Date of Award
Master of Science (MS)
Dr . Dr. Mohammed S El - Shahawi
A.M.Shams El Din
Mostafa M Kamal
Many substances pollute the marine and air environments but non-biodegradable compounds are the most dangerous. Heavy metals and most of the pesticides are known for their high toxicity. Mercury and lead in particular tend to accumulate in liver and kidney and inhibit the biosynthesis of heme protein because of their affinity for thiol and phosphate containing ligands. Thus, it affects the permeability of the membranes of kidney, liver and brain cells. Soluble inorganic mercury (II) species can be transformed into methylmercury under aerobic conditions by the actions of microorganisms. The target organ of methylmercury in humans is the brain where it disrupts the blood brain barrier and upsets the metabolism of the nervous systems.
The dangers involved from the presence of pesticides in the environment are derived not only from their persistence and toxicity but also from the remarkable degree of accumulation they undergo through the trophic chain. The pesticides can enter the marine media from various sources e.g. crop spraying, rainfall, run-off from agricultural land, direct entry from the industrial and sewage effluent. Thus, the detection and determination of these species are of great importance.
The use of polyurethane foams for extraction, recovery and preconcentration of various inorganic and organic species from aqueous, non-aqueous and gaseous mixtures has received considerable attention during the past two decades. Polyurethane foam allows the isolation of the analyte from the matrix and yields an appropriate enrichment factor. The quasi-spherical membrane structure, the good hydrodynamic and resilient properties of the open cell polyurethane foam offer real advantages over the well-known granular supports. E.g. Voltaleff which is considered one of the most excellent supports in the literature in separation and preconcentration of trace amounts of organic and inorganic pollutants from different media. Thus, the application of unloaded polyurethane foams immobilizing some chromogenic organic reagents (chromoforms) as cellular solid extractor for inorganic and organic pollutants is considered as a useful addition to the field of chemical separation and preconcentration techniques.
In the present investigation, the detection and semi quantitative determination of mercury (II) and lead (II) in aqueous acidic media by polyether foam employing 1,5-di-(2-fluorophenyl)-3-mercaptoformazan, (F2H2Dz) have been critically investigated employing polyether based polyurethane foams. Untreated polyester based polyurethane foam also has been used as a trapping medium for the preconcentration and quantitative recovery of some chlorinated insecticides (commonly in use by the Ministry of Agriculture and Fisheries of UAE) from large volume sample of waters.
The sensitive detection and semi quantitative determination of mercury (II) and lead (II) in aqueous acidic solution (pH<6) employing the chromogenic reagents H2Dz- and F2H2Dz- immobilized or plasticized in tri-n-butyl phosphate (TBP) loaded foams were achieved via batch static and dynamic modes of extraction:
- i. In the static extraction mode, the detection of 0.1 ppm of mercury (II) in aqueous acidic solution was easily achieved from a mixture containing the tested Hg2+ ions, F2H2Dz and unloaded foams. The detection of 0.05 and 0.01 ppm of mercury (II) were also achieved with polyurethane foam treated with F2H2Dz loaded-polyurethane foams and plasticized F2H2Dz-TBP foams. The semi quantitative determination of mercury (II) and lead (II) in aqueous acidic solution employing polyurethane foam loaded with F2H2Dz and plasticized foams with F2H2Dz-TBP were successfully carried out.
- ii. In the dynamic (column) technique, the detection and semi quantitative determination of mercury (II) and lead (II) ions were successfully achieved at the ng cm-3 (ppb) concentration level using immobilized F2H2Dz foams and plasticized polyurethane foam with the reagents F2H2Dz-TBP. As low as 1 and 50 ppb of mercury (II) and lead (II) in aqueous acidic media were easily achieved, respectively. The length of the coloured zone was found proportional to the concentration of each metal ion. Thus, it was taken as a semi quantitative measure of metal ion (Hg2+ or Pb2+) concentrations.
- iii. The selectivity of the proposed F2H2Dz-loaded for the detection of 1µg mercury (II) and lead (II) in aqueous acidic media in the presence of various interfering ions by batch mode of extraction was critically carried out. Removal of the interference caused by some ions on the detection of both Hg2+ and Pb2+ ions was successfully achieved.
Untreated polyester polyurethane foams were employed in static and dynamic modes for the retention and separation of a series of chlorinated insecticide, e.g. Diazinon, Malathion and Dursban from aqueous media. The influence of different parameters, e.g. solution pH, insecticide concentration, temperature, salt effect, contact time, extraction media, and cation size of adding salts affecting the sorption behavior of each compound on the unloaded foam was investigated. The sorption profiles of Diazinon and Malathion were consistent with the “solvent extraction mechanism”. This conclusion was supported by the fact that in the presence of different univalent cations the retention profiles by the unloaded foams increased with cation size in the order:
Li+ > Na+ > K+ > NH4+
On the other hand, the sorption profiles of Dursban by the unloaded foam in the presence of Li+, Na+, K+ and NH4+ follow the sequence:
K+ > NH4+ > Na+ > Li+
Indicating sorption of this compound by the “cation chelation mechanism”. The thermodynamic parameters, ΔH° and ΔS° for the sorption process of the tested insecticides by the unloaded foams were computed. The column performance, the critical capacity, the highest equivalent to the theoretical plates (HETP) and the number of theoretical plates (N) for the unloaded foam column were also calculated and discussed. Separation of some of the tested insecticides was also achieved.
Separation of the tested species can be achieved provided that there is a sufficiently large difference in the optimum condition of extraction of each compound. Open cell type resilient polyurethane foam exhibit rapid separation in column mode operations at relatively high flow rate without significant impairment of the separation efficiency. Moreover, the foam offers a wide range of modifications than normal granular solids. The good hydrodynamic properties of the foam sorbent offer unique advantage in rapid, versatile and preconcentration of the tested compounds.
Saleh, Mahboob Hassan, "Extraction, recovery and separation of some organic and inorganic pollutants by polyurethane foams and other extracting agents" (1996). Theses. 377.