Heavy metals extraction by microemulsions

摘要

The objective of this study is the heavy metal extraction by microemulsion, using regional vegetable oils as surfactants. Firstly, the main parameters, which have influence in the microemulsion region, such as: nature of cosurfactant, influence of cosurfactant (C)/surfactant (S) ratio and salinity were studied, with the objective of choosing the best extraction system. The extraction/reextraction process by microemulsion consists of two stages. In the first one, the heavy metal ion present in the aqueous phase is extracted by the microemulsion. In a second step, the reextraction process occurs: the microemulsion phase, rich in metal, is acidified and the metal is recovered in a new aqueous phase, with higher concentration. The used system had the following parameters: surfactant―saponified coconut oil; cosurfactant―n-butanol; oil phase―kerosene; C/S ratio = 4; salinity―2% (NaCl); temperature of 27 +- 1℃; water phase aqueous solution that varied according to the heavy metal in study (Cr, Cu, Fe, Mn, Ni and Pb). A methodology of experimental planning was used (Scheffe Net) to study the behavior of the extraction in a chosen domain. The extraction was accomplished in one step and yielded extraction percentage higher than 98% for all metals. In the reextraction HCl―8M was used as reextraction agent and the influence of the pH and time were verified. This work showed the great efficiency of the microemulsion, indicating that it is possible to extract selectively the heavy metals from the aqueous phase.