REVIEW ON HEAP LEACHING OF COPPER ORES

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REVIEW ON HEAP LEACHING OF COPPER ORES

• Carlos Avendaño V.
• Sociedad Terral S.A.

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• The common approach observes the ore
• behavior, which has been detected through
  test work
• and experience, with minimum manipulation.

Terrals Approach
- Recognizes the characteristics and behavior of
the ore. - Separates the conditions to be
observed and the available degrees of freedom. -
Conciliates both aspects, establishing and
reaching an objective based on the economical
criteria of the operation.
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• AN IDEAL LEACHING
• Must maximize metallurgical recoveries.
• Must minimize consumption of acid, water and
  energy.
• Must consider that the resulting PLS complies
  with
• the copper and acid conditions, which will be
  further required
• by the SX plant in order to maintain its maximum
  efficiency.
• Must generate a clean PLS, without suspended
  solids,
• colloids, iron, chlorine, manganese or total
  sulfates, so that
• transfers to the electrolyte and risks of crud
  formation are
• minimized.

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• AN IDEAL LEACHING
• Must eliminate the effects of eventual reducers
  and clays with ion exchange capacity and complex
  silicates in the ore.
• Curing doses - when used - must be calculated
  in a way that they are consistent with
• - Maximum benefit of kinetics,
• - Minimum enhancement of the acid consumption
  and
• contribution to excess in the PLS
• - No inclusion, or minimum amount, of soluble
  impurities in
• the PLS.
• Must avoid formation of phreatic layers and
  local flooding that might cause channeling,
  slipping or heap erosion.

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• AN IDEAL LEACHING
• Ideally, it must allow a joint treatment of
  ores with diverse mineralogy, including oxide and
  sulfide species.
• Must allow managing the iron behavior, in order
  to
• - ensure that the required quantities and
  ratios of ferric- ferrous are present, allowing
  to regenerate acid, to create oxidizing
  conditions and to co-precipitate impurities
• - avoid formation of ferric colloidal
  precipitates, which promote channeling of
  solutions
• - allow water removal from the precipitates
  when these formations cannot be prevented
• - ensure the appropriate contents for
  bacterial activity in sulfide leaching.

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• 1. THE BASIC EQUATION
• ACID CONTRIBUTION CONSUMPTION ACID
  EXCESS

• - By copper and by gangue
• The acid excess only appears
• when consumption is
• finished.

• - In Curing
• - In Irrigation
• - By internal generation

The equity problem deals with the fact that
gangue acid consumption depends on the acid
availability (at least within a range)
therefore, the consumption also depends on the
contribution and the terms of the equation are
mutually dependent.
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• If ACID CONTRIBUTION lt ACID CONSUMPTION
• Then - Metallurgical recovery is affected

• If ACID CONTRIBUTION gt ACID CONSUMPTION
• Then
• A maximum metallurgical recovery is almost
  achieved
• A good kinetics is obtained
• - The net consumption" of acid increases
• - Impurities are incorporated to the solutions
• - Acid excess in PLS may occur

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• If ACID CONTRIBUTION ACID CONSUMPTION
• UNDER LOW ACID CONCENTRATION IN A PLS AND WITHIN
  AN ENVIRONMENT THAT PROMOTES REDOX REACTIONS.
• Then we can expect

• Positive effects
• Iron and copper oxidation are triggered
• Interfering agents are inactivated reducers
  are oxidized and
• clays with ion exchange capacity remain
  passive
• A maximum metallurgical recovery is achieved,
  due to the
• contribution of both Fe3 in sulfide
  leaching, and Cu0 , which was
• precipitated by reducers.
• Decreased consumption of net acid.
• Solutions are cleaned and fewer impurities are
  added to the
• system.
• Negative effects
• Kinetics is affected

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• 2. The irrigation ratio
• The irrigation ratio provides irrigation
  solutions that activate the Physical-Chemistry of
  the system.
• It is associated to the conditions that
  determine
• - the required acid to obtain the copper
  concentrations, acid and impurities that were
  targeted in the PLS,
• the interactions among the kinetics of copper
  recovery, of acid consumption and impurity
  dissolution, and
• the definition of a feasible recovery target,
  under economical criteria based on both the
  conditions studied in metallurgical tests and in
  the operation.

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The way to use the irrigation ratio leads to
leaching techniques, which contain
parameters and dependent variables.
The combination of both will lead to process
configurations that, simultaneously,
solve the operational problems, which are
usually related to
Mineral handling Crushing, agglomeration,
loading and heap configuration. Solutions
handling Irrigation configuration, sequence of
solution application, irrigation media and rates,
forms of collection of solutions, water
consumption. Operational aspects Drag of fines,
flooding and channeling of solutions, heap
erosion, air injection and others.
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• ACID IMPURITIES BALANCE
• 1st Series of Reactions
• 4 FeSO4(impregn) O2(gas) 10 H2O 4
  Fe(OH)3(solid) 4 H2SO4(solut.)
• 4 Fe(OH)3(solid) 6 H2SO4(solut.) 2
  Fe2(SO4)3(solut.) 12 H2O
• 4 FeSO4(impregn.) O2(gas) 2 H2SO4(solut.) 2
  Fe2(SO4)3(solut.) 2 H2O

• Iron species dissolve mainly to Fe2 state.
• - Fe2 impregnates the rock when irrigation is
  stopped.
• - Fe3 is oxidized upon contact with gasified
  air or by bacterial action, and
• - Fe3 changes to hydrolyzed state, either
  simple or complex.
• - The hydrolyzed Fe3 is re-dissolved in the
  following irrigation acid, consuming 0,86 Kg of
  fresh acid/Kg of oxidized ferric ion.
• Fe3 eventually participates in redox reactions
  and returns to ferrous
• state Fe2.

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• 2nd Series of Reactions
• Combining the previous reaction with
• 12 FeSO4(impregn.) 3
  O2(gas) 6 H2O 4 Fe(OH)3(solid) 4
  Fe2(SO4)3(soluc.)
• 4Fe(OH)3(solid)4Fe2(SO4)3(solut.)2Na2SO412H2O
  4NaFe3(SO4)2(OH)6(solid) 6H2SO4(solut.)
• 12FeSO4(impregn.) 3O2(gas) 6H2O
  2Na2SO4 4NaFe3(SO4)2(OH)6(solid)
  6H2SO4(solut.)

• - Consequent oxidizations from the 1st Series are
  repeated, or
• - the previous hydrolyzing Fe3 participates
  re-dissolved, according to reactions.
• - When pH increases due to mineral acid
  consumption and the presence of other ions,
  formation of jarosites occurs.
• - Thus, solutions lose iron (Fe3), sulfates
  (1,15 Kg/KgFe) and other ions that are present
  (e.g. Na 0,13 Kg/KgFe) by precipitation,
  which is virtually permanent, and 0,86 Kg of
  sulfuric acid/Kg of precipitated iron.
• - Consequently, jarosites contribute to impurity
  elimination from the solutions and to the return
  of part of the consumed acid.
• The various jarosites incorporate other co-abated
  elements (Mg, Al and others) .
• Jarosites are re-dissolved in environments with
  higher acidity than the one in which they were
  formed.

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• The concentration of Fe3 ions available in the
  solution depends on the balance between
• FERRIC CONTRIBUTIONS FERRIC
  CONSUMPTION

• By
• Initial presence of Fe3
• Presence of Fe2 oxidization
• Re-dissolution of hydrolyzed Fe3

• By
• Fe3 consumption from the ore
• and reduction to Fe2
• - Precipitation of jarosites

• The causes of the balance cannot be possibly
  analyzed in leaching
• Accounting of the especies is external it
  measures outgoing and incoming ions. Only the
  consequent overall abatement or dissolution
• is observed.
• Meanwhile, many dissolutions and ion abatements
  take place at the same time inside the test,
  which are recorded from outside.
• Thus, the quantity of precipitates can only be
  detected through the
• gravel mineralogy, but not through metallurgical
  accounting

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• INTERMITTENT OR PULSE IRRIGATION
• Leaching takes place over a sequence of short
  irrigation and resting periods
• Resting periods allow solution drainage and
  squeezing
• the particles remain humid but with no liquid
  that may isolate them from the air in the ore bed

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• Metallurgical Effects
• A decrease in the required irrigation ratio
  to achieve target recovery, since the mineral
  particles absorb the reagents of each of the new
  irrigation solutions more easily and efficiently.
  Likewise, products are also poured off during
  squeezing in each resting stage.
• This effect makes it unnecessary to urge on
  irrigation rates for improving kinetics and
  recoveries and, at the same time, avoids
  impairment of the copper concentration of the
  PLS.

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• Physical-Chemical Effects
• Particles exposure to air during pulses,
  oxidizes the reducers as well as the metallic
  copper precipitated by them it alters and
  inhibits the action of clays with ion exchange
  capacity and the formation of colloidal and
  silicates during the process.
• Particles exposure to air allows oxidation of
  Fe2 impregnated ions, which easily precipitate
  by hydrolysis, but in a disseminated way and with
  minimum amounts of water, which avoids formation
  of colloidal gels that cause channelling.
• When association with other ions is possible,
  part of the hydrolyzed Fe3 will dissolve when
  acid is made available in the subsequent
  irrigation, and part of the iron will precipitate
  to the state of disseminated jarosites almost
  permanently.
• In bacterial leaching, it provides oxygen to
  bacteria.

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• Physical-Chemical Effects
• Re-dissolved Fe3 ions support copper recovery
  and return to the Fe2 state, and then repeat
  the cycle in the following irrigation pulse,
  according to acid availability in the next
  irrigation solutions.
• In the permanent precipitation of jarosites,
  ions from impurities are markedly dragged through
  diverse mechanisms among them a considerable
  portion of chlorides and sulfates.
• Depending on the pH environment around the Fe2
  ion, when oxidizing to Fe3 occurs during the
  resting period, the acid is partially
  regenerated, which joins the new solution as an
  active agent, being then deducted from external
  consumption.

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• Hydraulic effects
• Decreased channeling, because during the
  resting periods of each pulse, the previous
  irrigation channeling is erased, which compels
  formation of new access routes in the following
  irrigation cycle.
• Flooding and heap slipping risks decrease,
  since it is possible to perform ore bed drainage
  before saturation.
• During resting periods, the huge colloidal
  jarosite gels are dehydrated and change into the
  most dehydrated sol state - - smaller in size -
  which maintains the ore bed porosity.

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• CONCLUSIONS
• - Metallurgical recovery can be a target goal -
  and not necessarily a result or a variable
  depending on the ore -within a range that is
  usually bigger than expected.
• - This target recovery goal is limited by
  economical factors that are associated to the
  leaching techniques.
• - Different leaching techniques involve different
  kinetics and costs.
• - Consequently, the main independent variable is
  the most convenient leaching technique to
  achieve the target recovery.