Flocculation is an important part of the carbon cycle. It is therefore crucial to understand how flocculation is regulated and how different environmental factors impact. A dilemma is that it has been found difficult to measure flocculation experimentally. In this thesis, flocculation of dissolved organic carbon in a Swedish lake was measured in a series of laboratory experiments. The method used was Dynamic Light Scattering (DLS). DLS is used to determine the size distribution profile of, for instance, small particles in suspension. DLS measures Brownian motion and relates it to the particle size by measuring the fluctuation in scattering intensity. It is not very effective to measure the frequency spectrum contained in the intensity fluctuations directly, so instead, a digital auto correlator is used. Since factors such as pH, salinity and calcium chloride content varies in lakes and is thought to have an impact on flocculation, this was investigated as well. As pH was changed in a range of 3 to 9, small changes in size distribution could be detected. Salinity and calcium chloride content have quite an impact on flocculation. Time also has a great impact, samples that were set to rest for a week showed a significant increase in particle size. For DLS to work, the samples need to be filtered of centrifuged to get rid of large particles. Different types of filters were tested to see which filter material was the best to use. When filtering the water we only want to filter out the large particles. Natural organic matter has a hydrophobic component which adsorbs to some filter types but not to others. It is crucial to know which filters this hydrophobic component adsorbs to, so that the loss of dissolved organic carbon during filtration can be minimalized.

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Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xii, 138 p. : ill. Includes abstract. Includes bibliographical references (p. 111-118).

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Iron oxide is a crucial hydrophilic mineral in the minerals, metals and materials industries. Colloidal iron oxide dispersions have proven difficult to dewater to high solid-loading during routine hydometallurgical processes. Despite this, there are a limited number of studies integrating interfacial chemistry, flocculation and dewatering behaviour of iron oxide in the literature. / In this study, fundamental investigations of the principles underpinning hematite pulp dewatering behaviour were examined to determine the effectiveness of four polyacrylamide ploymers (home-polymer, PAM N, anionic carboxylate substituted copolymer, PAM A, anionic sulphonate substituted copolymer, PAM S, and cationic trimethyl amino ethyl substituted copolymer, PAM C) as flocculants and four metal salts, Mn(NO), MnSO, and MnC1and KSO) as coagulants. Effects of flocculant structure type and concentration, metal salt type and pH on the surface chemistry, pulp rheology and the dewaterability of dispersions were considered. Experiments were conducted at the isoelectric point (iep-pH 8.5), below (pH 6) and above (pH 11) the iep of the hematite to investigate particle charge effect in the presence and absence of the coagulants and/or flocculants. / Investigations into the polymer adsorption mechanisms conducted using infrared spectroscopy found PAM A to chemically adsorb onto hematite particles via bidentate chelation on either side of the iep, and via monodentate chelation at the iep. These bonding mechanisms were found to influence the pulp particle interactions (rheology) and hence dewatering behaviour. Hydrogen bonding also occurred between PAM A and PAM N and the hematite particles. Spectroscopic evidence was also provided, for the first time, of the partial hydrolysis of non-ionic polyacrylamide at high pH. / Flocculation in general was found to be most effective when the polymer was of similar charge to the hematite particles. Settling rates of over 100 m/h were achieved at and below the iep after flocculation with the charged polymers, whilst consolidation was generally unaffected by flocculation at any pH. Bridging mechanisms between polymers of similar charge to the particles was most effective. Electrostatic and charge patch flocculation mechanisms prevailing between oppositely charged polymer and hematite particles provided less-improved dewatering. / Surface chemistry was greatly influenced by the anionic polymers at and below the iep of hematite. Addition of sulphate ions caused pronounced particle surface charge suppression with significant zeta potential reduction below the iep. The sulphate ion also facilitated PAM A adsorption above the iep which led to a significant improvement in settling rate. Dewatering of flocculated pulps was more efficient at and below the iep of hematite, with the negatively charged dispersion at high pH generally comprising a turbid supernatant. Manganese salts in synergy with PAM A significantly enhanced settling rates at and below the iep, however, the effect was subtle when compared to the addition of the sulphate ion. Application of mechanical shear to the pre-sedimented pulps produced outstanding improvement in particle consolidation, with up to 20 wt% increase in solid loading observed. / Thesis (PhDApSc(MineralsandMaterials))--University of South Australia, 2008.

In this research project gibbsite is taken as a model for understanding and improving dewatering behaviour. The main aim of this study was to investigate primary process variables such as polymer functionality, charge type/density and molecular weight, pH and shear influence interfacial chemistry and particle interactions and the concomitant dewatering behaviour of gibbsite dispersions. In addition the study explored how using these variables, pulp dewaterability might be optimized. / Thesis (MEngineering)--University of South Australia, 2006.

The main aim of this study was to investigate how primary process variables such as clay mineral type, polymer functionality, agitation intensity and temperature influence flocculant-mediated interfacial chemistry and particle interactions and the concomitant dewatering behaviour of colloidally stable clay dispersions. It is also an arching aim to explore how using these variables, pulp detwaterability might be optimised. / Thesis (PhDApSc(MineralsandMaterials))--University of South Australia, 2006.

It is widely accepted that flocculation improves filtration performance by increasing cake permeability. This principle is important in submerged membrane filtration for drinking water applications where the feed material can potentially contain fouling components which prohibit the extended operation of the filter. Less well understood is the impact of floc properties on the hydraulic properties of the fouling layer formed on the membrane or the impact of hydrodynamic conditions during treatment on the floc-fouling layer relationship. In order to advance knowledge of this area, a set of tools were developed to characterise the cake formed during constant pressure filtration in terms of the compressive yield stress and permeability as a function of solid volume fraction. Using an iterative procedure, the optimal parameters for these models are calculated as are pressure and solid fraction distribution profiles. Input parameters to the numerical analysis are flux and final cake height data obtained from batch filtration experiments which are driven to steady state. The calculated material properties are compared against piston and centrifuge data with good agreement. Application of the material properties to constant flux filtration involved development of a numerical model for simultaneous consolidation and cake formation. Flocculated yeast was used as the test system with the predicted transmembrane pressure rise as a function of time under constant flux conditions compared with experimental data. Good agreement is observed between model and experimental trends. The close correspondence between experimental and predicted results also suggests that it may be possible to predict trans-membrane pressure rise during constant flux filtration on the basis of material properties determined through simple constant pressure steady state experiments. A good account of the data was also achieved through extension of the general equation to include an empirical model for the consolidation time constant. These new tools were applied to characterise the cakes formed under well controlled shear conditions. To avoid complications with modeling the sheared filtration system, the filtration was performed below the critical shear rate for particle rejection. This was verified by in-situ particle counts and size measurement. The material properties were determined for flocculated yeast filtered in a coni-cylindrical Couette at several shear rates below the critical shear. Comparison of the compressive yield stress showed that cakes subjected to shear required less compressive stress to collapse. It is shown that the general equation for constant flux could be modified to encompass this effect through inclusion of an empirical shear parameter. The transmembrane pressure rise is able to be described well by this model. DEM particle simulation was performed to investigate the effect of floc size and structure on cake permeability. Flocs of known size and structure were placed in a virtual suspension and the process of consolidation simulated by application of a compressive force. The permeability of the cake was calculated by computational fluid dynamics at various stages of the consolidation showing that the larger compact floc showed the highest permeability despite the highly compact structures formed. Comparison of pore size distribution also confirmed that several larger pores remained after consolidation of the larger compact flocs. Further work needs to be undertaken to pin point the microstructural mechanism governing this behaviour and whether the presence of fluid passing through these pores under normal filtration flows affects the retention of permeability of cakes under compression. Furthermore, the shear environment required to minimise the detrimental effects caused by shear enhanced cake collapse and also to form flocs of compact structure and large size needs to investigated.