by increasing the pH and temperature and by chemical modification of theme

Pressure, special chemicals, temperature and pH will change the solubility.

Particle size of particle is important for solubility.Particle size id depends on foaming agent, foaming time along with factors mentioned in above two ans. Try to do solubility chk for diff particle size

u have to make a study about the powder you got ! the practicle size and how fast will it react when mixed with water !!

Also use different mixer speed ! 

You may also think about changing the solution's pH (in wich u will mix the powder) 

I agree fir changing pH is correct option

But

Here I think more study and options needs to be on improving solubility of powder without considering modifications in solvent.

So, you need to study different foaming agents which will give smaller particle size

try to reduced drying time, for drying time surface of particles may get hardened.

For higher drying time surface of particle may get hardened, for this drying time needs to be lower