4. Nickel and cobalt may be produced by leaching of laterite ores. These are oxidized, near-surface...

   

Transcribed Image Text:

4. Nickel and cobalt may be produced by leaching of laterite ores. These are oxidized, near-surface deposits containing oxides, hydroxides and aluminosilicates. Nickel may be present in a (mainly) goethite matrix, Fe(O)OH, at 1-2% grade. Cobalt is usually present at roughly 1/10 this amount. Ores are leached in autoclaves at high pressures and temperatures (250C) using strongly acidic H2SO4 solution. Goethite is converted into hematite, Fe2O3, and in the process nickel and cobalt are leached into solution. After leaching and cooling the slurry is typically subjected to solid-liquid separation via counter-current decantation. This is successfully practiced at Moa Bay, Cuba. (In this case the clarified solution is then treated with hydrogen sulfide to precipitate a Ni-Co-Cu bulk "concentrate," which is shipped to Fort Saskatchewan for conversion into pure nickel and cobalt.) Other nickel laterite processes purify the clarified solution and then recover nickel and cobalt by electrowinning. Do all questions using Excel. Handwritten answers will not be accepted, except where otherwise indicated. Show example calculations for your work. (No marks without illustrative calculations.) Use the following symbols and terms as required: S = solids mass flow rate O wash water flow rate n = number of wash stages C* = solute concentration in feed solution F = feed solution flow rate U = underflow solution flow rate O/U = wash ratio V = overflow solution (final PLS) flow rate Wash efficiency (as per course notes) R = recovery of solute in % C. = Solute concentration in lead thickener solution Dilution of feed = ratio of solute concentration in lead thickener overflow / solute concentration in feed solution C = solute concentration in final underflow solution Assume all solutions have a density of 1 kg/L (this is an oversimplification for concentrated solutions). (a) There are a total of 5 thickeners in the CCD circuit. The aqueous solution flow rate associated with the feed slurry to CCD washing is 1000 m/h. The feed slurry has 35% solids; the feed solution nickel concentration is 1 g/L. The solids content associated with the underflows from each thickener is 42% by weight. The wash water flow rate is 1605 m/h. Determine the following quantities and also report appropriate units. Report your answers in a table. Determine: (i) The number of wash stages in the circuit. (ii) The solids flow rate in t/h through the process. (iii) The underflow solution flow rate. (iv) The clarified overflow solution flow rate. (v) The O/U ratio (vi) The wash efficiency (4) (vii) The recovery of Ni+2 from the circuit (viii) What will the clarified overflow solution nickel concentration be? (ix) If the nickel price is $7.70/lb, what is the annual cost of the loss of nickel from the CCD circuit? (b) Some things can go wrong with an improperly tested or engineered CCD circuit. Determine the effects of the following problems. (i) Frequent failures mean that much of the time there is one wash thickener down (the "walls fall off"). How does this affect recovery and revenue losses? Comment. (ii) Starting with the case of part (a), what if the underflow % solids was actually 37%? Comment on the effect on recovery. (c) What will the effects of the following changes be? (i) Starting with the base case of part (a) an extra wash stage is added. Comment on the effect on recovery. (ii) Starting with the base case of part (a) what is the effect of increasing the wash water flow rate to 2300 m/h? Comment on the various effects of this change. 4. Nickel and cobalt may be produced by leaching of laterite ores. These are oxidized, near-surface deposits containing oxides, hydroxides and aluminosilicates. Nickel may be present in a (mainly) goethite matrix, Fe(O)OH, at 1-2% grade. Cobalt is usually present at roughly 1/10 this amount. Ores are leached in autoclaves at high pressures and temperatures (250C) using strongly acidic H2SO4 solution. Goethite is converted into hematite, Fe2O3, and in the process nickel and cobalt are leached into solution. After leaching and cooling the slurry is typically subjected to solid-liquid separation via counter-current decantation. This is successfully practiced at Moa Bay, Cuba. (In this case the clarified solution is then treated with hydrogen sulfide to precipitate a Ni-Co-Cu bulk "concentrate," which is shipped to Fort Saskatchewan for conversion into pure nickel and cobalt.) Other nickel laterite processes purify the clarified solution and then recover nickel and cobalt by electrowinning. Do all questions using Excel. Handwritten answers will not be accepted, except where otherwise indicated. Show example calculations for your work. (No marks without illustrative calculations.) Use the following symbols and terms as required: S = solids mass flow rate O wash water flow rate n = number of wash stages C* = solute concentration in feed solution F = feed solution flow rate U = underflow solution flow rate O/U = wash ratio V = overflow solution (final PLS) flow rate Wash efficiency (as per course notes) R = recovery of solute in % C. = Solute concentration in lead thickener solution Dilution of feed = ratio of solute concentration in lead thickener overflow / solute concentration in feed solution C = solute concentration in final underflow solution Assume all solutions have a density of 1 kg/L (this is an oversimplification for concentrated solutions). (a) There are a total of 5 thickeners in the CCD circuit. The aqueous solution flow rate associated with the feed slurry to CCD washing is 1000 m/h. The feed slurry has 35% solids; the feed solution nickel concentration is 1 g/L. The solids content associated with the underflows from each thickener is 42% by weight. The wash water flow rate is 1605 m/h. Determine the following quantities and also report appropriate units. Report your answers in a table. Determine: (i) The number of wash stages in the circuit. (ii) The solids flow rate in t/h through the process. (iii) The underflow solution flow rate. (iv) The clarified overflow solution flow rate. (v) The O/U ratio (vi) The wash efficiency (4) (vii) The recovery of Ni+2 from the circuit (viii) What will the clarified overflow solution nickel concentration be? (ix) If the nickel price is $7.70/lb, what is the annual cost of the loss of nickel from the CCD circuit? (b) Some things can go wrong with an improperly tested or engineered CCD circuit. Determine the effects of the following problems. (i) Frequent failures mean that much of the time there is one wash thickener down (the "walls fall off"). How does this affect recovery and revenue losses? Comment. (ii) Starting with the case of part (a), what if the underflow % solids was actually 37%? Comment on the effect on recovery. (c) What will the effects of the following changes be? (i) Starting with the base case of part (a) an extra wash stage is added. Comment on the effect on recovery. (ii) Starting with the base case of part (a) what is the effect of increasing the wash water flow rate to 2300 m/h? Comment on the various effects of this change.