Two case studies on the value of metal recovery from wastewater
It’s no secret that industrial pollution is harmful to the environment and human health.
I don’t think I need to spend time convincing anyone that proper disposal of industrial wastewater is imperative to the health of our planet, but I do think it’s worth taking the time to show how it can be economical, if not profitable.
This blog will cover the types of industrial wastewater that require further treatment for metal recovery, and how to do so in a cost-effective manner.
Two mini case-studies on electroplating and semiconductor fabrication wastewater solutions will be presented, showing how nickel, cobalt and copper recovery from wastewater can turn wastewater from an expensive burden into a source of revenue while closing the supply chain loop for these industries.
These case studies will provide you with real numbers on the economics of wastewater treatment and metal recovery.
Industrial wastewater comes from many sources, including but not limited to:
- Battery Manufacturing
- Electric Power Plants
- Electronics Manufacturing
- Electroplating
- Food Industry
- Industrial Oil Contamination
- Iron and Steel Industry
- Metal Powders
- Mines and Quarries
- Nuclear Industry
- Organic Chemicals Manufacturing
- Petroleum Refining and Petrochemicals
- Pulp and Paper Industry
- Textile Dyeing
- Water Treatment
- Wood Preserving
The sources highlighted in blue are those that have been identified to have heavy metal contamination in their wastewaters. Some metals of interest are:
There are six main methods of wastewater treatment and metal recovery, however only one of them boasts metal selectivity and pure metal recovery.
This method is electrowinning; in most cases, electrochemical methods require no consumption of chemicals, another advantage for this technique for wastewater treatment and metal recovery.
The main methods are:
- Adsorption (Activated Carbon, Natural Zeolite)
- Chemical Coagulation
- Chemical Precipitation
- Electrochemical (Electrowinning, emew)
- Ion Exchange (IX)
- Membrane and Ultrafiltration
IX is also metal selective (like electrowinning) and can be used in tandem with electrowinning for maximum metal recovery.
The most simple and inexpensive method is chemical precipitation; this purifies the wastewater and does not recover the pure metals, but rather precipitates a mixture of metal oxides, hydroxides, or salts.
The real takeaway from this list of methods is not that there is only one solution, but rather combining these can provide a clean effluent for safe disposal, along with recovery of valuable metals from the wastewater.
To better understand how the methods come together to create a closed-loop, sustainable wastewater treatment process, I will walk you through two case studies that showcase how saleable metals can be recovered from industrial wastewater.
Case Study No. 1
The first case study is on a waste solution from a nickel/cobalt plating bath; the approximate chemical composition as listed in Table 1.
In addition to nickel and cobalt, this solution also contains lead, copper, and cadmium, as well as organic contamination from oils and solvents. The nickel and cobalt concentrations have decreased over time, along with the pH, making this solution no longer suitable for plating; it is ready for disposal.
Various jurisdictions have different waste guidelines, the EPA’s are listed in Table 1.
The second and third columns show the allowable limits for wastewater disposal, with the rightmost column showing the acceptable limits on drinking water, significantly more stringent than the wastewater disposal limits as one would expect.
The reason I have highlighted these values is that they showcase how low the metal content of a solution must be for safe disposal. The drinking water guidelines give perspective on what is safe for our consumption, to truly have “zero impact” on the environment. The metal contents in this wastewater are significantly higher than the allowable limit.
Disposal fees for this type of waste can range from 0.50 – 4 USD/L, making metal recovery from this solution a valuable investment.
Using spot prices as of May 23, 2018, the value of cobalt and nickel within this solution is 0.75 USD/L which in comparison to the disposal fee, can result in significant savings to improve profitability.
The math of figuring out the value for the solution is easy enough, but the trickier part is the pre-treatment and processing.
Table 1. Concentrations of Impurities in Spent Electroplating Bath Wastewater and Allowable Limits
Values current as of May 21, 2018
*e-CFR Title 40 / Chapter I / Subchapter N / Part 413.14 / Subpart A / Part C
Using the example solution in Table 1, the block flow diagram below shows how to maximize metal recovery and purify the solution for re-use, Fig. 1.
Fig. 1. Block Flow Diagram of Spent Plating Solution Treatment
In the above example, cobalt and nickel can be plated together to produce a salable alloy, as these metals are electrochemically similar.
If separation of cobalt and nickel is required, solvent extraction (SX) or ion exchange (IX) can be used to produce pure cobalt and pure nickel cathodes by creating separate streams for electrowinning.
To evaluate the cost-benefit analysis of emew vs. disposal, I’ve calculated disposal, emew capital, as well as yearly operational costs and placed it against the possible revenue generated from electrowinning cobalt and nickel.
The value of the metal cathode is shown in Table 2, while the cost comparison is shown in Table 3.
Table 2. Value of Cobalt/Nickel Cathode
*Based on spot prices on May 23, 2018
**Assumes 90% of Ni/Co LME value due to mixed metal cathode
Calculating the cost of disposal of the spent plating bath compared to treatment to recover the valuable nickel/cobalt cathode, the payback period is less than one month! Not to mention the net annual revenue of over $5 million each year thereafter.
Table 3. Comparison of Annual Operating Costs and Savings with and without emew
Case Study No. 2
The second case study will cover a waste solution from semiconductor fabrication.
Semiconductors are used in a wide variety of consumer electronics. For example, temperature sensors are made with semiconductors; CPUs are made with semiconductors, as well as digital cameras, LED bulbs, smartphones, and televisions.
One of the top semiconductor manufacturers uses copper for it’s connections in the metallization layer, the back end of line (BEOL), in their semiconductor integrated circuits.
In their process approximately 3,785,400 L of hazardous wastewater is generated, containing significant a concentration of copper as copper sulfate, hydrogen peroxide, and sulfuric acid, Table 4.
Table 4. Concentrations of Impurities in Semiconductor Manufacturing Wastewater and Allowable Limits
Values current as of May 21, 2018
*e-CFR Title 40 / Chapter I / Subchapter N / Part 469.14 / Subpart A
**e-CFR Title 40 / Chapter I / Subchapter N / Part 433.13 / Subpart A / Part A
The copper concentration in the aforementioned solution not only exceeds the EPA effluent limits for copper and acid, but the concentration of hydrogen peroxide brings this wastewater into the category of ignitable hazardous waste. The EPA therefore requires this wastewater to be treated prior to disposal.
Although copper extraction is required for safe disposal of this solution, an inquisitive person would notice that (based on the spot value of copper on May 23/18 of 6,289 USD/tonne), the value of copper in this solution is very low. At a recovery rate of 30 tonnes per annum, this results in a revenue of only 188,670 USD/year, but don’t stop reading!
The story does not end here.
The most interesting part to me and why I chose this case study, is that the value is not in the copper itself but rather in the solution without the copper. With copper in it, this solution must be disposed of offsite at considerable cost.
Assuming a disposal fee of 0.53 USD/L, that adds up to 2 million dollars a year. That’s 2 million dollars wasted on waste, Table 5.
Table 5. Value of Copper Cathode
Recovery of copper from the solution can be accomplished in various ways, but there is one technology that will solve both the issue of copper and hydrogen peroxide in solution.
That technology is emew.
By electrowinning copper from the solution and using the hydrogen peroxide to strip copper from the emew polishing cells, the peroxide is destroyed concurrently. The continuous cycle of destroying the hydrogen peroxide and extracting the copper generates a clean acid solution that can either be circulated back into the manufacturing process, leading to no waste at all, or neutralized and safely discarded.
The annual savings we are now looking at adds up to 2.1 million USD/year with a payback of less than 6 months, Table 6.
Table 6. Comparison of Annual Operating Costs and Savings with and without emew
Although the above two case studies were specific to spent electroplating and semiconductor wastewater solutions, analogous metal recovery processes can be applied to other industries.
Metal recovery is always important in terms of the economics and the environment.
For example, battery manufacturing produces wastewaters that are high in chromium, cobalt, copper, iron, lead, manganese, mercury, nickel, silver, and zinc; organic chemicals manufacturing produces wastewater that contains chromium, copper, lead, nickel, and zinc; electrical power plants produce wastewater that contains cadmium, chromium, lead, and mercury; mines and quarries produce acid mine drainage that is rich in heavy metals; and textile dyeing produces effluent with chromium, copper, lead, and zinc.
There is hidden value in these wastewaters, which can only be accessed through a series of pre-treatment steps followed by electrowinning for recovery of saleable metal cathodes.
When assessing wastewater treatment options, it’s imperative to consider not only the value of the metals within the wastewater, but also the cost of disposing of the solution.
I hope that the examples I have chosen showcase the value of metals in wastewater and the savings that can be achieved from wastewater treatment for the recovery of metals. The first case demonstrated the higher value of the recovered metals, whereas the second case demonstrated the savings of not having to pay for offsite hazardous waste disposal, two very different situations, each with very profitable outcomes.
Sources Used:
https://en.wikipedia.org/wiki/Industrial_wastewater_treatment
https://www.conserve-energy-future.com/causes-effects-of-industrial-pollution.php
https://www.iwapublishing.com/news/removal-technologies-wastewater-treatment
https://www.atimetals.com/Products/Pages/nickel-cobalt.aspx
https://www.lenntech.com/periodic/elements/co.htm
https://www.mining.com/markets/commodity/group/base-metals/
https://iopscience.iop.org/article/10.1088/1757-899X/17/1/012021/pdf
https://link.springer.com/article/10.1007/s41061-017-0118-7
https://www.hitachi-hightech.com/global/products/device/semiconductor/life.html
Title 40 / Chapter I / Subchapter N / Part 413.14 / Subpart A / Part C. https://www.ecfr.gov/cgi-bin/text-idx?SID=7e2e50f207072b35927561ef22e99dfa&mc=true&node=pt40.31.413&rgn=div5#se40.31.413_110
e-CFR Title 40 / Chapter I / Subchapter N / Part 469.14 / Subpart A . https://www.ecfr.gov/cgi-bin/text-idx?SID=15fce157e9392626e17498783cc47368&mc=true&node=sp40.32.469.a&rgn=div6
e-CFR Title 40 / Chapter I / Subchapter N / Part 433.13 / Subpart A / Part A. https://www.ecfr.gov/cgi-bin/text-idx?SID=716d9527c319c0995c7debf0235f4ea1&mc=true&node=sp40.32.433.a&rgn=div6
http://www.rfcafe.com/references/general/density-building-materials.htm
https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a
https://www.dailymetalprice.com/metaltables.php
https://www.westmetall.com/en/markdaten.php?action=show_table&field=LME_Ni_cash
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