Dissertations / Theses on the topic 'Iron slag – Environmental aspects'

The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy. Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K. The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath. The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite. The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction. The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming.
QC 20100914

Arsenic contamination in drinking water is a severe problem worldwide. The best way to prevent hazardous diseases from chronic arsenic exposure is to remove the exposure. Efforts to remediate arsenic in drinking water have taken two tracks. One is to provide surface or shallow well water sources as an alternative to the arsenic contaminated deep wells. Another approach is to remove arsenic from the contaminated water. Different removal technologies like oxidation, chemical coagulation, precipitation, adsorption and others are available. There are problems and benefits associated with each of these approaches that can be related to cultural, socio-economic and engineering influences. The method proposed in this research is adsorption of arsenic to iron coated limestone. Different iron coated limestone samples were prepared. Standard solutions of 100ppb arsenic were prepared and batch and kinetic experiments were conducted. The final solution concentrations were analyzed by Graphite Furnace Atomic Adsorption Spectroscopy (GFAAs) and the results showed that iron coated limestone removed arsenic below 10ppb with 5 grams of material. Variations in iron coverage impacted efficiency of arsenic removal.

Biofilm formation may increase survival and persistence of Escherichia coli in the highly variable conditions of soil environments, though it remains unknown the extent variation in biofilm formation affects survival. We asked what genetic traits influence biofilm formation in phylogroup D E. coli isolates from surface soils, and are they associated with the soil environment? Biofilm density was analyzed and compared with soil environment characteristics. Isolates produced more biofilm per unit growth at 15°C than 37°C. Biofilm formation was greater in soil isolates than fecal isolates and in soils with moisture and higher calcium and pH levels. A GWAS analysis found variants involved in cell envelope formation and structure were associated with biofilm formed at 37°C, and stress response and iron acquisition variants were associated with biofilm formed at 15°C. Motility variants were associated with a negative effect on biofilm formed and adhesion variants associated with a positive effect.
National Science Foundation (NSF) award no. DEB-1453397 to P.W.B.
ND-EPSCoR

Zero valent iron (ZVI) has demonstrated its reactivity and effectiveness for in-situ groundwater and soil remediation. The potential of the high reducing activity of nanoscale ZVI (nZVI) for environmental decontamination has attracted more attentions in recent years, as nZVI may be injected with water to the pollution sites for in-situ remediation. However, rapid oxidation and instant agglomeration of nZVI make it difficult for large-scale engineering application. Effort has been made to improve the stability and mobility of nZVI for effective in-situ remediation. In the present study, a novel Ca-based surface coating method has been developed for protection of nZVI and enhancement of its transport in environmental applications. A simple thermal deposition method was employed to coat a Ca-based layer on the surface of micro- or nano- ZVI particles in water or methanol environment. According to microscopic observations, Ca(OH)2 nano-layer was formed on the ZVI surface. A clear core-shell structure was observed for the coated nZVI/Ca(OH)2 particles based on the TEM observations. The Ca(OH)2 coating layer had a thickness about one fifth of the nZVI diameter and the Ca to Fe ratio was below 0.2. With the Ca(OH)2 shell, nZVI particles can be effectively protected against corrosion according to the standard natural spray corrosion tests. Thus, the Ca(OH)2 coating layer is able to greatly improve the stability of nZVI during storage, transportation and application. In addition, based on the result of the dissolution tests, the Ca(OH)2 shell could be readily dissolved in water with a low Ca content or a low ionic strength. After dissolution of the Ca(OH)2 shell, the reactivity of nZVI was found to be at the similar level as bare nZVI, which could remove Cr(VI) from water by more than 90% in about 20 min. The pseudo-first order rate constants for Cr(VI) reduction by bare nZVI and nZVI/ Ca(OH)2 after shell dissolution were 0.064 and 0.072 min-1, respectively. Moreover, the Ca(OH)2 coating shell would not only function as a protection layer but also improve the mobility of nZVI particles in in-situ applications. The aggregation and sedimentation of nZVI/Ca(OH)2 particles became considerably slower compared to bare nZVI without the coating. Clean-bed water filtration tests were conducted with sand and glass columns to evaluate the mobility and transport of nZVI in porous media. The results show that bare nZVI in the particle suspension deposited mostly at the top of the filters with little penetration. In comparison, the nZVI/Ca(OH)2 particles were able to penetrate through the filter media during the filtration process, and the dark iron particles could fill up the entire filter columns. The penetration rate increased from nearly 0 m/hr for bare nZVI to 0.43 m/hr for nZVI/Ca(OH)2 through the filter media. The Ca-based coating materials are known as of low cost and environmentally friendly. Thus, the new coating method developed in this study provides a cost-effective means for both the protection of nZVI and improvement of its transport and delivery in porous media for environmental decontamination.
published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy

Thesis (MSc)--Stellenbosch University, 1998.
One copy microfiche.
ENGLISH ABSTRACT: The biologically catalysed oxidation of pyrite in the outer layers of coal waste dumps leads to the formation of acid mine drainage. The oxidation of pyrite to ferric iron and sulphate is a complex process involving various abiotic and biologically catalysed reactions. Pyrite is abiotically oxidized by ferric iron, with the formation of thiosulphate and ferrous iron. Thiosulphate decomposes to form various inorganic sulphur compounds. Bacterial catalysis of pyrite oxidation is achieved by iron-oxidizing bacteria oxidizing ferrous iron to ferric iron. Bacteria that oxidize sulphur compounds assist the catalysis by oxidizing thiosulphate and its decomposition products. Heterotrophic organisms may play a role by consuming organic substances inhibitory to the lithotrophic bacteria. Abiotic ecological factors, acid formation and populations of iron-oxidizing bacterial groups were studied in 10 differently constructed pilot scale coal waste dumps, as the second phase of a study which started in September 1993. Gas samples were withdrawn weekly from coal waste through permanently buried stainless steel probes, for analysis in the field using a portable oxygen/carbon dioxide meter. Samples of coal waste were extracted by auger for analysis of moisture, pH and microbial populations. The analyses of oxygen and pH can be recommended for the routine monitoring of rehabilitated waste dumps. Covers of Avalon soil 0.3 or 0.5 m thick, were not adequate to prevent acidification. Coal waste covered with 0.7 m compacted beneath 0.3 m uncompacted Avalon soil, showed a slow pH decline, but reached approximately pH 3 in 1997. Covers of compacted Estcourt soil beneath tmcompacted Avalon soil to a cover depth of 1 m were effective in preventing acidification and generally kept the coal waste anaerobic. However, all covers developed cracks during drought conditions in 1995, allowing aeration. Low pH of some samples from these dumps during 1995/1996 may have indicated the start of acidification. Bacteria oxidizing high concentrations of ferrous iron and considered to be Thiobacillus ferrooxidans, were monitored routinely, but may not have been the dominant iron-oxidizer, as population counts using media with a lower ferrous iron concentration were higher. The majority of the latter organisms could also not oxidize sulphur, hence were not T. ferrooxidans. The populations of the high ferrous iron-oxidizing bacteria were affected by pH, tending to be high in acidified and low in non-acidified coal waste. Investigations of microbial populations forming iron-oxidizing consortia in enrichment cultures from coal waste and acid drainage samples showed the presence of T. ferrooxidans, the heterotrophic bacterial genus Acidiphilium, fungi of the genus Penicillium, unidentified filamentous fungi, including Cladophialophora-like morphological types, and a yeast of the genus Dipodascus. In interaction studies, the Penicillium isolate had an inhibitory effect on T. ferrooxidans (subjected to organic compound stress), but the Cladophialophora-like fungi reduced inhibition by organics. Fungi have not previously been studied in detail as components of iron-oxidizing consortia, but the bacterial isolations agree with those elsewhere, indicating that appropriate conclusions from acid mine drainage research in other parts of the world can be applied in KwaZulu-Natal.
AFRIKAANSE OPSOMMING: Die biologies gekataliseerde oksidasie van piriet in die buitenste lae van steenkoolafvalhope lei tot die vorming van suur mynafloopwater. Die oksidasie van piriet tot ferri-yster en sulfaat is 'n komplekse proses wat abiotiese en biologies gekataliseerde reaksies insluit. Piriet word abioties deur ferri-yster geoksideer, met die vrystelling van tiosulfaat en ferro-yster. Tiosulfaat verval om verskeie anorganiese swawelverbindings te vorm. Bakteriese katalise van pirietoksidasie word deur ysteroksiderende bakteriee wat ferro-yster na ferri-yster oksideer, bewerkstellig. Bakteriee wat swawelverbindings oksideer maak 'n bydrae tot die katalise deur tiosulfaat en vervalprodukte daarvan te oksideer. Heterotrofe organismes mag ook 'n rol speel deur organiese verbindings wat die litotrofe bakteriee mag inhibeer, te verbruik. Abiotiese ekologiese faktore, suurvorming en bevolkings ysteroksiderende bakteriee is in 10 verskillend gekonstrueerde loodsskaal steenkoolafvalhope bestudeer, as die tweede fase van 'n studie wat in September 1993 begin het. Gas monsters is weekliks uit die steenkoolafval onttrek deur vlekvrye staal peilers wat permanent daarin begrawe is, en met behulp van 'n draagbare suurstoflkoolstofdioksiedanaliseerder in die veld ontleed. Monsters van die steenkoolafval is met behulp van 'n kleiboor vir die analise van vog, pH en mikrobepopulasies geneem. Die analise van suurstof en pH kan aanbeveel word vir die roetiene monitering van gerehabiliteerde afvalhope. Bedekkings van 0.3 of 0.5 m Avalongrond was nie voldoende om suurvorming te verhoed nie. Steenkoolafval wat met 0.7 m gekompakteerde en 0.3 m ongekompakteerde Avalongrond bedek is, het 'n stadige pH-daling getoon, maar het in 1997 ongeveer pH 3 bereik. Bedekkings van gekompakteerde Estcourtgrond onder ongekompakteerde A valongrond met 'n totale dikte van 1 m, was effektief in die voorkoming van suurvorming. Hulle het oor die algemeen die steenkoolafval anaerobies gehou, maar aile bedekings het tydens die droogte in 1995 krake ontwikkel, wat suurstof laat binnedring het. 'n Lae pH gedurende 1995/1996 by sommige monsters uit hierdie hope mag die begin van suurvorming aangedui het. Bakteriee wat hoe konsentrasies ferro-yster oksideer en wat as Thiobacillus ferrooxidans beskou is, was moontlik nie die dominante ysteroksideerder nie, aangesien bevolkingstellings waar 'n medium met 'n laer konsentrasie ferro-yster gebruik is, hoer bevolkings getoon het. Die meerderheid van laasgenoemde organismes kon ook nie swawel benut nie en dus nie T. ferrooxidans was nie. Die bevolkings van die hoe ferro-ysteroksiderende bakteriee is deur pH beInvloed, met 'n geneigdheid tot hoe bevolkings in suur en lae bevolkings in minder suur steenkoolafval. Ondersoeke na die rnilcrobebevollcings wat in ysteroksiderende konsortia in verryldngslculture vanaf steenkoolafval- en suur mynafloopwatermonsters voorgekom het, het die teenwoordigheid van 7'. ferrooxidans, die heterotrofe balcteriegenus Acidiphilium, fungi van die genus Penicillium, ongeIdentifiseerde fungi, insluitend Cladophialophora-agtige tipes en 'n gis van die genus Dipodascus aangetoon. By interaksiestudies het die Penicillium-isolaat 'n inhiberende effek op T ferrooxidans (onderworpe aan organiese verbindingstres) gehad, maar die Cladophialophora-agtige fungi het die inhibisie deur organiese verbindings verminder. Fungi is nog the in detail as komponente van ysteroksiderende konsortia bestudeer the, maar die isolasies van bakteried stem saam met die van elders wat aandui dat toepaslike gevolgtreldcings ten opsigte van suur mynafloopwatemavorsing vanaf ander dele van die wereld ook in KwaZulu-Natal toegepas kan word.

Dagvatten från vägar innehåller ofta tungmetaller. De vanligaste metallerna i vägdagvatten är bly, koppar, kadmium, nickel och zink. Dessa föroreningar utgör en belastning i recipienter som tar emot dagvattnet. I denna rapport har bly, koppar och zink reducerats från vägdagvatten genom filtrering i kolonner med amorf, granulerad masugnsslagg och sand. Masugnsslagg, som är en biprodukt från framställningen av järn, är en alkalisk produkt med goda sorptionsegenskaper vilket gör den lämplig att använda som filtermaterial för vatten förorenade med metaller. Sanden användes i studien som referensmaterial. Masugnsslaggen som användes i denna studie är hyttsand från Merox, Oxelösund. Reningshalten för hyttsanden i denna studie uppgick till 79 % för bly, 82 % för koppar samt 92 % för zink. Hyttsandens reducerande förmåga har även undersökts i batchförsök.

Stormwater from roads often contain heavy metals. The most common metals in storm water from roads are lead, copper, cadmium, nickel, and zinc. These pollutants constitute a stress for organisms in recipients that receive the stormwater. In this report lead, copper and zinc have been reduced from road storm water through filtration in columns with granulated iron slag and sand. Iron slag is a by-product from the iron making process, with a high sorption capacity, which makes it suitable as a filter material for water polluted with metals. The sand in this study has been used as reference material. The reducing capacity in the stormwater for the iron slag used in this study, “hyttsand”, was 79 % for lead, 82 % for copper and 92 % for zinc. The reducing capacity of the iron slag was also investigated in batch studies.

Thesis (MMed)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: There is growing interest in how genetic and environmental risk factors interact to confer risk for dysregulated iron homeostasis, which is considered a possible pathogenic mechanism in multiple sclerosis (MS). While iron deficiency has been associated with greater disability and disease progression, cerebral accumulation and overload of insoluble iron has also been reported in MS patients. Variation in the matriptase-2 (TMPRSS6) gene has recently been described that may lead to reduced iron levels, which raised the question of whether it may be involved in dysfunctional iron regulation as a pathogenic mechanism in MS. The aims of the study were as follows: 1)) comparison of the allele frequencies and genotype distribution for TMPRSS6 A736V (rs855791, c.2207C>T) and HFE C282Y (rs1800562, c.845G>A) between patients diagnosed with MS and unaffected controls; 2) determination of the effects of clinical characteristics, relevant lifestyle factors and genotype on serum iron parameters in MS patients compared to population matched controls; and 3) determination of clinical outcome in relation to age of onset and degree of disability in MS patients. The study population included 121 Caucasian MS patients and 286 population-matched controls. Serum iron, transferrin, ferritin and transferrin saturation levels were available from previous studies and lifestyle factors were subsequently documented in a subgroup of 68 MS patients and 143 controls using the study questionnaire. Genotyping of TMPRSS6 A736V and HFE C282Y were performed using allele-specific TaqMan technology. The genotype distribution and allele frequencies of TMPRSS6 A736V and HFE C282Y did not differ between MS patients and controls. MS patients homozygous for the iron-lowering minor T-allele of TMPRSS6 A736V had significantly lower serum iron levels (p=0.03) and transferrin saturation levels (p=0.03) compared to CC homozygotes. In MS patients the iron-loading minor A-allele of HFE C282Y was also associated with a paradoxical decrease in serum ferritin (p<0.01) compared to GG homozygotes. When considering the combined effect of the minor alleles of TMPRSS6 A736V and HFE C282Y with opposite effects on iron levels, we found a significant reduction in serum ferritin levels (p<0.05), independent of age, sex, body mass index (BMI) or dietary red meat intake in MS patients. A similar effect was not observed in the population- and age-matched controls. Higher dietary red meat intake correlated significantly with increased ferritin only in controls (p=0.01 vs. 0.21 for MS patients). In the presence of the minor allele of HFE C282Y, the TMPRSS6 A736V CT and TT genotypes were associated with a significantly earlier age of onset of MS when the post hoc test was applied (p=0.04). All the study aims were successfully accomplished. Our results support the possibility of an epistatic effect between TMPRSS6 A736V and HFE C282Y associated with reduced ferritin levels in MS patients. Pathology-supported genetic testing (PSGT) applied in this study as a new concept for analysis of complex diseases with a genetic component, is well placed to optimise clinical management in patients with MS.
AFRIKAANSE OPSOMMING: Daar heers toenemende belangstelling in hoe die wisselwerking tussen genetiese en omgewingsfaktore die risiko tot wanregulering van yster-homeostase beïnvloed. Laasgenoemde is ‘n moontlike patogeniese meganisme vir meervoudige sklerose (MS). Alhoewel verhoogde gestremdheid en siekteprogressie met ystertekort geassosieer is, is ysterophoping in die serebrum asook ‘n oormaat onoplosbare yster al by MS-pasiënte gevind. Variasie in die matriptase-2 (TMPRSS6) geen wat tot verlaging in ystervlakke kan lei, is onlangs beskryf en laat die vraag ontstaan of dit betrokke is by wanregulering van yster-homeostase as patogeniese meganisme in MS. Die doelwitte van die studie was as volg: 1) vergelyking van alleelfrekwensies en genotipeverspreiding vir TMPRSS6 A736V (rs855791, c.2207C>T) en HFE C282Y (rs1800562, c.845G>A) tussen MS-pasiënte en ongeaffekteerde kontroles; 3) bepaling van die effekte van kliniese indikators, relevante leefstylfaktore en genotipe op serum yster parameters in MS-pasiënte in vergelyking met populasie-ooreenstemmende kontroles; en 4) bepaling van kliniese uitkoms ten opsigte van aanvangsouderdom en graad van MS-aantasting. Die studiepopulasie het uit 121 kaukasiese MS-pasiënte en 286 kontroles van dieselfde populasie, wat nie die siekte het nie, bestaan. Serum yster, transferrin, ferritien en transferrien-versadigingsvlakke was beskikbaar vanaf vorige studies. Leefstylfaktore is in ‘n subgroep van 68 MS-pasiënte en 143 kontroles gedokumenteer met behulp van die studie-vraelys. TMPRSS6 A736V en HFE C282Y genotipering is met alleel-spesifieke TaqMan-tegnologie uitgevoer. Beide pasiënte en kontroles het dieselfde genotipeverspreiding en alleelfrekwensies getoon. Die A-alleel van HFE C282Y is met ‘n paradoksale verlaging in serum ferritien geassosieer (p<0.01) in MS-pasiënte met TMPRSS6 A736V, moontlik weens geen-geen interaksie wat nie deur ouderdom, liggaamsmassa-indeks of inname van rooivleis in die dieet beïnvloed is nie (p<0.05) en nie by kontroles gevind is nie. MS-pasiënte wat homosigoties is vir die T-alleel van TMPRSS6 A736V, het statisties betekenisvolle laer serum ystervlakke (p=0.03) en transferrienversadiging (p=0.03) getoon in vergelyking met CC-homosigote. In MS-pasiënte was die yster-oorlading A-alleel van HFE C282Y ook geassosieer met ‘n paradoksale afname in serum ferritien (p<0.01) in vergelyking met GG-homosigote. Wanneer die gekombineerde effek van die risiko-geassosieerde allele van TMPRSS6 A736V en HFE C282Y met teenoorgestelde effekte op ystervlakke geanaliseer word, is daar ‘n statisties beteknisvolle afname in serum ferritienvlakke (p<0.05), onafhanklik van ouderdom, geslag, liggaamsmassa-indeks of rooivleisinname in MS-pasiënte. ‘n Soortgelyke effek is nie waargeneem in populasie- en geslag-gelyke kontroles nie. Die inname van rooivleis in die dieet was betekenisvol minder by MS-pasiënte teenoor kontroles (p=0.03) en dit het slegs betekenisvol met verhoogde ferritien by kontroles gekorreleer (p=0.01 teenoor 0.21 by MS-pasiënte). In die teenwoordigheid van die risiko-geassosieerde alleel van HFE C282Y, is die TMPRSS6 A736V CT en TT genotipes geassosieer met ‘n statisties-betekenisvolle vroeër aanvangsouderdom van MS soos bepaal met die post hoc-toets (p=0.04). Al die doelwitte van die studie is suksesvol uitgevoer. Die resultate ondersteun die moontlikheid van ‘n epistatiese effek tussen TMPRSS6 A736V en HFE C282Y wat geassosieer is met ‘n verlaging in ferritienvlakke in MS-pasiënte. Patologie-gesteunde genetiese toetsing soos toegepas in hierdie studie as ‘n nuwe konsep vir analise van komplekse siektes met ‘n genetiese komponent, is goed geplaas om kliniese hantering van MS-pasiënte te optimaliseer.

Thesis (MSc)--Stellenbosch University, 1997.
ENGLISH ABSTRACT: The activity of iron-oxidizing bacteria, for example, Thiobacillut. ferrooxidans, in the outer layers of coal waste dumps results in the oxidation of pyrite with the formation of large volumes of acid mine drainage. The process requires atmospheric oxygen and moisture. Acid mine drainage may possibly be controlled by creating unfavourable environmental conditions in dumps for the iron-oxidizing bacteria. The present research investigated the possibility of inhibiting these bacteria and consequently acid formation in coal waste dumps by means of different dump construction techniques. Physical and chemical conditions, acid formation and populations of four groups of bacteria which might produce acid were studied in the outer layers of ten differently constructed pilot scale coal waste dumps at the Kilbarchan Mine near Newcastle, Kwazulu-Natal, from September 1993 to July 1995. Dump covers consisting of a 30-cm or 70-cm layer of Estcourt soil of low permeability covered with 70 cm or 30 cm, respectively, of more permeable Avalon soil produced anaerobic conditions in the dumps throughout most of the 22 months of the test period, as did a cover of 70 cm compacted plus 30 cm uncompacted Avalon soil alone. An uncoMpacted 30-cm or compacted 50- cm Avalon soil cover proved ineffective in causing prolonged anaerobic conditions. Uncovered dumps showed only slight reduction of oxygen in the coal waste after heavy rains. Pockets of acidity were detected on several occasions in the coal waste below the 50-cm Avalon soil layer from the time of construction and progressively increasing acidity in the uncovered dumps and the waste below the 30-cm Avalon soil cover. Iron-oxidizing bacterial populations of the T. ferrooxidans type have tended to be higher in the uncovered dumps and Avalon soil-covered dumps showing acidification than in the non-acidified dumps covered with 1 m of Avalon soil or Avalon and Estcourt soil. Associated populations of iron-oxidizing bacteria of the Metallogenium type, acidophilic and non-acidophilic thiosulphate-oxidizing bacteria were generally low in the coal waste of the dumps. Thus, five of the soil covers, all with a thickness of 1 m, but not covers with a thickness of 0.5 m or less, proved effective for almost 2 years in inhibiting the diffusion of oxygen to the underlying coal waste in the pilot scale dumps and also appeared to suppress the populations of iron-oxidizing bacteria believed to be implicated in acid formation in the coal waste. These results suggest that coal waste dumps in South Africa should be covered with soil layers of 0.5-1.0 m thick to prevent the generation of acid mine drainage.
AFRIKAANSE OPSOMMING: Die aktiwiteit van ysteroksiderende bakteriee soos Thiobacillus ferrooxidans, in die buitenste lae van steenkoolafvalhope, veroorsaak die oksidasie van piriet met die gevolg dat groot volumes suur mynafloopwater gevorm word. Hierdie proses benodig suurstof en vog. Suur mynafloopwater kan moontlik beheer word deur 'n situasie te skep waar die toestande in die hope ongunstig is vir die ysteroksiderende bakteriee. Die huidige navorsing het die moontlikheid ondersoek om hierdie bakteriee te inhibeer deur verskillende afvalhoopontwerpe op die proef te stel en sodoende suurvorming in steenkoolmynhope te beperk. Die fisiese en chemies kondisies, suurvorming en populasies van vier verskillende bakterie-groepe wat dalk by suurvorming betrokke is, is vanaf September 1993 tot Julie 1995 bestudeer in die buitenste lae van tien verskillend gekonstrueerde loodsskaalafvalhope by die Kilbarchan myn naby Newcastle in KwaZulu-Natal. Afvalhoopbedekkings bestaande uit 'n 30-cm of 70-cm Estcourt grond met 'n lae permeabiliteit bedek met'n 70-cm of 30-cm laag van meer deurlaatbare Avalon grond het anaerobe kondisies veroorsaak. Ongekompakteerde 30-cm en gekompakteerde 50-cm Avalon grondlae het egter nie bestendige anaerobe kondisies in die hope veroorsaak nie. Die onbedekte hope het aerobics gebly met slegs effense dalings van suurstofkonsentrasies gedurende en na swaar reens. Geisoleerde monsters uit die steenkoolafval onder die 50-cm Avalon grondlaag het vanaf die begin van die toetsperiode tekens van suurvorming getoon. Die onbedekte steenkoolafval en die van die sel met 'n 30-cm Avalon grondlaag het met verloop van tyd al hoe meer suur geword. Die ysteroksiderende bakterie-populasies van die T. ferrooxidans tipe het geblyk om in die onbedekte en Avalon grondbedekte hope wat tekens van suurvorming getoon het hoer te wees as in die hope wat met 'n 1-m laag Avalon grond of Avalon en Estcourt grond bedek is en geen tekens van suurvorming getoon het nie. Ysteroksiderende bakteriepopulasies van die Metallogenium tipe, nieasidofiele en asidofiele tiosulfaatoksiderende populasies was oor die algemeen laag in die steenkoolafvalhope. Vyf van die grondlae wat alma! 1 m dik was het dus geblyk om effektief te wees in die bekamping van die infiltrasie van suurstof na die onderliggende steenkoolafval in die loodskaalhope. Dit lyk asof daardie lae die ysteroksiderende populasies betrokke by suurvorming onderdruk het. Die 0.5-m grondbedekking het egter nie so 'n sterk onderdrukkende effek op die suurstofinfiltrasie of die bakteriepopulasie gehad nie. Na aanleiding van hierdie resultate blyk dit dat steenkoolafvalhope in Suid-Afrika met minstens 0.5 tot 1..0 m grond bedek moet word om effektief die probleem van suur mynafloopwater te bekamp.

Thesis (M.Sc.) -- University of Limpopo, 2005
Six aerobic bacterial strains [GM 10(1), GM 10 (2), GM 14, GM 15, GM 16 and GM 17] were isolated from an antimony mine in South Africa. Heavy-metal resistance and biosorptive capacities of the isolates were studied. Three of the isolates (GM 15, GM 16 and GM 17) showed different degrees of resistance to antimony and arsenic oxyanions in TYG media. The most resistant isolate GM 16 showed 90 % resistance, followed by GM 17 showing 60 % resistance and GM 15 was least resistant showing 58 % resistance to 80 mM arsenate (AsO4 3-). GM 15 also showed 90 % resistance whereas isolates GM 16 and GM 17 showed 80 % and 45 % resistance respectively to 20 mM antimonate (SbO4 3-). Arsenite (AsO2 -) was the most toxic oxyanion to all the isolates. Media composition influenced the degrees of resistance of the isolates to some divalent metal ions (Zn2+, Ni2+, Co2+, Cu2+ and Cd2+). Higher resistances were found in MH than in TYG media. All the isolates could tolerate up to 5 mM of the divalent metal ions in MH media, but in TYG media, they could only survive at concentrations below 1 mM. Also, from the toxicity studies, high MICs were observed in MH media than TRIS-buffered mineral salt media. Zn2+ was the most tolerated metal by all the isolates while Co2+ was toxic to the isolates. The biosorptive capacities of the isolates were studied in MH medium containing different concentrations of the metal ions, and the residual metal ions were determined using atomic absorption spectroscopy. GM 16 was effective in the removal of Cu2+ and Cd2+ from the contaminated medium. It was capable of removing 65 % of Cu2+ and 48 % of Cd2+ when the initial concentrations were 100 mg/l, whereas GM 15 was found to be effective in the biosorption of Ni2+ from the aqueous solutions. It was capable of removing 44 % of Ni2+ when the initial concentration was 50 mg/l. GM 17 could only remove 20 % of Cu2+ or Cd2+. These observations indicated that GM 16 could be used for bioremediation of xvi Cu2+ and Cd2+ ions from Cu2+ and Cd2+-contaminated aqueous environment, whereas GM 15 could be used for bioremediation of Ni2+.
National Research Foundation and the University of the North Research Unit

[Truncated abstract] Acidic mine lakes are formed as a result of the oxidation and dissolution of metal sulfide minerals and are primarily characterized by low pH values of 2 – 4. Many strategies for the bioremediation of acidic mine lakes depend on the alkalinity generation capabilities of microbial ferric and/or sulfate reducing bacteria. However nearly all mine lakes are oligotrophic, with very low concentrations of available organic carbon and nutrients; all required for healthy microbial growth. There is also an unusual class of mine lakes characterized by low concentrations of organic carbon and also very low concentrations of dissolved iron and sulfate. Our ability to promote microbial activity in these systems is especially challenging. This study focuses on one of these systems, Lake Kepwari, a coal mine lake in Western Australia. Numerical modeling of remediation strategies is an efficient way of testing scenarios prior to expensive in-field trials. However such modeling relies on good descriptions of microbial processes, including kinetic parameterizations of ferric and sulfate reduction. There has been little research to date on the study of kinetic parameterizations of the chemical and biological alkalinity generation in acidic mine lakes. The objectives of this thesis were to investigate the viability of microbial ferric and sulfate reduction in an ultraoligotrophic, acidic mine lake, to assess the impact of these microbial processes on water quality and to parameterize the Dual Monod kinetics of neutralization under dual limitation conditions. Molecular analyses including most probable number, DNA extraction, polymerase chain reaction, polymerase chain reaction – denaturing gradient gel electrophoresis were used to examine the microbial communities in the lake sediments. ... The Monod maximum specific microbial growth rates with respect to dissolved organic carbon and ferric, and as determined in batch experiments, were 0.07 ± 0.01 and 0.048 ± 0.02 day-1, respectively, and their corresponding Monod half saturation constants and were 14.37 and 5.6 mmol L-1. The Monod maximum consumption rates under ferric and OC limitation were also estimated. The Monod maximum specific microbial growth rates with respect to dissolved organic carbon and sulfate, , and were 0.05 ± 0.01, 0.08 ± 0.01 and 0.07 ± 0.02 day-1, respectively, and their corresponding Monod half saturation constants, and were 75.5, 131.8 and 10.2 mmol L-1. The Monod maximum consumption rates under sulfate and OC limitation were also estimated. The results of this study suggest that strategies for the remediation of ultraoligotrophic, acidic mine lakes may rely on microbial ferric and sulfate reduction, however additions of both organic carbon and sulfate/ferric are essential. These results can be immediately applied to mesocosm studies in outdoor enclosures and to the management of acidic mine lakes. Furthermore, this thesis has provided a new, valuable understanding on the Dual Monod kinetic parameterizations of neutralization for an ultraoligotrophic, acidic mine lake environment. These parameterizations are essential for the lake ecological models that will be used to investigate remediation scenarios for acidic mine lakes.

Iron and steel plants in general are significant sources of PM10 pollution. Many studies have concluded that PM10 is harmful to human health and well being. ArcelorMittal Vanderbijlpark Works falls within the jurisdiction of the Vaal Triangle Airshed Priority Area (VTAPA) and has been given PM10 reduction targets in the Air Quality Management Plan. The aim of this study is to use dispersion modelling to determine the impact of the Vanderbijlpark Works steel plant on ambient PM10 and to assess the effectiveness of the reduction strategies with respect to PM10 The AERMOD dispersion model was chosen for the exercise because of its reliability when modelling near field dispersions on relatively flat terrain. Meteorological data was obtained from on-site stations. Emissions data was obtained from an already existing emissions inventory on site. The study modelled the PM10 baseline for 2010 and then modelled the predicted concentrations after implementation of the strategies as outlined in the VTAPA. The modeling scenarios were compared to the measured PM10 data from the fence line monitors. The following findings were made: Point sources were not significant contributors to PM10 emission. Modeling of area sources and other fugitive dust sources were found to be high and when compared to measured concentrations were found to be over predicted. It is concluded that the fugitive sources have been found to be the major source of PM10 emissions and that reduction of fugitives should feature prominently in emission reduction plans going forward. In addition, the fugitive emissions inventory needs to be refined to enhance the accuracy of the predictions.

Metals are naturally found in ecosystems but can also enter via human activity such as fossil fuel combustion, and disposal of metal products. Copper, lead, and iron have frequently been detected throughout Indiana freshwaters based on historical samples. Since microbial activity is a holistic measure of ecosystem function, changes in microbial activity in response to metals may indicate potential areas of concern. Metal concentrations in seven streams of the Upper White River watershed of central Indiana were measured during spring (May) and summer (August) in conjunction with measurement of sediment nitrification rates using the nitrapyrin-inhibition technique. Additionally, the influence of copper, lead, and iron on microbial nitrification was studied using in vitro mesocosms inoculated with stream sediment from selected sites. Copper, lead, and iron concentrations in stream sediment and water varied among sites with sediment concentrations ranging 654 – 1985 mg Fe/kg sediment and 1.00 - 2.91 mg Cu/kg sediment. Water concentrations ranged from below detection to 0.10 mg Fe /L, and 0.01 – 0.02 mg Cu/L. Lead concentrations were below detection at all sites except in May at one site (Pleasant Run Creek 0.47 mg Pb/kg sediment) and in August at one site (Mud Creek 0.38 mg Pb/ kg sediment). Stream sediment nitrification rates were positively correlated to stream sediment copper concentration (r = 0.78, p = 0.001). There was no significant correlation between sediment nitrification rates and stream sediment iron, pH, dissolved iron, or total dissolved solids (TDS; p > 0.05). Positive correlations were found between nitrification response rates and total Fe (r = 0.61, p = 0.02) and Cu (r = 0.74, p = 0.002) concentrations. Experimental mesocosms indicate metal addition of 127 mg/L may reduce stream sediment nitrification rates though stream physiochemical characteristics and history of metal exposure likely dictate microbial response. Further, metal concentrations in the stream sediment may have more of an influence on nitrifying microbes than dissolved metal in the water column.
Department of Biology

M.Sc. (Environmental Management)
With the rapid expansion of the industries in South Africa, environmental problems including air pollution have been increasing. Among industries that cause air pollution is the iron and steel industry. Air pollution impacts negatively on the environment and therefore the measures implemented to improve air quality by this industry were investigated. The purpose of this thesis was to critically analyse the air pollution control measures implemented by the iron and steel industry in South Africa and to find out what they are doing to address the problem of air pollution, as well as their processes in involving and encouraging community involvement with regard to environmental issues. The key findings from this study were that the South African iron and steel companies are doing their best in trying to control the problem of air pollution. Some of them do not only rely on the South African legislation, they also do self-regulation by monitoring and controlling the air pollution problems even if not strictly required to by legislation. The iron and steel industry does also involve communities, through participation in public environmental forums. Air pollution has always been an issue in South Africa, but due to a lack of enabling legislation in the country, many people were not aware of their environmental rights. Now that the South African Constitution highlights the rights of people to an environment that is not harmful to their health or wellbeing, people are becoming more aware and have started taking the issue of air pollution in a very serious light. With the new environmental legislation including the National Environmental Management Act 108 of 1009 and the National Environmental Management: Air Quality Bill (Draft 1, April 2003), most of the issues relating to air pollution will be dealt with in a better and more enforceable way.

As the world population has exceeded 7 billion in 2011, the global awareness of sustainability arises more than ever since we are facing unprecedented challenges in energy, water, material and climate change, in order to sustain our current and future generations on this planet. The Guardian has named the Iron Bridge opened in 1781 across the River Severn, Shropshire, UK as the cradle of the modern world, which is the world's first cast-iron bridge and remains as the enduring symbol of the Industrial Revolution (Guardian, 2009). Ever since, in the spanning of 250 years, iron and steel have been the cornerstone of modern industries from developed countries to developing ones especially for those which are still experiencing their major urbanization process. Nevertheless, iron and steel making are among the most raw material-dependent and energy intensive industries with large gaseous pollutants, CO2 and waste generations in the world. Therefore there is a pressing need to solve these resource and environmental problems associated with the iron and steel making. This work addresses a number of challenges stated above by focusing on the improvement of the overall sustainability of this highly energy-intensive industry via (1) utilizing inexpensive iron ore tailings to enhance the material sustainability, (2) CO2 reduction by mineral carbonation using its own solid waste stream, i.e., iron and steel slags, and (3) slag valorization through the use of carbonated slags as sustainable construction materials. This work begins with the study of an ironmaking plant using the direct reduced iron (DRI) process, which is a molten iron production method utilizing fluidized bed and melter-gasifier technologies. This technology allows the direct production of the molten iron using the inexpensive iron ore tailings and the non-coking coal, during a gas-solid reaction in the fluidized bed. Practically, a higher percentage of the fine particles (i.e., iron ore tailings) is favored to mix in the feedstock because it is cheaper than the traditionally used coarse particles (i.e., bulk and fine iron ores). The challenge of this novel technology is attributed to the entrainment of the fine particles during the gas-solid fluidization. Since the electrostatic phenomenon was significant during the particulate fluidization systems which might affect the particle entrainment, the electrostatic charge generation and accumulation were investigated for binary and quaternary particulate systems. Specifically, the effect of the addition of two different iron ore tailings (i.e., hematite and magnetite) in the fluidized bed was studied in terms of particle-particle interactions, electrostatics, and entrainment rates. The behaviors of different particulate systems were found to be highly dependent on the chemical and physical properties of the particles. The results suggested that the enhanced electrostatic forces between the fine and coarse particles due to the electrostatic charging during the fluidized bed operation retained the fines to some extent and the sintering of the fine particles could happen on the surface of the coarse particles during the iron ore reduction. Therefore, for this fluidized bed based DRI process, iron ore tailings are proved to be able to replace the coarse iron ores to the extent that fine particles will sinter but not be entrained and thus the overall cost of raw materials could decrease. In iron and steel making, limestone and dolomite are also mixed in the feedstock to remove the impurities of the iron ores, mostly silica, which forms slag as a silicate-based material in the downstream of this process. Slags of different types have been reused as cement clinker, aggregate, road base and fertilizer. Recently, iron and steel slags have also been deemed as alternatives for mineral sequestration because these slags are similar to natural Ca/Mg-bearing silicate minerals. The accelerated weathering of natural minerals or industrial wastes is an environmentally benign route to thermodynamically stabilize carbon. Thus, another study of this work is fixing the CO2, especially emitted from the iron and steel plant, into the slag, a solid waste generated from the same processing stream. In particular, the stainless steel slag has been a focus since its application in construction materials has been limited due to the high content of FeO and the environmental concern of heavy metals leaching (e.g., Cr). Along with the iron and steel making, the cement industry is also among the largest industrial CO2 emitters. Mixing carbonated slags as a filler material in the cement mortar while guaranteeing the overall quality of the cementitious material could reduce the usage of limestone and the carbon emissions from limestone calcination and reduce energy input during the cement production. In this study, the production of environmentally benign cementitious material was coupled with the direct carbonation of stainless steel slag. Compressive strength, exothermic behavior and leaching behavior of the mixed cement mortar were investigated. Particularly, mixing 10 wt% of the direct carbonated stainless steel slag sample prepared at 30 °C in a Portland cement did enhance the compressive strength of the cement mortar. Also, the mixing retarded the hydration and overall setting time. Finally, the Cr leaching of the cement mortar with the addition of the direct carbonated stainless steel slag was minimized. Thus, the iron and steel industry and cement industry should collaborate, to minimize their overall material input, energy usage and carbon emission jointly. During the direct carbonation, stainless steel slag and CO2 flows are introduced into the solvent simultaneously. Whereas for the two-step process, calcium ions are extracted from the solid matrix into an aqueous phase, and then the CO2 is bubbled through and reacts with the Ca. The two-step route allows optimizing the conditions for both the dissolution and the carbonation. Moreover, the precipitated end products (e.g., precipitated calcium carbonates, PCC) from the two-step process, normally with higher quality compared to direct carbonated slags, can be adapted for various industrial and construction applications. However, the overall reaction is constrained by the kinetics of the stainless steel slag dissolution. Thus several organic and inorganic chelating agents were applied in order to accelerate the dissolution. Some of these agents were found to be desirable for the dissolution of stainless steel slag at different pH via the differential bed study. Ligand concentration and temperature affected the extent of the extraction in the batch reactor. For the carbonation step, PCC from the modeled chemical solution and the dissolved stainless steel slag solution were non-identical, which was also affected by the reaction pH and temperature. The properties of the PCC prepared in the batch reactor and the bubble column reactor were also found to be dissimilar. Thus, for an iron and steel plant that adopts the two-step carbonation of slags for CO2 reduction, the end products could be engineered by tuning the reaction conditions to meet different end-user requirements. On the other hand, there have been significant efforts to reduce the cost of the two-step carbonation, including the utilization of value-added byproducts like iron oxide. In particular, silicate minerals or industrial waste often contain 5~20 wt% of Fe and by dissolving the iron into aqueous phase, a variety of Fe-based materials can be synthesized by precipitation. In this work, Fe-based catalysts were synthesized from serpentine and stainless steel slag (SSS) and applied to the biomass-to-hydrogen conversion via an alkaline thermal treatment pathway. The synthesized Fe-based materials were compared with the purchased hematite and magnetite and the reduced Fe-based catalyst derived from SSS was found to be catalytically active. This suggests an opportunity to produce inexpensive catalysts from the solid waste of the iron and steel making. Finally, a novel iron making scheme based on a fluidized bed DRI system was proposed by this study. It combined all the studies above that inexpensive iron ore tailings were used as a feedstock for the iron production, slags were utilized for sequestering CO2 and ended as filler materials for cement mortar. Preliminary economical and life cycle assessment was investigated based on the current scale of an existing industrial plant. An economically, environmentally and ecologically favored iron, steel and cement production system could be potentially achieved with improved overall material sustainability and carbon footprint.

The mixed metal compound, Chromated Copper Arsenate, or CCA, has been widely used as a wood preservative. The metal ions in CCA, CrO��������, Cu�����, and AsO��������, have been found in contaminated surface and subsurface soils and groundwater nearby some wood preservative facilities and nearby wood structures. Iron oxides are a ubiquitous soil-coating constituent and are believed to be a main factor in controlling the transport and fate of many metals in the soil solution. In this research, iron-oxide-coated sand (IOCS) is used as a surrogate soil to investigate the adsorption and transport behavior of the mixed metals solution, copper, chromate, and arsenate, in the subsurface environment. Copper adsorption increases with increasing pH. The presence of arsenate in the solution slightly increases, while chromate has minimal effect, on the amount of copper adsorbed. Chromate adsorption decreases with increasing pH. With arsenate present in solution, chromate adsorption is significantly suppressed over the pH range studied. In contrast, the presence of copper slightly increases chromate adsorption. Similar to chromate, arsenate adsorption decreases with increasing pH. The presence of chromate or copper does not affect the amount of arsenate adsorbed over the range of concentrations studied. Two surface complexation models, the triple layer model (TLM) and the electrostatic implicit model (EIM), were used to simulate equilibrium adsorption in both single-metal and multi-metal systems. Simulations using the specific surface complexation equilibrium constants derived from either the single-metal or the multi-metal systems with both the TLM and the EIM were successful in fitting the adsorption data in that respective single or multi-metal system. The local equilibrium assumption using batch-derived sorption isotherm parameters from the EIM failed to predict the copper and arsenate transport, while it adequately described chromate transport. The breakthrough curves of all three metals were asymmetrical and showed long-tailing behavior. This nonideal behavior is caused by nonlinear sorption and/or non-equilibrium conditions during transport. The two-site chemical non-equilibrium model, which accounts for the kinetically controlled adsorption sites, was able to fit the observed breakthrough curves for all three metals in single-metal systems. However, the model was partially successful in predicting transport in multi-metal systems.
Graduation date: 2002

The eco-friendly alternatives use is increasing momentum in a conscious effort towards sustainability. In this regards, the relevance and the economic value of using copper slag as a concrete aggregate are explored in this study in order to contribute towards metallurgical waste recycling. Emphasis is placed on the evaluation of the concretes strengthening prepared with copper slag contents and produced under four curing methods: water immersion, water spraying, plastic sheet covering and air-drying. In each curing case excluding for water immersion, was duplicated in indoors (i.e. in the laboratory) and outdoor exposure (so was prone to varying environmental conditions). This was specifically aimed at capturing the effects of tropical weather conditions typical of the Lualaba province in the Democratic Republic of Congo. The control mix was designed to reach 25 MPa of compressive strength. Copper slag was successively incorporated as sand replacement at the following mass fractions: 20 %, 40 % and 60 %. Freshly mixed concrete samples were evaluated for workability. Cube specimens were cast accordingly, cured for 28 days and then tested for density and compressive strength. Results indicated an increase in strength up to 20 % of replacement rate for all the curing methods. Further additions resulted in reduction in the strength, but the rate of reduction depended on curing conditions. The increase in strength was mainly credited to the physical properties of copper slag that could have contributed to the cohesion of the concrete matrix. It has been found that appropriate ways of curing can still achieve greater results than that of the control mix since 80 % of humidity is ensure. The two-way ANOVA test performed on the 28-days compressive strength values confirmed the significant influence of the curing methods, of copper slag content and the interaction between them. It has been found that considerable influence is attributed to copper slag content and that warm environmental conditions further extend the concrete strengthening.
College of Engineering, Science and Technology
M. Tech. (Chemical Engineering)

The overall efficiency of plants to remediate soils contaminated by metals depends on their growth ability especially on soils with low-fertility. For twelve weeks, the ability of Psoralea pinnata to grow well and remove chromium and iron from artificially contaminated soil was tested. The concentrations of chromium and iron in two soils obtained from different sources namely, University of South Africa premises (US) and commercial potting soil (PS) were 80 ppm, 130ppm, 180ppm, 230ppm, 280ppm, 330ppm, 380pp, 430ppm and 480ppm. Psoralea pinnata was transplanted into the contaminated soils and the experiments were watered daily to maintain 70% moisture at field capacity in a greenhouse. Shoot height and root length of Psoralea pinnata before and after planting were measured. Other parameters that were measured were number of leaves, wet shoot and dry weights, and wet root and dry weights. The growth of Psoralea pinnata, after 12 weeks of experimentation was noticeably affected by the concentrations of chromium and iron in the soil. The percentage increases in shoot height of Psoralea pinnata in the PS Soil (C-PS, 48cm from initial shoot height of 12.6cm) treatments were generally higher than the increases in the US Soil (C-US, 45.2cm from initial shoot height of 12.8cm) treatments. Psoralea pinnata in the (US) treatments accumulated Fe (50.02 ppm) from the soil more than Cr (32.38ppm). In the (PS) treatments, Psoralea pinnata also accumulated more Fe (60.57 ppm) than Cr (38.34 ppm). In the experiments containing both Fe and Cr, the US treatments with 40 ppm each of Cr and Fe, chromium was initially mostly accumulated by Psoralea pinnata (68%). At higher concentrations (320 ppm) of the combined metals (Cr and Fe) treatment, more Fe (55%) was accumulated in Psoralea pinnata. This study however showed that Psoralea pinnata may not be an efficient phytoextraction plant for hyperaccumulation.
Environmental Sciences
M. Sc. (Environmental Management)

The aim of this study was to assess the strength, durability properties and corrosion resistance of concrete samples using supplementary cementitious blended materials. In this investigation, three supplementary concrete materials (SCMs) were used together with ordinary Portland Cement (OPC) to form cementitious blends at different proportions. The supplementary materials are silica fume (SF), ground granulated blast furnace slag (GGBS) and fly ash (FA). Sixteen (16) different proportions of the cementitious blends were produced. Tests carried out on concrete samples include slump test, compressive strength, oxygen permeability, sorptivity, porosity, chloride conductivity test, resistance to chloride and sulphate attack. The electrode potentials of tested samples were also observed using electrochemical measurements. Concrete specimens prepared with 10%, 20%, 30%, 40%, up to 60% of blended cements replacement levels were evaluated for their compressive strength at, 7, 14, 28, 90 and 120 days while the specimens were evaluated for durability tests at 28, and 90 days respectively. The results were compared with ordinary Portland cement concrete without blended cement. Voltage, and temperature measurements were also carried out to understand the quality of concrete. The corrosion performance of steel in reinforced concrete was studied and evaluated by electrochemical half-cell potential technique in both sodium chloride, and magnesium sulphate solutions respectively. The reinforced concrete specimens with centrally embedded 12mm steel bar were exposed to chloride and sulphate solutions with the 0.5 M NaCl and MgSO4 concentrations respectively. An impressed voltage technique was carried out to evaluate the corrosion resistance of the combination of quaternary cementitious blended cement, so as to get the combination with optimum performance. Improvement of strength, durability, and corrosion resistance properties of blended concrete samples are observed at different optimum percentages for binary, ternary and quaternary samples. The effect of cementitious blends is recognized in limiting the corrosion potential of the tested SCM concrete samples. Generally, the cementitious blends with limited quantity of SF to 10% have the potential to produce satisfactory concrete. These should however be used for low cost construction, where high quality concrete is not required.
Civil and Chemical Engineering
M. Tech. (Chemical Engineering)