In the Psalms David describes the word of God as pure. Like silver tried how many times?

For best purity they try the silver seven times. It is likely that David is referring to the process of Cupellation to separate Silver from lead. It’s worth an internet search.

Source: Psalm 12:6

In the book of Isiah how did God refine the house of Jacob?

God refined the house of Jacob with the furnace of affliction.

Source:

Isiah 48:10

In the book of Revelations which church does God tell to buy gold tried in the fire?

This is the church of Laodicea. Fire was one way to purify gold and be sure it was really Gold.

Source:

Revelation 3:18

What book of the old Testament contains this phrase, “he shall sit as a refiner and purifier of silver”?

This Phrase is in the book of Malachi chapter 3. The prophet is talking about purifying the Priests so that they may offer to the Lord in righteousness.

Source:

Malachi 3:3