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Gum Karaya Stabilised Nanoscale Zero-Valent Iron For Water Treatment - Czech Republic
4 Oct 2021
Nanoscale zero-valent iron (NZVI) is a popular technology that has been investigated for the remediation of contaminated water due to its high reactivity towards a wide range of contaminants.
Researchers at the Czech Academy of Sciences and the Technical University of Liberec in the Czech Republic, Glyndwr University in Wales, and Mangalore University in India have studied gum karaya (GK) – a natural polysaccharide and hydrocolloid gum obtained from the karaya tree – as an inexpensive and environmentally friendly material for NZVI stabilisation that can be used for water treatment.
NZVI has been reported to be reactive with chlorinated, nitro and aromatic organic compounds, as well as heavy metals and radioactive nuclides – the list is endless. To be effective for remediation technology, NZVI particles need to move freely for a long time without aggregating in aqueous environments. Their mobility can often be restricted due to interactions between the iron (Fe) particles and other residues in the water, resulting in lowered specific surface area and subsequently causing reduced reactivity and stability. Potential solutions to overcome these challenges have looked at modification of the surface properties of NZVI using a combination of natural and engineered polymers, together with surfactants that are non-toxic, biodegradable, and have superior physicochemical properties.
GK has been used for centuries as a food additive – for promoting emulsification, stabilisation and thickening – and a pharmaceutical ingredient. It is known to contain sugars such as rhamnose, galactose and arabinose, which have various functional moieties, including hydroxyl and carboxylic groups. These play a crucial role in binding of toxic metal ions from aqueous solutions to the gum biopolymer structure, making GK useful as a natural biosorbent. Researchers at the Czech Academy of Sciences and the Technical University of Liberec in the Czech Republic, Glyndwr University in Wales, and Mangalore University in India have assessed the stability, sedimentation, aggregation behaviour and reactivity of NZVI–GK (GK stabilised NZVI) and bare NZVI towards chromium (Cr) species and volatile organic compounds (VOCs) in contaminated water.1
Sample Preparation and Analysis
GK powder was purified, and the molar mass distribution and radius properties determined. Nanoparticles of zero-valent iron were activated using standard protocols based on preparation of a 20 % slurry by dispersing air-stable NZVI in ELGA® ultrapure water of resistivity of 18.2 MΩ/cm, prepared using a PURELAB® flex system. The activated particles, Fe(0), were mixed in various ratios with purified GK to produce NZVI–GK suspensions before adjusting to different pH conditions (2–10) with 1.0 N NaOH or HCl. The stability, sedimentation, aggregation behaviour and reactivity of NZVI–GK and bare NZVI towards Cr(VI), Cr(III) and VOCs – cis-1,2-dichloroethane, perchloroethene and trichloroethene – in ground water from the Pisecna region of the Czech Republic were assessed. The stabilisation mechanism of NZVI–GK was demonstrated using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and particle size analysis using inductively coupled plasma mass spectrometry (ICP-MS).
The Results
The NZVI–GK nanoparticle suspension was found to be stable for at least three months, suggesting that GK has a superior stability rendering property that forms a scaffold to prevent NZVI from aggregating or sedimentation. Batch experiments confirmed that NZVI–GK was more reactive than bare NZVI. XPS and ICP-MS results revealed that Cr(VI) was reduced to Cr(III) by NZVI–GK and the remaining Cr(III) in solution was adsorbed onto the GK polymer, therefore completely removing chromium from the contaminated water. The study suggests that the properties of GK play an important role, in conjunction with NZVI, to remove all chromium and VOCs from water.
Future Applications
This study is a stepping stone for future research of NZVI-GK, and modifications of NVZI to enhance or tailor the properties to potentially completely eliminate other common contaminants in water. This will not only be beneficial for larger scale treatment of water supplied to our homes and for drinking, but, also for the removal of toxic chemicals that may disperse, leach or directly contaminate the habitats of other living organisms, such as surface or ground waters.
Why Choose ELGA LabWater in the Czech Republic?
The presence of impurities in laboratory water can be a major problem in research experiments, and can seriously compromise results. ELGA LabWater has been a trusted name in pure and ultrapure water since 1937. We believe in providing you with water purification solutions that can meet a wide range of needs and applications, backed by excellent service and support. For more information on our Type I ultrapure water systems, check out our PURELAB Quest, PURELAB Chorus 1 Complete and our PURELAB flex models.