In Brazil about 1/6th of the population were slaves, half the Confederate percentage. Brazil's Constitution did not enshrine slavery. Brazil did not suffer horrific casualties and catastrophic economic damage to preserve slavery. Yet Brazil didn't end slavery until 1888.
The idea that the Confederacy would end slavery earlier than OTL's Brazil is ASB.
You raise a excellent point by bringing up the case of Brazil.
I agree that the end of slavery in the CSA before the same occurred in Brazil is ASB. However, it is important to notice that in the latter, there were a series of abolitionist laws created to ensure gradual emancipation(in no small part due to international pressure). in 1871 the "Ventre livre" law was established, it determined that any children of slaves born after the proclamation of said law was free, however they still had to work for their masters until it reached the age of 21. In 1885 the sexagenary law freed every slave above 65.
So slavery was going to die in Brazil sooner or later, if not by a general emancipation like it ocurred in 1888, then at the latest in 1935(when the slave born before the law of 1871 reached 65 years of age).
If these laws had not been enacted, I could see much greater british pressure on Brazil. The same has to be considered for the CSA. A gradual move towards abolition is something that would be demanded. At the very least in paper only. And that's not even considering Union pressure, slave rebellions(which would only grow more frequent and might receive Union support with the intent of weakening it's regional rival).
I can imagine the CSA holding out on any real attempt until the 1890's, but eventually a fundamental change to their constitution would've to be organized, to allow for the gradual, slow, safe end to the end of the slave practice. I can see the institution alive for a few decades after that, an system based socioeconomical disparity coupled with repression of any rights that would ensure a
de facto servile society.