Settled soap, Treatment

Second. The good settled soap, testing 62-63 per cent, fatty acids. The subject of removing and treatment of this layer is fully dealt with in the next chapter. 

First, a cooling and settling step is used to separate the soaps and fatty acids. The fatty acids are less soluble at lower temperatures and rise to the surface, where they can be removed by skimming. Other heavy materials will settle to the bottom and remain in the tank untU it is cleaned periodically. This skimming of the fatty acid is best done in the soap plant before the lyes are transferred to the treatment plant (Figure 1). 

Second, the skimmed and settled lye is transferred to the first treatment tank. It is good practice to heat the lye to 50-60°C during the transfer pumping or in the treatment tank the treatment process is most efficient at this temperature. In the first tank, the lye is acidulated to pH 4.6-5.0 with sulfuric or hydrochloric acid. Hydrochloric acid is recommended to avoid the formation of sulfates. These sulfates can build up in the recovered salt, which is returned to the soap-making area where sulfates are not desirable. This acidulation step liberates fatty acids, which may be skimmed, as most are insoluble in water. 

Vegetable Oils,—The other vegetable oils come to the soap-maker s hand in a refined condition occasionally, however, it is desirable to remove a portion of the free fatty acids, which treatment also causes the colouring matter to be precipitated. This is effected by bringing the oil and a weak solution of caustic lye into intimate contact. Cocoa-nut oil is often treated in this manner. Bometimes it is only necessary to well agitato the oil with li per cent, of its weight of a 12° Tw. (8° B.) solution of caustic soda and allow to settle. The foots are utilised in the soap-pan. 

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