Expert Commentary: Iodine Recycling
Iodine


Iodine Recycling: Has the full potential been reached?

Author: A. Eccheveria (Product Manager Iodine & Lithium, SQM), 2015

Current iodine recycling capacity

 

Around 6 thousand metric tons of iodine are being recycled annually and sold back to the merchant market as fresh product, mostly to the same companies who originated the recyclable iodine stream (Table 1). This amount corresponds to approximately 18% of the total world iodine demand, and is additional to the internal recycling done by iodine users, who have included iodine recovery as part or of their regular productive processes. Main drivers for recycling are savings in costs as well as environmental and regulatory considerations.

 

The main sources of iodine recovery are the following:
 

Chemical synthesis where iodine is used as an intermediate (transient use):
 

Production of fluorochemicals

Iodine recycling from production of fluorochemicals
 

Iodine is used in the production of perfluoroalkane derivatives, which are obtained by telomerisation technology to generate fluoroiodoalkane (CF3-CF2-I), resulting from the reaction of tetrafluoroethylene (TFE) with iodopentafluoride (IF5) and elemental iodine (I2) in presence of a suitable catalyst.
 

Iodine is not incorporated in the final product, but serves as a “transient” process enabler and is eventually released and recovered either by the fluorochemical producer himself or through specialized third party vendors.
 

Recovery rates of iodine are estimated to be in the range of 70%. Reaching higher recycling levels is not considered feasible at this moment, due to restrictions imposed by both technology and economic hurdles.

Since only a handful of companies are producing fluorotelomers, the supply structure facilitating the overall iodine recovery is rather concentrated.
 

Recycled iodine obtained from this application is around 1.5 thousand metric tons per year.

Organic molecule synthesis

Iodine recycling from organic molecule synthesis
 

Depending on the process and the derived end molecule, iodine is used in organic synthesis as a structural component or as a synthesis enabler.

  • Component: effectively incorporated in the final molecule, almost invariably involving the use of elemental iodine either directly or through a reagent like iodine monochloride (ICl). Examples of iodinated derivatives are ionoxinyl (a herbicide) or amiodarone (a cardiovascular drug).
  • Synthesis enabler: iodine, while playing an essential role in the synthesis is not incorporated in the end molecule. Various types of iodine derivatives are used as enablers, including methyl iodide and potassium iodide.

 

Once incorporated in an end molecule, it is not feasible to recover and recycle iodine. In contrast, a substantial share of the iodine used as enabler in organic synthesis is eventually recycled. Given both cost as well as regulatory considerations, there is an increasing drive to recover iodine having served as synthesis enabler out of the spent reaction media and residues.
 

According to feedback gathered from industry contacts, recovery rates of “transient” iodine going to the synthesis outlet are tentatively estimated to approximate 1.5 thousand metric tons per year.

 
Recoverable wastes from production processes for iodine-containing products:
 

LCD optical film polarizers

Iodine recycling from production of LCD optical film polarizers
 

The production of optical polarizing polymeric films used in LCD screens to enhance the quality of the image and color resolution involves the incorporation of iodine in the polymeric matrix. Iodine provides the dichroic properties responsible for the polarizing effect, namely the differential absorption of radiation depending on the incidence angle.
 

The production process consists of the impregnation of a polymeric film (most often polyvinylalcohol (PVA)) with a solution containing a mixture of elemental iodine and an iodide salt, usually potassium iodide. Existing impregnation techniques include coating and dipping in a bath, the latter being reported to be the most widely applied. Dipping bath contains 0.5-2% iodine and the bath has to be periodically replenished or changed.
 

Following further processing, the optical polarizing film is incorporated in the LCD, serving as component in electronic devices such as mobile phones, PC, tablets or TV sets.
 

Production of optical film polarizers is led by a handful of Japanese and Korean companies. It is estimated that between 2 and 2.5 thousand metric tons of iodine are being recovered annually and recycled from spent dipping baths as well as from films rejected as out-of-specs during the production process.
 

Recycling iodine from LCD screens incorporated in discarded electronic devices is limited. Small quantities are currently being recovered in Korea, Taiwan and Japan. In other parts of the world recycling systems for Electrical & Electronic Equipment waste are still in in their infancy, a situation that is expected to evolve gradually.

X-ray contrast media

Iodine recycling from production of X-ray contrast media
 
Iodine is an essential component in X-ray contrast media serving for in-vivo medical diagnostic procedures, since the iodine atom provides the required radiation absorption properties.
 
Iodine is incorporated in the contrast media through electrophilic substitution of the aromatic moiety of this type of molecular structures. The iodination reagent iodine monochloride (ICl) is obtained by reacting elemental iodine with chlorine.
 
The synthesis process of iodinated contrast media involves extensive recovery and recirculation of spent iodine: Most iodinated waste and residues are recycled either by the X-ray producer himself or by specialized third party vendors.
 
Very little iodine is lost from the process; more than 95% is recovered. This percentage has increased steadily over the years, following continuous process optimization initiatives.
Most X-ray contrast media producers have their own in-house recycling capacity, but a few of them also rely on third party vendors to recycle iodine.
 
The recycled iodine obtained from this application is estimated to be 0.6 thousand metric tons per year.

Other uses

Iodine recycling from other uses
 
Small volumes of iodine used in applications like electroplating and etching are also reported to be recycled, probably totaling around 100 Ton.

Also modest quantities of iodine (estimated to 50-100 Ton) are recycled from the production process of the biocide iodopropynyl butylcarbamate (IPBC).

 
Several industrial iodine consumers have their own facilities enabling them to recycle the iodinated stream by themselves. Other companies send low iodine concentration solutions to third parties, specialized in retrieval of iodine or iodine derivatives from those solutions.
 
Japanese iodine producers play a major role in iodine recycling, leading recovery worldwide. Other producers of iodine and iodine derivatives in Europe, India and America are active recyclers as well.
 

Table 1. Summary of quantities of iodine being recycled annually from different sources.
Iodine Use Recycling
(Metric Ton x 1000)
LCD Film polarizers 2-2.5
Fluorochemicals ~ 1.5
X-ray contrast media (3rd parties) ~0.6
Organic synthesis (process enabler) ~ 1.5
Other uses 0.1-0.2
TOTAL ~ 6

 
Outlook on future iodine recycling
 
Regardless of the decline in iodine price observed in the market since middle 2013, the share of recycled iodine is still expected to increase in the future, irrespective of future price trend. Nevertheless, growth will be limited due to a number of reasons:

  • The currently adopted -technically feasible- recovery processes are already optimal and the most recent innovations have been implemented in the period 2011-2013, when iodine prices rocketed to above USD 50 per kg.
  • Loss of some iodine that is incorporated in products is inevitable when these have been applied by the end-user. For instance, it is not feasible to collect disinfectants, biocides or some polyamide threads after use.
  • Economic constraints: Costs of recovery from low-iodine concentration streams are relatively high, and the iodine concentration in these is so low that they can be released to the environment.

Despite these hurdles, the share of recycling is expected to continue to increase moderately, driven by regulatory restrictions and a growing concern for sustainability of production processes. The main growth is expected from the emergence of specific collection systems for Electrical & Electronic Equipment waste in the future. This may enable an increase in recovery of iodine from LCD polarizing films.
 
All in all, the share of recycled iodine on the total world iodine supply is expected to be limited, and grow from current approximately 18% to no more than 20% of total world iodine demand in the next years.
 
References:
SQM’s market intelligence reports and third party study (ADL: Iodine recycling – Unde venit et quo vadit?, April 2014)