Examining the bentonite produced in a biodiesel refinery process as soil amendment in a well-draining soil

The expansion of biofuels produced from cooking oils and vegetal oils is expected to increase, together with the production of exhausted clay used in the refinery process. Clay produced in the process is considered waste as it is not intended for further applications. This study has assessed a sample of clay produced by a vegetal oil refinery plant and tested it for environmental applications with two types of vegetal species. In the experiment, the oily clay was added to a sandy loam soil in different percentages in order to modify the soil texture and assess the effect on the hydrological and chemical properties. The results demonstrated that on the one hand, oily clay does not change the pH in the soil mixture and it enriches the elemental composition (in terms of Mg, Cu and Zn), but, on the other hand, there are counteracting effects. Even if oily clay did not have toxic effects on seed germination, when applied to the soil, the presence of Ni did affect the plants' growth. The results thus suggest the need for phytoremediation prior to any application of such clay in soil.