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):
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.
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:
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.
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.
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)
Iodine Reserves
Iodine
Although seawater is the world’s largest iodine reserve, with around 34.5 million tons, no economical direct extraction is feasible because of the extremely low concentrations of this element (less than 0.05 ppm).
The main reserves of iodine in brines or caliche ore are in Japan, Chile, USA, Turkmenistan, Azerbaijan and Indonesia. Iodine is also obtained as a by-product in the processing of sodium alginate, mainly in China. Not more than 2% of total iodine consumption is derived from this source. Due to the renewable nature of this raw material, total reserves are not possible to calculate.
Japan’s iodine is found in brines associated with gas wells. Deposits are located in five different zones: Chiba, Niigata, Sadowara, Okinawa and Oshamambe. Actually, only the first three zones are producing, with Chiba, by itself, responsible for 80% of Japan’s total production.
Iodine from Chile is produced from Caliche Ore, mined in the Atacama Desert of northern Chile and west of the Andes Mountains. The Atacama Desert is known as the driest of the world’s deserts, where measurable rainfalls (1 mm or more) may be as infrequent as once every 5 to 29 years. The caliche deposits occupy an area averaging 700 km in a north-south direction by 30 km in an east-west direction.
All current commercial production of iodine in the US comes from deep well brines in northern Oklahoma (mostly from the area known as the Woodward Trench). Historically, commercial iodine production did occur in other states (California, Louisiana and Michigan), but all of those sites have been abandoned for economic and/or environmental reasons.
Iodine production in the Community of Independent States is concentrated in two areas: Turkmenistan (Cheleken, Nebit Dag), and Azerbaijan (Neftchala). In the past iodine was also derived in Russia (Krasnodar), associated with oil extraction, but these operations seem to be closed nowadays. Production in Azerbaijan and Turkmenistan is not associated with oil extraction, their wells were specifically drilled for brine to produce iodine. Iran and Uzbekistan have also been reported to produce iodine from brines but information on current activities is hard to find.
Iodine exploitation in Indonesia comes from brine typically not associated with gas or oil. Deposits are located in Mojokerto, East Java. Production is limited and mainly consumed domestically.
Table: estimated iodine reserves per region
Sources: 2016 USGS Mineral Commodity Summary.
| Origin | Region | Reserves x1000 ton |
| Underground brines | Japan | 5000 |
| USA | 250 | |
| Indonesia | 100 | |
| Turkmenistan, Azerbaijan, Russia |
360 | |
| Caliche Ore | Chile | 1800 |
| Seaweed | China | 4 |
| Total estimated reserves | 7514 |
Iodine Sources
Iodine
No less than 99.6% of the earth’s mass can be accounted for by thirty-two of the chemical elements. The remaining 0.4% is apportioned among sixty-four elements, all of which are present as traces. Iodine is number 61 on this list, making Iodine one of least abundant non-metallic elements in the total composition of the earth.
Although not abundant in quantity, iodine is distributed almost everywhere. It is present in rocks, soils, waters, plants, animal tissues and foodstuffs. Except for a few rare occasions, elemental iodine is not readily found in nature. Iodine is mostly found combined with other elements, such as oxygen, hydrogen or carbon. Due to the ease with which it can accept or donate electrons in its ionic states, it is readily incorporated in inorganic salts or complex organic compounds such as the mammalian hormone thyroxine.
A few substances characteristically contain iodine in relatively large quantities. Natural accumulating organisms are seaweeds, sponges and corals. For industrial purposes, the main sources of Iodine are deposits of minerals, either as solid ore (Caliche) or in underground brines. The iodine in these deposits is chiefly of oceanic origin, transferred to the atmosphere as iodine-rich organic material and as gaseous iodine formed by photochemical oxidation of iodine at the ocean surface.
IODINE SOURCES AND CONCENTRATIONS
| Origin | Iodine Form | Typical Concentration |
| Underground Brines Caliche Ore Seaweed |
Sodium Iodide Calcium Iodate Sodium/Potassium Iodide |
30 – 150 ppm 400 ppm 950 ppm* |
*Dry basis.
Caliche is the name for the deposits of natural saltpeter containing minerals in the Atacama Desert of northern Chile and west of the Andes Mountains. Lautarite [Ca (IO3)2] and Dietzeite [7Ca (IO3)2] * 8CaCrO4], are the two crystalline forms in which iodine naturally occurs in caliche ore with an iodine content of around 0.04% (400 ppm).
To become part of the Caliche deposits, iodine was oxidized to iodate by photochemical reactions in the troposphere and at ground level in the nitrate fields.
In subsurface brines associated with oil and gas deposits, iodine occurs frequently as sodium iodide with an iodine concentration in the range of 30 to 150 ppm. About 45% of the iodine currently consumed in the world comes from brines processed in Japan, the USA, the Community of Independent States (CIS) and Indonesia.
Before the development of iodine extraction from caliche, seaweed was an important source. Today, no more than 2% of the total iodine consumption comes from this source. Some types of seaweed, particulary brown seaweeds of the Laminaria family, contain significant amounts iodine in the form of sodium and potassium iodide. Iodine concentration is variable, on average around 950 ppm in dried seaweed. Seaweed is grown by companies dedicated to production of this crop.
Iodine is obtained as a by-product in the processing of sodium alginate from seaweed. Yearly output is dependent on the crop and harvest efficiencies which are subject to environmental factors.
Iodine Diversity
Iodine
Elemental Iodine is easily reduced or oxidized. The ease of these chemical reactions gives rise to a high diversity of ionic, iodine containing molecules. Ionic iodine can be found in different states of validity, often bound to oxygen or hydrogen. For instance, in the salt Potassium Iodide (KI), iodine is present with a negative validity (1–) in the ion I–. In the salt Potassium Iodiate (KIO3), iodine is molecularly bound to oxygen, and is present with a positive validity (5+) in the ion IO3–. The reducing or oxidative properties of iodine containing molecules make them particularly suitable as catalysts in a wide range of chemical synthesis processes.
In its elemental state, Iodine can be bound to carbon, oxygen or hydrogen in organic molecules. These can be relatively small molecules, such as methyliodide (CH3I), or complex molecules, for instance when Iodine is incorporated in organic matter in the soil to iodo-organic molecules, or in mammalian thyroid hormones.
Elemental Chemistry
Iodine
Iodine is the first member of the halogen family to be solid at ordinary temperatures in its elemental state. The most striking property of elemental iodine is its capacity to change states when exposed to heat: from solid dark purple crystals to vivid violet gas. It also has an unusually high specific gravity, and can be rather easily either reduced or oxidized to one of a diversity of ionic states, resulting in a range of positive or negative validities. Iodine is only slightly soluble in water, but dissolves in many organic solvents and the color of the resulting solutions varies with the nature of the solvent from violet to brown color.
The oxidizing properties of iodine containing compounds and their benign environmental character -compared to other halogens- stimulate the development of industrial uses.
New uses for the reactivity of iodine and its derivatives in the synthetic and structural chemistry are still being developed.
PHYSICAL PROPERTIES OF Elemental IODINE
| Property | Solid | Liquid | Gaseous |
| Color Melting Point [°C] Boiling Point [°C] Density, [kg/m3] Crystal Structure Viscosity, [Pa • s] at 116°C Vapor Pressure, [Pa] at 25°C Specific Heat Cp, [J/(kg • K] at 25°C |
Bluish-black 113.6 – 4.93, at 20°C Orthorhombic –
41.33
–
|
Bluish-black – 184.4 3.96, at 120°C – 2.27 • 10-3
–
–
|
Violet – – 6.75×10-3, at 185°C – –
–
146.5 |
Need for Iodine
Iodine
Iodine and its derivatives are indispensable in a wide range of nutritional, pharmaceutical and industrial applications.
