Method for selectively capturing metal ions

#This invention relates to a method for selectively capturing metal ions from a solution containing ions of heavy metals, and preferably at least two such metals.

#Industrial effluents from metal mines and factories contain a variety of metal ions among which heavy metal ions are known to have an adverse influence on human and animal bodies and thus are desired to be removed completely before the effluents are actually discarded into rivers, lakes, oceans and other bodies of water. As ways for eliminating such metal ions, there have been proposed a method wherein industrial effluents are treated with a metal capturing agent such as a condensed phosphate or ethylenediaminetetraacetic acid and a method wherein industrial effluents are biologically treated with microorganisms. However, these methods are not as yet practically applicable for several disadvantageous reasons. Thus, in the first case, the metal capturing agent is too expensive for the treatment of large amounts of effluent and, in the second, a sufficient level of elimination is not achieved by the biological treatment. On the other hand, if a variety of metals contained in effluents could be recovered selectively and separately, it would be a significant advance in the art, particularly in respect to re-utilization of the recovered metals. However, there is up to now no known method for treating effluents which can serve this purpose.

#It is an object of this invention to provide a practical method for easily and effectively eliminating metal ions contained in effluents from mines and factories.

#Other objects, features and advantages of this invention will be apparent from the following description when read in conjunction with the accompanying drawings in which FIGS. 1 - 7 represent plots of the metal ion recovery rates, expressed as a percentage, against varying pH for various combinations of two or more types of metal ions, identified by appropriate chemical symbols, and illustrating the different threshold values at which substantial recovery for the respective metals takes place .

#It has now been found that a condensation product of a higher fatty acid with an excess of a polyamine possesses extremely high adsorptivity for various metal ions and displays selective adsorptivity to particular metals when the pH condition is varied adequately.

#In accordance with this invention, there is provided a method for selectively capturing metal ions which comprises treating, with adjustment of pH, a solution containing metal ions, and preferably at least two kinds of metal ions, with a metal ion capturing or complexing agent composed of a condensation product of a higher fatty acid with an excess of a polyamine.

#The condensation product of a higher fatty acid and a polyamine used in the invention as a metal ion complexing agent is prepared by condensing a higher fatty acid, or a reactive functional derivative thereof, for example, an ester or halide of the higher fatty acid, with an excess molar amount of polyamine.