sludge formed while attempting to neutralise caustic

[amitchopra]

while washing plastic scrap grinding I tried to neutralize the caustic present in it with HCl.The addition of HCl caused a grey sludge which would float to the top leaving clear water below.I had thought that the resulting NaCl would be soluble in water and not create a problem but the floating sludge is problematic.When the water turns basic the sludge mixes with the water again.Has any one faced any similar difficulties? What is this floating sludge? How does one handle it?

 

[bimr]

Would suspect it is oil, but with knowing so little, somewhat hard to say. You have not supplied any information on the water quality, plastic, or why the plastic scrap has sodium hydroxide or anything else mixed into it. If you drop the pH, if there is emulsified oil present, it will break the emulsion and cause the oil to release.

 

[amitchopra]

The Plastic grinding was of bottle cap coming from a plant which crushes and washes and reclaims PET from PET bottles.The caustic was a remnant.I was trying to reclaim the plastic.The water used was tap water.The sludge did not seem to be oily.

 

[omjee]

Hi there,

You might want to consider dissolved air flotation to remove this unsettling sludge. Dissolved air helps float the sludge so that the floating sludge can be removed from the surface as scum by a mechanical skimmer.

Cheers,
Wan