CATALYSTS
PM precursor
Synthesis
Support material
EFFICIENT USE OF PRECIOUS METALS
Figure 2 – Catalyst manufacturing at Heraeus
Recycling metals
Recycling is an increasingly important issue when it comes to precious metal catalysts Gaiser noted . Heraeus ’ recycling and refining processes have yielded about 120 tonnes of PGMs , 370 of gold and 1,270 of silver to date . 60 % of the PGMs and 23 % of the gold and silver processed in its plants by volume are secondary material .
The company applies a wide range of preparation , sampling and purification techniques to the different materials that come in . By these different means , it can separate out all eight precious metals as well as rhenium and process them into different outputs , including chemical precursors as well as bars , grains and sponges ( Figure 3 ).
Secondary metals like these now account for 24-33 % of the process stream and Heraeus aims to push it even higher for both environmental and economic reasons . Not only are the materials intrinsically valuable , when recycled their carbon footprint measured against primary metals in
CO 2 eq ./ gram produced is 97-98 % lower for all four PGMs and iridium . Since 2019 , Heraeus has had a goal of being carbon-neutral for its own operations by 2025 and to have completely eliminated fossil fuels and achieved net zero GHG emissions by 2033 . Recycling the metals is thus crucial to achieving these targets .
New catalyst
Subsequently , at the P2X conference in Frankfurt in November , Heraeus launched a new ruthenium-based catalyst for proton exchange membrane ( PEM ) water electrolysis . Developed with South African firm Sibanye-Stillwater , this is said to combine the high activity of ruthenium-based catalysts with unprecedented stability during hydrogen production .
Heraeus said that 40 % of the planned 175 GW of hydrogen due onstream by 2030 is expected to be produced using PEM electrolysis , which itself depends on iridium . Today , on average about 400 kg of iridium is required to build one GW of capacity . This needs to be reduced to 100 kg to avoid supply bottlenecks as only 9 tonnes / year of iridium are mined worldwide . The new catalyst can reduce iridium use by 85 %.
The new catalyst is said to solve the problem of ruthenium ’ s lack of stability in a PEM electrolyser stack “ by combining both ruthenium and iridium oxide in a novel manner , enhancing stability while maintaining the increased catalytic activity provided by ruthenium ”. It can also achieve up to 50 times higher mass activity compared to iridium oxide , Heraeus said , while accelerated degradation tests confirmed its stability after 30,000 cycles , with significantly lower activity loss than for ruthenium oxide and on a par with iridium oxide . ●
Dr Detlef Gaiser
HERAEUS PRECIOUS METALS
TECHNICAL SALES MANAGER k + 49 6181 35 3324 J detlef . gaiser @ heraeus . com j www . heraeus-precious-metals . com
Figure 3 - Precious metal catalyst recycling at Heraeus
Materials Preparation , Separation , Purification Output
Heterogeneous catalysts on various carriers |
Sampling & Milling |
Converting |
Recrystallisation |
Bars |
Industrial catalysts |
Homogenise material and determine PM content |
|
|
Incineration |
High efficiency burning / pyrometallurgical concentration of alloys
Precipitation
|
|
|
Purification of PM salts by dissolution and precipitation cycles
Wet-chemical reduction
|
Grains |
Automotive catalysts |
Burning organic components , metal enriched ash residue |
Separate by reduction , oxidation , hydrolysis or complexation |
Reduction of pure PM compounds to fine PM sponge |
Sponge |
|
Smelting |
Distillation |
Electrolysis |
|
Homogeneous catalysts |
Extraction of PM in collector metals |
Volatilises , separates metals by vaporizing at different temperatures |
Applies electrical current , deposits metals from solution |
Precursors |
24 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981