For a long time, there were numerous threads and questions regarding processing MLCCs. So I decided to show my way on how I do them, share my experiences and suggestions, and whole process in general to the PGM dore. In the future, I will probably come to the disclosure of the purification of the multi-metal dore to the PM mixture (speaking about PtPdAg here). Since I do not have any interest in resolving the Pt and Pd one from another.
FEED: 192 + 102 g of old soviet MLCCs. 192 g of orange and yellow "KMs" and 102 g of green "KMs". These components are famous for their very nice PtPd content, some types climbing to nearly 70g/kg PGMs. It is obvious that bigger pieces has better yields, as ratio of the weight of ceramics to the "dead" weight of legs, resin and solder is much higher. So because of this, yield fluctuate from like 25-65g/kg depending on type, size and manufacture year. There are exceptions, but usually yield of mixed batch is somwhere in the middle of this. And with ratio of Pt-Pd fluctuating depending on what types are predominantely present (there are mainly Pd ones with trace Pt, and Pt ones with trace Pd).
Stock photo of the issued material - "fat" orange/red/yellow and green ones were present in this batch. There is numerous more types with varying PGM content.
COMPOSITION: orange KMs are pieces of ceramic with soldered legs on the sides of the ceramic rectangle, dipped in thick resin filled with silica dust. Material of the ceramic is predominantely BaTiO3, but strangely - ceramic also contain bismuth and some % of Si and Al. Embedded in ceramic, there are PGMs foils with small % of silver. On the sides of the ceramic "sandwich", ends of PGM foils are soldered to the copper legs. Solder is typically of composition of PbSnCd. I do also measure some silver. Mainly because cadmium in the solder, this material is cumbersome to process in "contained" way, because cadmium will burn happily when heated upper than 400°C or so. Also, there is toxic barium in the ceramics, which can be easily leached out by acids, producing very toxic solutions, which should be dealt with responsibly.
TYPICAL WAYS OF PROCESSING: On you tube, Owltech has great series of videos issuing processing this refractory and hard material. I recommend watching them and learn from his experience, successes, mistakes and advices. Generally, first step is to remove the resin coating off the caps. There are two main ways of doing this. First easy looking, but far harder to do safely - incineration. And second more tedious, but more contained - solvent disintegration or digestion.
With incineration, material is burnt - by doing this, cadmium in the solder also burn and evaporate as CdO yellow-brown cobwebs and smoke. Very hazardous operation, if not done in good fumehood with scrubber. Solder typically contain up to 10% Cd in mixed lots (some caps do not have Cd in solder, some do), and solder comprise of roughly 10-15% weight of the average lot, so not negligible ammount.
With solvent disintegration or digestion, caps are soaked in organic solvent (usually DMSO, but DMF also works), which swell the resin coating and enable to peel it off. This process is tedious as you need to do it one by one by hand. But it is very "clean" and all Cd stays in place. Digestion is decomposition of the resn in strong NaOH boiling solution. This operation is very messy - as honey-like goo is mainly produced from orange/yellow types of caps, which is then PITA to strip off the ceramics. Only convenient way I know is to decant the liquid, wash the goo with water, drip out as much water as possible and then cover with DMSO and take it near to the boiling point of DMSO (to at least 150°C) - this will slowly liquify the goo and it can be poured off the ceramics. On many occasions, whole boards with components are dipped in clear varnish - and this is resistent to NaOH. So in this case, you need to prior remove the varnish and then proceed with NaOH disintegration.
Overall, with ceramics stripped from resin, you heat the material in mesh basket with torch or more conveniently heatgun, and by shaking motion shake off the legs and good majority of the solder out. By doing this, you "enrich" the metal fraction in PGMs, removing the stubborn Sn, Pb and Cd - and practically all copper. Little PGMs follow the solder and are contained in it, but if the ceramics are not too much beaten or cracked, it is low number.
With bare ceramics in hand, there are generally two ways of approach. Pyro and wet route. Pyrometallurgic one is based most of the times on pulverizing the ceramics in the grinder, then mixing them with fluxes and collector metals and smelting them to obtain metallic dore, which is then cupelled free from lead (or scorifyed) and processed with nitric acid.
Wet route rely on disintegration of the ceramics in boiling HCL leaving PGM foils and some undissolved ceramic stuff, which is very crumbly and is washed from foils easily. Recovery rates are varying depending on the flux mixtures, temperature of the smelt etc... But generally, if not appropriate flux is used and temperature is lower than 1200°C or so, yields decrease. Wet route is time consuming, producing quite a bit of toxic liquid waste - but can be done in near perfect recovery. So can be pyro route, but conditions for achieving full recovery by pyro means are much more harsh, and propane furnance rarely gonna make it
FEED: 192 + 102 g of old soviet MLCCs. 192 g of orange and yellow "KMs" and 102 g of green "KMs". These components are famous for their very nice PtPd content, some types climbing to nearly 70g/kg PGMs. It is obvious that bigger pieces has better yields, as ratio of the weight of ceramics to the "dead" weight of legs, resin and solder is much higher. So because of this, yield fluctuate from like 25-65g/kg depending on type, size and manufacture year. There are exceptions, but usually yield of mixed batch is somwhere in the middle of this. And with ratio of Pt-Pd fluctuating depending on what types are predominantely present (there are mainly Pd ones with trace Pt, and Pt ones with trace Pd).
Stock photo of the issued material - "fat" orange/red/yellow and green ones were present in this batch. There is numerous more types with varying PGM content.
COMPOSITION: orange KMs are pieces of ceramic with soldered legs on the sides of the ceramic rectangle, dipped in thick resin filled with silica dust. Material of the ceramic is predominantely BaTiO3, but strangely - ceramic also contain bismuth and some % of Si and Al. Embedded in ceramic, there are PGMs foils with small % of silver. On the sides of the ceramic "sandwich", ends of PGM foils are soldered to the copper legs. Solder is typically of composition of PbSnCd. I do also measure some silver. Mainly because cadmium in the solder, this material is cumbersome to process in "contained" way, because cadmium will burn happily when heated upper than 400°C or so. Also, there is toxic barium in the ceramics, which can be easily leached out by acids, producing very toxic solutions, which should be dealt with responsibly.
TYPICAL WAYS OF PROCESSING: On you tube, Owltech has great series of videos issuing processing this refractory and hard material. I recommend watching them and learn from his experience, successes, mistakes and advices. Generally, first step is to remove the resin coating off the caps. There are two main ways of doing this. First easy looking, but far harder to do safely - incineration. And second more tedious, but more contained - solvent disintegration or digestion.
With incineration, material is burnt - by doing this, cadmium in the solder also burn and evaporate as CdO yellow-brown cobwebs and smoke. Very hazardous operation, if not done in good fumehood with scrubber. Solder typically contain up to 10% Cd in mixed lots (some caps do not have Cd in solder, some do), and solder comprise of roughly 10-15% weight of the average lot, so not negligible ammount.
With solvent disintegration or digestion, caps are soaked in organic solvent (usually DMSO, but DMF also works), which swell the resin coating and enable to peel it off. This process is tedious as you need to do it one by one by hand. But it is very "clean" and all Cd stays in place. Digestion is decomposition of the resn in strong NaOH boiling solution. This operation is very messy - as honey-like goo is mainly produced from orange/yellow types of caps, which is then PITA to strip off the ceramics. Only convenient way I know is to decant the liquid, wash the goo with water, drip out as much water as possible and then cover with DMSO and take it near to the boiling point of DMSO (to at least 150°C) - this will slowly liquify the goo and it can be poured off the ceramics. On many occasions, whole boards with components are dipped in clear varnish - and this is resistent to NaOH. So in this case, you need to prior remove the varnish and then proceed with NaOH disintegration.
Overall, with ceramics stripped from resin, you heat the material in mesh basket with torch or more conveniently heatgun, and by shaking motion shake off the legs and good majority of the solder out. By doing this, you "enrich" the metal fraction in PGMs, removing the stubborn Sn, Pb and Cd - and practically all copper. Little PGMs follow the solder and are contained in it, but if the ceramics are not too much beaten or cracked, it is low number.
With bare ceramics in hand, there are generally two ways of approach. Pyro and wet route. Pyrometallurgic one is based most of the times on pulverizing the ceramics in the grinder, then mixing them with fluxes and collector metals and smelting them to obtain metallic dore, which is then cupelled free from lead (or scorifyed) and processed with nitric acid.
Wet route rely on disintegration of the ceramics in boiling HCL leaving PGM foils and some undissolved ceramic stuff, which is very crumbly and is washed from foils easily. Recovery rates are varying depending on the flux mixtures, temperature of the smelt etc... But generally, if not appropriate flux is used and temperature is lower than 1200°C or so, yields decrease. Wet route is time consuming, producing quite a bit of toxic liquid waste - but can be done in near perfect recovery. So can be pyro route, but conditions for achieving full recovery by pyro means are much more harsh, and propane furnance rarely gonna make it
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