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Chemical - Electrochemical Method for the Recovery of Copper From Dilute Solutions

IP.com Disclosure Number: IPCOM000048029D
Original Publication Date: 1983-Jun-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Bindra, P: AUTHOR [+3]

Abstract

The quantities of Cu in the earth's crust are enormous but not infinite. Therefore, while Cu will always be available for critical applications, unless cheaper methods are found for the recovery of Cu from low grade ores and for Cu recycling, the price may get to be very high. This method relates to a chemical-electrochemical method for the recovery of Cu from dilute solutions, such as electroplating rinse solutions.

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Chemical - Electrochemical Method for the Recovery of Copper From Dilute Solutions

Background

The quantities of Cu in the earth's crust are enormous but not infinite. Therefore, while Cu will always be available for critical applications, unless cheaper methods are found for the recovery of Cu from low grade ores and for Cu recycling, the price may get to be very high. This method relates to a chemical-electrochemical method for the recovery of Cu from dilute solutions, such as electroplating rinse solutions. In particular the process pertains to the use of a complexing agent for Cu(I), e.g., a chloride, and a reducing agent for Cu(II), such as a sulfite.

Previously, Cu recovery methods often use chemical precipitation. For example, a mixed caustic soda - sodium carbonate solution at pH 8 to 9, containing hydrazine, is added to the effluent to precipitate cuprous oxide which contains 50 - 60% copper [R. Prinner and V. Crowler, Electroplating and Metal Finishing 24, 13-31 (March 1, 1971). Precipitation methods, however, are relatively costly, and the value of the precipitated sludge is far lower than that of electrodeposited Cu.

Description of Process

This process derives from the stability of Cu(I) ion in the presence of complexing ligands. The electrochemical reduction of Cu(II) in aqueous media has been shown to occur via the following step-wise mechanism:

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where Step (l) is the rate-determining step and Cu(I) represents a reaction intermediate. In non-complexing media Cu(I) is unstable and the polarization curve for copper deposition consists of a single wave. In the presence of complexing ligands, such as C1- ion, which can stabilize Cu(I), the polarization curve for the metal deposition reaction consists of two well-defined waves corresponding to the following reactions.

(Image Omitted)

The reaction intermediate in this case is CuCl2- + e- . Clearly the efficiency of Cu deposition and hence of Cu recovery may be increased by a factor of two if the Cu(I) complex CuC12- can be produced by a chemical reaction in the bulk of the solution before the start of the Cu electrodeposition. The diffusion coefficient of the cuprous complex CuCl- is 1.33 x 10-5 cm2/sec. as compared to a 2 value of 0.78 x 10-5 cm2/sec. for the diffusion of the Cu2+ ion in the same medium. The larger diffusion coefficient of the cuprous complex also increases the efficiency of the Cu deposition. Further...