Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating process fluid by means other than agitation or...
Reexamination Certificate
2002-04-16
2004-02-17
Koehler, Robert R. (Department: 1775)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating process fluid by means other than agitation or...
C205S574000, C205S586000, C210S660000, C210S663000, C210S665000, C210S688000
Reexamination Certificate
active
06692628
ABSTRACT:
The present invention relates to the removal of ferric iron and other impurities from copper electrolyte solution used in the electro-winning of copper or other acidic aqueous solutions containing metal ions.
Copper metal is produced from copper-bearing ore using several well-known processes. One of the most commonly used processes is referred to as heap leaching. In this process dilute sulfuric acid is passed over copper-bearing ore that has been placed atop an impermeable liner. As the dilute sulfuric acid solution percolates through the copper-bearing ore, copper and other impurities are leached from the ore. This solution, referred to a pregnant leach solution or PLS, is collected atop the impervious liner and is routed to a processing facility to recover the copper and return a copper-depleted solution for subsequent leaching.
Copper is recovered from the PLS using a multi-step process called solvent extraction and electro-winning (SX-EW). In the first step, copper ions are extracted from PLS using a kerosene-type solvent mixture. The copper depleted PLS is then returned to the heap leach for additional leaching. Copper is then stripped from the solvent mixture using a copper sulfate-sulfuric acid mixture (CuSO
4
—H
2
SO
4
). The final step of the process is electroplating copper from the copper-enriched solution of the copper sulfate-sulfuric acid mixture.
Small amounts of iron are commonly transferred with the copper to the electroplating solution. Iron is either chemically co-extracted with the solvent or is mechanically introduced as entrainment of the aqueous solution from the stripping. As copper is plated out of solution, the iron content in the electrolyte increases. The build-up of iron in the electro-winning solution results in a decrease in the current efficiency due to continuous oxidation and reduction of iron (Fe
++
/Fe
+++
). Operating conditions of the copper electro-winning circuit are such that iron cannot be reduced to metal at the cathode; hence iron remains in the system. The loss of current efficiency can amount to 1-3% per gram of iron per liter of electrolyte. Normal plant practice to control iron in the electrolyte is to occasionally bleed iron rich copper electrolyte and replace it with sulfuric acid electrolyte.
The copper electro-winning process uses lead-alloy anodes. Soluble cobalt is added to the electrolyte (40-250 ppm) to minimize corrosion of the anodes and to prevent lead contamination of the copper metal plated at cathode. During the bleed of the electrolyte to control iron, cobalt is therefore lost and fresh cobalt must be added to the electro-winning electrolyte to maintain the needed level to minimize corrosion of the anode. Replenishing of cobalt to the electrolyte is a major operating expense in copper SX-EW operations. A method of removing iron from electro-winning electrolyte without removing cobalt has long been desired.
The following patents provide proposals for the selective removal of iron from an acidic solution; but none has provided a satisfactory method which is suitable for use in the removal of impurities from a process of electro-winning of copper.
Gula et al in U.S. Pat. No. 5,582,737 describe a process that selectively separates iron (III) from sulfuric acid solutions containing copper and cobalt using an ion exchange resin that contain gem-diphosphonic functional groups. The resin preferentially adsorbs iron (III) and copper and cobalt are returned to the electroplating solution. Loaded resin is regenerated using sulfurous acid (H
2
SO
3
) generated by aspirating SO
2
gas into water containing copper (I) ions. Sulfurous acid reduces the adsorbed iron (III) ions to iron (II) that are easily removed and discarded as a waste product.
Cameron in U.S. Pat. No. 5,603,839, describes a process for the recovery of waste sulfuric acid generated at industrial operations. An ion exchange resin is used to separate sulfuric acid from waste sulfuric acid. The patent teaches that the resin is regenerated with water to produce a acid-rich solution and a salt-rich solution. The acid-rich solution is then further concentrated with a multi-step evaporator to produce a concentrated acid-rich stream for recycle.
Dreisinger et al. in U.S. Pat. No. 5,948,264 describe an improved gem-diphosphonic resin regeneration process for the removal of iron (III) from aqueous metal ion containing sulfuric acid solutions. The patent teaches that increasing the temperature of the sulfurous acid to 65-95° C. improves the regeneration of the ion exchange media.
Bauman et al in U.S. Pat. No. 2,738,322 describe a process for removing sulfuric acid from aqueous solutions of inorganic sulfates using anionic exchange resin. They teach that any anionic exchange resin containing primary, secondary, or tertiary amino groups or quaternary ammonium groups may be employed in the process. Aqueous solutions of inorganic sulfates containing sulfuric acid are passed through a bed of anion exchange resin. Sulfuric acid is retained on the resin and the inorganic sulfate salts pass through. Sulfuric acid is then recovered from the anion exchange resin by washing the resin with water. The process can be operated at room temperature.
Alexander et al, U.S. Pat. No. 6,232,353, teach that by synthesizing an ion exchange resin with both sulfonic and diphosphonic acid functional groups the selectivity for iron (III) is improved over transition metal. Iron loaded resin. However, the resin must be regenerated with hot sulfuric acid solution containing Cu(I) solution. This is an improvement in the selectivity of the resin over the diphosphonic resin described by Dressinger, et al, U.S. Pat. No. 5,948,264.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for electro-winning of copper n which impurities and particularly iron is removed.
According to the invention there is provided a method for the electro-winning of copper comprising:
providing electrodes in an electrolyte comprising a copper-enriched aqueous solution of a copper sulfate-sulfuric acid mixture containing iron (III) as an impurity and passing current therethrough to effect extraction of copper by electroplating of the copper from the electrolyte;
the extraction of the copper causing a relative build up in the level of the iron impurity in the electrolyte;
after extracting copper, removing at least a part of the electrolyte solution;
removing the iron (III) impurity from the aqueous sulfuric acid electrolyte solution containing the iron impurity by:
contacting the removed electrolyte solution with an anionic strong base solid ion exchange medium in which the medium binds the sulfuric acid in preference to the iron (III) ions to form a solid/liquid admixture, wherein the ion exchange medium is comprised of an insoluble cross-linked polymer having a plurality of quaternary amine groups (N::) as the exchanging group;
contacting the electrolyte solution with a sufficient amount of ion exchange particles for a time period required to solid phase-bind the sulfuric acid to leave an aqueous phase containing the iron impurity;
separating the solid and liquid phase;
extracting the iron impurity from the liquid phase;
removing the sulfuric acid from the solid ion exchange medium;
and returning at least part of the sulfuric acid and the liquid phase after extraction of the iron impurity to the electrolyte solution for further electrolytic plating of the copper.
Preferably the liquid phase is mixed an acid-neutralizing agent to raise the pH of the liquid phase to a value of at least 2.5 but less than 4.0, causing the iron (III) to form a solid phase iron hydroxide (Fe(OH)
3
) for separation therefrom.
Preferably the solid phase iron hydroxide is then separated from the liquid phase and the liquid phase is returned to the electrolyte solution for further copper extraction.
Preferably the acid neutralizing agent is sodium hydroxide solution.
Preferably the sulfuric acid is removed from the ion exchange medium by contacting the solid phase-bound sulfuric acid with wa
Koehler Robert R.
Larson & Taylor PLC
SBR Ventures, LLC
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