• Biomineralisation performance of bacteria isolated from a landfill in China

      Rajasekar, Adharsh; Wilkinson, Stephen; Sekar, Raju; Bridge, Jonathan; Medina-Roldán, Eduardo; K.S. Moy, Charles (2018-08-27)
      We report an investigation of microbially induced carbonate precipitation by seven indigenous bacteria isolated from a landfill in China. Bacterial strains were cultured in a medium supplemented with 25 mmol/L calcium chloride and 333 mmol/L urea. The experiments were carried out at 30 °C for 7 days with agitation by a shaking table at 130 r/min. Scanning electron microscopic and X-ray diffraction analyses showed variations in calcium carbonate polymorphs and mineral composition induced by all bacterial strains. The amount of carbonate precipitation was quantified by titration. The amount of carbonate precipitated in the medium varied among isolates, with the lowest being Bacillus aerius rawirorabr15 (LC092833) precipitating around 1.5 times more carbonate per unit volume than the abiotic (blank) solution. Pseudomonas nitroreducens szh_asesj15 (LC090854) was found to be the most efficient, precipitating 3.2 times more carbonate than the abiotic solution. Our results indicate that bacterial carbonate precipitation occurred through ureolysis and suggest that variations in carbonate crystal polymorphs and rates of precipitation were driven by strain-specific differences in urease expression and response to the alkaline environment. These results and the method applied provide benchmarking and screening data for assessing the bioremediation potential of indigenous bacteria for containment of contaminants in landfills.
    • Characterisation of Potential Replacements for Nickel Compounds used in Decorative Chromium Plating

      Oduoza, Chike.F.; Hingley, Stacey Louise (University of Wolverhampton, 2013-11)
      The electroplating industries use soluble nickel salts in numerous applications. Over the past few years this has become problematic due to the reclassification of these salts from a harmful substance to now a toxic substance. The introduction of the legislation REACH (Registration, Evaluation, Authorisation & restriction of CHemicals) has meant the electroplating industry has had to use less harmful chemicals where possible, thus meaning companies are investing in research to find an alternative to the nickel deposit. In this study, alternative deposits under investigation as a potential replacement to the nickel deposit under the decorative chromium deposit has been characterised in terms of the appearance, surface topography and corrosion resistance by using spectrophotometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), linear polarisation, electrochemical impedance spectroscopy (EIS) and accelerated corrosion salt spray methods. Spectrophotometry identified that a white Cu-Sn alloy gave a bluer appearance in comparison to the nickel deposit, when the chromium deposit was plated on top this modified the colour slightly giving the white Cu-Sn alloy with chromium a similar appearance to the nickel and chromium deposit. The yellow Cu-Sn alloy was yellow in colour with a visibly dull appearance, but when chromium was plated on top of the yellow Cu-Sn alloy the colour was improved but still remained dull. The SEM and AFM results identified that the white Cu-Sn alloy deposit had similar nodulated topography to the nickel deposit and when the chromium was plated on top the topography changed only slightly. While the yellow Cu-Sn alloy deposits showed a more crystalline structure and increased roughness in comparison to the nickel deposit, the chromium deposit plated on top did not change the structure of the underlying deposit but it did reduce the roughness slightly. Electrochemical corrosion tests showed the white Cu-Sn alloy to have a higher polarisation resistance compared to the nickel deposit, thus suggesting it would provide similar corrosion protection to the nickel deposit. The yellow Cu-Sn alloy proved to have a faster corrosion rate in comparison to the nickel deposit. Accelerated corrosion tests proved the white Cu-Sn alloy to be more corrosive than the nickel despite the electrochemical test results, it was concluded that the white Cu-Sn alloy deposit was porous and therefore provided less corrosion protection to the substrate in comparison to the nickel deposit. The yellow Cu-Sn alloy had a lower corrosion protection than the nickel deposit and when combined as a duplex Cu-Sn alloy with the white Cu-Sn alloy deposit there was no improvement in corrosion performance. The plated chromium deposit did improve the corrosion protection for most deposits but none of the alternatives could match the corrosion protection offered by the standard nickel with chromium deposit. This study concluded that the white Cu-Sn alloy with chromium deposit was found to be a potential alternative to the nickel with chromium deposit for applications where appearance is primary, no alternative could be found to match the corrosion protection provided by the standard nickel and chromium process.
    • Synthesis of Zeolites and Zeotypes by Hydrothermal transformation of Kaolinite and Metakaolinite.

      Rios, Carlos A.; Williams, Craig D.; Maple, Martin J. (Bucaramanga, Colombia: Universidad de Pamplona, 2007)
      The synthesis of zeolitic materials by hydrothermal transformation of kaolinite and metakaolinite in NaOH solutions of various concentrations was investigated between 100 and 200 degrees C, over different reaction times, using in some cases precipitated SiO2 or organic templates. Materials were obtained, including clathrasils: cancrinite (CAN), sodalite (SOD), and Linde Type A (LTA), faujasite (FAU), NaP1 (GIS), analcime (ANA) and nepheline hydrate I (JBW) zeolites. In general, co-crystallization of CAN and SOD, likely via an unstable LTA zeolite intermediate, was observed after dissolution of kaolinite at low temperature; although the feldspathoids tend to be unstable at high temperature. LTA zeolite was synthesized after metakaolinite reaction, with minor amount of FAU zeolite, ANA and SOD. Solids were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA).