I am working on tertiary treated sludge i.e. sludge treated by Polyaluminium Chloride (PAC) for phosphorus removal. I want to investigate how Phosphorus interact with PAC i.e by simple precipitation, adsorption and know what sort of bonding in between them. I am interested to investigate by spectroscopic studies.
Precipitation means reducing solubility of a dissolved species that compound gets insoluble. E.g. precipitating heavy metals by sulfide or in other cases salting out. For adsorption you need an interface, i.e. something insoluble.
Dear Dr. Sobisch,
Thank you so much for your reply. The PAC is soluble in water but it gives little turbidity when we use. It means that phosphorus most probably interact with PAC by precipitation mechanism but in some papers also suggested the adsorption by PAC. I think it might be possible that both mechanism undergoes simultaneously.
Do you have any idea which spectroscopic studies are useful to investigate these mechanism?
Thank you
Al or Fe chloride solution is usually added to the wastewater and flocculated by the addition of base. The solid is separated and added to the other solids. Flocculation is needed to reduce the concentration of Al or Fe in the water that is discharged.
This is not a process I have direct knowledge of, but it is likely that phosphate-Al or -Fe species form in solution and as well as P sorbing to the precipitated phase. That is there will be both sorption and incorporation. The distribution may change as the products age.
Why are you interested ?
Dear Dr Milham.
Thank you so much for your answer. We are working on Phosphorus recovery from SSA and from sludge and also studying how flocculant (PAC) interact with P. PAC treated sludge has significant amount of P which is recoverable through wet chemical extractions. Secondly, the heavy metals are in very low concentration, so it has potential to be used as fertilizers.
Thank you so much.
Dear Umair,
as Paul wrote, dissolved iron and aluminum salts tend to form insoluble complexes.
The related changes may be characterized by turbidimetry.
If dissolved compounds lead to precipitation of phosphate they likely will form a dense
sediment. The more it contains insoluble hydroxo complexes the less will be the packing density after centrifugation. Further sediments are compressible opposite to the pure precipitate which forms incompressible sediments.