The aim of the TKI Polishing Pellets project is to convert liquid iron sludge into granular pellets suitable for filter application for high-capacity removal of arsenic and/or phosphate and/or hydrogen sulfide from both gas- and liquid streams.
Intermediate results presented at the As2021 conference were well-received by the audience and are promising:
- The produced pellets outperformed the commercial reference for arsenate and phosphate adsorption capacity;
- Binder chemistry clearly affects the adsorption capacity and mechanical strength of the pellets
Follow-up research will focus on 1) mechanical strength of pellets, 2) optimization of a washing procedure to prevent unwanted leaching of manganese and natural organic matter present in the pellets and 3) pilot-scale research to remove phosphate.
Arsenic removal by adsorption technologies
(7 June 2021 – Session 4.1-III)
With a total of nine speakers and over 100 attendees, the session chaired by Arslan Ahmad (Sibelco, ex-KWR) and co-chaired by Case van Genuchten (GEUS) was of clear interest to the As2021 participants. Recent findings and observed performance of various types of arsenite and/or arsenate adsorbents were discussed, including metallurgic slags, (magnetic) nanoparticles, zero-valent iron, membrane coatings, iron-oxide coated sand and, of course, pelletized iron sludge.
In a TKI-funded consortium together with Aquaminerals, Waternet and Vitens, KWR started a 3-year project called ‘Polishing Pellets’. The aim of this project is to convert liquid iron sludge into granular pellets suitable for filter application for high-capacity removal of arsenic and/or phosphate and/or hydrogen sulfide from both gas- and liquid streams. By application of the rotating disk pelletization method using partially dried iron sludge, further transportation costs of filter material are decreased and the market opportunities of iron sludge residual are broadened. With special thanks to our chemical laboratory, our very recent lab results could be included in the talk which was well-received by the session’s audience. Especially the fact that ‘our’ pellets seem to outperform a well-known commercial adsorbent for both arsenic and phosphate adsorption capacity, triggered attention. By comparing the pellets’ strength to the commercial reference as well (work in progress), we might need to further optimize the promising, bio-degradable binder to further improve the mechanical stability of the pellets.
Depending on the final application (arsenic removal in drinking water treatment, phosphate removal from surface water, hydrogen sulfide removal from produced biogas, …), pellet-wash strategies for unwanted leaching of manganese and natural organic matter might be subject of upcoming activities.
Personal experience & questions on the presentation
As it was the first time for me to submit an abstract and present it during an international congress, every part of it was exciting for me. Thanks to the knowledge input and help from my colleagues Roberta Hofman and Erwin Beerendonk during the preparation of the presentation, the message from our work was clearly conveyed. This message also reflected in the motto of the congress ‘bridging science to practice for sustainable development’, strikingly similar to the KWR motto.
One of the moderators of the follow-up general discussion, prof. Alper Baba, posted the remark that in order for arsenic adsorbents to work in developing countries, they should be 1) cheap and 2) readily available and/or produced locally. The polishing pellets development currently in place at KWR perfectly suits this goal, as drinking water production from groundwater everywhere around the globe, typically results in the formation of iron sludge with left-over arsenic- and phosphate adsorption capacity. To be(come) able to transform a locally generated residual stream in conventional drinking water treatment in a useable adsorbent in relatively low-tech equipment is a clear advantage of the practice-oriented research KWR is executing compared to some of the previously mentioned alternative adsorbent materials.
Other questions posted by the audience included some detailed questions about the applied experimental methodology, identity of the commercial reference and nature of the testing method for the mechanical strength of the pellets.
All in all, it was an amazing experience that triggered lots of thoughts and ideas. Many thanks to the As2021 organizing committee for granting me this opportunity to share some of our work.