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
  • C25C1/06—Electrolytic production, recovery or refining of metals by electrolysis of solutions or iron group metals, refractory metals or manganese
  • C25C1/08—Electrolytic production, recovery or refining of metals by electrolysis of solutions or iron group metals, refractory metals or manganese of nickel or cobalt

Definitions

• ABSTRACT A nickel electrowinning process carried out in a bagfree cell characterized by maintaining the electrolyte at a temperature in excess of 60C and a pH of about 1.5 to 2.0 and feeding pregnant electrolyte to and withdrawing spent electrolyte from the cell to maintain a nickel bite of at least grams per liter while operating at relatively high current densities.
• An important feature is inclusion of substantial amounts of boric acid in the cell electrolyte to permit nickel bites of about to grams per liter when operating at C to C. Operation without diaphragms permits use of current densities up to five times those used in conventional diaphragm cells without an increase in power requirements.
• the present invention is concerned with electrowinning of nickel and more particularly with electrowinning of nickel using a bag-free nickel electrowinning cell operating at reasonably large bites and low power requirements.
• cathode boxes and bags involve not only high capital cost in constructing a nickel electrowinning tank house but also involve high operating cost.
• the high operating costs arise basically out of the need to treat each cathode separately with due care to avoid tearing of diaphragms or bags as well as the need for replacing of boxes, and bags due both to tearing and to normal deterioration.
• the high capital cost involves not only the original provision of the cathode boxes and feeding means but also the facts (1) that a low current density of about 2 amperes per square decimeter is normally used in nickel electrowinning cells having cathode boxes and (2) that the cathode boxes take up cell space which could more profitably be used for additional anodes and cathodes.
• Low current density implies the need for a relatively large number of cells to provide a given productive capacity of a tank house.
• the present invention contemplates a process of electrowinning nickel from aqueous sulfate electrolytes comprising electrodepositing nickel at a cathode current density of about 2 to about 10 amperes per square decimeter from a nickel-containing sulfate electrolyte maintained at a temperature in excess of 60C and at a pH of about 1.5 to about 2.0 (as measured at cell temperature) and contained in a cell having no diaphragm isolating the cathode from an essentially insoluble anode and in which vigorous agitation of the electrolyte is maintained while feeding nickel-containing electrolyte (pregnant electrolyte) at a relatively high pH to said cell and withdrawing nickelcontaining electrolyte (spent electrolyte) from said cell at rates to maintain a substantially constant volume of electrolyte in said cell, to maintain the required pH in said cell and to maintain a difference in nickel content between electrolyte fed and electrolyte withdrawn of at least about 5 grams per liter.
• the electrolyte usually contains at least about 40, e.g., 40 to about 130 gpl of nickel as sulfate, greater than about 0.5 gpl magnesium sulfate, up to about 150 gpl sodium sulfate, up to about gpl boric acid and is maintained at a temperature in excess of about 70C.
• the magnesium sulfate content of the electrolyte is no greater than about 30 gpl and the boric acid content is at least about 5, e.g., about 5 to about 50 gpl.
• the operating pH of the cell is about 1.7 to about 1.9 at cell measured at operating temperature and the pH of the incoming feed electrolyte is about 5 .5 as measured at room temperature.
• the nickel bite, i.e., the difference in nickel concentration between the pregnant electrolyte and the spent electrolyte is advantageously about 7 to about 15 gpl.
• the temperature of the cell in the novel nickel electrowinning process of the present invention is advantageously about 70C to about 90C and, even more advantageously, the temperature is about C to about C.
• temperatures in the range of 85C to 90C there is achieved a greater current efficiency for nickel deposition and an increased buffer capacity of the sulfate ion-sulfuric acid equilibrium in the pH range of about 1.5 to about 2.0.
• This increased buffer capacity at high temperatures results in consumption of more acid (equatable to a greater nickel ion bite) for any given change of pH in the aforestated range.
• the buffer efficiency is also further increased by inclusion of substantial amounts of an additional buffer, e.g., boric acid in the aqueous electrolyte.
• the boric acid serves to inhibit pH change with increasing hydrogen ion content rather than the prevention of the formation of nickel hydroxide which is normal function of this material in nickel plating baths of higher pH (e.g., 4 5.5 pH). For this reason it is advantageous to have at least l0 gpl of boric acid in the nickel electrowinning electrolyte. From operational point of view, it is practical when nickel electrowinning at a temperature in the range of 85C to 90C with a current efficiency of 75% to take a 12 to 15 gpl of nickel bite when about 20 to 50 gpl of boric acid is present whereas only a 7 to 8 gpl nickel bite is practical when only 5 gpl of boric acid is present.
• One aspect of the present invention is that the cell operates under conditions of very efficient agitation at the cathode due to the combined effects of high temperature (low viscosity and high diffusion coefficients), agitation by anode gas and by hydrogen gas discharged at the cathode corresponding to about 25% of the total current.
• very high current densities i.e., greater than about 5 amp/dm some additional means of artificial agitation may be required.
• Efficient agitation of the electrowinning baths, especially in the vicinity of the cathode surface can readily be achieved using the air sparging techniques as disclosed in Canadian application Ser. No. 163,360 by the present applicant.
• insoluble anodes made of titanium and having a conductive surface layer made with a metal of the platinum group can be used with advantage as insoluble anodes.
• Other types of insoluble anodes which can be used in the process of the present invention include other platinum-group metal surfaces anodes, anodes having a surface of magnetic iron oxide and like materials which are not detrimentally affected by the electrolysis conditions.
• EXAMPLE II Using a dimensionally stable anode and a sandblasted, edgemasked titanium cathode blank (spacing 5 cm.), electrolysis was performed at a current density of 5 amp/dm with air sparging near the cathode with NiSO solution containing 80 gpl Ni, 75 gpl Na SO gpl H 80 and 5 gpl MgSO in a bag-free electrolytic cell at 85-90C.
• the electrolyte at a pH of 5.5 was fed into the cell so that the cell pH did not decrease below a value of 1.6 to 1.7 during the course of a 22 hr. run.
• Bright and pit free Ni was electrodeposited at a current efficiency of 76.5%, the nickel bite and cell voltage, being 13.4 gpl and 2.7V respectively.
• EXAMPLE 111 Using a dimensionally stable anode and a sandblasted edgemasked titanium cathode blank (spacing S cm.), electrolysis was performed at a current density of 10 amp/dm with air sparging near the cathode with NiSO solution containing 83 gpl Ni, 49.5 gpl H 80 5 gpl MgSO and gpl Na SO in a bag-free electrolytic cell at 8590C.
• the electrolyte at a pH of 5.5 was fed into the cell so that the cell pH did not decrease below a value of 1.8 to 1.9 during the course of a 23 hr. run.
• Bright and pit free Ni was electrodeposited at a current efficiency of 78.0%, the nickel bite and cell voltage, being 11.9 gpl and 4.2 volts respectively.
• Air-sparging rate (cubic feet per hour) Area of sandblasted, edgemasked) titanium cathodez) Anode:
• EXAMPLE 1 Smooth and compact nickel was obtained by electrolyzing aqueous NiSO solutions containing 80 gpl Ni, 5 gpl H B0 and 5 g'pl MgSO in a bagfree cell maintained at 85C.
• Table 1 shows that large bites of nickel, for example in excess of about 10 gpl can be taken when boric acid levels are relatively high, that is above about 20 gpl.
• the value of including some amounts of sodium sulfate in the electrolyte is shown by the slightly lower cell voltages of examples 6 and 7.
• a process of electrowinning nickel from aqueous sulfate electrolytes comprising electrodepositing nickel at a cathode current density of about 2 to about 10 amperes per square decimeter from a nickel-containing sulfate electrolyte maintained at a temperature in excess of 60C and at a pH of about 1.5 to about 2.0 (as measured at cell temperature) and contained in a cell having no diaphragm isolating the cathode from an essentially insoluble anode and in which vigorous agitation of the electrolyte is maintained, while feeding nickel-containing electrolyte at a relatively high pH to said cell and withdrawing nickel containing electrolyte from said cell at rates to maintain a substantially constant volume of electrolyte in said cell, to maintain the required pH in said cell and to maintain a nickel bite of at least about 5 grams per liter.
• a process as in claim 1 wherein the electrolyte in the cell contains about 40 to about 130 grams per liter of nickel as the sulfate, at least about 0.5 grams per liter of magnesium sulfate, up to about grams per liter of sodium sulfate and up to about 75 grams per liter of boric acid and is maintained at a temperature of at least about 70C.
• a process as in claim 2 wherein the boric acid content of the electrolyte is about 5 to about 50 grams per liter.
• a process as in claim 1, employing a current agitation is provided.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

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Cited By (12)

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Citations (1)

• 1974
  • 1974-04-09 CA CA197,211A patent/CA1019278A/en not_active Expired
• 1975
  • 1975-02-24 US US552247A patent/US3928153A/en not_active Expired - Lifetime
  • 1975-03-06 GB GB9413/75A patent/GB1496417A/en not_active Expired
  • 1975-03-10 ZA ZA00751444A patent/ZA751444B/xx unknown
  • 1975-03-10 JP JP50028132A patent/JPS50133922A/ja active Pending
  • 1975-04-03 FI FI750999A patent/FI58166C/fi not_active IP Right Cessation
  • 1975-04-04 NO NO751171A patent/NO143389C/no unknown
  • 1975-04-07 FR FR7510724A patent/FR2267391B1/fr not_active Expired

Patent Citations (1)

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