Biological leaching of metals from printed circuit boards

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4 years ago

I just thought of sharing my old research when I was still studied geology. Yes, I've liked microbes even back then XD It's a bit of a long read but I hope you find it fascinating

Introduction

Electronic waste or e-waste is described as discarded electrical or electronic devices which have reached the end of their useful life (Das et al, 2016; Peralta, 2006). As of date, E-wastes generated increases at an exponential rate of nearly 10% yearly (Sakunda, 2013; cited in Kaya, 2016) and has been an alarming problem since e-waste manufacturing is a factor that causes metal depletion. It was also cited in the work of Torres, 2016, metals like Copper, silver, iron and gold as well as an additional 15, to 40 (Arshadi, et al., 2016), to 57 valuable elements (Kaya, 2016) contained in the PCB are either in its elemental form or exists as an alloy (Cui and Zhang, 2008; Tuncuk et al., 2012; Yang et al., 2011). Although some components to these e-wastes are harmful to the environment like an e-waste’s non-metallic components and the heavy metals which are embedded in it, it is still a feasible source of metals; a secondary source or “Secondary ores” as it’s called, in the process of urban mining (Das et al, 2016).  Recovering metals from these e-wastes in the form of recycling provides a good solution to minimizing the e-wastes that go into landfill which will pose a greater problem to the environment. 

Recycling methods for e-wastes include mechanical separation of components, chemical dissolution of the metals and metallurgical processes, all of which are either energy intensive and high cost or makes use of highly toxic chemicals with low metal recovery rate or if not low then are non-selective to the metal of interest. These methods have been the traditional ways of recovering metals from e-wastes for the past few decades; none which offers a solution in delaying environmental destruction but rather, worsens it. In light of these consequences, bioleaching was found to be a good alternative method for recycling e-wastes. 

Bioleaching, or biological leaching, which is under biometallurgy, exploits the ability of a microorganism of either bacteria or fungi, to transform solid compounds into soluble and extractable metals which can be recovered (Krebs, 1997). The microorganism produces lixiviants or leachates which are at a biogenic level than that used in chemical processes to form water-soluble metal complexes or salts with the metals of interest. Advantages for this method, as cited by Kumar, 2017, is the lowering of demand for resources such as energy, ores and landfill space, but its application is only in its infancy (Ruan et al, 2014) since further research on bioleaching has only boomed when the first patent was published in 1958 and has continued to progress, especially in 2016 when earth was at the peak of its toxicity and numerous researches about bioleaching was done in said year. But despite its infancy, the last 20 years of research on bioleaching has led to 10 bio-heap leaching plants, 7 bio reactor plants for sulphidic concentrate and countless pilot scale operations have started worldwide (Kocadagistan, 2017).  In the Philippines, the only people to have done research on bioleaching as of date is the Mines and Geosciences Bureau (MGB) which took place in 2013, and some applications of bioleaching in the mining industry but besides that, no further development has occurred in the field of bioleaching in the Philippines.  

Besides the method being a good alternative to the above mentioned traditional methods, the execution of leaching itself is simple since steps involved are only culturing of microorganisms, addition of the shredded e-waste and the collection of the e-waste particles from the leaching medium after a given time. The entire leaching time usually takes 3-4 days to one week, depending on when the addition of the shredded e-wastes was and based on which bioleaching method was used. Methods for bioleaching include “one-step” where the shredded e-waste is added whilst culturing the microorganism, “two-step” which is done by adding the shredded e-waste into the culturing medium when the major lixiviant/leachate production is reached, and “spent medium” leaching where the microorganism is separated from the culturing medium and the shredded e-waste will only be added after removing the microorganism. 

 All methods are appropriate for all types of microorganisms that can produce metabolites which can leach metals but in bioleaching, three main microbial groups are often used in this process, as cited by Isildar, 2015, those being: chemolithotropes, those which get energy from non-carbon compounds via oxidation (Xiang et al. 2010), heterotrophic, microbes that cannot produce their own foods and instead take organic materials as sustenance (Chi et al, 2011), and thermophiles or heat loving microbes (Brandl et al, 2001). An addition to the list would be the cyanogenic microbes which are able to produce cyanogenic compounds as a metabolite or as a secondary metabolite; this microbial group is specific to recovering gold since it is a known fact that cyanide is a primary leachate to gold.


Primary sources:

Das, S., Natarajan, G., Ting, Y. P., (2016), Bio-Extraction of Precious Metals from Urban Solid Waste, AIP Conf. Proc. 1805, 020004-1–020004-8, Retrieved from: 10.1063/1.4974410

Isıldar, A., Van de Vossenbrerg, J.,  (2015 November 22), Two-step bioleaching of copper and gold from discarded printed circuit boards (PCB), Waste Management 57 (2015) Pp. 149-157, retrieved from: http://dx.doi.org/10.1016/j.wasman.2015.11.033

Kaya, M., (2016 August 16), Recovery of metals and non-metals from electronic waste by physical and chemical recycling processes, Waste Management 57 (2016)Pp. 64–90, Retrieved from: http://dx.doi.org/10.1016/j.wasman.2016.08.004


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Comments

Brilliant

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4 years ago

good article

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4 years ago

I never knew there was such a thing as Electronmic Waste, or that biological agents could act on Electronic components.

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4 years ago

Well your phone will eb e-wastes when you break it xD same with appliances. And those microbes are cool, they can make natural compounds that mobilize the metals UwU

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4 years ago

Oh Wow

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4 years ago

Wow interesting . You have written too good . And maybe you will be a great writer in future

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4 years ago

That feeling that I want to comment something but I am having a hard time understanding the article hahahaha. Ayoko na 😅

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User's avatar Yen
4 years ago

Oof sorry :"" just saw some people posting good research materials so i thought i could do the same with my old researches. Hard to simplify further though, best ko na yan

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4 years ago

No comment here 😅😅 that's actually a good idea making article bout our research paper.. unfortunately, mine is at home.

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4 years ago

I keep all my researches in my Google drive account. I just remembered them when i saw people writing about good research topics. Kinda wanted to do but it was impossible to simplify. And i know nobody here is a materials researcher like me :"" i was just taking a long shot at this

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4 years ago

I only understand the first part about recycling the electronic wastes and recover the metals that is still be usable😅

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4 years ago

Oof well that was the point. To sum it up, i used bacteria to extract gold from e-wastes when i was doing this research

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4 years ago

Oooh so its the way how you extract gold from e-wastes. I never expected it to be a bacteria😁. I thought its another chemical but lesser toxic than mercuries. I learned that leaching from from my dad, he's a small-scale miner so was my husband. He said they used chemicals to extract gold from the grounded rocks they mine but its not safe for the waters
because the waste flows into the rivers.

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4 years ago

It's another way and it's adapted in some parts of africa for their mining industries. I think they use cyanide or aqua regia for extracting gold from the ores since you'll barely get anything if it doesn't go through chemical processing like that and in this study i did. But the thing with my study is that the chemical isn't toxic

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4 years ago

my head went swirling.. I don't understand it even reading it twice🤣

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4 years ago

My gosh I had a headache reading hahaha I didn't understand 😆😂

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4 years ago

Oof sorry :""" i couldn't simplify further without losing the citations and the important terms

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4 years ago

When I was in college we used to study about it

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4 years ago

The circuit boards or the microbes that can mobilize those metals? 😂😂😂😂

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4 years ago

Hahah nah just the circuitboards and there used to be always discussion what future they might have

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4 years ago

Lol they don't have much a future unless they could be reutilized again. Have you heard of the bioreactors in africa that make use of this technology?

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4 years ago

Yeah you are right. Recycling is the future for most of the things and that includes technology also. Didn’t hear of bioreactor technology

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4 years ago

You haven't? It's cool though. They made use of this study for large scale application in ore purification through that. No more toxic chemicals, just microbial metabolites UwU

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4 years ago