【作者】 夏文成；

【导师】 杨建国；

【作者基本信息】 中国矿业大学 ， 矿物加工工程， 2014， 博士

【摘要】 细粒氧化煤因其可浮性差，难以通过常规的浮选方法进行高效回收，干扰选煤厂的正常生产运行，直接影响了煤炭企业的经济效益，并造成煤炭资源的浪费。本论文以太西无烟煤为例，探究了氧化煤的形成机制和难浮机理，提出了氧化煤可浮性改善的有效策略并揭示了这种改善背后的原因，最后探讨了浮选过程优化对氧化煤浮选效果的作用及影响。论文主要的研究结论如下：1、通过在实验室条件下模拟太西新鲜煤样的氧化过程揭示了氧化煤的形成机制。煤的氧化过程按作用条件分为自然风化和高温氧化两大类。自然风化又分为室内风化和室外风化。煤炭在室内的风化过程缓慢，两年后，其表面性质仍类似于新鲜煤样；但煤炭在室外受到风吹、日晒、雨淋作用，风化过程迅速且剧烈，新鲜煤样在室外风化三个月，即可从本质上改变煤炭的表面性质，造成煤炭表面疏水性官能团迅速下降，亲水性官能团迅速增加，从而造成煤炭可浮性的迅速降低。煤炭受到高温氧化后，其表面的疏水性基团含量降低，亲水性基团含量相对增加，煤炭表面新生成大量孔洞、沟壑和裂隙，造成煤炭可浮性迅速下降；将经过高温氧化后的煤炭置入水中，在高温氧化煤的表面将会发生二次氧化的过程，进一步降低了高温氧化煤的可浮性。自然风化过程和高温氧化过程均能降低煤炭的表面疏水性，改变煤粒表面的微观形貌，导致煤炭可浮性下降。2、基于现场煤样物性特征的氧化煤难浮机理研究。太西选煤厂的氧化煤可分为风化煤和自燃煤（高温氧化煤）。在实验室条件下模拟得到的氧化煤，在物理化学性质上与现场氧化煤相似，证明实验室条件下模拟的两种氧化过程具有一定的代表性和可靠性。采用FTIR、XPS、SEM和接触角对现场氧化煤进行物性特征分析，结果表明：导致氧化煤表面亲水性强的原因主要为煤粒表面基团种类、含量和煤粒表面微观形貌。氧化煤表面亲水性含氧基团在水中容易和水分子发生弱氢键键合作用，致使氧化煤表面被较厚的水化膜覆盖，降低其可浮性。氧化煤表面孔洞、沟壑和裂隙在浮选矿浆中容易被水填充，进一步增加了水化膜的厚度，增强了水化膜的稳定性，造成氧化煤表面难以和捕收剂进行有效作用。因此，氧化煤可浮性差，采用常规油性捕收剂（煤油、柴油）难以实现其高效浮选回收。3、研磨预处理改善氧化煤的可浮性及其作用机制研究。风化煤由于表层受到风化作用，煤粒内部受风化作用影响小。研磨预处理可以将风化煤表层剥落，暴露出其内部的新鲜表面，从而改善风化煤的可浮性。自燃煤表面孔隙众多，在矿浆中迅速被水填充和覆盖，导致自燃煤表面水化膜厚且稳定。研磨虽然也可以暴露出自燃煤内部的较疏水性表面，但由于自燃煤的可浮性受到其表面形貌的影响较大，因而研磨并不能很好地改善自燃煤的可浮性；但研磨可以通过减小自燃煤的入浮粒度来促进其浮选回收，最佳的自燃煤浮选粒度范围应介于22~74微米。4、新型高效捕收剂增强自燃煤的可浮性及其作用原理研究。自燃煤经过研磨预处理后，采用生物柴油和氧化柴油可以显著增加自燃煤的浮选回收。FTIR结果表明：生物柴油和氧化柴油的碳氢链上均含有较多的含氧基团，可与自燃煤表面的含氧基团发生弱氢键键合作用，促进生物柴油、氧化柴油与自燃煤表面发生有效作用，从而增加自燃煤的可浮性。实验室制备的DCT捕收剂与生物柴油、氧化柴油具有性质上的相似性，DCT捕收剂的碳氢链上也含有较多的含氧官能团，同时DCT捕收剂含有较多的不饱和键。DCT捕收剂较普通柴油更能降低自燃煤表面的亲水性含氧基团含量，增加自燃煤表面的疏水性碳氢基团含量，从而DCT捕收剂较普通柴油更能改善自燃煤的可浮性。5、浮选过程优化改善自燃煤的浮选效果及其作用机制研究。预润湿时间对自燃煤的浮选影响显著。预润湿时间越短，自燃煤浮选回收效果越佳。当预润湿时间为零时，自燃煤浮选回收率最高。捕收剂调浆时间对自燃煤浮选回收的影响主要表现在：当预润湿时间为某一确定值时，存在着较为合适的捕收剂调浆时间。同时，合适的调浆强度和浮选搅拌强度对自燃煤的浮选至关重要。微波预处理可以显著降低原煤的水分含量，较低的原煤水分有利于自燃煤的浮选回收，原因可能在于：较低的原煤水分可以使得煤粒表面在浮选矿浆中不易迅速被水覆盖，使得水化膜厚度较薄，促进自燃煤表面与捕收剂的有效作用，因而有利于自燃煤的浮选回收。自燃煤表面的灰分矿物主要为硅酸盐类矿物（SiO2和Al2O3）。采用糊精作为抑制剂，HTAB作为捕收剂，即可在一定程度上实现自燃煤的反浮选回收。反浮选工艺尤其适合于较粗粒级自燃煤的浮选回收。更多还原

【Abstract】 Fine oxidized coal is difficult to float using common flotation processes since thelow floatability of oxidized coal surface, which is a serious waste of coal resource.The economical loss of Taixi Coal Preparation Plant is caused by its low flotationrecovery of oxidized coal. This dissertation based on Taixi oxidized coal, is to find outboth the formation and difficult-to-float mechanisms of Taixi oxidized coal. Theimprovement strategies for oxidized coal flotation are proposed as well as theirimprovement principles are also revealed. The effects of flotation processesoptimization are also discussed. The main conclusions are as follows:Formation mechanism of Taixi oxidized coals is revealed by simulating freshcoal oxidation processes under laboratory conditions. Oxidation processes containnatural weathering and high temperature oxidation processes. Natural weatheringprocesses contain inside and outside weathering processes. Inside weatheringprocesses are more moderate than outside. Coal surface after two years insideweathering processes is similar to fresh coal surface. However, Coal surface after3months outside is changed greatly and the floatability is decreased qucikly. Hightemperature oxidation processes increases the number of holes and cracks anddecreases the floatability of coal surface. High temperature oxidized coal surface canbe oxidized into a further state by water immersion. Both natural weathering and hightemperature oxidation processes can reduce coal hydrophobicity and change surfacemicroscopic morphology, and hence reduce the floatability of coal surface.Difficult-to-float mechanism of Taixi oxidized coal is investigated based onphysicochemical characteristics. Taixi oxidized coal contains both weathered coal andspontaneous combustion coal. It is representative that simulated oxidized coalproperties under laboratory conditions are similar to Taixi oxidized coal. FTIR, XPS,SEM and contact angle measurements are used to indicate oxidized coal properties.Floatability of oxidized coal is determined by surface groups and surface morphology.Hydrophilic oxygen containing groups can be bonded with water molecules, whichcauses oxidized coal surface to be covered by a thick hydrated film. This thickhydrated film always makes oxidized coal difficult to float. The holes, ravines andfissures on oxidized coal surface can be also filled with water, and hence the thicknessof hydrated film can be further enhanced. It is difficult for oily collectors, such asdiesel and kerosene to contact with oxidized coal surface. Floatability of oxidized coals is improved by grinding pretreatment. Grindingcan expose fresh, hydrophobic surfaces. Therefore, the floatability of weathered coalcan be improved. There are many holes, ravines and fissures on spontaneouscombustion coal surface, and hence the hydrated film on spontaneous combustioncoal surface is very thick. The inner surface of spontaneous combustion coal can bealso exposed by grinding. However, it is disappointed that the floatability ofspontaneous combustion coal is primarily affected by surface morphology. Grindingpretreatment may improve spontaneous combustion coal flotation by reducing the sizecomposition of feeding. The suitable size range should be between22and74μm.Floatability of spontaneous combustion coal can be enhanced by new effectivecollectors. Biodiesel and oxidized diesel can improve the floatability of groundspontaneous combustion coal. FTIR results show that biodesel and oxidized sieselhave many oxygen containing groups which can be bonded with the same oxygencontaining groups on spontaneous combustion coal surface, and hence the floatabilityof spontaneous combustion coal is enhanced. DCT collector is made under laboratoryconditions. DCT collector also has the similar performance of the improvement in thefloatability of spontaneous combustion coal surface. XPS results show that DCTcollector can increase the floatability by reducing the content of oxygen containinggroups but increasing the content of hydrophobic hydrocarbon groups.Improved flotation processes promote the flotation recovery of spontaneouscombustion coal. The flotation performance is affected greatly by prewetting time.The shorter prewetting time, the higher flotation recovery is. Flotation recovery is thehigheset while prewetting time is zero. There is one suitable collector conditioningtime related to one prewetting time. The suitable condition intensity and impellerspeeds are very important during flotation processes. The moisture content ofspontaneous combustion coal samples can be reduced by microwave pretreatment.The decreasing of moisture content can improve the flotation of spontaneouscombustion coal. The main ash minerals are silicate (SiO2and Al2O3). Dextrin andHTAB were used as depressant and collector, respectively. Reverse flotation issuitable for the recovery of coarse oxidized coals.更多还原