Activation of a Local Bentonite and Testing its Bleaching Efficiency




Naturally occurring bentonites may show very little efficiency in bleaching of oils and fats. It is for this reason that acid-activation of clays with inorganic acids is usually done in order to promote their adsorptive capacity of vegetable oils. This work aims to experimentally determine the efficiency of acid activated bleaching earth for the bleaching of vegetable oil during refinery.

In this work bentonite clay of different mesh sizes (75, 100, 200 and 300) were washed, dried and then activated using hydrochloric acid and sulphuric acid solution of concentrations 1.0M, 2.0M, 3.0M and 4.0M and 0.5M, 1.0M, 1.5M and 2M respectively and the bleaching capacity of the activated clay samples determined. The activation was done by heating a mixture of sulpuric/hydrochloric acid and 5g of clay for one hour at 90o C.


The result revealed that optimum acid activation occurred when 100 ml of acid was used in clay mixture.  The efficiency in bleaching of the activated clay was determined by measuring the visible spectra of the neutralized (unbleached oil) and the oil that has been treated with the activated clay. The raw clay had a bleaching capacity of about 3% while the clay activated with sulphuric acid gave a better bleaching compared to that of hydrochloric acid. However the bleaching efficiency was not convincing enough to enable the clay to be used for commercial purposes comparable to bleaching efficiency of the commercial bleaching earth which was 98% hence more treatment techniques such as increasing activation time should be applied to check whether more bleaching can be achieved.


Other parameters such as pH and the moisture content were also determined while the elemental analysis of the raw un-activated clay and the acid activated clay was also done using atomic absorption spectroscopy.


Keywords: Bentonite, Acid activation, Bleaching, Bleaching efficiency.

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