Can colloid change back into solution?

Only when an appropriate amount of HCl is added.

Although FE(OH)3 is an alkali insoluble in water,

However, because hydrochloric acid is a strong acid, there are a lot of free hydrogen ions in water, which can be neutralized with hydroxide ions under alkaline conditions (including intolerance).

The reaction produces ferric chloride.

But FeCl3+3H2O=Fe(OH)3 is not a reversible reaction! ! !

Supplement to the answer:

The landlord should understand the relationship between colloid and alkali. ...

Colloid is a kind of system, which belongs to metastable system. Some substances and water can form this system, including alkali of course. Alkali is just a substance, which has nothing to do with its state and system, but only depends on its molecular composition.

So iron oxide colloid is of course alkaline. All bases can react with compatible strong acids.

You got it?