Science Buddies: "Ask an Expert"

I am trying to examine the change in lead content from printed circuit boards in the 1990's to 2006. But I am having trouble figuring out a solution to extract the lead from the PCB without extracting other metals in the PCB also. I know of dithizone, but am not sure if this will work. And once this solution is found, how do I proceed about this?

I'm not a chemist -- I'll see if I can get one to help, but it may take time or may not even be possible.

Meanwhile, BE VERY CAREFUL. Soluble forms of lead are very toxic. You must have expert adult supervision and the necessary lab space and protective equipment (gloves, hood, etc) to handle toxins. Be sure to consult the science fair rules concerning poisonous materials.

An alternative to chemical means would be to melt the solder off the board. This is commonly done in electronics labs using a desoldering station, but it can be done with just a soldering iron with the right technique (I've seen it done but it's beyond my skill level and, I'd guess, yours). Again expert supervision will be a must.

To paraphrase an old saying: there are old chemists, and there are bold chemists, but there are no old, bold chemists!

Hi,

John has given you some really good advice for starting this project. Please do be careful.

This is a really great project idea! The problem with older printed circuit boards is that they contain a combination of copper, lead, and tin. The copper is valuable and could be recycled if it could be separated from the toxic lead. However, this is going to be a very challenging science project.

The basic procedure for recovering the copper will be to dissolve the copper, lead, and tin in either an acidic or basic solution, and selectively recover the copper by precipitating the lead and using electroplating to recover the pure copper. You need to read scientific references to find out what has been done on this topic in the past.

Here are some references on this topic reporting different approaches to solving this problem. Unfortunately, I could not find any articles with complete access to all of the details, but there is useful information in the abstract and the figures for each article. There is a wide variety of approaches for copper recovery, so this suggests that no one has developed the perfect protocol yet, so this is definitely a worthwhile topic to investigate.


Here is a reference that used a dilute caustic solution to dissolve the metals. The lead was precipitated, and the copper was recovered by electroplating.

http://www.sciencedirect.com/science/ar ... 499190037O

This paper describes a method for recovering lead and copper from nitric acid etching solutions used to manufacture PCB’s. The nitric acid was removed and the pure copper was recovered by electroplating; the Sn was precipitated by adjusting the pH. The figures and tables from the article are included with the abstract on this article.

http://www.sciencedirect.com/science/ar ... 6X03000458

Here is an interested article that reports a method for leaching copper from printed circuit boards using microbial leaching. Unfortunately, only the abstract is available.

http://www.tandfonline.com/doi/abs/10.1 ... -200034763

Here is an abstract that reports solubilizing the lead, tin, and copper in nitric acid, and precipitation of the tin. The lead and copper are selectively deposited at the cathode and anode electrodes, respectively. This procedure sounds like it is worth trying.

http://onlinelibrary.wiley.com/doi/10.1 ... ated=false

Here is an abstract that includes some details. The copper was selectively dissolved from the pcbs with an ammonium-ammonium sulfate/chloride solution, extracted in a solvent called alkyl substituted 8-hydroxy-quinoline, and then recovered by electro deposition.

http://www.sciencedirect.com/science/ar ... 6X07001168

Here’s an abstract that used electroplating to recover the copper. Figures are included.

http://www.sciencedirect.com/science/ar ... 9406004614

Here is basic information on electroplating, which you will need to use to recover the copper:

http://chem1.eng.wayne.edu/~yhuang/Pape ... g_ECHP.pdf

You will need more details about the exact protocols used so it would be very worthwhile to visit a local university library to look up some of these references or similar references. The details should be included in the materials and methods sections. Or, you could send an e-mail message to the primary authors of the more recent papers and perhaps they would send you the information that you need.

You can do a search for “Google Scholar,” and then search for information about recovering copper from printed circuit boards (pcb's) . Using Google Scholar will bring up the scientific references that you need for background information for a science project.

You could also visit a local recycling company and ask for additional information.

Here is a demonstration for dissolving copper in nitric acid. This would also dissolve the Pb and Sn. Please note that nitric acid is hazardous and you will need a laboratory and protective equipment to work with this acid.

http://www.angelo.edu/faculty/kboudrea/ ... u_HNO3.htm

And, here are the chemical equations for the reaction:

http://pubs.acs.org/doi/pdf/10.1021/ed067p183.2

The entire process for recovering copper from pcb’s is very complex. For a science project, I would recommend limiting your experiments to one aspect of the process. For example, you could optimize the dissolution of the metals from the pcb’s, or you could work with known mixtures of lead, copper, and tin, and optimize the electroplating process.

And. John has made a very good point about the hazardous nature of this project. You will definitely need to get prior approval for doing this project since it involves using hazardous chemicals. Here is the information on this topic from this website:

https://www.sciencebuddies.org/science- ... chem.shtml

Please post again in this topic when you have more questions. Good luck!

Donna Hardy

Thanks for your expert help Donna.

In re "I am trying to examine the change in lead content from printed circuit boards in the 1990's to 2006" I would imagine your end-point of 2006 has something to do with the legally-mandated removal of lead from solder as of 2006? By now I expect that the lead content would be close to zero in the solder used in all electronics with only a few exceptions for applications that absolutely must have high reliability electronics. The last time I looked into it (about 2004) the only viable substitute for lead/tin solder was pure tin. This was a very problematic choice because of a peculiarity of tin (see Wikipedia article Whisker metallurgy), none-the-less it became necessary in Europe and I think the US. So from a recycling perspective the only thing that can be recovered from solder is tin. The circuit-board traces are still copper. Anyway, the data point for the lead content for 2006 is ~0%.

Hi Deepti,

John has made some very helpful comments regarding the expected change in composition of the pcb’s from the 1990’s to 2006. The protocols I suggested will dissolve Sn, Cu, and Pb and the elements can be separated from each other by various procedures depending on your objective.

Perhaps you can clarify exactly what you are trying to do. Are you trying to develop a recycling procedure to recover copper from pcb’s manufactured during any time between 1190 and 2006, or are you primarily interested in analyzing the elements? Perhaps we could make some additional suggestions if you can explain the overall purpose of your project. What are you trying to accomplish?

Donna Hardy

Hello all,
Thanks for your helpful comments. My purpose is merely an investigation. I am just trying to examine the change in LEAD content from the past and present. I don't care much of the extraction of the other elements, just lead.

Thanks,
Deepti

The majority of lead content of all electronic assemblies has always been the tin-lead solder and component lead plating (tin-lead) to make them solderable. The typical tin-lead solders were 30 to 40 percent lead by weight.

Manufacturers have slowly transitioned to lead-free assemblies by changing to other higher melting point lead free solders and lead plating materials. Lead free assemblies are marked with a Pb (chemical atomic symbol for lead) in a circle with a diagonal line through it. If the assembly doesn't have this symbol on it, the assembly is almost guaranteed to contain lead. Manufacturer's definitely want to take credit for going lead free and they will definitely advertise the absense of lead!