KJV:
And he shall sit as a refiner and purifier of silver: and he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the LORD an offering in righteousness.
NASB:
"He will sit as a smelter and purifier of silver, and He will purify the sons of Levi and refine them like gold and silver, so that they may present to the LORD offerings in righteousness.