Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions
  • C25C1/12—Electrolytic production, recovery or refining of metals by electrolysis of solutions of copper

Definitions

• TITLE METHOD OF MAINTAINING AND TESTING FOR PROPER CONCENTRATIONS OF THIOUREA IN COPPER REFINING ELECTROLYSIS CELLS.
• This invention is concerned with the electrolytic refining of copper, and more particularly, with a process for constantly maintaining an effective thiourea concentration in the electrolyte solution during the electrolytic refining of copper.
• copper has been purified in a process wherein an electric current is transmitted between cast anodes of impure copper to cathodes which have a substantially pure copper deposit plated thereto, both anodes and cathodes being immersed in a suitable electrolyte.
• the electrolyte which has found universal acceptance in the art is an aqueous solution of copper sulfate and sulfuric acid.
• the refining process first dissolves the impure anode copper into the electrolyte solution and then transports the copper ions (Cu 2+ ) to a nearby cathode, where the copper is plated out as virtually pure metal, Cuo. After a period of time a desired thickness of copper is deposited on the cathodes, whereupon they are removed and later melted for casting into several common product shapes.
• Several problems occur during this operation and have consequently formed the subject of extensive research. As the cost of energy continues to soar, the importance of increasing current efficiency in electrorefining has become a paramount consideration. A change of 1% in the current efficiency of a large modern electrolytic copper refinery can result in a substantial increase in copper capacity, or a decrease in electricity per unit of pro duction.
• an improved method for the electrolytic refining of copper comprising creating an electrolyte useful in copper refining including an aqueous solution of sulfuric acid and copper sulfate, together with minor amounts by weight of addition agents, one of which is thiourea, the electrolyte residing during plating in a suitable container means, which has both an inlet stream and an outlet stream of electrolyte passing through inlet and outlet flow passage means; adding at least a sufficient amount of thiourea to the inlet stream in order to maintain the outlet stream concentration of thiourea at a value at least above trace concentrations, that is, at least a measurable amount, the maximum acceptable concentration in the outlet stream being a value above which cathode deposited copper contamination becomes significant, that is, above which impurities present in the electrolyte materially affect the quality of the deposited copper, and at least periodically repeating the above while electrorefining copper in the container means.
• Fig. 2 discloses a copper electrolyte circulation cycle where the tankhouse is comprised of a single section.
• Electrorefining is a process of first electrochemically dissolving impure copper from an anode and then selectively plating the dissolved copper in virtually pure form onto a cathode. Such a process thus serves two purposes; it virtually eliminates impurities which are harmful to the electrical and mechanical properties of copper, and it also separates valuable impurities from the copper, which can be either recovered as by-product metals if economically feasible, or otherwise disposed of.
• Electrorefining as practiced in industrial tankhouses today is almost exclusively carried out using the "multiple" or "parallel" system, in which all the anodes and cathodes in each electrolytic cell are interleaved in an electrically parallel arrangement.
• Viewing Figures 1A and IB two alternative arrangements of arranging anode-cathode and cell connections are illustrated.
• all the anodes 2A, 2B in a particular cell are activated at one electrical potential, while all the cathodes 4A, 4B are at a second, lower potential.
• Each anode 2A, 2B is positioned between two cathodes 4A, 4B in order that all the anodes will dissolve at a substantially uniform rate.
• each section generally made up of about 20-45 cells, constitutes a separate independent part (module) of the refinery tankhouse, which can be electrically and chemically isolated from the other sections for such operations as inserting and removing electrodes, cleaning anode residues from the bottom of the cell, and maintenance services.
• each adjacent cell is connected in series with its adjoining member, all the cathodes in each cell are in direct connection, i.e. the same potential, with the anodes in the adjoining cell.
• the electrolyte used for copper refining today is an aqueous solution of about 40-50 g/1 copper and 175-225 g/1 sulfuric acid, along with small amounts of impurities, mainly nickel, arsenic, iron and antimony.
• Steam heaters keep the solution at a temperature of about 60-65°C. at the refining cell inlet, and as the electrolyte circulates through the cells while processing the copper, its temperature drops to a range of about 55-60°C. at the outlet.
• the flow rate, or circulation of the electrolyte in and out of the cell causes the typical large industrial cell to recirculate its electrolyte once every 5-6 hours. Such circulation is essential for several reasons, one of which is to transport dissolved impurities out of the cell and to insure uniform copper ion concentrations at the electrode surfaces.
• the electrolyte has several "addition agents" which are added to it in an effort to improve performance. If these addition agents were not mixed into the electrolyte the finished plated copper deposits would become either soft or coarsely crystalline deposits.
• Common addition agents found in refinery use today are bone glue, hydrolysed casein, sulphonated wood fibres such as goulac, bindarene and lignone and petroleum liquors, particularly the well known "Avitone A”.
• One such additive which has been found to be extremely significant in the optimization of refinery potential is the usage of thiourea in controlled amounts.
• thiourea means any organic compound containing a thiourea nucleus, viz.
• Fig. 2 is a schematic flowsheet of a copper refining process in which the tankhouse refinery is comprised of a single section.
• Mixer tank 2 functions as a source of thiourea for the refining process, as well as the source of several other addition agents and salt additives.
• Thiourea can be added either continually, or periodically, into the electrolyte, depending on the particular type of system used.
• the thiourea in tank 2 passes through tube or other suitable flow means 4 and goes past flow regulator 6 whereupon it joins the main electrolyte circulation in tube 8.
• the inlet concentration of thiourea in tube 8 is typically kept between about 800-2500 ppb, or most typically, about 1500-2000 ppb.
• the inlet concentration should vary so that the outlet concentration of thiourea from each tankhouse section is present in at least trace concentrations, that is, at least a measurable amount, and preferably at least about 100 ppb.
• thiourea concentrations of the order of 5000 ppb have been used in the inlet, with satisfactory results.
• the electrolyte then enters into section or module 10, which is divided into many cells 12, each cell being constructed in the manner as seen in Fig. 1.
• section or module 10 which is divided into many cells 12, each cell being constructed in the manner as seen in Fig. 1.
• any suitable cell or tankhouse design can be used in the process of this invention, and this particular tankhouse design, employing but a single section, is used in order to simplify the analysis.
• the electrolyte solution leaves through outlet tube 14.
• the outlet concentration of thiourea in the electrolyte is sampled at orifice 16, the sample then measured by measuring means 18, the location of which is not important, so long as the correct outlet concentrations can be quickly and accurately measured so that system changes can be promptly made.
• DPP differential pulse polarography
• the tankhouse electrolyte solution is diluted to one-tenth strength and analyzed.
• the reason for the electrolyte dilution is to eliminate any interference in the analysis by other impurities present, particularly chlorine.
• the polarograph is preferably set at a slow scan rate, about 2-5 mV/sec, and a 25 mV pulse height setting, in order to best display the polarograph readings. This technique gives accurate concentration readings down to about 100 ppb, which could not be done by the recommended method of operating the machine, despite the manufacturers' claims to the contrary.
• any suitable polarograph can be quickly adapted for use in the process of this invention, and any other measuring means that can quickly and accurately generate thiourea concentrations of this order of magnitude is also perfectly suitable for the process of this invention, although none are believed currently available.
• the effluent concentration of thiourea is an important parameter in optimizing tankhouse efficiency. More particularly, a thiourea effluent concentration at a value at least above trace concentrations, that is, at least a measurable amount. and preferably above about 100 ppb will lead to increased current efficiency, smoother cathodes, fewer short circuits between anode and cathode, and a lower impurity concentration in the cathodes.
• electrolyte solution After circulating electrolyte solution is sampled at 16, it flows through tube 20 and enters tank 22, which functions as a source of fresh electrolyte, i.e. CuSO 4 and H 2 SO 4 .
• the fresh electrolyte solution Upon exiting tank 22 the fresh electrolyte solution passes through tube 24 and pumping means 26, until entering heat exchanger 30 and tube 28, which raises the temperature of the electrolyte to about 65°C, whereupon the fluid exits through tube 32 into and out of head tank 34.
• the electrolyte is next fortified by thiourea and other addition agents before the entry into section 10 , as the cycle is continued indefinitely.
• the invention in its preferred form consists of a novel improved process of electrolytic copper refining which occurs in a tankhouse or other suitable container means wherein the improvement comprises measuring the concentration of thiourea in the electrolyte outlet with a suitable measuring means, preferably by differential pulse polarography, readjusting the thiourea concentration by adding an effective amount of thiourea to the inlet stream so that the outlet concentration stays within a desired range, the range having a maximum value above which impurities develop in the copper cathodes and a minimum concentration being at least a measurable, amount and preferably about 100 ppb, below which nodule formation accelerates; and periodically repeating the above procedure so that the measured outlet thiourea concentration stays between these upper and lower values, preferably about 100-2500 ppb for the typical electrorefining tankhouse.

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• 1983
  • 1983-02-28 AT AT83901288T patent/ATE33408T1/de not_active IP Right Cessation
  • 1983-02-28 WO PCT/US1983/000298 patent/WO1984003307A1/en active IP Right Grant
  • 1983-02-28 DE DE8383901288T patent/DE3376228D1/de not_active Expired
  • 1983-02-28 AU AU14724/83A patent/AU558737B2/en not_active Ceased
  • 1983-02-28 JP JP58501347A patent/JPS60500453A/ja active Granted
  • 1983-02-28 EP EP83901288A patent/EP0137776B1/en not_active Expired
• 1984
  • 1984-05-17 IN IN413/DEL/84A patent/IN163215B/en unknown
  • 1984-10-16 FI FI844070A patent/FI77059C/fi not_active IP Right Cessation

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