SciELO - Scientific Electronic Library Online

 
vol.56 issue2Effect of the Ligand in the Synthesis of 1-Sulfonyl-1,2,3-triazoles Through Copper-Catalyzed Alkyne-Azide CycloadditionTowards the Bioassay Activity Landscape Modeling in Compound Databases author indexsubject indexsearch form
Home Pagealphabetic serial listing  

Services on Demand

Journal

Article

Indicators

Related links

Share


Journal of the Mexican Chemical Society

Print version ISSN 1870-249X

Abstract

RIVERA, Isauro et al. Silver Precipitation Using Sodium Dithionite in Cyanide Media. J. Mex. Chem. Soc [online]. 2012, vol.56, n.2, pp.156-162. ISSN 1870-249X.

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 Ag recovery 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 of CN- 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 results obtained 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 precipitation period, 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--S2O42- is controlled by chemical reaction, characterized by high activation energy, and is independent of the hydrodynamic variables of the system.

Keywords : Silver precipitation; sodium dithionite; sodium cyanide; chemical kinetics; reaction order.

        · abstract in Spanish     · text in English     · English ( pdf )

 

Creative Commons License All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License