Ion exchange in hydrometallurgy - Purolite.com

Purolite Product Bulletin Hydrometallurgy
Purolite Product Bulletin_________________________
Ion Exchange
in Hydrometallurgy
Hydrometallurgy 09 2012 0
Ion Exchange in Hydrometallurgy

Purolite Product Bulletin Hydrometallurgy
Hydrometallugy
Metals can be extracted from ores using several
methods. They can be extracted using chemical
solutions (Hydrometallurgy), using heat
(Pyrometallurgy) or using mechanical means.
Hydrometallurgy is the process of extracting
metals from ores by dissolving the ore
containing the metal of interest into an aqueous
phase and recovering the metal from the
resulting pregnant liquor.
Hydrometallurgy often offers the most costeffective
and environmentally friendly techniques
for extracting and concentrating different metals.
Often, various hydrometallurgical processes are
used in the same flowsheet, such as combining
ion exchange and solvent extraction for the
recovery and purification of uranium.
Hydrometallurgical processes can also be
combined with non - hydrometallurgical
extractive metallurgy processes.
Table 1 - Applications of ion exchange in hydrometallurgy
Origin of stream to be treated Ion exchange application
This bulletin discusses the use and advantages
of ion exchange resins for sorption and recovery
of target metals.
1. Applications of Ion Exchange (IX)
Ion exchange technology is used for the primary
recovery of metal(s) of interest or the removal of
specific impurities in order to increase the value
and purity of the final product.
A wide variety of process streams benefit from
the application of ion exchange resins, as shown
in Table 1.
2. Ion Exchange Contactor Design
Ion Exchange contactor designs are quite
diverse and customized. They generally fall into
three categories: Fixed Bed, Fluidized Bed and
Resin in Pulp. The design varies as a function
of the properties of the medium being treated
and overall capital expense optimization
considerations.
Ion exchange contactors perform two key
functions:
1. They provide conditions that favor
efficient mass transfer between the
process solution or pulp and the ion
exchange resin
2. They ensure the efficient mechanical
separation of the ion exchange resin
from the solution or pulp.
Ore, after heap or agitated leach Primary recovery of metal(s) of interest, e.g. gold, uranium
Volatile compounds captured in offgases
from smelters and roasters
Slags and calcines from roasting and
smelting operations
Electrolyte
Tailings treatment
Acid mine drainage
Recovery of rhenium from off-gases produced by roasting of
molybdenite and smelting of copper concentrates
Recovery of various metal(s) of interest, after leaching
Removal of copper and zinc impurities from cobalt and nickel
advance electrolytes, to ensure higher metal purity
Recovery of copper, cobalt, gold, etc from historical mine
tailings, as well as current arisings
Treatment of process water to enable recycling to the plant or
safe disposal
Hydrometallurgy 09 2012 1

Purolite Product Bulletin Hydrometallurgy
An important factor that determines the design
of an ion exchange contactor is the suspended
solids content of the pregnant liquor/pulp. A
certain quantity of suspended particles is always
present in the actual pregnant solutions from
which the metal(s) of interest is to be recovered.
A suitable ion exchange contactor design must
be selected based on the suspended solid
content in a pregnant flow, as summarized in
Table 2.
Table 2 - Choice of IX contactor based on
solids content of feed
Solids content
Clear liquid, Pb 2+ > Zn 2+ > Cd 2+ >
Ni 2+ > Ca 2+
Phosphonic resins: Cu 2+ > Zn 2+ > Cd 2+ > Mn 2+
> Co 2+ > Ni 2+ > Ca 2+
Aminophosphonic resins (at acidic pH): H + >
Fe 3+ > Pb 2+ > Cu 2+ > Zn 2+ , Al 3+ > Mg 2+ ≥ Ca 2+ ≥
Cd 2+ > Ni 2+ ≥ Co 2+ > Na +
Iminodiacetic resins: Cr 3+ > In 3+ > Fe 3+ > Al 3+
> Hg 2+ > UO 2+ > Cu 2+ > Pb 2+ > Ni 2+ > Cd 2+ > Zn 2+
> Co 2+ > Fe 2+ > Mn 2+ > Ca 2+ > Mg 2+
Strong acid resins: Fe 3+ > Ca 2+ > Fe 2+ > Cu 2+
> Mg 2+ > K + > NH4 + > H +
Strong base resins: SO4 2- > CO3 2- > NO3 - > Cl -
- - -
> HCO3 > F > OH
Bis-picolylamine resins: Cu 2+ > Ni 2+ > Fe 3+ >
Zn 2+ > Co 2+ > Cd 2+ > Fe 2+ > Mn 2+
Hydrometallurgy 09 2012 3

Purolite Product Bulletin Hydrometallurgy
The usual complement of parameters that are to
be controlled during production includes:
� Functionality: determines the selectivity
of the resin for certain metals over
others
� Ion exchange capacity: a high capacity
is desirable to reduce the size of the
plant and subsequently the cost of
capital investment and elution reagents
� Grading: smaller beads are used in fixed
bed operations, which benefits from the
improved kinetics of smaller beads. RIP
operations require larger beads, to allow
for ease of separation of the resin and
pulp.
� Mechanical stability
� Osmotic stability
All the characteristics of IX resins are
interdependent and performance of the resin is a
trade-off between the different technical
parameters of the resin.
4. Principles of Resin Volume Estimation for a
specific project
In order to make an initial estimate of ion
exchange plant size, it is necessary to calculate
the resin volume that is sufficient to reach the
performance target. This is calculated from the
mass balance equation for the target metal:
Mass balance: CPLS × FPLS = CR × FR
CPLS: Metal concentration in PLS, kg/m 3 (PLS)
FPLS: Flow rate of PLS, m 3 (PLS)/hr
CR: Operating metal capacity of the resin,
kg/m 3 (R)
FR: Flow rate of the resin, m 3 (R)/hr
IX resin flow rate: FR = (CPLS × FPLS)/CR
Total Resin Inventory (m 3 ):
VR = FR × (T1 × k + T2 + T3)
T1 – Residence time at sorption provided that:
� The concentration of the metal is
reduced to the tail limits (e.g., < 5 ppm
for most uranium projects).
� The metal capacity of the resin reaches
maximum.
A resin "safety" volume should be provided for
the sorption stage; for this volume, the Т1
parameter should be multiplied by a k factor with
a value of 1.1 – 1.5 (the process-designer
selects the actual value).
T2 – Residence time at desorption
T3 – Residence time in auxiliary operations
By minimizing FR and T, CAPEX can be
reduced.
In order to minimize FR a resin must have a
maximum capacity.
In order to minimize T1, a resin must have the
best ion exchange kinetics.
In order to minimize T2, a resin must have
efficient desorption; i.e., complete and rapid.
In order to minimize T3, the desorption and
regeneration processes must be simple, so as to
avoid or minimize additional operations.
Hydrometallurgy 09 2012 4

Purolite Product Bulletin Hydrometallurgy
5. Selecting the Optimum Resin
There are a number of important considerations
in choosing the correct resin. They include:
� The target metal. Is it a valuable metal(s)
or an impurity?
� The matrix. e.g. acidic (sulfate, chloride,
etc.) or alkaline (cyanide, sodium
carbonate, etc.)
� The solution pH. The performance of IX
resins can be affected by pH.
� Recovery from pulp (RIP) or clear solution
Resin in Solution (RIS). This will
determine the type of contactor required,
as well as dictate certain physical
properties of the resin (size, physical
strength).
� Presence of competing ions. It is important
to choose a resin with a high selectivity for
the metal of interest.
� The solution temperature. While increased
temperatures generally benefit most
reactions, IX resins are temperature
sensitive and for hydrometallurgical
applications a maximum operating
temperature of 60 °C is usually
recommended.
� Integration with other unit operations. i.e.
the choice of elution reagent is often
dictated by requirements/limitations of
downstream processes.
� Process flexibility. Is it possible to change
the pH of the solution to possibly benefit
the IX unit operation while having a
minimal impact on the rest of the circuit?
� Environmental limitations. The choice of
elution/regeneration reagents is influenced
by regulations on the disposal thereof.
Table 3 shows a number of
hydrometallurgical applications and the
suggested Purolite resin(s)
Table 3 - Hydrometallurgical Application and the suggested Purolite resin(s)
Target metal Detail Purolite ® resin(s)
Gold Cyanide liquors and pulps
Purogold A193
Purogold S992
Gold Thiosulphate leach Purolite ® A500/2788, Purolite ® A530
Gold Acidic liquors or pulps Purolite ® S920, Purolite ® S924
Platinum Group Metals Acidic liquors or pulps
Purolite ® S920, Purolite ® S924,
Purolite ® S985
Molybdenum Acidic liquors or pulps Purolite ® A100Mo
Rhenium Acidic liquors or pulps
Purolite ® A170/4675,
Purolite ® A172/4635
Gallium Recovery from Bayer solutions Purolite ® S970
Rare Earth Elements Acidic liquors or pulps
Copper, nickel, cobalt, zinc Acidic liquors or pulps
Nickel Acidic liquors or pulps Purolite ® S960
Copper & zinc impurity
removal
Cobalt and nickel electrolyte Purolite ® S950
Selection of cation exchange
resins
Purolite ® S930Plus,
Purolite ® S930/4884, Purolite ® S960
Mercury Various liquors and waste waters Purolite ® S920, Purolite ® S924
Antimony Various liquors and waste waters Purolite ® S957
Bismuth Various liquors and waste waters Purolite ® S957
Ferric iron Copper and nickel electrolyte Purolite ® S957
Hydrometallurgy 09 2012 5

Purolite Product Bulletin Hydrometallurgy
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Hydrometallurgy 09 2012 6