Separation and recovery of copper metal from ammoniacal solutions

Abstract

Copper is recovered from solutions containing cupric ammoniacal complexes by reducing copper in the complexes to the cuprous state and thereafter precipitating the copper as cuprous acetylide by passing acetylene through the solution. After the cuprous acetylide is separated from the solution and washed thoroughly, it is reacted with acetonitrile and an acid to form acetylene and a cuprous-acetonitrile complex: Cu(CH.sub.3 CN).sub.2.sup.+. The solution containing this complex is then flash distilled to remove the acetonitrile and to disproportionate unstable cuprous ions into copper metal and cupric ions. Following the disproportionation, the components are separated and copper metal is collected. SU BACKGROUND OF THE INVENTION This invention relates to the recovery of copper from ammoniacal solution which may also contain nickel, cobalt, and other ions. In practicing the invention, very pure copper metal is obtained without the need to employ ion exchangers, acid stripping, electrowinning, or electrorefining. It is known that copper (as well as nickel and cobalt) can be leached from the ores with ammoniacal leach liquors. One method of separating the copper values from such leach liquors while leaving the nickel and other metals in the raffinate, is disclosed in U.S. Pat. No. 2,440,612 to M. Lichtenwalter entitled Separation of Copper. In accordance with the process disclosed therein, the copper is recovered from the ammoniacal leach solutions by first reducing the copper values to the cuprous state and then precipitating the reduced copper by reacting it with acetylene to yield insoluble copper actylide which may be separated from the solution by filtration. If silver, mercury, or gold components are present in the leaching solution with the copper, these will also be precipitated out. In addition to the above process, it is known that solutions of cuprous salts can be thermally or electrochemically disproportionated to produce copper and solutions of cupric salts. This method is disclosed in U.S. Pat. No. 3,865,744 to Alan J. Parker et al. In general, this method involves reacting a cuprous salt with a ligand, i.e., an organic nitrile, to form a cuprous nitrile complex such as Cu(CH.sub.3 CN).sub.2.sup.+. The solution containing the complex can then be distilled to produce copper powder, a cupric salt, and an organic nitrile. The present invention provides a method of isolating and purifying copper utilizing a novel combination of the above two known copper recovering processes. SUMMARY OF THE INVENTION The process of the present invention produces copper metal from an ammoniacal solution containing cuprous ions. The process comprises the steps of precipitating the cuprous ions from the ammoniacal solution as a cuprous acetylide, separating and washing the cuprous acetylide precipitate, acid hydrolyzing the cuprous acetylide in the presence of a cuprous ion stabilizing ligand, e.g., a nitrile, and disproportionating the resulting cuprous complex to produce copper metal and cupric salt. The process of the present invention is characterized by the use of reactions which take place at or near ambient temperatures and pressures, and thus a system for utilizing the process can be built at a relatively low cost. In addition, many of the reagents in the process can be recycled, allowing further cost savings, and the process is quite energy efficient. Also, upwards of 99% of the available copper can be recovered and the product metal is of very high purity. Accordingly, it is an object of the present invention to provide a process for obtaining pure copper from ammoniacal copper containing solutions which avoids the necessity of electrowinning the copper, is capable of continuous operation on an industrial scale with a relatively low capital outlay, involves reactions which occur at or near ambient temperatures and pressures, and employs reagents which are neither unduly corrosive nor consumed. Another object of the invention is to provide such a copper recovery process which is energy efficient and significantly diminishes the quantities of waste involved when compared with prior art processes by regenerating and recycling reagents. Still another object of the invention is to quantitatively separate copper from ammoniacal solutions containing copper and other metals such as nickel, cobalt, iron, manganese, etc., without using an ion exchanger. Another object of the invention is to produce copper of very high purity by precipitating cuprous ions from solutions as a cuprous acetylide, separating the cuprous acetylide precipitate, reacting the acetylide with an acid and a nitrile to form a cuprous-nitrile complex, and disproportionating the cuprous ion to produce copper metal.

Dependencies are inferred from the claim text.