How will Hashem return His hand on Yerushalayim?
Rashi: Blow after blow, until the sinners are eradicated.
Radak: Time after time, until I refine you, and you remain clean. The Sigim and Bedil are the Resha'im.
What is "ka'Bor"?
Rashi: It is an expression of Boris (soap). It is an expression of cleansing, like "u'Var Levav" (Tehilim 24:4), for it cleans the garment from its stains.
Radak: Like the matter that is Mevarer (clarifies and selects) the silver from the Sigim, and [the silver] remains clean.
What are "Sigayich"?
Rashi: Above (23) "Kaspech Hayah l'Sigim" is copper mixed with silver. Also here it is a mixture of Resha'im with Kesherim. I will eradicate the sinners, who are the Sig.
What are "Bedilayich"?
Rashi: It is Bedil (tin) mixed with silver, i.e. sinners among you. Radak - the plural includes all mixtures mixed with it.
Why does it say both "va'Etzrof
Malbim: First I will refine the silver in a smelting pot, to separate all Sigim from the silver. Then I will remove all Bedilayich - they will not be found in the world at all. There will not be found people who mix in inferior metals to fake [pure] silver.