TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The aqueous alkali treatment step is followed by an adsorptive treatment step. The silica hydrogel is used as the adsorbent in the adsorptive treatment step. An acid degumming step is performed before the vacuum stripping step. A filtration step is performed before the vacuum stripping step or acid degumming step. The filtration step is performed at 70-100 degrees C. The vacuum stripping step is conducted at 200-260 degrees C and under a pressure of 3-10 hectopascals (hPa). The vacuum stripped fatty waste material has a fatty acid content of less than 2 wt.% expressed as oleic acid. The aqueous alkali step is conducted at 60-100 degrees C with an amount of alkali that exceeds the molar equivalent of the free fatty acids present in the stripped fatty material by 0.3-3 kg per tonne of fatty waste material. The aqueous alkali strength is below 14 wt.%. The adsorptive treatment is conducted at 40-70 degrees C with an amount of silica hydrogel of 0.4-0.6 wt.% of the fatty waste material. EXAMPLE - A treatment of a sample of a low quality chicken fat having a free fatty acid content of 20.2% and high levels of phosphorus and earth alkali metals for a feedstock for biodiesel production was carried out. The sample was heated to 70 degrees C and washed with water (3%). The washed sample was introduced into a deodorizer, heated to 220 degrees C and stripped under a vacuum of 3 hectopascals (hPa) with 1 wt.% of steam over 60 minutes. After cooling, the sample was neutralized. The neutralization process involved: heating the deodorized sample to 90 degrees C; adding phosphoric acid solution (40 wt.%) in an amount of 0.2 wt.%; dispersing this acid solution into the oil; allowing the phosphoric acid to react for 10 minutes; adding caustic soda as an aqueous solution (14 wt.%) in an amount that was a molar equivalent to the free fatty acid present; dispersing caustic solution into the oil; adding water (3 wt.%); holding the reaction mixture for 10 minutes; and separating the phases by centrifuge for 15 minutes, to obtain the neutralized material. The neutralized sample was subjected to an adsorptive treatment involving: heating the neutralized sample to 70 degrees C; adding a solution of citric acid in water (30 wt./wt.%) in an amount of 0.3 wt.%; dispersing the acid solution into the oil; adding water (0.5 wt.%); holding the acidified oil for 15 minutes at 70 degrees C; adding Trysil 300 (RTM: silica hydrogel) (0.5 wt.%); agitating to form a suspension for 30 minutes to prevent the silica from settling; drying the suspension by heating to 90 degrees C and applying a vacuum of 50 hPa for 30 minutes; and removing the spent silica by filtration, to obtain the purified waste chicken fat. Samples were taken at certain stages of the process and analyzed for free fatty acids (FFA) (measured as oleic acid) and for the elements phosphorous (P), iron (Fe), calcium (Ca) and magnesium (Mg). The FFA (% oleic)/P (ppm)/Fe (ppm)/Ca (ppm)/Mg (ppm) contents after various stages were as follows: in starting material: 20.2/101.2/17.6/34.7/7.4; after deodorization: 1.1/120.2/22.5/40/7; after neutralization: 0.17/47.3/11.1/22.5/3.4; and after silica treatment: not determined/39.7/9.8/18.4/2.8. The results demonstrated that stripping the waste chicken fat with steam under vacuum, drastically reduced the free fatty acid content of the sample. Since this FFA reduction decreased the weight of the sample, the contents of P, Fe, Ca and Mg increased. The neutralization step not only reduced the free fatty acid level to a considerably lower level, but it also removed more than 40% of the P, Fe, Ca and Mg from the deodorized sample. Accordingly, the neutralized sample constituted a highly suitable starting material for the production of biodiesel by transesterification. The final adsorptive treatment with silica hydrogel caused a further reduction in the contents of unwanted elements P, Fe, Ca and Mg.