A cyclic voltammetric simulation that can be applied to an electrochemically mediated enzyme reaction involving any substrate and mediator concentrations was developed. Concentration polarization of the substrate in the vicinity of an electrode was considered as well as mediator concentration. Reversible and quasi-reversible electrochemical reactions with one electron followed by an enzyme reaction with two electrons were modeled. The differential equations for the mediator and substrate were solved using digital simulation techniques. The calculated cyclic voltammograms showed prepeaks when there was a low substrate concentration, high mediator concentration, and high enzyme activity. Digital simulation was applied to the determination of the kinetic constants of glucose oxidase (GOx). Cyclic voltammetry was carried out experimentally in a phosphate buffer solution containing GOx, ferrocene derivatives, and glucose. The ratio of the catalytic to the diffusion-controlled current, ik/id, was evaluated. The kcat, KMM, and KMS values were determined from the current values obtained by simulation and by experimentation at various enzyme, mediator, and substrate concentrations. The kcat, KMM, and KMS values for GOx, ferrocenedimethanol, and glucose were 340 s-1, 110 microM, and 30 mM, respectively.
A new process for dissolving platinum group metals (PGMs) from automotive catalyst scrap using metal vapor was proposed. To improve the PGMs dissolution ratio from scraps, vapor of reactive metals (R), such as magnesium (Mg) or calcium (Ca), was reacted with the automotive catalyst scrap in a closed stainless steel vessel at 1173 K for 3 hours. Under these experimental conditions, Mg and Ca vapor was supplied to the entire body of catalyst scrap. After the reactive metal treatment, the specimens were crushed and dissolved in aqua regia at 323 to 333 K for 1 hour. The PGMs dissolution ratios were improved after the reactive metal treatment, and the dissolution ratios reached 88 pct in Pt, 81 pct in Pd, and 72 pct in Rh, while they were 77 pct in Pt, 69 pct in Pd, and 38 pct in Rh without the treatment. Even when the specimens were dissolved in aqua regia without heating, the PGMs dissolution ratios from the catalyst scrap after reactive metal treatment showed high values, 78 pct in Pt, 74 pct in Pd, and 57 pct in Rh at a maximum. These results show that the reactive metal treatment is effective for the recovery of PGMs from automotive catalyst scrap.
To develop an effective process for the recovery of precious metals from scrap, a new platinum (Pt) extraction process using alloy formation by calcium (Ca) vapor and successive leaching with an aqueous solution were investigated. Pure Pt samples were reacted with Ca vapor at constant temperatures ranging between 1073 and 1173 K for three to twelve hours, and Ca-Pt alloy samples were synthesized. The obtained Ca-Pt alloy was then dissolved in aqua regia or in an aqueous HCl solution at room temperature. Platinum was recovered from the leaching solution by conventional (NH 4 ) 2 PtCl 6 precipitation method, and the amount of Pt obtained by each process was analyzed. It was found that more than 90% of the Pt was recovered by this process. After Ca vapor treatment, 100% of the Pt was dissolved when kept in aqua regia for one hour, whereas only 14% of untreated pure platinum was dissolved when kept in aqua regia for four hours. In some experiments, the obtained Ca-Pt alloy samples were oxidized in air for reducing the amount of acid needed for dissolution. Although Pt hardly dissolves in aqueous HCl solution at room temperature, it was found that Ca vapor treatment followed by oxidation is effective in increasing the rate of dissolution in aqueous HCl solution.
To develop an effective process for the recovery of precious metals from scrap, we investigated a new platinum extraction process using alloy formation by magnesium vapor and successive leaching with an aqueous solution. Pure platinum plates were reacted with magnesium vapor at constant temperatures ranging between 873 and 1173 K for 3 h, and Mg-Pt alloy samples were synthesized. The obtained Mg-Pt alloy was then dissolved in aqua regia or in an aqueous HCl solution at room temperature. Platinum was recovered from the leaching solution by conventional precipitation technique, and the platinum obtained by each process was analyzed chemically. It was found that 94% of the platinum was recovered by this process. After Mg vapor treatment, 100% of the platinum was dissolved when kept in aqua regia for 1 h, whereas only 25% of untreated pure platinum was dissolved when kept in aqua regia for 4 h.
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