Date

2014

Author

Çırak, Mustafa

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Kırka borax formation in Turkey is the largest borate deposit in the world. However, this important boron mineral is associated with significant amount of dolomite and clay gangue. When the run-of-mine ore is processed via simple crushing/washing/scrubbing methods, these gangues are discharged from the concentrator in the form of a stable colloidal suspension. The resultant dolomite/clay/borax-containing tailing creates a critical bottleneck threatening safe and sustainable borax production. To analyze this problem under controlled conditions, dolomite/clay/borax-containing suspensions were prepared in the lab and subjected to polyethylene oxide (PEO)-induced flocculation. Colloidal behavior of these suspensions was elucidated with the characterization studies: d 80 ≤7µm, ζ≤- 76.4mV. Also, the challenge in the flocculation was linked to H-bonding incapability of the minerals’ surfaces. To overcome the challenges, the effects of different physical and chemical parameters on the PEO-induced flocculation were experimented. During these experiments, intense mixing at 108-306s -1 proved beneficial due to increased collision probability between particles and polymers. pH adjustment and preconditioning with Ca/Mn coagulants played a significant role in the removal of supernatant turbidity, the volume-based reduction of the flocculated sediments and the polymer consumption. This chemical improvement was disclosed with the increased amount of hydrolyzed species CaOH + and Mn 2 (OH) 3 + (actually max. at pH 11.5 and 9.4, respectively) because these species were adsorbed strongly by particle surfaces and served as a cation bridge between particle and polymer. Clinker particles were also used as an unconventional ballast material prior to flocculation and the results suggested that clinker ballasting (hetero-flocculation) can be an esteemed alternative to coagulant pretreatment. On the contrary to these favorable parameters, some undesirable results were obtained. For instance, the performance of PEO was tried to be increased with cationic polyacrylamide preconditioning; however, this anticipation was not substantiated due to excessive interaction between polymer macromolecules. Besides, the flocculation almost completely deteriorated at high temperatures. It was explained with viscosity measurements of PEO that the polymer chains were immoderately sensitive to high temperatures (75°C) although they were durable against intense mixing. In conclusion, it was proved that dolomite/clay/borax-containing colloidal suspensions can be completely flocculated within seconds if the PEO treatment is consolidated with proper physical/chemical parameters.

Subject Keywords

Flocculation., Polyethylene oxide., Borax., Viscosity.

URI

http://etd.lib.metu.edu.tr/upload/12617493/index.pdf
https://hdl.handle.net/11511/23658

Collections

Graduate School of Natural and Applied Sciences, Thesis