Unfortunately my chemistry doesn't extend as to how difficult it is. What is however clear is the difficulty will depend on what the other metals are that need to be removed and some will be easier than others.
An overly simplistic analogy is how difficult is it to get washing clean? The task of getting washing clean is broadly the same (except there's a lot less dirt to remove) - remove any dirt/grime without destroying the original product. Some types of stain are easy to get clean. Others need special spray's and I'm sure most (all?) people will have had stain's on clothes that have been extremely difficult to remove or they have been unable to remove the stain. While the type of clothes helps, removing stains is about the type of stain. While the starting grade of Mn helps, removing all the other metals/minerals depends on what's there.
Matt Fernley has provided a very informative linked in article (link below). As author of Battery Metals Review, he is more informed than your average poster. Carbonate ore's which include Butcherbird are the "easy" pathway. Many, perhaps even most ore's will be able to be purified - but at a cost and possibly with technical difficulties. These non-carbonate ore's are likely to become the RHS of the cost curve. Although the article is 3 years old, its naming the same companies that are appearing in western HPMSM discussions.
https://www.linkedin.com/pulse/some-manganese-more-equal-than-others-matt-fernley
Some manganese is more equal than others (linkedin.com)The statement below was a key one from this article around the frequency of ore that is readily transformed to HPMSM:
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