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首页> 外文学位 >Reverse flotation as a method of coal cleaning for preparation of coal-water slurries.
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Reverse flotation as a method of coal cleaning for preparation of coal-water slurries.

机译：反向浮选作为制备水煤浆的洗煤方法。

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摘要

Due to strongly attractive hydrophobic forces that operate between hydrophobic particles in water, aqueous suspensions of bituminous coals are characterized by high yield stresses and behave as non-Newtonian systems. Since coal must be cleaned before it can be used to prepare coal-water slurries (CWS), flotation is commonly applied to clean fine coal. However, coal flotation has never been optimized with regard to CWS and the use of flotation reagents in coal flotation renders the final clean coal product even more hydrophobic making CWS preparation even more difficult.; The objectives of this thesis include the following: (i) to study reverse coal flotation as a cleaning method for the preparation of coal-water slurries, (ii) to study the applicability of amines in reverse coal flotation, and (iii) to elucidate the mode of action of various polymers used as either coal flotation depressants or CWS dispersants.; In order to study the effect of coal surface properties on coal reverse flotation, a very hydrophobic bituminous coal, oxidized bituminous coal and sub-bituminous coal were utilized.; As flotation and rheological experiments showed, anionic (polystyrene sulfonate, carboxymethyl cellulose, humic acids) and nonionic (dextrin, hydroxyethyl cellulose) polymers of low molecular weight were capable of acting as both flotation depressants and CWS dispersants for bituminous coals. Using humic acids as a model additive, this dual action of polymers was attributed primarily to increased coal hydrophilicity and to a higher coal surface charge in the presence of these additives.; Contrary to literature reports, dodecyltrimethyl ammonium bromide (DTAB) was shown not to be able to depress the flotation of high rank coals below the critical micelle concentration, as determined through contact angle and flotation studies. It was concluded from adsorption and zeta potential measurements that DTAB molecules assume a flat orientation on a hydrophobic coal surface.; DTAB behaved as a weak flotation collector for low rank/oxidized coals. It was shown that the quaternary amine did not increase water contact angles on these coals despite a very high amine adsorption density. This behavior was related to a highly chaotic orientation of the adsorbed amine molecules at the “gel-like” coal/water interface. The adsorption mechanism involved electrostatic interactions between the cationic surfactant and the negatively charged coal surface.; Reverse flotation experiments on artificial coal/silica mixtures revealed that while humic acids were necessary in the reverse flotation of a hydrophobic bituminous coal, the reverse flotation of a sub-bituminous coal did not require any depressant. The separation of silica from coal was a strongly kinetic process taking place in a very narrow range of relatively high DTAB dosages.; Contact angle and adsorption studies revealed that, despite a low adsorption density, DTAB could strongly increase the hydrophobicity of silica. This collecting action of DTAB in the flotation of silica was associated with the deposition of DTAB molecules at the air/silica interface upon collisions with air bubbles. The observed beneficial effect of a short conditioning time with DTAB on the selectivity of coal reverse flotation supports such a mechanism.
机译：由于在水中的疏水颗粒之间有很强的吸引力疏水作用，烟煤的水悬浮液的特点是高屈服应力并表现为非牛顿体系。由于必须先清洁煤才能将其用于制备水煤浆（CWS），所以浮选通常用于清洁细煤。但是，煤浮选从未在CWS方面进行过优化，在煤浮选中使用浮选试剂会使最终的洁净煤产品更加疏水，从而使CWS的制备更加困难。本论文的目标包括：（i）研究反向煤浮选作为制备水煤浆的一种清洁方法，（ii）研究胺在反向煤浮选中的适用性，以及（iii）阐明用作煤浮选抑制剂或CWS分散剂的各种聚合物的作用方式；为了研究煤的表面性质对煤反浮选的影响，采用了疏水性很强的烟煤，氧化烟煤和次烟煤。如浮选和流变学实验所示，低分子量的阴离子型（聚苯乙烯磺酸盐，羧甲基纤维素，腐殖酸）和非离子型（糊精，羟乙基纤维素）聚合物既可以用作浮选抑制剂，又可以用作烟煤的CWS分散剂。使用腐殖酸作为模型添加剂，聚合物的这种双重作用主要归因于煤亲水性的提高和在这些添加剂存在下煤表面电荷的增加。与文献报道相反，通过接触角和浮选研究确定，十二烷基三甲基溴化铵（DTAB）不能抑制低于临界胶束浓度的高品位煤的浮选。从吸附和ζ电势测量可以得出结论，DTAB分子在疏水煤表面上呈平坦取向。 DTAB表现为低等级/氧化煤的弱浮选捕收剂。结果表明，尽管胺的吸附密度非常高，但季胺并未增加这些煤上的水接触角。此行为与“凝胶状”煤/水界面处吸附的胺分子的高度混乱取向有关。吸附机理涉及阳离子表面活性剂与带负电的煤表面之间的静电相互作用。对人造煤/二氧化硅混合物的反浮选实验表明，尽管在疏水性烟煤的反浮选中必须使用腐殖酸，但亚烟煤的反浮选却不需要任何抑制剂。从煤中分离二氧化硅是一个很强的动力学过程，发生在相对较高的DTAB剂量的非常狭窄的范围内。接触角和吸附研究表明，尽管吸附密度低，但DTAB仍可大大提高二氧化硅的疏水性。 DTAB在二氧化硅浮选中的这种收集作用与在与气泡碰撞时DTAB分子在空气/二氧化硅界面处的沉积有关。 DTAB短的调理时间对煤反浮选的选择性产生的有益影响支持了这种机理。

著录项

  • 作者

    Pawlik, Marek.;

  • 作者单位

    The University of British Columbia (Canada).;

  • 授予单位 The University of British Columbia (Canada).;
  • 学科 Engineering Mining.
  • 学位 Ph.D.
  • 年度 2002
  • 页码 248 p.
  • 总页数 248
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 矿业工程;
  • 关键词

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