ABSTRACT
This study evaluated the natural and activated bleaching powers of some selected
Nigerian clays with a view to initiating their utilization for bleaching earth manufacture.
Fourteen clay samples were collected from eleven different locations in Nigeria: [Ilorin,
Igbaja, Moniya, Omiadio, Ogbomosho. Ile Ife, Osogbo, llesha, Kankara, Alexander
Hall (ABU) and Bomo.]
The chemical analyses were carried out to determine their elemental
composition. They were activated by (three) different acid treatments [using
Hydrochloric acid (HC1). Method I consist of the use of 5.5MHC1 on clay sample on
a 5:1 ratio; Method II consist of the use of 5MHC1 on clay sample on a 2:1 ratio; and
method III consist of the use of 1M, 3M and 5MHC1 on clay samples in a slurry form
in a ratio of 4:1 1 . Palm oil was use as the adsorbate and the clay as the adsorbent.
Standard clay was used in the bleaching comparism, and their extent of bleaching was
monitored spectrophotometrically.
Four of the samples were found to have good bleaching properties taking 60%
colour reduction as a good performance index. S5 69.19%, S1() 66.09%, S2(II) 61.76%,
and 60.68%) S8; Seven samples Sl(B), S2(1), S3(II), S6, S7, S9, and SII have bleaching
performance above 50% and below 60% while three samples S1(A), S4, and S3(1) have
bleaching performance below 50% in their natural state.
After acid activation of the clay samples the second acid activation of the clay
gave the best bleaching performance compared to the other two methods.
The acid to clay ratio as exemplified in the second activation method; the bleaching
temperature; volume of the acid used; and the percentage mass of the had pronounced
effect on the bleaching performance of the clays.
Among the local clays used S5 clay in both the natural and activated state was
found to be superior in its bleaching ability over all the other clays and in comparism
with the fuller’s earth at 105oC. Fuller’s earth used at S2°C had a better bleaching
ability over the local clays. Activated S5 followed very closely.
v
The higher bleaching ability of the clays in the activated state was related to the
percentage sum of the oxide of aluminium, silicon and sodium present in the clays and
also lost on ignition in their natural states. It was found that alkali refining of the crude
oil reduced part of the colours from the crude oil and thus increasing the percentage of
colour reduction when the local clay were used on them. Also some of the activated
Nigerian clays showed higher apparent bulk densities and consequently a corresponding
lower oil retention than the fuller’s earth.
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