• Remediation of oil spills using zeolites

      Fullen, Michael A.; Kelay, Asha; Williams, Craig D. (2011)
      Current research is testing the hypothesis that zeolites can efficiently and cost effectively adsorb oil spills. To date, this aspect of zeolites science has received little attention. A series of five Master of Science (M.Sc.) Projects at the University of Wolverhampton have shown that the zeolite clinoptilolite can effectively adsorb oil. Various sand-clinoptilolite mixes were tested in replicated laboratory analyses in terms of their ability to adsorb engine oil. Adsorption increased with clinoptilolite amount. The relationship between percentage clinoptilolite and oil adsorption was asymptotic. Thus, on a cost-effective basis, a 20% clinoptilolite: 80% sand mix seems the most costeffective mix. However, a particularly exciting finding was that it was possible to burn the oil-sand-zeolite mix and reuse the ignited mix for further oil adsorption. Experiments are ongoing, but to date the ignition and adsorption cycle has been repeated, on a replicated basis, seven times. Still, the ignited mix adsorbs significantly more oil than the sand control. Initial results suggest that the temperature of ignition is critical, as high temperatures can destroy the crystal and micro-pore structure of zeolites. Thus, low temperature ignition (~400oC) seems to allow the retention of structural integrity. Similar results were obtained using the zeolite chabazite and experiments are in progress on phillipsite, which is the third major zeolite mineral. If the hypotheses can be proven, there are potentially immense benefits. Sand-zeolite mixtures could be used to effectively adsorb terrestrial oil spills (i.e. at oil refinery plants, road accidents, beach spills from oil tankers and spills at petrol stations) and thus remediate oil-contaminated soils. The contaminated mix could be ignited and, given the appropriate infrastructure, the energy emission of combustion could be used as a source for electrical power. Then, the ignited mix could be reused in subsequent oil spills. This offers enormous potential for an environmentally-friendly sustainable ‘green’ technology. It would also represent intelligent use of zeolite resources. On a global scale, including Europe, clinoptilolite is the most common and inexpensive zeolite resource.
    • Synthesis of zeolites and their application as soil amendments to increase crop yield and potentially act as controlled release fertilizers.

      Williams, Craig D.; Fullen, Michael A.; Hocking, Trevor J.; Jakkula, Vijay S. (University of Wolverhampton, 2005)
      Zeolites have been used in agriculture since the 1960s, due to the effectiveness of these crystalline microporous solids as soil amendments for plant growth, their cation exchange capacity (CEC) and slow-release fertilizer properties. Most work on slow-release fertilizers has focused on natural Clinoptilolite, Phillipsite and Chabazite. The aim of this study was to synthesize zeolites, study their effectiveness as soil amendments and their ability to act as controlled release fertilizers to decrease nitrate leaching. Nitrate pollution of groundwater is a major agro-environmental concern. The zeolites Phillipsite and Linde-type F were synthesized from aluminosilicate gels; ion exchanged to introduce ammonium and characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Thermo-gravimetric analysis (TGA) and Scanning electron microscopy (SEM) techniques, both before and after ion exchange. Ammoniumexchanged Phillipsites (natural and synthetic), ammonium-exchanged synthetic Linde-type F (the zeolite having highest affinity towards ammonium) and ammonium exchanged Phillipsites (high crystalline and high aluminium) were compared with conventional NPK fertilizer.Three glasshouse experiments were performed to study the effects of zeolite-amended soils on maize growth. Ion exchanged synthetic and natural Phillipsites were first used as soil amendments (w/w 2, 4, 8% zeolite to soil). Synthetic Phillipsite, at 2% loading, resulted in the most significant improvement in both plant growth and phased ammonium release. The synthetic ammonium-exchanged zeolites Phillipsite and Linde-type F (at w/w 1, 2, 4%) were then compared; synthetic Phillipsite, at 2% loading, again resulted in the most significant plant growth response with an increase (≥15%) in shoot dry weight and a decrease (≥30%) in nitrate leaching. Experiments using unexchanged synthetic Phillipsite (at w/w 2%), but with added NPK fertilizer, showed increased plant growth and decreased nitrate leaching, compared with parallel experiments containing unexchanged synthetic Linde-type F (at w/w 2%) and a conventional fertilizer amended soil. This revealed the beneficial effect of Phillipsite for soil amendment, even without ion exchange to the ammonium form. To study the physico-chemical properties affecting the release of ammonium from the Phillipsite framework; high crystalline/low aluminium and low crystalline/high aluminium forms were synthesized and ion exchanged. Both forms were introduced as soil amendments (at w/w 1 and 2%) and experiments showed that the lower zeolite crystallinity decreased cation exchange and therefore decreased nitrate leaching. Experimental results from the glasshouse experiments and cation exchange capacity (CEC) experiments suggest that synthetic Phillipsite, at lower loadings (1 and 2% w/w zeolite to soil) have most potential as soil amendments for both plant growth and controlled-release applications. This conclusion is supported by soil leachate and shoots dry weight analysis. Furthermore, Phillipsite, synthesized in a low crystalline and low ammonium form, may be an even better soil amendment for controlled release of ammonium, which will thereby further decrease nitrate pollution.