Significance Statement
The objective of the research by Chen Wang and colleagues from University of Alberta was to help the Canadian oil sand industry with the accumulation of mature fine tailings which caused environmental, economic, political and technical problems. To solve this issue, the researchers believed any tailings treatment technology provided must be able to function continuously and reliably on large scale. The research work is published in the journal, Energy Fuels.
Although current industry practices exist for tailings management but many are inefficient as they yield incomplete capture of suspended fine solids, causing turbid recycle water and accumulation of fine solids in the production circuit. The researchers believed the combined flocculation-filtration process is a viable industrial-scale tailings treatment method, which can generate clarified recycle water and reduces fine solids accumulation. Proper choice and application of flocculants are important factors to consider in achieving the desired filtration performance of flocculated oil sand tailings. Flocculation must produce clear supernatant and large strong flocs.
As regard to this, the most common flocculants used in the oil sands industry are polyacrylamides with anionic charges (A-PAMs) because they are generally inexpensive and the toxicity effect of the chemical is manageable. Typically the dry flocculant powder is dissolved in process water in-situ, and the resultant flocculant solution is mixed with tailings. There are also C-PAMs (cationic polyacrylamides), which are commercially available. They are usually more costly and toxic when compared to A-PAMs, however C-PAMs are generally much more efficient at fine solids capture. Due to the shortcomings of both A-PAMs and C-PAMs, the authors examined a commercial C-PAM called Zetag 8110. It is desired to look for any means to reduce Zetag 8110 dosage (and hence cost) for prospective tailings filtration processes, while minimizing the compromises on flocculant performance.
When experimenting with Zetag, the authors noticed for Zetag 8110 to work as desired, there is need to condition its solution. Instead of dissolving Zetag 8110 normally (at room temperature and typical process water pH), the authors increased solvent temperature and/or pH and investigated their effects on flocculation.
Tests were carried out on Zetag in two different categories, for normally prepared Zetag solution over 18 hours, and Zetag solutions prepared at a variety of solvent temperatures and solvent pH over 18 hours. Viewing from the focused beam reflectance measurement (FBRM), an average floc size of only 38-60 μm was detected when normal Zetag solution was used up to a dosage of 4 kg/t. Also, supernatant turbidity exceeded instrument limit of 1100 NTU.
For pre-conditioned Zetag solutions, all test cases generated FBRM-based average floc sizes much greater than the baseline (normal) Zetag solution at a dosage of only 1.5 kg/t. At optimized solvent conditions, applying just 1.5 kg/t of Zetag flocculant solution caused near-complete fines capture and settling in the oil sand mature fine tailings sample, with supernatant turbidity in the range of 150-200 NTU, or about one-tenth of the suspended solids typically encountered in oil sands process water from current operations.
The authors were able to enhance mature fine tailing flocculation by introducing a modified way to deploy a commercial cationic flocculant which can greatly improve overall solids capture and producing quality recycle water for oil sand operation.
The flocculant Zetag 8110 was able to generate the desirable supernatant as well as large flocs that settled rapidly. This research has served as an eye opener to heated polymer dissolution of cationic Zetag, so as to offer insight on choosing the best practices for flocculant solution preparation in oil sand tailings related research efforts.
Journal Reference
Chen Wang, Chao Han, Zehui Lin, Jacob Masliyah, Qingxia Liu, Zhenghe Xu. Role of preconditioning cationic Zetag flocculant in enhancing mature fine tailings flocculation. Energy Fuels, 2016, 30 (7), pp 5223–5231.
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada.
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