General → Reset and then for good measure, Reset All Settings too.