Magpie Polymers MPX-315 for PGM recovery from silver electrolyte

Magpie Polymers
MPX-315 for PGM recovery from silver electrolyte
14/03/2014
MPX resins are very efficient at removing precious platinum group metals (PGM) from industrial
effluents, giving high performance and high selectivity in difficult situations. In silver electrolysis,
depending on the source of the silver, there can be traces of platinum, palladium and other PGM in the nitric
acid electrolyte. A selective removal of these valuable impurities using Magpie materials can be achieved at
two levels:
•
During silver electrolysis: to ensure a 99.99% pure silver without PGM contamination
•
After silver electrolysis: in order to remove all valuable metal traces from the spent electrolyte
MPX-315 can be safely used in effluents containing up to 15 % HNO 3, making it perfectly suitable for these
applications. The material does not bind silver and copper, and other common metals like lead or nickel.
This application note details the technical specification and performance of the PGM capturing resin
Table 1: Technical specifications, performance and application diagram of MPX-315 in silver electrolyte filtration.
Process Stage and Aim
Filtration Type
Performance
PGM loading*
During silver electrolysis:
closed loop with
Maintain low PGM concentration recirculation of electrolyte
Below a set limit depending 25 – 40 g/L
on requirements
After silver electrolysis:
Recover all PGM
99% recovery or <1 mg/L
single pass filtration of
spent electrolyte
>50 g/L
*based on data obtained on a specific effluent presented in this note
MPX-315 filtration
to maintain low PGM
concentration during
process
Silver electrolysis bath
Spent electrolyte:
filtered by MPX-315
after process
Magpie Polymers – www.magpie-polymers.com - +33 (0)1 64 28 90 78
DURING ELECTROLYSIS:
MPX-315 to limit the PGM concentration
MPX-315 has chelating thiourea and phosphine oxides functional groups, leading to strong affinity for PGM.
When contacted with a solution that contains common metals and silver in tens or even hundreds of grams
per liter and traces of PGM in milligram per liter concentrations, the Magpie material binds the PGM
selectively. The filtration speed, expressed in bed volumes (BV) per hour can be around 25 BV/h. For a 10L
column this corresponds to 250 L/h.
In this application the Magpie material is best used to keep the PGM-concentration constant at a low level.
This manner of operation prevents the PGM from rising above a level at which they negatively impact the
purity of the final silver product. Therefore, the continuous recirculation of the electrolyte through the
Magpie column ensures that the PGM-levels are maintained low throughout the process and facilitate the
achievement of 3 or 4N silver purity
Depending on the size of the electrolysis bath and the throughput, Magpie Polymers can assists its customers
in finding the optimum column size, treatment time and pumping speed. If required Magpie Polymers can
deliver ready-to-use filtration installations.
For higher concentrations of HNO3 Magpie Polymers recommends MPX-310 as it is more acid resistant.
Although MPX-315 can be applied, its lifetime will be shortened due to deterioration under such strong
oxidizing conditions. The maximum loading onto MPX-310 is lower than that obtained on MPX-315.
Neither material reacts violently with nitric acid, however, due to slow gas evolution, the system should be
opened to atmosphere or exhaust, in order to avoid pressure build-up.
Figure 2: A single column of MPX-315 for recirculating silver electrolyte.
Magpie Polymers – www.magpie-polymers.com - +33 (0)1 64 28 90 78
Industrial application example during electrolysis
In an industrial application example, a solution of a volume of 20 BV containing silver palladium and
platinum as well as other common metals (Table 2) was treated in a closed loop at a filtration rate of 25 BV/h
using MPX-315. The PGM-concentration dropped within 5 hours, reaching the minimum after 22 h (93%
PGM-removal, Figure 3).
Table 2: Concentration of the silver electrolyte prior to electrolysis.
Cu (g/L)
Pb (g/L)
Ag (g/L)
Pt (g/L)
Pd (g/L)
49.6
18.7
74
0.091
0.320
Pt
Pd
300
250
200
150
100
50
0
0
5
10
15
20
25
30
Time, h
Figure 3: PGM concentration as a function of treatment time with MPX-315 in a closed loop column at 25 BV/h.
At this point the solution is replaced with a fresh solution and this procedure is repeated for 6 batches. The
loading of the PGM on the MPX-315 resin as a function of final concentration is plotted below for Pd and Pt.
Pt
Pd
PGM
50
Loading, mg/ml
40
30
20
10
0
0
20
40
60
80
100
120
140
160
Concentration, ppm
Figure 4: Loading of Pd and Pt on MPX-315 as a function of the residual concentration.
(Fig. 4). This shows that when the final PGM concentration is around 100 mg/L (the maximum target
concentration for this particular example) the amount of PGM captured onto the resin is about 40 g of PGM
per liter of resin. At this point the material is saturated and can replaced and dispatched for PGM refining.
Magpie Polymers – www.magpie-polymers.com - +33 (0)1 64 28 90 78
AFTER ELECTROLYSIS:
MPX-315 to remove PGM to the very last trace
When silver is no longer present at high concentration and the objective is to remove PGM to the very last
trace, MPX-315 is used in a single pass through at low flow speed of between 1-5 BV/h will ensure complete
and selective removal of the PGM.
By placing two columns in series, the first column or head column, can be saturated whilst any leakage is
prevented by the second, tail column. For this purpose, Magpie has developed a simple filtration unit shown
in Figure 5, which can be adapted for specific needs in terms of column size, pumping speed and degree of
automation.
Figure 5: A two column treatment unit for PGM removal using MPX-315.
Magpie Polymers – www.magpie-polymers.com - +33 (0)1 64 28 90 78
Industrial application example after electrolysis
In an application example, a solution containing mainly copper and lead with traces of platinum and
palladium (Table 3) was pumped through a column of MPX-315 at a speed of 1.5 BV/h, for 250 column bed
volumes.
Table 3: Metal concentrations in the spent silver electrolyte used in the example.
Cu (g/L)
Pb (g/L)
Ag (g/L)
Pt (g/L)
Pd (g/L)
28.9
2.72
0.07
0.048
0.158
Figure 6 shows the concentration of Pt (blue), Pd (orange) and PGM combined (yellow) as a function of the
volume of the electrolyte treated. In the first 150 bed volumes no PGM is detected after treatment, then the
breakthrough starts appearing. In a double column setup (Fig. 5) this 'leakage' would be retained entirely by
the second column.
It is important to function in such a double-column setup in order to maximize the loading on the head
column. As illustrated in Figure 7, the total loading of PGM, composed of Pt/Pd in a 1:3 mass ratio in this
example, surpasses 50 g/L or about 5 mass% upon saturation with a PGM level after filtration below 1
mg/l. Once this loading is achieved, the head column is removed for PGM refining. The tail column is then
connected in the first position, a fresh column is placed as the tail, and the PGM capture continues.
Pd
Pt
60
Pd
PGM
50
150
Loading, g/L
Concentration PGM at exit, mg/L
Pt
200
100
40
30
20
50
10
0
0
50
100
150
Volume treated, BV
200
250
0
0
20
40
60
80
100
120
Concentration PGM at exit, mg/L
Figure 6: Pt, Pd and combined PGM concentrations at the
Figure 7: Pt, Pd and combined PGM loading after
exit of the column of MPX-315 (after treatment).
treatment with a single column of MPX-315 at 1.5 BV/h.
Magpie Polymers – www.magpie-polymers.com - +33 (0)1 64 28 90 78

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