| dc.description.abstract | In this study, the potential of rice husk ash (RHA) to (i) adsorb phenol, resorcinol and
2-chlorophenol and (ii) be used in the detection of pyrogallol and pyrocatechol dissolved in
aqueous solutions have been investigated and optimum conditions of operation identified.
For the adsorption experiments, the sorbent power for RHA for the three phenolic
compounds was evaluated and their adsorption behaviour investigated at diverse
RHAlsolution ratios, pH, temperature, contact time and phenolic compound concentration
using batch equilibration technique. For the 'detection' studies, effects of contact time, initial
phenolic compound concentration, pH, sonication, and solution temperature were studied.
Quite high adsorption capacities were obtained after one hour of contact time: 93% of
5xlO-5M phenol/l g RHA, 90% of 5xlO-5M resorcinol/l g RHA, and 98% of 2.45 xlO-5M 2chlorophenolllg
RHA were realised. Instantaneous adsorption measuring 36% and 15% of
lxl0-4M/0.5g RHA f;r phenol and resorcinol, respectively, were recorded while 11% of
5xl0-5M/0.5g RHA of2-chlorophenol was achieved.
The % adsorption versus time curves indicated a two-stage adsorption phenomenon
for both phenol and resorcinol, with the first-phase of equilibration occurring after only ten
minutes and lasting for about fifteen minutes before the onset of the second-phase. This
adsorption phenomenon was further evident from the near S-like sorption isotherms obtained
for the two phenolic compounds. The % phenol adsorbed also increased with the ratio of
weight of RHA to phenol concentration. Maximum phenol adsorption was evident at near
neutral conditions of pH6.8 to 7.0, while sonication had a near-negative effect on %phenol
adsorption rates. Temperature had no appreciable effect on adsorption rate.
RHA proved to be quite a good indicator 'reagent' for the detection of pyrogallol and
pyrocatechol in aqueous solution. Linear dynamic ranges of 3.2xlO-sM to 2.3xlO-4M and
3.3xlO-sM to 5xlO-4M pyrocatechol and pyrogallol respectively were evident, while
sensitivity values of 1332.79a.u./M and 120.55a.u./M of pyrocatechol and pyrogallol
respectively, were obtained. Both temperature and sonication time had positive effects on the
phenol-detection experiments. Slightly acidic conditions (pH 5.6) were considered as
optimum in the detection experiments of both pyrogallol and pyrocatechol. | en |
