Fertilized croplands unintentionally export large amounts of reactive nitrogen (N), which degrades water and air quality and contributes to climate change. In this dissertation, I focus on how these reactive N losses are likely to change in the near future as agriculture intensifies in the tropics, and ecological intensification strategies to mitigate N losses are more widely adopted. I use a combination of empirical field measurements in Mato Grosso, Brazil and Skåne, Sweden, literature review, and statistical models to quantify trends. In chapter one, I quantified emissions of nitric oxide (N₂O) and nitrous oxide (N₂O) in forest, single cropped soybean, and N-fertilized double-cropped soybean-maize at three nitrogen fertilizer levels within the largest area of recent cropland expansion on earth, in the Amazon and Cerrado biomes in Mato Grosso, Brazil. I found that NO emissions do not increase when forests are converted to croplands under current fertilization levels, and that NO will respond more strongly than N₂O fluxes to increases in fertilizer applications. In chapter two, I investigated anion exchange capacity and soil nitrate (NO₃¯) pools in deep soils in Mato Grosso, Brazil in the southern Amazon. I found that soil NO₃¯ pools in the top 8 m increased from 143 kg N ha¯¹ in forest to 1,052 and 1,161 kg N ha¯¹ in soybean and soybean-maize croplands. This NO₃¯ accumulation in croplands compared with forest soils matched the estimated amount of surplus N from the croplands, and could be explained by the soil’s positive charge through its anion exchange capacity. In chapter three, I conducted a meta-analysis of the effects of fertilization amount on of NO₃¯ leaching, N₂O emissions, NO emissions, and ammonia (NH₃) volatilization, totaling over 1,000 observations. I found that the relationship between N inputs and losses differed little between temperate and tropical croplands, although total NO losses were higher in the tropics. Among the potential drivers I studied, the N input rate controlled all N losses, but soil texture and water inputs also controlled NO₃¯ leaching losses. In chapter four, I explored the differences in NO₃¯ leaching, fertilizer N use efficiency, and soil N cycling in perennial wheat, which is being domesticated as a more sustainable alternative to annual crops, and annual wheat at a long-term experimental site in Skåne, Sweden. I found that NO₃ leaching was more than two orders of magnitude lower in perennial wheat, overall ecosystem recovery of fertilizer was quite high and not significantly different between perennial and annual wheat after the first growing season, and that measures of soil N cycling were largely the same between both crops. Together, these chapters highlight that reactive N losses will remain a critical global challenge in the coming decades, but that there are also key opportunities to reduce N losses by increasing the use of perennial crops and focusing tropical agricultural intensification on Oxisol soils which buffer against NO₃¯ leaching.

The chemical characterization of sediments accumulated in catch basins and stormwater ponds provides important information for assessing risks associated with management of these residuals upon removal of accumulated deposits in stormwater systems. In this study, over a period of 15 months, more than 150 residual samples were collected from 77 catch basin units and 22 stormwater ponds from 16 municipalities throughout the state of Florida. Concentrations (mg/kg) of metals and metalloids (arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, and zinc) and trace organics (volatile organics, semi-volatile organics, herbicides, and pesticides) in the sediments were measured. In addition, the synthetic precipitation leaching procedure (SPLP) was utilized to evaluate pollutant leachability risk for a subset of the samples collected. Measured pollutant concentrations were compared to corresponding risk-based guidelines in Florida (i.e., Florida soil cleanup target levels) to assess potential human health risks of beneficial use of these residuals through land application. Leached concentrations were compared to risk-based water quality guidelines (i.e., Florida groundwater cleanup target levels) to examine the potential for groundwater contamination. Although several metals (arsenic, barium, chromium, copper, nickel, lead, and zinc) were routinely detected in the catch basin and stormwater pond sediments, their concentrations were generally lower than the Florida's risk-based cleanup target levels for soils. A small number of organochlorine compounds (e.g., 4,4′-DDE, 4,4′-DDT) were detected, but only in a limited number of the samples (less than 10%); leaching of trace organic pollutants above the Florida risk-based groundwater thresholds was rare. The results suggest that when land-applied or beneficially used, these residuals are not expected to pose a significant threat to human health or the environment and the results of this research will provide stormwater managers and environmental management authorities with a useful resource to examine proper disposal and beneficial use of catch basin and stormwater pond sediments.

Disposal and beneficial-use options for street sweeping residuals collected as part of routine roadway maintenance activities in Florida, USA, were assessed by characterizing approximately 200 samples collected from 20 municipalities. Total concentrations (mg/kg or μg/kg) and leachable concentrations (mg/L or μg/L) of 11 metals and a number of organic pollutant groups (volatile organics, semi-volatile organics, pesticides, herbicides, carbamates) in the samples were measured. The synthetic precipitation leaching procedure (SPLP) was performed to evaluate the leachability of the pollutants. From the total metal analysis, several metals (e.g., arsenic, barium, chromium, copper, nickel, lead, and zinc) were commonly found above their detection limits. Zinc was found to have the highest mean concentration of all metals measured (46.7 mg/kg), followed by copper (10.7 mg/kg) and barium (10.5 mg/kg). The metal with the smallest mean concentration was arsenic (0.48 mg/kg). A small fraction of the total arsenic, barium, lead, and zinc leached in some samples using the SPLP; leached concentrations were relatively low. A few organic compounds (e.g., 4,4′-DDT, endrin, and endosulfan II) were detected in a limited number of samples. When the total and leaching results were compared to risk-based Florida soil cleanup target levels and groundwater cleanup target levels, the street sweepings were not found to pose a significant human-health risk via direct exposure or groundwater contamination.

Due to the growing population, waste generation and food supply industries need to move towards a circular economy and take advantage of by-products. Metallurgical slag is a main by-product during steel production which contains several valuable minerals and can be used for several further applications, including water purification and agriculture. This thesis has a focus on the issue(s) that need to be assessed to be able to determine the suitability of Petrit-E steel slag from Höganäs AB for agricultural use after it has been used for water purification. This slag by-product has been tested and it was successful to purify wastewater from phosphorus (P). The use as a fertilizer is most promising because it contains the major fertilizer substances and it contains P which is a limited resource. Calculations were done for the mean value and standard deviation of the substances for three years and after for Cr (chromium) and Ni (nickel) contents in Petrit-E because these two metals that are present in the slag and are regulated in the regulation for limit values. The total contents of Cr and  Ni were higher than the limit values so there are these two metals that need to be assessed further. Since Petrit-E is not a sludge and not a virgin material either, it requires other methods such as leaching tests by accredited laboratories. These tests are suitable for risk assessments and to estimate the amounts of metal availability for leaching. Leaching tests based on the site specific (local) chemical and physical processes and characteristics in the soil are necessary to estimate the suitability of Petrit-E.

Deck and coworkers previously showed that Me3Si substituents adjacent to group 4 metallocene dichlorides (M = Ti, Zr, Hf) are converted to corresponding BrMe2Si groups using BBr3, and that these BrMe2Si substituents are highly reactive to nucleophilic reagents such as water. The high reactivity of the Si-Br bonds suggested that these substituents could react with hydroxyl groups on the surface of partially dehydroxylated silica, forming covalently immobilized metallocene catalysts. This dissertation concerns the synthesis of electrophile-functionalized zirconocene dihalide complexes and the use of functionalized zirconocene dihalides as precursors to silica-supported metallocene olefin polymerization catalysts. Our first objective was to extend the metallocene "functionalization" chemistry to obtain substituents bearing more than one electrophilic bond. The reactivities of Me3Sn and Ph2MeSi substituents were explored in detail. (Me3Sn)2C5H4 combined with CpZrCl3 in toluene to afford (h5-Me3Sn-C5H4)CpZrCl2 (A). Reactions of A with electrophiles (E-X = Cl2B-Cl, I-Cl, and I-I) afforded (ï ¨5-XMe2Sn-C5H4)CpZrCl2 (and E-Me) cleanly. The reaction of A with BBr3 afforded either (ï ¨5-BrMe2Sn-C5H4)CpZrBr2 (25 ï °C, 10 min) or (ï ¨5-Br2MeSn-C5H4)CpZrBr2 (25 ï °C, 15 h). Ph2MeSi-C5H4Li combined with ZrCl4·2THF to afford (h5-Ph2MeSi-C5H4)2ZrCl2 (B). The reaction of B with BCl3 led to incomplete cleavage of the Ph-Si bonds, however treatment of B with BBr3 afforded (h5-Br2MeSi-C5H4)2ZrBr2 (C) efficiently. The Sn-X bonds of the stannylated metallocenes were however relatively unreactive toward water and were excluded as candidates precursors for supported metallocene catalysts. X-ray crystal structures of (h5-ClMe2Sn-C5H4)CpZrCl2·½toluene, (h5-Br2MeSn-C5H4)CpZrBr2·THF, B, and C were obtained. The functionalized metallocene C reacts with water to afford an oligosiloxane-supported zirconocene dibromide. Combinations of solution 1H NMR, solid state CPMAS 13C NMR, and solid state CPMAS 29Si NMR spectroscopy suggested a stereoregular structure in which the metallocene units have local Cs (meso) symmetry. Although only sparingly soluble, the oligomeric substance showed activity for homogeneous ethylene polymerization (toluene solution, MAO cocatalyst, Al:Zr = 5000, 50 ï °C) similar to Cp2ZrCl2. Supported metallocene olefin polymerization catalysts were prepared by combining a functionalized metallocene precursor (Cp2ZrBr2 bearing either BrMe2Si or Br2MeSi groups) and partially dehydroxylated silica. Ethylene polymerization activity of the resulting catalysts was examined as a function of the precursor structure (number of reactive "tethering" groups, one vs. two Si-Br bonds per tethering group) and the immobilization conditions (time, temperature, presence or absence of NEt3 promoter). The activities of the immobilized zirconocene catalysts decreased and the stabilities increased with increasing number of tethers. The immobilized catalyst prepared from (ï ¨5-Br2MeSi-C5H4)2ZrBr2, which is assumed to form two "double-tethers" to silica, was significantly more active than the catalyst prepared from [ï ¨5-1,3-(BrMe2Si)2C5H3]2ZrBr2, which is assumed to form four "single-tethers" to silica. Catalyst leaching was observed in all the immobilized zirconocene catalysts. The use of NEt3 in the immobilization reaction enabled more metallocene to be supported, but the resulting activity was lower. The dissertation also includes model studies on the immobilization reaction and the stability of the Si-O-Si bonds. The reaction of C with tBuMe2SiOH results in the formation of Si-O-Si bonds; addition of NEt3 results in further reaction to afford Si-O-Zr bonds. The reaction of Reaction of Me3Si-O-SiMe3 with MAO showed that Si-O-Si bonds can be cleaved under the conditions of our polymerization reactions. / Ph. D.

A low-cost titanium production process, the CSIR-Ti powder process, which aims to produce titanium powder directly by metallothermic reduction of titanium tetrachloride with lithium, has been under development at the Council for Industrial and Scientific Research (CSIR). Crude titanium powder produced using the CSIR-Ti process is inevitably contaminated with by-products such as lithium chloride, lithium and titanium dichloride. These by-products tend to become sources of impurities in titanium powder, specifically oxygen and chloride impurities. The presence of oxygen and chloride impurities has marked effects on the mechanical properties of titanium finished products. Consequently, for the crude titanium powder to be rendered useful downstream, it must be purified and the by-products reduced to concentrations specified in the commercial standards. The present study was undertaken to examine whether acid leaching could be used to selectively dissolve and prevent hydrolysis of the by-products—specifically excess lithium and unreacted titanium dichloride in the crude titanium powder produced by the CSIR-Ti process. A further objective was to determine whether a purified product that meets both oxygen and total residual chloride content as specified by the standards can be achieved. The effects of key leaching variables and their interaction were also investigated to gain fundamental understanding of these effects on the by-products leaching behaviour. A literature study to select a suitable lixiviant and to establish the aqueous chemistry of the byproducts and their effect on the leaching conditions was undertaken. It showed that of the various acids suggested in the literature, hydrochloric acid was the cheapest and that it was more suited for the CSIR-Ti leaching process than nitric acid, due to the common ion chloride. This simplifies the leachate purification process downstream. The literature study established that Ti(II) has no aqueous chemistry but instead is oxidised to Ti(III) in solution. It was found that Ti(III) is easily oxidised to TiO2+ by dissolved oxygen and water. However, the oxidation rate was slow in hydrochloric acid solutions with the advantage that hydrolysis of the ions could be minimised and the precipitation of the oxides or oxychlorides prevented. It was further revealed that the lithium neutralisation reaction is highly exothermic, with the possibility of raising the leachate temperature to 60°C, resulting in the contamination of the titanium powder particles by the oxide layer and precipitated hydrolysis products. Batch leaching tests were carried out using factorial design of experiments to investigate the effect of initial hydrochloric acid concentration, which was estimated by varying the concentration between 0.032 M and 1 M; particle size, which was varied between −10 mm and +10 mm; and the initial temperature, varied between 14°C and 30°C. The resulting data were modelled and analysed using the analysis of variance statistical method. The solid residues were analysed for oxygen and total residual chloride content. The solid residue was also characterised by scanning electron microscopy (SEM) to examine the morphology of the leached particles. Leaching kinetics model fitting was also conducted. The statistical analysis showed that of the three factors investigated, temperature was the factor with the most statistical significance on both the oxygen and chloride concentration in the purified product, followed by particle size. The effect of acid concentration proved to be minimal, a phenomenon attributed to low concentrations of acid-consuming impurities, specifically excess lithium in the crude product. Thus, the two concentrations of hydrochloric acid investigated were found to be efficient to prevent hydrolysis product formation. Scanning electron micrographs revealed that crushing the crude product with a jaw crusher occluded crude titanium pores, thus locking in some by-products in addition to the pores locked by sintering during the metallothermic reduction. The observation showed that residual chloride impurities in the purified product are not just a consequence of hydrolysis products but also byproducts locked deeper in the pores of the product. Based on the parameter ranges evaluated in the study, a product that satisfied both oxygen and chloride standard specifications was achieved when the crude product was leached in both 1 M and 0.032 M initial HCl concentrations, temperature of 30°C and particle size of +10 mm. The combination of (−10 mm and 14°C) at all concentrations also yielded acceptable oxygen and chloride content levels. Overall, it was concluded from the present work that purification of crude CSIR-Ti product by leaching in dilute HCl is technically feasible. / Dissertation (MSc Applied Sciences (Metallurgy))--University of Pretoria, 2014. / Materials Science and Metallurgical Engineering / MSc (Applied Sciences (Metallurgy)) / Unrestricted

The Council for Scientific and Industrial Research (CSIR) in South Africa is developing a process to produce titanium tetrachloride from a low-grade material such as ilmenite. Titanium tetrachloride can then be used as feed material for titanium metal or pigment-grade titanium dioxide production. Titanium tetrachloride is commercially produced by chlorinating synthetic rutile (<92% TiO2) or titanium dioxide slag (<85% TiO2) at ~900 ˚C. A drawback of chlorination at this temperature is that any constituents other than TiO2 will end up as hazardous waste material. A characteristic step in the CSIR’s proposed process is to nitride titanium dioxide contained in the feed material before it is sent for chlorination. The chlorination of the resulting titanium nitride is achieved at a much lower temperature (~200 ˚C) than that of the existing titanium dioxide chlorination reaction. An added advantage of the low-temperature chlorination reaction is that chlorine is selective mostly towards titanium nitride and metallic iron, which means that any other constituents present are not likely to react with the chlorine. The result is reduced chlorine consumption and less hazardous waste produced. The nitrided ilmenite must, however, be upgraded by removing all iron before it can be sent for chlorination. Commercial ilmenite upgrading processes, called synthetic rutile production, also require the removal of iron and other transition metals before chlorination. A literature review of existing ilmenite upgrading processes revealed four possible process options that could remove iron from nitrided ilmenite. Two of these process options, the Becher and Austpac ERMS SR processes, are proven process routes. The other two are novel ideas – one to passivate iron contained in the nitrided ilmenite against chlorination and the other to use ammonium chloride (as used in the Becher process) as a stoichiometric reactant to produce a ferrous chloride solution. A preliminary experimental evaluation of these process options indicated that the Austpac ERMS SR process is the most viable option for removing iron from nitrided ilmenite. The Austpac ERMS SR process was therefore selected as a template for further process development. A detailed Austpac ERMS SR process review found that two process units in the Austpac ERMS SR process could be used in a process that separates iron from nitrided ilmenite. These are the Enhanced Acid Regeneration System and the Direct Reduced Iron process units. The review also concluded that another leach unit would have to be developed. It was therefore necessary to further investigate the dissolution of nitrided ilmenite in hydrochloric acid. A detailed experimental evaluation of nitrided ilmenite dissolution in hydrochloric acid found that hydrochloric acid could be used as the lixiviant to selectively remove iron from nitrided ilmenite. The dissolution of metallic iron in 90 ˚C hydrochloric acid reached levels of at least 96% after only 60 minutes. An average “combined resistance” rate law was found that could be used to describe this dissolution reaction. The observed activation energy and Arrhenius pre-exponential factor were found to be equal to 9.45 kJ.mol-1 and 30.8 s-1 respectively. The Austpac ERMS SR process review and experimental results described above were then combined and used to propose a process that could be employed to remove iron from nitrided ilmenite. The proposed process was modelled using the Flowsheet Simulation module in HSC Chemistry 7.0 / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2010. / Chemical Engineering / MEng (Chemical Engineering) / unrestricted

Acid Sulfate soils (AS) are recognized for being a source of acidity in freshwaters in America, Europe, Australia, and Asia. Apart from the problematic acid leachate, AS soil serves as a possible source of toxic heavy metals in freshwaters, a problem which has received far less attention than problems related to acid leachate. This study assessed to what extent heavy metals enriched in sediments from the area around lake Persöfjärden (North-eastern Sweden) could be attributed to export from AS soils. I found that: i) Nickel (Ni), Zink (Zn), Copper (Cu) and Iron (Fe) in the sediments had a partial likely origin from AS soils; ii) vertical variations in Ni, Zn, Cu and Fe concentrations suggested events of increased metal transport in the past; and iii) there is a tendency that Zn and Ni assumed from AS soils have caused elevated metal concentration in marine sediment deposited in Persöfjärden. Inferred sediment rates suggest that elevated metal concentrations occurred in sediment deposited during the 18-19th and 20th century. I argue that these periods correspond to periods of increased drainage of the AS soils during past agricultural activities in the catchment.

The economic impact of reducing the amount of nitrate leached out of the root zone under irrigation in the arid West was examined. A general introduction into the nature of the problem and a review of the literature was provided in chapter I. In chapter ll the economic incentives of irrigation management were evaluated under the assumptions of both profit-maximizing and utility-maximizing (in reducing cost and effort expended in irrigation) decision-making criteria. The results indicate that there is a coincidence of interests of the farmer and the environment. Both behaviors result in less nitrate leaching than less profitable or less utilityproducing irrigating practices. In chapter lli the economic impact of reducing the amount of nitrate leached out of the root zone under irrigation with various nitrogen sources and application methods was examined. The economic incentives of nitrogen management were evaluated under the assumption of profit-maximizing behavior. The results indicate that there is a coincidence of interests for irrigators who respond to economic incentives and environmentalists who wish to reduce nitrate residuals in irrigation drainage and the groundwater. Profit-maximizing behavior results in less nitrate leaching than less profitable irrigating practices when salt balance is not a major concern.

A 2 x 3 x 2 factorial arranged split plot experiment was used to determine the decrease of dry matter yield from field-dried alfalfa hay caused by the application of a measured quantity of artificial rain (sprinkling irrigation). The three hay treatment factors were (1) alfalfa hay was cut at late vegetative and early bloom stage of maturity and (2) leached by 0, 5 mm or 20 mm of artificial rain applied by sprinkling and (3) sprinkled in the swath, 24 or 48 hours after cutting. Changes in dry matter yield were not significantly (P<.05) related to stage of maturity of forage, level of artificial rain applied or the time of application of artificial rain. There were no significant interactions for dry matter yield. The non-significant interactions for dry matter yield. The non-significant results were probably due to the variability of the alfalfa stand among the specific areas harvested for each treatment and insufficient replications to control the variability. Forty-eight lambs were fed for 56 days on the twelve experimental hays with four lambs (replications) per treatment. The 56 day feeding period was split into four 14-day pen-type feeding periods. (1, paired feeding in pen; 2, individual feeding in pen; 3, individual feeding in cage; and 4, paired feeding in pen.) There was no significant response of the lamb to alfalfa hay quality (feed intake, weight gain or feed efficiency). Lambs increased feed intake when fed individually compared to pair feeding. The result was increased weight gain and feed efficiency of individually fed lambs. This was particularly evident during period two. There was a significant (P<.05) increase of feed intake associated with advancing maturity of forage during the individual pen feeding period. Feed intake was higher during the second paired pen feeding period relative to the first paired pen feeding, but lower than the single pen feeding. Lambs consumed the rain damaged hay as well as or better than the control hay when fed individually. The also gained faster with the greater feed intake. These results show that sheep will utilize rain leached hay efficiently if it is not heat damaged. The complication of heat damage needs additional study.