Highly Effective Removal of Metal Cyanide Complexes and Recovery of Palladium Using Quaternary-Ammonium-Functionalized MOFs

In this study, quaternary-ammonium-functionalized metal&ndash
organic frameworks (MOFs) Et-N-Cu(BDC-NH2)(DMF), were prepared, characterized, and applied for the highly effective removal of metal cyanide complexes, including Pd(CN)42&minus
Co(CN)63&minus
and Fe(CN)63&minus
Batch studies were carried out, and the maximum adsorption capacities of Pd(II), Co(III), and Fe(III) reached 172.9, 101.0, and 102.6, respectively. Adsorption was rapid, and equilibrium was established within 30 min. Et-N-Cu(BDC-NH2)(DMF) exhibited high thermal and chemical stability. Furthermore, absorbed Pd(CN)42&minus
was selectively recovered by two-step elution. First, Co(CN)63&minus
were eluted with a 1.5 mol L&minus
1 KCl solution. Elution rates of Co(CN)63&minus
were greater than 98.0%, whereas the elution percentage of Pd(CN)42&minus
was less than 2.0%. Second, &gt
97.0% Pd(CN)42&minus
on the loaded MOFs was eluted using a 2.0 mol L&minus
1 KI solution. The recovery rate of Pd(CN)42&minus
was greater than 91.0% after five testing cycles. Adsorption isotherms, kinetics models, and adsorption thermodynamics of Pd(CN)42&minus
on Et-N-Cu(BDC-NH2) (DMF) were also systematically investigated. The Et-N-Cu(BDC-NH2) (DMF) absorbent exhibited a rapid, excellent ability for the adsorption of metal cyanide complexes.