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

In this study, quaternary-ammonium-functionalized metal⁻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-, Co(CN)6³-, and Fe(CN)6³-. 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- was selectively recovered by two-step elution. First, Co(CN)6³- and Fe(CN)6³- were eluted with a 1.5 mol L-¹ KCl solution. Elution rates of Co(CN)6³- and Fe(CN)6³- were greater than 98.0%, whereas the elution percentage of Pd(CN)4²- was less than 2.0%. Second, >97.0% Pd(CN)4²- on the loaded MOFs was eluted using a 2.0 mol L-¹ KI solution. The recovery rate of Pd(CN)4²- was greater than 91.0% after five testing cycles. Adsorption isotherms, kinetics models, and adsorption thermodynamics of Pd(CN)4²- 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.

Isopentyl-Sulfide-Impregnated Nano-MnO2 for the Selective Sorption of Pd(II) from the Leaching Liquor of Ores.

Conventional separation methods are not suitable for recovering palladium present in low concentrations in ore leaching solutions. In this study, a novel isopentyl sulfide (S201)-impregnated α-MnO2 nanorod adsorbent (BISIN) was prepared, characterized, and applied for the selective adsorption and separation of palladium from the leaching liquor of ores. Batch studies were carried out, and the main adsorption parameters were systematically investigated, in addition to the relevant thermodynamic parameters, isotherms, and kinetic models. The thermodynamic parameters reflected the endothermic and spontaneous nature of the adsorption. Moreover, the experimental results indicated that the Langmuir isotherm model fits the palladium adsorption data well and the adsorption was well described by the pseudo-second-order kinetic model. The main adsorption mechanisms of palladium were elucidated at the molecular level by X-ray crystal structure analysis. Thiourea was found to be an excellent desorption agent, and the palladium-thiourea complex was also confirmed by X-ray crystal structure analysis. The results indicated that almost all of the Pd(II) (>99.0%) is adsorbed on BISIN, whereas less than 2% of the adsorbed Pt(IV), Fe3+, Cu2+, Ni2+, and Co2+ is observed under the optimum conditions. The proposed method can be used for the efficient adsorption and separation of palladium from the leaching liquor of ores.