Silver precipitation using sodium dithionite in cyanide media Article uri icon

abstract

  • The nature of the reaction and the main parameters affecting Ag precipitation rate in the system Ag -CN--S 2O 4 2- are studied. From the results obtained, a process of chemical precipitation for Ag recovery is proposed, using an environmentally-friendly reducing reagent (sodium dithionite, Na 2S 2O 4), 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%25, 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 [S 2O 4 2-] 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--S 2O 4 2- is controlled by chemical reaction, characterized by high activation energy, and is independent of the hydrodynamic variables of the system. © 2012, Sociedad Química de México.
  • The nature of the reaction and the main parameters affecting Ag precipitation rate in the system Ag %2b-CN--S 2O 4 2- are studied. From the results obtained, a process of chemical precipitation for Ag recovery is proposed, using an environmentally-friendly reducing reagent (sodium dithionite, Na 2S 2O 4), 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%25, 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 [S 2O 4 2-] 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 %2b] was 0.524. An activation energy of 77 kJ mol -1 was obtained. Under these conditions, Ag precipitation in the system Ag %2b-CN--S 2O 4 2- is controlled by chemical reaction, characterized by high activation energy, and is independent of the hydrodynamic variables of the system. © 2012, Sociedad Química de México.

publication date

  • 2012-01-01