Porous carbonaceous adsorbent materials possessing weakly acidic surface functional
groups have been evaluated for the selective removal of heavy metals from aqueous
solutions. Active carbons derived from both agricultural products (KAU carbons) and
polymeric resin (CKC carbon) have been oxidised by hot air or nitric acid to produce
samples with different degrees of surface oxidation. A novel phosphorus-containing
carbonaceous sorbent (PGP-P) has been prepared by pyrolysis of phosphorylated
phenol-formaldehyde resin. Surface modifications have been carried out to introduce
various acidic functional groups capable of selective heavy metal binding. The
properties of these sorbents have been compared to those of commercially available
polymeric carboxylic resin C 104 (Purolite) and oxidised Filtrasorb 400 (Chemviron).
Investigation into the physical structure of the adsorbents using microscopy and
nitrogen sorption at liquid nitrogen temperatures showed that the porous structure is
adversely affected by carbon oxidation. The surface area and pore volume decrease as
the degree of surface oxidation increases. The low surface area and pore volume of
PGP-P was attributed to the presence of phosphorus-containing functional groups
which protect the surface from excessive burn-off.
The surface functionality of the sorbcnts was determined by FT-IR, NMR and X-ray
photoelectron spectroscopy. Relatively high concentrations of different weakly acidic
functional groups were detected on the surface of the materials studied.
The ion-exchange properties of the sorbents were assessed by acid-base titration
techniques and electrophoretic mobility measurements. Oxidation of carbons with hot
air resulted in a greater proportion of relatively weaker type surface functionality (i.e.
phenolic) whereas nitric acid modification produced a higher concentration of
relatively stronger carboxylic groups. Electrophoretic mobility measurements
suggested that the carbon surface is negatively charged within the range of pH values
studied. pH titration results demonstrated relatively greater surface acidity of active
carbons compared to carboxylic resin. Active carbons were successfully applied for the selective removal of radionuclides.
The materials showed excellent decontamination factors for a-, b- and y emitters.
This was attributed to the presence of mineral admixtures and humic acids in carbons
as well as the surface functional groups.
Repeated cycles of lead sorption/elution indicated that the metal capacities of the
carbon-packed mini-columns were reduced but reached a steady level after 3-4 cycles.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.