With a POD of 1800 or later is it possible to end chattel slavery peacefully in the United States? If yes under what circumstances and when does slavery eventually end?
*The term "peacefully" is left up to your own discretion
Not likely, IMO. I mean, obviously, slavery certainly isn't going to last too much longer than, say, the 1940s or 1950s[1] even in the most radical outlier scenarios(primarily DoD and A Looser Union, though indenture in the latter TL doesn't quite seem to be slavery, whereas the former has slavery and more), and in more mainstream scenarios, probably not too much beyond 1880-1900 or so.
But, regardless of the time period, if it doesn't involve an actual civil war, then there will, unfortunately, likely be quite a bit of civil unrest, with plenty of heated political battles, terrorism, and perhaps escalated levels of violence in general; many of the slavers aren't likely to go down without a fight, that much is guaranteed.[2]
One of the biggest, and surprisingly, least addressed, problems that slavery presents, is the fact that wages of white(and other free) workers were quite depressed in the South when slavery was dominant over there; to make a long story very short and to the point, there might be many white workers who wouldn't care at all about the welfare of black workers(free or slave), one way or the other, and some who might actually truly support slavery, for whatever reason. But no worker, with very few exceptions, would be able to stomach working for crap money when he realizes that his lot in life might be better off without this source of nearly-free, or totally free labor sapping his wages, no matter what he might think of blacks, or Mexicans, etc.[3]
[1]TBH, the early 1960s might be barely plausible but you'd really be pushing it then. Anything after the mid '60s without a violent revolution and/or partial or complete collapse of the country might as well involve ASBs.
[2]OTL's Civil Rights struggle wasn't without a bit of bloodshed; here, it could be 100x worse.
[3]It can even be argued that a similar problem is in play in OTL's America today, only with undocumented immigrants and overseas labor taking the place of slaves in the antebellum South. After all, there are a fair number of skinflint CEOs out there, even today, who would rather employ a poor Chinese peasant (or perhaps an undocumented immigrant, from wherever.)and save a few million dollars, than pay American workers a fair wage and have to walk home with slightly lower profits.