Noble metal include gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt), wherein the platinum group metal (P , t Pd, Rh) are widely used in hydrogenation, oxidation, dehydrogenation, hydrogenolysis, ammonia synthesis, methanol synthesis, hydrocarbon synthesis, hydroformylation and carbonylation catalysts. However, due to the limited reserves of precious metals and low production, the recycling value of expensive metal catalyst regeneration resources has been valued by countries all over the world. Precious metal separation is a difficult problem in hydrometallurgy. At present, domestic and foreign methods for the extraction and separation of precious metals include chemical precipitation, ion exchange and adsorption, liquid membrane, solvent extraction and leaching resin.
The ion exchange method is a kind of “green extraction†technology. Due to high separation efficiency, simple equipment and operation, resin and adsorbent can be regenerated and reused, and environmental pollution is small. It has become an important method of separation and enrichment, showing a unique advantage. , petrochemical catalysts used in the recovery of attention.
I. Ion exchange resin separation technology
The ion exchange resin is a functional polymer material containing an ion exchange group in a crosslinked polymer structure, and is insoluble in a general acid, an alkali solution, and many organic solvents. The functions of salt removal, separation, refining, decolorization and catalysis are realized by functions such as exchange, selection, absorption and catalysis. They are widely used in municipal and power plant water treatment, hydrometallurgy, food industry, chemical process, pharmaceutical industry, environmental protection and The field of electronics.
(1) Principle of ion exchange
The ion exchange reaction is an ion exchange process caused by a chemical difference between the ion exchanger and the electrolyte solution. The concentration of counterion A in the ion exchanger phase is high, and when the ion exchanger is in contact with the electrolyte solution, the counterion is forced to diffuse into the solution having a low concentration. The ion exchanger is electrically neutrally destroyed and the ion exchanger receives an additional charge. In order to return the ion exchanger to its original electrically neutral state, counteracting the resulting charge, it is necessary to adsorb an equivalent of this symbolic charge from the solution, which ion should occupy the reactive group that is freed by the counterion leaving the resin. Since the ion exchange resin adsorbs ions from the solution, it becomes electrically neutral. Thus, the condition in which the ion exchanger remains electrically neutral in turn limits the diffusion of the counterion from the resin to the solution. When ion B replaces A on the resin from the solution, it offsets the charge of the fixed ions caused when ion A is transferred from the resin to the solution. The concentration gradient that causes diffusion on the one hand, and the electrostatic force that resists ion diffusion on the other hand, acts on each ion in the ion exchange resin-solution system.
(2) Classification of ion exchange resins
Different ion exchange resins according to the skeleton structure can be classified into a gel type and a macroporous type. According to the characteristics of the exchange functional group, it can be divided into cation exchange resin, anion exchange resin and other resins. According to the strength of acid or alkali on the functional group, it is divided into strong acid cation exchange resin, weak acid cation exchange resin; strong base anion exchange resin and weak base anion exchange resin.
Second, ion exchange technology to recover precious metals in the catalyst
(1) Recovery of platinum and palladium catalysts
The recovery process of the platinum group metal is usually to "completely dissolve" the catalyst, that is, to dissolve all the carrier and the platinum group metal with aqua regia or mixed acid (adding oxidizing agent), filter out the insoluble slag, and then use the ion exchange resin from the solution. Separation/concentration of metals. Since the platinum group metal easily forms a stable complex of [MClx]n- in the chloride solution, the anion exchange resin is usually used to adsorb the noble metal complex ions, and some of the chelating resins also have a good affinity for the noble metal ions.
The patent uses a polyamine anion exchange resin to separate and purify low concentration platinum group metals, the noble metal chloride solution is adsorbed, and most of the alkali metal flows out of the resin column. Zhang Fangyu studied the recovery of platinum, ruthenium and palladium from automobile exhaust catalysts. The R410 resin adsorbed noble metals such as platinum and palladium, and the exchange rate reached more than 99%. Zhang Fangyu used R430 resin for the recovery of platinum in the reforming catalyst. Up to 99.13%. Literature studies have shown that D401 chelating resin has good adsorption performance for palladium in hydrochloric acid medium at pH=2~4, and does not adsorb platinum at pH≥4, thus obtaining a method for separating platinum and palladium from hydrochloric acid medium resin column with pH=4. .
ShamsK recovers platinum from the solution with a pretreated anion resin, Ambertje 4200. By analyzing the EDX and resin concentration curves of the eluent, the results show that the purity of Pt recovered by NaOH pretreated OH-type resin is better than that of untreated Cl-type resin, but the treatment amount is reduced.
Gan Shucai and others used DT-1016 anion exchange resin to adsorb ultra-trace gold, platinum and palladium. It was found that when the adsorption medium was 0.025 mol·L-1 HCl, the enrichment effect of resin on gold, platinum and palladium was better. Preferably, the adsorption rates were 99.72%, 99.6%, and 99.75%, respectively, and the coexisting ions had no significant effect.
The noble metal-absorbing resin can be enriched in precious metals by incineration and elution. The product is obtained by the method of drying and ashing at 750 to 800 ° C, and the yield is 99.13%. However, the incineration method has high energy consumption, is polluted by the environment, and the resin cannot be recycled. Therefore, the elution method is more valued by researchers. The commonly used desorbent solution is thiourea solution, perchloric acid and ammonia. For different Pt, Pd catalysts or different resin columns, suitable desorbent should be selected and suitable desorption conditions should be found.
RupalS synthesizes a dithizone-anchored polyethylene (vinylpyridine) chelating resin for the separation and enrichment of noble metal platinum and palladium. The kinetic equation of resin adsorption was deduced. The mixture of 0.1 mol·L-1 hydrochloric acid and 1.0% thiourea or 0.1 mol·L-1 hydrochloric acid and 5.0% thiourea at pH=5.0. The mixed solution can completely elute Pt(IV) and Pd(II), while eluting Ni2+ with acetic acid solution, and eluting Au3+ with hydrochloric acid nitric acid mixture, and nitric acid and ammonium nitrate can elute Hg2+. Wang Wuzhou et al studied the recovery of Pt/Al2O3 catalysts, and compared the elution effect of different concentrations of solution on PtCl62- adsorbed by Amberlite IRA402 chlorine anion resin. The results showed that the desorption effect was better with hydrochloric acid and thiourea as eluent. The rate is 99.89%. Li Chunsheng investigated the enrichment effect of macroporous anion resin HHY-01 on platinum. By measuring the solution concentration, the desorption concentration and the flow rate, the optimized adsorption conditions are 1. 0 mol·L-1, the flow rate is 1.0 mL·min-1; the desorption condition is 2% thiourea solution, the flow rate is 1 0%。 The recovery rate of Pt is about 97. 7% ± 0. 9%. IkukoMatsubara modified the resin to recover traces of precious metals (P, t Pd, Au) by eluting a large amount of alkali metal (10 mg) and trace precious metals adsorbed by Amberlite IRA-35 resin with a mixture of thiourea and ethanol. 1μg), the recovery rate of precious metals is higher than 97%. This method was applied to other different types of resins, and the ideal separation effect was achieved on the other seven resins.
(2) Recovery of rhodium catalyst
Ion exchange technology is mainly used to separate Rh from Pt, Pd, Ir and other alkali metals in the recovery of rhodium catalyst. The double-charged anions PdCl2-4, PtCl2-6, PtCl2-4 and IrCl2-6 can be adsorbed by an anion exchange resin. IrCl3-6 and RhCl3-6 have weaker binding ability to anion resin. The rh-Cl anion is precipitated by NaOH and redissolved in a dilute acid to be quantitatively hydrolyzed into a hexahydrate cation [Rh(OH2)6]3+. Obviously, the Rh-containing cation is not adsorbed by the anion resin at all. Therefore, by using the difference in charge symbols, the ion exchange method was successfully applied to separate and refine the ruthenium. Jianglingen passes the solution or mixed solution of each metal ion with chlorine gas for 10 min and pH=2 through the resin column. The ruthenium ions are not directly occluded by the resin and flow directly through the column, while the platinum, palladium and ruthenium ions are quantitatively exchanged and adsorbed by the resin, so that ruthenium, platinum, palladium and ruthenium are completely separated. The eluent can be changed to completely rinse platinum, palladium and rhodium from the resin column. Zhang Guoying used this principle to study the adsorption behavior of platinum, palladium, rhodium and ruthenium on cation exchange resin in the presence of thiourea. As a result, it was confirmed that platinum and palladium can be adsorbed by the ion exchange resin at normal temperature. The adsorption of hydrazine is weak. A solution containing palladium and hydrazine in hydrochloric acid is mixed with a certain amount of thiourea solution and shaken. After passing through the 732 type cation exchange resin column, the column was rinsed with 0.1 mol·L-1 hydrochloric acid and aqua regia to obtain a solution containing ruthenium and palladium, thereby separating the ruthenium and palladium. Zhang Fangyu used Wang Shui to dissolve the calcined waste ruthenium catalyst, and the ruthenium was present in the presence of [RhCl3]3-complex ion, and then the 732 type cation exchange resin was used to adsorb the alkali metal to separate and purify the ruthenium. Romulus Gaita et al. studied the recovery of metal ruthenium in motor vehicle exhaust catalysts. The mixture was leached with a mixture of hydrochloric acid and sodium chlorate. The leaching solution was adsorbed by Amberlite IRA 93 anion resin, ruthenium and platinum palladium. Then, metal ruthenium was eluted with 6 mol·L-1 hydrochloric acid, palladium and platinum were eluted with different concentrations of ammonia water, and the recovery was investigated with the influence of acid concentration and temperature.
Third, the conclusion
The ion exchange resin has simple synthesis, large exchange capacity, stable performance, easy regeneration and reusability, and has become an important means for the recovery of precious metals in spent catalysts. However, the separation selectivity of ions of the same kind of charge ions and similar chemical and physical properties is not good; the resin elution regeneration with strong adsorption capacity is difficult. Therefore, it is necessary to further develop and modify the resin, optimize and improve the separation and leaching processes, and promote the development of ion exchange separation and purification of precious metals.
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