3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Development and application of functionalized polymeric materials for heavy metal ions recovery from industrial and mining wastewaters(2014-03-07) Saad, DaliaWater pollution is a serious environmental crisis all over the world hence unsafe water is rated among the top ten risks to health. Heavy metals are among the most threatening water contaminants because of their toxic effects on human health. This research was dedicated to the development of insoluble polyethylenimine derivatives; with the suitable functionalities for use as adsorbents to abstract specific toxic elements from mining and industrial wastewater. Branched polyethylenimine (PEI), well known for its metal chelating potential, was cross linked by epichlorohydrin in order to convert it into a water-insoluble form. The water-insoluble property gives the advantage of being used in situ and a possibility of regeneration and re-use, making it a more feasible and cost-effective method. Its surface was then modified for selective removal of uranium (U), mercury (Hg, arsenic (As), and selenium (Se). Three different functional groups were chosen according to the targeted elements namely: the phosphate group for selective removal of U and As; sulphate group for selective removal of Hg and Se, and the thiol group for selective removal of Hg. The adsorption performance of the developed materials was assessed in batch and column experiments. The selectivity of the synthesized materials as well as their ability to be regenerated for reuse was assessed. The results obtained demonstrated that the phosphonated derivative had a superior selectivity towards U with up to 99% adsorption (at pH 3 and 8) even in presence of competing ions, as well as a very good removal for As showing 88%. However, the removal mechanism of U by phosphonated cross-linked polyethylenimine (PCPEI) was found to be different from that of As in that while U was adsorbed onto PCPEI by complexation with the phosphate, As was adsorbed via anion replacement of the phosphate. The sulphonated derivative (SCPEI) was found to be very selective towards both Hg and Se giving removal percentages of 87% and 81% respectively (at pH 3 and 8). Interestingly, the performance of SCPEI towards Hg and Se is similar in both single (Hg or Se) or multi removal (Hg and Se), hence the mechanism is totally different. The thiolated derivative revealed a superior selectivity for Hg with 97% adsorption at pH of 3 and 8. Its adsorption capacity far exceeded that for the sulphonated derivative as a result of high affinity for Hg by the thiol group. The Langmuir and Freundlich isotherm models were used to interpret the adsorption nature of the metal ions onto the synthesized polymers. The Freundlich isotherm was found to best fit and describe the experimental data, thus implying adsorption onto heterogeneous surfaces. The kinetic rates were modelled using the pseudo first-order equation and pseudo second-order equation. The pseudo second-order equation was found to explain the adsorption kinetics most effectively, implying chemisorption. This was confirmed by the thermodynamic study which revealed that the adsorption process was accompanied by high activation energies (> 41 kJ mol-1). Desorption was conducted using 5 mol L-1 HNO3 for Hg and Se on SCPEI; 7 mol L-1 for U and As on PCPEI and 5 mol L-1 for Hg on TCPEI. The results pointed to a good desorption capacity using this solution and on re-use, the polymers still exhibited commendable adsorption. This desorption-re-use was done in five cycles, with only a small percentage loss in adsorption capacity. A continuous fixed-bed adsorption study was carried out using PCPEI (as one of the most efficient developed adsorbent) to assess the possibility of using these materials in filter systems for household use. The results obtained demonstrated that the performance of PCPEI in a fixed-bed column is dependent on the inlet concentration, flow rate, and bed height studied while the full description of breakthrough was accomplished by the Thomas and Yoon-Nelson models. The model constants belonging to each model were determined by linear regression and were proposed for use in column design. The problem of swelling that is usually associated with these resin-types of polymer was overcome by functionalization, a process similar to vulcanisation of rubber. There were no observed changes in the physical aspects of the polymers. The developed polymeric materials showed good results and potential to be applied for selective remediation of aqueous systems polluted by heavy metals. The study of adsorption in column systems showed that these materials have potential for use in filter systems for household taps, especially for communities accessing polluted drinking water sources.Item Development and application of polymeric materials for heavy metal ions recovery from industrial and mining wastewaters(2012-02-01) Saad, DaliaContamination of water bodies by heavy metals and metalloids is an established problem and several studies have been conducted to deal with it. South Africa is amongst those countries whose water systems are most affected as a result of intensive mining activities. This research was dedicated to the development of insoluble chelating polymers for use as adsorbents to abstract heavy metal ions from mining and industrial wastewater. Branched polyethylenimine (PEI), well known for its metal chelating potential, was cross linked by epichlorohydrin in order to convert it into a water-insoluble form. The water-insoluble property gives the advantage of being used in situ and a possibility of regeneration and re-use, making it a more feasible and cost-effective method. Its surface was also modified for selective removal of specifically-targeted heavy metal and metalloid ions. The binding affinity of the synthesized materials to heavy metal and metalloid ions has been determined as well as their ability to be regenerated for reuse. These processes demonstrated that cross-linked polyethylenimine (CPEI) exhibited good complexation ability with high affinity to Cr and some divalent metal ions such as Fe, Zn, and Ni. On the other hand, it showed very poor ability to bind oxo-anions such as SeO32- and AsO2- which has been attributed to the unavailability of suitable functional groups to interact with these ions. The observed order of complexation was: Cr > Zn> Fe >> Ni > Mn > Pb >> As > U > Se. The phosphonated polyethylenimine (PCPEI) showed high selectivity for As, Mn and uranyl ions. The observed order of removal was: U > Mn> Ni > Zn > As >> Cr > Pb > Fe >> Hg > Se; whereas the suffocated polyethylenimine (SCPEI) exhibited high affinity to Se, and Hg. The observed order of adsorption was: Hg > Se >> U > Zn >Pb > Ni >> As > Cr > Fe. v The adsorption behaviour of these polymeric materials involved more than one mechanism such as complexation, normal surface charge exchange, and anion replacement and all these mechanisms are governed by the functional groups. The nitrogen atom on the chelating group (-NH) in the cross-linked polyethylenimine; the phosphorus atom on the chelating group (-PO3H2) in phosphonated cross-linked polyethylenimine; and sulphur atom on the chelating group (-SO3H) in suffocated cross-linked polyethylenimine act as Lewis bases and donate electrons to metal cations which are considered Lewis acids. The existence of the chelating groups in SCPEI and PCPEI facilitate the removal of oxo-anions through anion replacement since they exist as bases in solution and hence cannot be electron acceptors. Thus, the expected mechanism is the normal anion replacement. This mechanism can explain the high removal of Se by SCPEI since Se has similar chemical behaviour as sulphur and are in the same group in the periodic table. As such they can easily replace each other. Sulphur is released from the polymer into the solution by replacing the selenium ions in the polymer. Similar behaviour occurs between phosphorus in PCPEI and arsenic ions as As and P belong to the same group in the periodic table and hence have similarities in their chemical behaviour. The Langmuir and Freundlich isotherm models were used to interpret the adsorption nature of the metal ions onto synthesized polymers. The Freundlich isotherm was found to best fit and describe the experimental data describing the adsorption process of metal and metalloid ions onto the synthesized polymeric materials The kinetic rates were modelled using the pseudo first-order equation and pseudo second-order equation. The pseudo second-order equation was found to explain the adsorption kinetics most effectively implying chemisorption. vi The thermodynamic study of the adsorption of metals and metalloids by the synthesized CPEI, PCPEI and SCPEI resulted in high activation energies > 41 KJ mol-1 which confirm chemisorption as a mechanism of interaction between adsorbate and adsorbent. So far, the developed polymeric materials showed good results and have potential to be applied successfully for remediation of heavy metal-polluted waters, and they have potential for use in filter systems for household use in communities that use borehole water impacted by mining and industrial waste waters. The desorbed metals can be of use to metal processing industries.