REMEDIATION OF TEXTILE AND MINING INFLUENCED EFFLUENTS USING NOVEL HETEROGENEOUS PAN CATALYST AND MODIFIED PAN MESH
The effectiveness of a modified PAN catalyst and hydrogen peroxide system in the treatment of textile effluent and a modified ion exchange PAN mesh in the remediation of non-coal mine drainage was investigated. The results show a tremendous potential in the treatment of such wastewaters. The treatment process for textile effluent was optimized in batch mode of operation. The influence of pH and catalyst was more pronounced compared to that of H2O2. At optimum conditions, 99.5 % decolourization and 91.9 % loss of aromaticity and 70 % mineralization were achieved in 100 minutes. The sorption of dye onto the catalyst is favourable and can be best described by a Langmuir adsorption isotherm model.The modelpredicts a maximum adsorption capacity for the PAN catalyst as 0.68 mg of RO16 per gram of catalyst. A direct relationship between pH, temperature and iron leaching was established. The leached iron has no significant contribution, by means of homogeneous catalysis, in the removal of dye. The system was successful in treating a real dye-bath effluent that was much more concentrated than usual textile effluents. The continuous flow treatment in a prototype of a rotating discs contactor revealed that 99.2 %, 73 %, 64.4 % and 50 % removal efficiencies for decolourization, loss of aromaticity, COD and mineralization at optimum conditions. The breakthrough of the system occurred after 50 days. The system was successfully regenerated in-situ three times and the lifetime of the catalyst extended to 103 days in total, decolourizing 25.3 g of RO16 dye from 546.7 L solution. The deactivation of catalyst occurred mainly due to the loss of iron and partially due to loss of functional groups that ligate iron. Similar to the batch experiments, the leached iron, in continuos flow experiment, has insignificant contribution in removing dye through homogeneous catalysis. The ion exchange capacity of the modified PAN fibre was determined though acid-base titration. The sorption of zinc onto ion exchange mesh is favourable and can be best described by Langmuir adsorption isotherm model. The pH of the medium was found to be the most influential parameter with maximum sorption observed at pH ≥ 5.5 at contact time ≥ 4 hours in batch mode of operation. A pilot scale field trial was performed to remediate mine effluent with elevated concentration of zinc, cadmium and lead demonstrates a tremendous potential applicability. According to analyses by UKAS accredited laboratory, the 170 days long trial successfully removed 5.59 kg, 8.53 g and 18.18 g of zinc-total, cadmium-total and lead-total from 131.46 m3 of mine effluent. The system also removed suspended solids, iron, copper, arsenic, nickel, aluminium, boron, manganese and nitrate (NO3-N). The performance of the system was not affected by the in-situ regeneration and seasonal variation in temperature. The best performance of the system was observed when the contact time ≥ 1.33 hours. The metal removal mechanism was ion exchange initiated (co)precipitation / sorption of metals onto the surface of ion exchange mesh. This technology can be applied in the remediation of all type of mine waters though pre-treatment to adjust pH and alkalinity may be needed.
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