The performance of flocculants used in the solid-liquid separation of red mud is often compromised by the methods used to mix the fast acting polymers into the slurry. A simple model of the relationship between flocculant performance and intensity of mixing is proposed and a device for mixing flocculant and slurry has been developed on the basis of the model.The intensity of mixing at the point of distributing the flocculant into the slurry is arguably the most important variable influencing the final flocculant performance. This relationship is established using data from flocculation tests in an agitated tank. The flocculant performance is monitored using an optical sensor and the settling rate of the solid-liquid interface is used as a comparison for the optical sensor. The difficulties, errors and merits of the optical sensor to study the flocculation of red mud and automatic control of flocculation processes are also assessed.The mixing device is connected to a pipe for flocculation tests with red mud. For the tests carried out, a high level of flocculation was recorded.The mixing device combines the flocculant and slurry as thin annular jets directed into one another. The opening for the slurry jet can be altered to provide a variation of the mixing that is achieved. The capability of the device to mix rapidly has been assessed using the diazo coupling reactions between l-naphthol and diazotised sulphanilic acid in alkaline, aqueous solution at room temperature. Variables studied included flow rate and slurry jet opening. Better mixing was indicated at higher flow rates and at reduced jet opening. The use of the diazo coupling reactions for studying micromixing is also assessed.

For the majority of tailings substrates, flocculant adsorption proceeds through hydrogen bonding of the amide functionalities with neutral surfaces. However, flocculation of Bayer process residue solids takes place in highly caustic liquors, typically using high molecular weight polyacrylates. This represents an almost unique situation, and implies a totally different adsorption mechanism. Direct examination of polyacrylate adsorption within the complex matrix of real liquors and a mixture of residue phases is difficult, making it necessary to focus on a model substrate (hematite) and synthetic liquors (pH 13 at high ionic strength). Previous spectral studies have used ex situ techniques, with sample drying potentially altering the adsorbed species, leading to inconclusive results. This study presents for the first time direct in situ evidence of polyacrylate adsorption onto hematite obtained by Fourier Transform Infrared-Attenuated Total Reflection (FTIR-ATR) Spectroscopy. Adsorption and hence concentration of dilute polyacrylate solutions onto hematite-coated zinc selenide optics has provided spectra of adsorbed polymer under a range of conditions, unbiased by any contribution from the bulk polymer solution. Analysis of the polyacrylate carbon-oxygen stretching frequencies established differing modes of adsorption at low and high pH conditions. At pH 2 adsorption proceeded through bidentate chelation of the carboxylate to a surface ferric ion, facilitated through deprotonation of a carboxylic acid group and removal of a hematite surface hydroxyl group, i.e. chemisorption. Unshifted carboxyl peaks in the spectrum enabled the unadsorbed 'loops' and 'tails' to be distinguished from the adsorbed polymer, and represented at least 70% of the total polymer chain length. / In contrast, at pH 13 adsorption of polyacrylate occurs via physisorption and was only possible with the addition of electrolyte. This adsorption was enhanced with increasing electrolyte concentrations up to 1 M NaCl. The hematite surface charge was negative at high pH, however with increasing ionic strength the specific adsorption of Na+ ions decreased the negative surface charge, and at very high salt concentrations the surface became positively charged. For electrolyte with different monovalent cations, polymer adsorption increased in the order Li+ > Na+ > Cs+. The identity of the monovalent cation had no effect on the polymer solution dimensions but the ability to reduce the magnitude of the hematite surface charge followed the same trend. This finding is consistent with the 'structure making - structure breaking' model proposed by Berube and de Bruyn. At both high and low pH, polyacrylate exhibited adsorption isotherms that are best described by the Langmuir expression. Surface coverage was greatest at low pH due to more available surface sites and the adsorbed polymer conformation (a greater fraction of loops and tails). Adsorbed conformation and hence maximum adsorption was independent of molecular weight at low pH, however at high pH maximum adsorption increased with increased molecular weight, indicating an adsorbed polymer configuration exhibiting a greater degree of loops and tails. While the individual carboxylate-surface interaction was stronger at low pH than high pH, both were relatively weak. Despite this, none of the polymers could be removed by washing, demonstrating the strength and irreversibility of the multi-attached polymer molecules. / The stronger individual carboxylate-surface interactions at low pH is indicative of a higher activation energy of formation, and may be a contributing factor to the slower rate of adsorption at low pH. The rate of polyacrylate adsorption was dominated by mass transport limitations in all cases. The initial rate of adsorption was greater at lower polymer molecular weight, consistent with the relative polymer diffusion coefficients. This rate of adsorption was much less dependent on polymer molecular weight at high pH than at low pH, suggesting significantly different polymer-solvent interactions. It was clearly demonstrated that the sodium ion concentration within the high ionic strength Bayer liquors is more than sufficient to facilitate polyacrylate adsorption on bauxite residue. There is no need to postulate calcium bridging between the polymer and surface, as has been suggested in previous studies. Improved settling and clarity associated with the presence of calcium on residue surfaces is more likely due to enhanced particle coagulation prior to flocculation. FTIR-ATR has been shown to be an excellent tool for the in situ examination of polyacrylate adsorption onto hematite, and will be a powerful technique for the characterisation and subsequent comparison of the adsorption behaviour of other systems.

The effect of pH, temperature, and ionic strength on the molecular conformation of five industrial polyacrylamide-based flocculants was investigated by determining intrinsic viscosities on dilute flocculant solutions. The Fedors equation was found to be most suitable for all flocculants for determining the intrinsic viscosity. The results indicated that the flocculants are fully extended in distilled water at natural pH and at 25°C as evidenced by the high intrinsic viscosities. The data pointed to the strong dependence of the intrinsic viscosity on the presence of salts as a result of the shielding of negatively charged carboxylate groups by the counterions. At a constant ionic strength of 0.01M NaCl, the flocculants assumed a coiled conformation, and further coiling was observed in the presence of small quantities of calcium chloride. CaC1₂ (0.001 mo1/L) There was a decrease in intrinsic viscosities at high pH (~8.5 and 10.5) that was merely attributed to an increase in ionic strength with the increase in concentration of Na⁺ at high pH. Intrinsic viscosity measurements at higher temperatures (35°C and 50°C) showed a small effect of temperature on the conformation of the flocculants. Higher temperature, however, seemed to accelerate the aging of the flocculant solutions. The degrees of anionicity of the flocculants were found to be in the range 1.5% to 50%, as determined through chemical analysis. It was established that determination of total organic carbon content and sodium assays is an accurate way of obtaining the degrees of anionicity of industrial flocculants. The solution stability of the flocculants in distilled water and in 0.01M NaCl was investigated over a period of three days. The reduced viscosities of the anionic flocculant in distilled water steadily decreased. The decrease was more dramatic at high temperature (50°C) than at room temperature, but no viscosity loss was observed in the presence of NaCl. The viscosity of the nonionic flocculant was stable in both distilled water and NaCl. The viscosity loss with time in the case of the anionic flocculant can be correlated with the hydrolysis of the weakly acidic carboxylate (C00⁻) groups to release OH⁻ ions and simultaneous association into uncharged carboxylic (C00H) groups that promote coiling of polyacrylamide. This effect is therefore very similar to the earlier-mentioned effect of sodium chloride.

The effect of pH, temperature, and ionic strength on the molecular conformation of five industrial polyacrylamide-based flocculants was investigated by determining intrinsic viscosities on dilute flocculant solutions. The Fedors equation was found to be most suitable for all flocculants for determining the intrinsic viscosity. The results indicated that the flocculants are fully extended in distilled water at natural pH and at 25°C as evidenced by the high intrinsic viscosities. The data pointed to the strong dependence of the intrinsic viscosity on the presence of salts as a result of the shielding of negatively charged carboxylate groups by the counterions. At a constant ionic strength of 0.01M NaCl, the flocculants assumed a coiled conformation, and further coiling was observed in the presence of small quantities of calcium chloride. CaC1₂ (0.001 mo1/L) There was a decrease in intrinsic viscosities at high pH (~8.5 and 10.5) that was merely attributed to an increase in ionic strength with the increase in concentration of Na⁺ at high pH. Intrinsic viscosity measurements at higher temperatures (35°C and 50°C) showed a small effect of temperature on the conformation of the flocculants. Higher temperature, however, seemed to accelerate the aging of the flocculant solutions. The degrees of anionicity of the flocculants were found to be in the range 1.5% to 50%, as determined through chemical analysis. It was established that determination of total organic carbon content and sodium assays is an accurate way of obtaining the degrees of anionicity of industrial flocculants. The solution stability of the flocculants in distilled water and in 0.01M NaCl was investigated over a period of three days. The reduced viscosities of the anionic flocculant in distilled water steadily decreased. The decrease was more dramatic at high temperature (50°C) than at room temperature, but no viscosity loss was observed in the presence of NaCl. The viscosity of the nonionic flocculant was stable in both distilled water and NaCl. The viscosity loss with time in the case of the anionic flocculant can be correlated with the hydrolysis of the weakly acidic carboxylate (C00⁻) groups to release OH⁻ ions and simultaneous association into uncharged carboxylic (C00H) groups that promote coiling of polyacrylamide. This effect is therefore very similar to the earlier-mentioned effect of sodium chloride.

The effect of pH, temperature, and ionic strength on the molecular conformation of five industrial polyacrylamide-based flocculants was investigated by determining intrinsic viscosities on dilute flocculant solutions. The Fedors equation was found to be most suitable for all flocculants for determining the intrinsic viscosity. The results indicated that the flocculants are fully extended in distilled water at natural pH and at 25°C as evidenced by the high intrinsic viscosities. The data pointed to the strong dependence of the intrinsic viscosity on the presence of salts as a result of the shielding of negatively charged carboxylate groups by the counterions. At a constant ionic strength of 0.01M NaCl, the flocculants assumed a coiled conformation, and further coiling was observed in the presence of small quantities of calcium chloride. CaC1₂ (0.001 mo1/L) There was a decrease in intrinsic viscosities at high pH (~8.5 and 10.5) that was merely attributed to an increase in ionic strength with the increase in concentration of Na⁺ at high pH. Intrinsic viscosity measurements at higher temperatures (35°C and 50°C) showed a small effect of temperature on the conformation of the flocculants. Higher temperature, however, seemed to accelerate the aging of the flocculant solutions. The degrees of anionicity of the flocculants were found to be in the range 1.5% to 50%, as determined through chemical analysis. It was established that determination of total organic carbon content and sodium assays is an accurate way of obtaining the degrees of anionicity of industrial flocculants. The solution stability of the flocculants in distilled water and in 0.01M NaCl was investigated over a period of three days. The reduced viscosities of the anionic flocculant in distilled water steadily decreased. The decrease was more dramatic at high temperature (50°C) than at room temperature, but no viscosity loss was observed in the presence of NaCl. The viscosity of the nonionic flocculant was stable in both distilled water and NaCl. The viscosity loss with time in the case of the anionic flocculant can be correlated with the hydrolysis of the weakly acidic carboxylate (C00⁻) groups to release OH⁻ ions and simultaneous association into uncharged carboxylic (C00H) groups that promote coiling of polyacrylamide. This effect is therefore very similar to the earlier-mentioned effect of sodium chloride. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

In this thesis, the effectiveness of microparticle retention aid systems comprising of different cationic starches (tapioca and waxy maize), cationic flocculants (flocculant 1, linear with low charge density and flocculant 2, branched with medium charge density polyacrylamides) and anionic colloidal silica in improving retention and drainage of thermomechanical pulp (TMP) suspensions loaded with precipitated calcium carbonate (PCC) is studied. While starch is primarily added as dry strength agent in PCC-filled TMP suspensions, it also has a significant role in improving retention and drainage. Tapioca starch, which has both amylose and amylopectin, is found to be a better retention and drainage aid than waxy maize starch, which only contains amylopectin. In the absence of starch, both flocculants are ineffective in improving retention and drainage. With starch, both flocculant and silica are significant in enhancing retention and drainage further. Increasing the dosage of either flocculant or silica generally increases retention as well as drainage. Flocculant 2 is found to give slightly worse total and filler retention but better drainage compared to flocculant 1. The dosage of flocculant 2 is only half that of flocculant 1 though – for this reason overall flocculant 2 is deemed more effective in improving retention and drainage than flocculant 1. Split starch addition, where a portion of the starch is premixed with PCC and the rest added to the pulp, causes a slight decrease in both retention and drainage. Therefore, should the papermaker decide to use this approach, the starch should be split in a 25:75 ratio between PCC and the pulp to minimize the negative effects. Due to the cost benefits of using increased amounts of PCC, it is desirable to increase PCC content beyond the standard currently used (250 kg/t OD pulp for communications-grade paper). However, at very high dosages of PCC (500 kg/t OD pulp), the best combination identified in this work (tapioca starch, flocculant 2 and silica) is unable to maintain good retention and drainage. Increasing retention aid dosages may help retain more PCC, however this tactic can rapidly become uneconomical. A new approach is thus needed to achieve such highly-filled papers.

In this thesis, the effectiveness of microparticle retention aid systems comprising of different cationic starches (tapioca and waxy maize), cationic flocculants (flocculant 1, linear with low charge density and flocculant 2, branched with medium charge density polyacrylamides) and anionic colloidal silica in improving retention and drainage of thermomechanical pulp (TMP) suspensions loaded with precipitated calcium carbonate (PCC) is studied. While starch is primarily added as dry strength agent in PCC-filled TMP suspensions, it also has a significant role in improving retention and drainage. Tapioca starch, which has both amylose and amylopectin, is found to be a better retention and drainage aid than waxy maize starch, which only contains amylopectin. In the absence of starch, both flocculants are ineffective in improving retention and drainage. With starch, both flocculant and silica are significant in enhancing retention and drainage further. Increasing the dosage of either flocculant or silica generally increases retention as well as drainage. Flocculant 2 is found to give slightly worse total and filler retention but better drainage compared to flocculant 1. The dosage of flocculant 2 is only half that of flocculant 1 though – for this reason overall flocculant 2 is deemed more effective in improving retention and drainage than flocculant 1. Split starch addition, where a portion of the starch is premixed with PCC and the rest added to the pulp, causes a slight decrease in both retention and drainage. Therefore, should the papermaker decide to use this approach, the starch should be split in a 25:75 ratio between PCC and the pulp to minimize the negative effects. Due to the cost benefits of using increased amounts of PCC, it is desirable to increase PCC content beyond the standard currently used (250 kg/t OD pulp for communications-grade paper). However, at very high dosages of PCC (500 kg/t OD pulp), the best combination identified in this work (tapioca starch, flocculant 2 and silica) is unable to maintain good retention and drainage. Increasing retention aid dosages may help retain more PCC, however this tactic can rapidly become uneconomical. A new approach is thus needed to achieve such highly-filled papers.

In this thesis, the effectiveness of microparticle retention aid systems comprising of different cationic starches (tapioca and waxy maize), cationic flocculants (flocculant 1, linear with low charge density and flocculant 2, branched with medium charge density polyacrylamides) and anionic colloidal silica in improving retention and drainage of thermomechanical pulp (TMP) suspensions loaded with precipitated calcium carbonate (PCC) is studied. While starch is primarily added as dry strength agent in PCC-filled TMP suspensions, it also has a significant role in improving retention and drainage. Tapioca starch, which has both amylose and amylopectin, is found to be a better retention and drainage aid than waxy maize starch, which only contains amylopectin. In the absence of starch, both flocculants are ineffective in improving retention and drainage. With starch, both flocculant and silica are significant in enhancing retention and drainage further. Increasing the dosage of either flocculant or silica generally increases retention as well as drainage. Flocculant 2 is found to give slightly worse total and filler retention but better drainage compared to flocculant 1. The dosage of flocculant 2 is only half that of flocculant 1 though – for this reason overall flocculant 2 is deemed more effective in improving retention and drainage than flocculant 1. Split starch addition, where a portion of the starch is premixed with PCC and the rest added to the pulp, causes a slight decrease in both retention and drainage. Therefore, should the papermaker decide to use this approach, the starch should be split in a 25:75 ratio between PCC and the pulp to minimize the negative effects. Due to the cost benefits of using increased amounts of PCC, it is desirable to increase PCC content beyond the standard currently used (250 kg/t OD pulp for communications-grade paper). However, at very high dosages of PCC (500 kg/t OD pulp), the best combination identified in this work (tapioca starch, flocculant 2 and silica) is unable to maintain good retention and drainage. Increasing retention aid dosages may help retain more PCC, however this tactic can rapidly become uneconomical. A new approach is thus needed to achieve such highly-filled papers. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Neste trabalho, um polímero eletrólito derivado de goma de cajueiro graftizada com poliacrilamida (GC-g-PAM) foi desenvolvido para uso como floculante no tratamento de águas. Foi investigado o efeito da concentração de acrilamida e do iniciador persulfato de potássio, da energia de micro-ondas e de ultrassom sobre a eficiência da reação, produtividade e viscosidade intrínseca dos copolímeros GC-g-PAM. As matérias-primas e os copolímeros graftizados foram caracterizados por espectroscopia de infravermelho, ressonância magnética nuclear, análise termogravimétrica, calorimetria exploratória diferencial e espalhamento de luz dinâmico. A síntese realizada por ultrassom permitiu a obtenção de copolímeros graftizados com elevada eficiência de grafting e viscosidade intrínseca, em curto período de tempo. Os copolímeros obtidos com baixa concentração de iniciador (1,90×10−4 mol e 2,85×10−4 mol) apresentaram raio hidrodinâmico 1,5 vezes maior do que o raio da goma de cajueiro devido à graftização de cadeias longas de poliacrilamida nas cadeias da goma de cajueiro. A estrutura química dos copolímeros graftizados afetou positivamente o desempenho destes quando utilizados como floculante no processo de floculação. Os copolímeros GC-g-PAM apresentaram eficiência superior a 90% na remoção da turbidez de suspensão aquosa de caulim, usada como referência, bem como em água de abastecimento in natura. A grande vantagem dos floculantes GC-g-PAM reside no fato destes apresentarem cadeia macromolecular biodegradável e cadeias laterais menores do que a cadeia principal da poliacrilamida comercial, não biodegradável, utilizada como floculante. O uso do floculante derivado da goma de cajueiro para recuperação e purificação de águas, em detrimento do floculante sintético, visa a longo prazo diminuir o impacto ambiental causado pelo acúmulo de floculante sintético no lodo, já que esse não é biodegradável. / In this work a polymer electrolyte derived from cashew gum with polyacrylamide (GC-g-PAM) was developed for use as a flocculant in water treatment. The effect of concentration of acrylamide and potassium persulfate initiator, as well as microwave and ultrasound energy over the grafting efficiency, productivity, and intrinsic viscosity of copolymers GC-g-PAM were investigated. The raw materials and grafted copolymers were characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and dynamic light scattering. The synthesis performed with ultrasound allowed the achievement of grafted copolymer with high grafting efficiency and intrinsic viscosity, in a short reaction time. The copolymers obtained at low initiator concentration (1.90×10−4 mol and 2.85×10−4 mol) presented a hydrodynamic radius 1.5 times larger than the one from cashew gum due to grafting of long chains of polyacrylamide onto cashew gum backbone. The chemical structure of grafted copolymers affected positively the performance of flocculants when they were used in flocculation processes. The turbidity removal of copolymer GC-g-PAM in kaolin suspension, used as reference, and in water treatment was higher than 90%. The great advantage of flocculants GC-g-PAM lies in the fact that they show biodegradable macromolecular chain with branches that are shorter than polyacrylamide commercial, non-biodegradable, used as a flocculant. The use of flocculant derived from cashew gum for water purification and recovery, instead of synthetic flocculant, in long term will decrease the environmental impact caused by the accumulation of synthetic flocculant in the sludge, since it is non-biodegradable.

The use of natural environmentally benign agents in the treatment of drinking water is rapidly gaining interest due to their inherently renewable character and low toxicity. We show that the common Mexican cactus produces a gum-like substance, cactus mucilage, which shows excellent flocculating abilities and is an economically viable alternative for low-income communities. Cactus mucilage is a neutral mixture of approximately 55 high-molecular weight sugar residues composed basically of arabinose, galactose, rhamnose, xylose, and galacturonic acid. We show how this natural product was characterized for its use as a flocculating agent. Our results show the mucilage efficiency for reducing arsenic and particulates from drinking water as determined by light scattering, Atomic Absorption and Hydride Generation-Atomic Fluorescence Spectroscopy. Flocculation studies proved the mucilage to be a much faster flocculating agent when compared to Al2(SO4)3 with the efficiency increasing with mucilage concentration. Jar tests revealed that lower concentrations of mucilage provided the optimal effectiveness for supernatant clarity, an important factor in determining the potability of water. Initial filter results with the mucilage embedded in a silica matrix prove the feasibility of applying this technology as a method for heavy metal removal. This project provides fundamental, quantitative insights into the necessary and minimum requirements for natural flocculating agents that are innovative, environmentally benign, and cost-effective.