I think its the right company but I dont think the buckets are from a mixer ,The mixer is chain belt driven no buckets on it.
The chain belt co. was named that from 1891- 1964 and was making bucket elevators from about 1900-?.
I think they are from a bucket elevator and may not have had a single use but could be used on a variety of material.
The company (now rexnord)still makes bucket elevators and list the cast iron buckets as mill duty buckets.
When I was a kid, my neighbors had that chain and bucket system like that to get water from their cistern. It might have been a re-purposed use, but that's what I witnessed.