It is difficult to purify wastewater from chemical or petrochemical plants before it can be discharged into the environment. The difficulty increases with the severity of the standards imposed by various laws intended to protect the environment, particularly those relating to the chemical oxygen demand (COD).
Numerous methods have been proposed to purify such waters; for example, those based on oxidation, passage over solid adsorbing substances (French Patent No. 84/15174), or centrifugation (French Patent No. 74/19446).
Liquid-liquid extraction has also been used; but the processes based on this principle require the use of costly, toxic chemicals which are applicable only to the removal of certain specific chemicals. For example, amine solutions have been proposed to extract humic acids (Vom Wasser -- 1973 -- 41-27-44), and 2-ethylhexanol has been used to purify wastewaters which result from the production of dialkylphthalates (Informations Chimie, No. 136, October 1974, pages 193-197). However, the solubility of these compounds in wastewater is, at times, significant, so that discharge of the purified waters becomes a separate problem, especially if the extracting compound remaining therein is not biodegradable.
The process that is the object of this invention utilizes a liquid-liquid extraction technique which does not exhibit the drawbacks indicated above.