You've said this a couple times now, and you've been given bad information.
A- banning through police powers is not the same as expropriation. If the government is not taking the property to own and derive public benefit from it then it is not expropriation and those legal guidelines don't apply.
B- Re- Compensated Emancipation - they didn't have to, they chose to - as a combination of bribe to enact the desired policy change and bailout to the impacted industries. Sommerset v Stewart laid out that there was no basis for slavery (people as property) under british common law in 1772.