Silver Precipitation Using Sodium Dithionite in Cyanide Media
The nature of the reaction and the main parameters affecting Ag precipitation rate in the system Ag+-CN--S2O42- are studied. From the results obtained, a process of chemical precipitation for Agrecovery is proposed, using an environmentally-friendly reducing reagent (sodium dithionite, Na2S2O4), lea...
| Autores: | , , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2012 |
| País: | México |
| Institución: | Universidad Autónoma del Estado de Hidalgo |
| Repositorio: | Redalyc-UAEH |
| OAI Identifier: | oai:redalyc.org:47523306013 |
| Acceso en línea: | https://www.redalyc.org/articulo.oa?id=47523306013 |
| Access Level: | acceso abierto |
| Palabra clave: | Química Reaction order Sodium cyanide Sodium dithionite Chemical kinetics Silver precipitation |
| Sumario: | The nature of the reaction and the main parameters affecting Ag precipitation rate in the system Ag+-CN--S2O42- are studied. From the results obtained, a process of chemical precipitation for Agrecovery is proposed, using an environmentally-friendly reducing reagent (sodium dithionite, Na2S2O4), leaving a residual content of Ag into the permitted environmental levels (<5 mg L-1 Ag). The levels ofCN- in liquids wastes are of the order of 0.816 mol L-1, and they can be treated by ozonization processes for inerting cyanide. The resultsobtained indicate that Ag precipitation is achieved in less than 1 hour, with recoveries close to 99%, at room temperature. Silver precipitation is characterized by an induction period followed by a precipitationperiod, leaving a metal amount in solution less than 1 mg L-1. The main kinetic parameters studied lead to obtain the following apparent reaction orders: with respect to the initial [S2O42-] was n = 1.675, with respect to [CN-] was -1.24, with respect to [OH-] was ¿0 (between 10-4 and 10-2 mol L-1) and with respect to the initial [Ag+] was 0.524. An activation energy of 77 kJ mol-1 was obtained. Under these conditions, Ag precipitation in the system Ag+-CN--S2O4 2- is controlledby chemical reaction, characterized by high activation energy, and is independent of the hydrodynamic variables of the system. |
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