MgO = Magnesium OxideAccording to todays report and going on...

MgO = Magnesium Oxide
According to todays report and going on todays report,
Smelters can be a bit funny in the impurities in the ore and the way the ore needs to be processed.
In MBN's case depending on which smelter(s) will sign the offtake agreement, that smelter will put conditions on the amount of impurities that it allows in the ore to be processed. Some are ok with abit of MgO others might want it removed.
I dont see this as negative in any sense, this is simply the technical side of the business, Supplier showing that it can supply to the Smelters requirements.

I see this as a very positive announcement, it shows how close MBN is to getting an offtake agreement and I believe the flow of good news will continue.
e.g TSX listing, Palestina Deposit results, upgrade of Santa Rita and BFS.