You’re using the wrong rank token. Using a Rabbit token will get you a Peacemaker weapon, however, for a Molten weapon you will need to use a Paid Tournament token.
You can get these tokens by salvaging Solo Queue and Team Queue rewards, e.g. Forge weapons or Orrian armor (see here for a list of skins that have a chance to salvage into Free or Paid Tournament tokens).
PvP Achievement Rewards chests drop the same items as the Solo Queue and Team Queue reward chests.
Hope this helps. 
Pureblade – Maelstrom Warriors [MW] – Gandara (EU)
8/9 Professions, Asura Guardian main.
8/9 Professions, Asura Guardian main.