Felix E. Okieimen

Heavy Metals in Contaminated Soils: A Review of Sources, Chemistry, Risks and Best Available Strategies for Remediation

Scattered literature is harnessed to critically review the possible sources, chemistry, potential biohazards and best available remedial strategies for a number of heavy metals (lead, chromium, arsenic, zinc, cadmium, copper, mercury and nickel) commonly found in contaminated soils. The principles, advantages and disadvantages of immobilization, soil washing and phytoremediation techniques which are frequently listed among the best demonstrated available technologies for cleaning up heavy metal contaminated sites are presented. Remediation of heavy metal contaminated soils is necessary to reduce the associated risks, make the land resource available for agricultural production, enhance food security and scale down land tenure problems arising from changes in the land use pattern.

Kinetics of the preparation of rubber seed oil alkyds

Abstract The kinetics of the polyesterification of glycerol, phthalic anhydride and rubber seed oil leading to the formation of alkyd resins were studied at temperatures between 230 and 250 °C. Six samples of the resin having oil contents of 20% (I), 30% (II), 35% (III), 40% (IV), 50% (V) and 60% (VI) were prepared. The extent of reaction was monitored by determining the acid value of aliquots of the reaction mixture at various intervals of time and by measuring the volume of water evolved. The extent of reaction (pa) and average degree of polymerization ( DP ) were calculated from end group analysis of aliquote of the reaction mixture withdrawn at various intervals of time. The initial reaction rates followed second order kinetics and thereafter deviations were observed. The average degree of polymerization calculated in the region of deviation from second order kinetics suggests the occurrence of chain branching at relatively short intervals along the polymer chain. The second order rate constants were found to be of the order of 10−5 g (mg KOH)−1 min−1.

Graft copolymerizations of modified cellulose: Grafting of methyl acrylate, ethyl acrylate and ethyl methacrylate on carboxy methyl cellulose

Abstract Graft copolymers of methyl acrylate, ethyl acrylate and ethyl methacrylate on carboxy methyl cellulose (d.S 0.4–0.5) were obtained by the use of ceric ion in aqueous media at 35 °C. The extent of graft polymer formation was measured in terms of graft level, molecular weight of the grafted polymer chains, and frequency of grafting. It was found that, although the reaction conditions were similar, the frequencies of grafting of the monomers were not of the same order of magnitude. It was suggested that graft polymer formation may not be due mainly to propagation by radicals formed on the backbone polymer by interaction with ceric ions.

Graft copolymerizations of modified cellulose, grafting of acrylonitrile, and methyl methacrylate on carboxy methyl cellulose

Graft copolymers of acrylonitrile (ACN), methyl methacrylate (MMA), and their mixtures on carboxy methyl cellulose (d.S 0.4–0.5) were prepared by the use of ceric ion initiator in aqueous medium. The graft copolymers were characterized by IR spectroscopy. The extent of graft copolymerization of ACN and MMA was measured in terms of graft level, molecular weight of grafted polymer chains, and the frequency of grafting as functions of ceric ion concentration. It was found that at comparable reaction conditions, the molecular weight of the grafted polymer chains and the frequency of grafting were not of the same order of magnitude. For the monomer mixtures, the copolymer compositions obtained from the total nitrogen contents of the copolymer samples showed that a disproportionately low amount of ACN monomeric units were incorporated into the graft copolymer, even at high ACN content of the feed.

Preparation and properties of thioglycollic acid modified epoxidised natural rubber and its blends with natural rubber

Abstract Solution prepared epoxidised natural rubber (ENR) was modified while still in solution with thioglycollic acid (TGA) (0.3 mol phr) to yield a material with 17% conversion of its initial NR epoxide. This material (ENR–TGA) and its blends with natural rubber were black filled and vulcanised using the semi-EV system. The modified ENR material exhibited low tensile strength (4.4 MPa), but showed better resistance to solvent and mineral oil than a similar natural rubber compound. Blending natural rubber with the modified ENR material at a level of 10 parts ENR–TGA phr increased the modulus values by 46%. At the aforementioned blend composition, the hardness and resistance to swelling in solvents and mineral oil were also increased, but the reverse were the case for tensile strength and elongation at break. Cure behaviour and flex-cracking properties of the blends were also studied.

Studies on miscibility of poly(vinyl chloride) with natural rubber‐graft‐polyacrylonitrile and natural rubber‐graft‐poly(methyl methacrylate)

The miscibility of poly(vinyl chloride)/natural rubber-graft-polyacrylonitrile (PVC/NRPACN) and PVC/NR-graft-poly(methyl methacrylate) (PMMA) were studied by differential scanning calorimetry (DSC) and viscometry. DSC curves of PVC/NR graft copolymer blends showed a major endotherm at about 265°C that was assigned to the thermal decomposition of PVC. PVC/NRPMMA blends showed a minor endothermic peak at about 124°C and the PVC/NRPACN blends showed a broad peak (which develops into two peaks) at about 160°–180°C, respectively. Absolute viscosity versus weight percent PVC plots of the two sets of blends were nonlinear. X-ray diffraction patterns of the PVC/NRPACN blends showed overlapping spacings due to the constituent polymers. Phase-contrast micrographs of the PVC/NRPACN blends showed gross phase discontinuity. The heats of mixing solutions of PVC blended with NRPMMA were found to be well above the upper limit of miscibility.

Graft copolymerization of vinyl monomers on cellulosic materials

Graft copolymers of acrylonitrile, ethyl acrylate, methyl acrylate, ethyl methacrylate and methyl methacrylate and of acrylonitrile/ethyl methacrylate and acrylonitrile/methyl methacrylate monomer mixtures on carboxymethylcellulose (degree of substitution 0.4-0.5) were prepared by use of ceric ion initiator in aqueous medium. The extent of graft polymer formation was measured in terms of graft level. molecular weight of grafted polymer chains and frequency of grafting as function of ceric ion concentration. It was found that at comparable reaction conditions, the molecular weight and frequency of grafting were not of the same order of magnitude. For the monomer mixtures, the copolymer compositions obtained from the total nitrogen content of the acrylonitrile/alkyl methacrylate copolymer samples showed that a relativity low amount of the acrylonitrile monomeric units were incorporated into the graft copolymer even at high acrylonitrile content of the feed.

Studies on the grafting of acrylic acid on starch

Abstract Graft copolymers of acrylic acid on starch were prepared by the use of ceric ion at various concentrations in aqueous media at 29°C. The attachment of the grafts to starch led to marked improvement in the water retention capacity and metal ion binding capacity of the polymeric substrate. The equilibrium sorption data for Cu(II) ions on starch graft copolymers fitted the Freundlich isotherm, with the coefficient and exponent of the isotherm being 0.40 and 0.60 respectively. The distribution coefficient for Cu(II) ions between the polymeric substrate and the bulk aqueous phase depended on the concentration of the metal ion in solution, indicating that Cu(II) ions may be strongly adsorbed on the starch graft copolymers.

Chemical Fractionation and Phytoavailability of Heavy Metals in a Soil Amended with Metal Salts or Metal-Spiked Poultry Manure

Chemical fractionation patterns and plant tissue concentrations were used to assess nickel, copper, zinc, cadmium, and lead phytoavailability to maize in a soil amended with metal salts or poultry manure. A sandy loam was treated with 80–400 mg kg−1 doses of a quinternary mixture of the metal nitrates either directly or as spiked poultry manure. The European Communities Bureau of Reference sequential extraction procedure partitioned the metals among three operationally defined pools in the soil. Metal mobilities were lower in the poultry manure–amended than the metal salt–treated soil, indicating the manures ability to fix the metals in soil. Pot experiments revealed high metal transferabilities with no apparent phytotoxic symptoms in maize at the doses applied, suggesting some degree of tolerance to the metals. Heavy-metal concentrations in maize increased linearly with metal doses in metal salt–treated soil, but were less phytoavailable in soil amended with poultry manure. Heavy-metal concentrations in maize were reasonably predicted from soil parameters using stepwise multivariate regression models. The findings are useful in the assessment and remediation of heavy metal–contaminated soils.

Thermal dehydrochlorination of PVC in the presence of metal soaps derived from rubber seed oil

Abstract Thermal degradation of PVC was studied in nitrogen in the presence of 3 wt% of the barium, cadmium and lead soaps from rubber seed oil. The time required for dehydrochlorination to attain 1% conversion (tDH) and the rates of dehydrochlorination at 1% degradation (RDH) in the presence of the metal soaps were compared with values obtained with the metal soaps from oleic and linoleic acids. The results from these kinetic studies, together with the data from viscosity measurements of the degraded samples in cyclohexanone, show that the soaps from rubber seed oil are relatively effective in suppressing thermal dehydrochlorination of PVC and also that chain scission was a predominant reaction during the degradation of PVC in the presence of the metal soaps.