Wednesday, 25 March 2015

Where there's muck there's brass

If I had seen this a week today I would have assumed it was an April Fool's joke, but at the annual meeting of the American Chemical Society in Denver Dr. Kathleen Smith, lead scientist at the US Geological Survey suggested that human waste could be processed to extract metals, including gold, silver, copper and vanadium, flushed down lavatories every year. In Britain alone this could account for as much as £500 million worth of values. She said that gold has been identified in waste from sewage treatment plants at levels which, if found in rock, would be worth mining.
The tiny particles of metal are believed to come from everyday items such as hair care products, detergents and food or drink. Many find their way into the body and are excreted. They then end up in sewage treatment plants where they are concentrated in leftover biosolids. Organic biosolids are used as fertiliser on fields while the rest is incinerated or buried.

Dr. Smith suggested that these biosolids could be leached to recover the metals, She said  “the gold we found was at the level of a minimal mineral deposit. There are metals everywhere — in your hair care products, detergents, even nanoparticles that are put in socks to prevent bad odours.”

What do you think- worth pursuing or just a load of crap?


  1. Hi Barry

    Can I refer you to this old publication of mine:

    A. Jowett, N.M. Rice, J.R. Barton, D. Neale and W. de Oliveira, Recovery of metal values from an incinerated municipal sewage sludge, I. Chem. Eng. Symp. Series No. 41,"The application of Chemical Engineering to the Treatment of Effluents and Waste", York, 1975, (W.L. Wilkinnson, Ch.), Inst. Chem. Eng., London, pp U1 - U15.

    It involved the Leeds incinerator where the waste was contaminated by effluents from the local metal electroplating industry. This reference was also used by some US lawyers in Palo Alto California to settle a dispute involving local municipality and a US research lab.

    The work was done as a couple of final year projects (JRB - who was at Warren Spring and is now (I think) at the University of Leeds Civil Eng Dept) and DN. And as an MSc Pollution Control project (W de O who was from Rio in Brazil). Alan Jowett ( still living in Canberra as far as I am aware) had a contact with a chap on the Leeds city council whose name I cannot recall but who had interests in recycling and environmental matters.

    The main conclusion was that it would not be an economic process at the scale of waste available.

    Another local problem was lead in the municipal compost made from the leaves swept up from the street in autumn. With lead free petrol that is no longer a problem and in fact the lead was fixed in the compost as insoluble PbCO3 so it did not transfer to the vegetables. A late colleague - Chris Dell - investigated this problem as he used to use the compost!

    Nevill Rice, UK

    1. Many thanks for this Nevill. It reinforces my beliefs that many researchers are not delving deeply enough into past literature, much of which might not be digitised. This waste topic would be of great interest at next year's Sustainable Minerals '16 conference in Falmouth by the way.

  2. Very interesting; it shows that future in very challenging to recover minerals/metals.
    Good beginning.

  3. Mining from waste is certainly happening in Japan.
    Peter Marteene, Cytec, USA

  4. Good opportunity for bioleaching or chelation process.
    Mike Albrecht, USA

  5. The Ashbridges Bay sewage plant in Toronto operated sludge incinerators for several years. The incinerated residue was relatively high grade in silver and gold. When gold and silver prices were high, it actually paid to ship sludge to Timmins for incorporation into gold mill feed.

    About 30 years ago, I managed a project investigating the establishment of a plant in Toronto to extract Au/Ag without the expense of trucking the material 600 km to the nearest gold mill. We did a fair bit of testwork and it turned out the Au/Ag is fairly refractory in incinerated sludge and getting decent recovery was tough. With gold prices at the time, the project was uneconomic.

    John Goode, Toronto

    1. Thanks John (and Peter). Just shows- go back far enough and you can often find work hidden away

  6. We looked at San Jose sludge in the early 80's and could not carry on due to funding problems and wrong business model. Along with spent refinery catalysts. Metal prices were low. Technically we had some success producing marketable product (molybdic acid) etc. but it was business failure due to our model. We were basing it on metal recovery instead of hazardous waste disposal. The feed material was free but hydrometallurgical processing cost was high, Charging for hazardous waste disposal would have made the project viable. By the way, the idea was to recover precious metals from the municipal incinerated sludge. Unfortunately it was the wrong time, and I have lost all the research papers (lab and pilot plant) of the work we did.
    Naseem Mian, The Highland Group, USA


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