Recovery of gold(III), palladium(II), and platinum(IV) by aminated lignin derivatives

Conventional metallurgical processing of precious metals involves the use of large amounts of toxic chemicals. Realizing a need to develop environmentally benign metallurgical technology for precious metals, we prepared two types of adsorption gels, containing primary amine and ethylenediamine functional groups and abbreviated as PA-lignin and EN-lignin, respectively, from wood powder. Both of these adsorption gels were found to be effective for the adsorption of Au(III), Pd(II), and Pt(IV) from weak to strong hydrochloric acid media. In contrast, base metals such as Cu(II), Fe(III), Ni(II), and Zn(II) were almost not adsorbed on either gel. The above-mentioned precious metals were adsorbed on the gels according to the Langmuir adsorption model, and the highest maximum adsorption capacity was observed for Au(III). The formation of ion pairs of metalchloro complex anions and protonated adsorption gels in acidic media was proposed to be the main adsorption process. However, in the case of Au(III) adsorption, a reductive adsorption mechanism was confirmed to occur by reference to XRD spectra and SEM images of the gels obtained after adsorption.