Enhanced settling of mature fine tailings (MFT) by paramagnetic nanofluids based on nanoiron

ABSTRACT The extraction of bitumen from sand by utilizing hot water processes results in the production of a slurry waste which is stored in so called “tailings ponds”. Within these ponds, while fast settling sand particles segregate from the slurry in relatively short time, the fines fraction accumulates in the center of the pond and then settles, becoming mature fine tailings (MFT). Most of the water content of the pond is recycled back, however around 86% of the volume of MFT consist of water and it cannot be recycled. It takes a few years after placement for MFT to settle to around 35% solids. By 2008 there were about 750 million cubic meters of MFT within the tailing ponds. Assuming the tailing management remains the same, the amount of fluid tailings is expected to reach two billion cubic meters by 2034. In 2009 it was estimated that there were around 130 square kilometers of tailings ponds in the oil sand region at Canada. Thus, one of the most important environmental challenges regarding oil sands mining is developing a process to separate water from the fine tailings within a reasonable time frame, in order to allow for the reclamation of the site. Bearing in mind these problems we initiated a preliminary applied research program in order to prove the concept of speeding up sedimentation of MFT by means of nanoparticles, and more specifically by using paramagnetic nanofluids manufactured with these nanoparticles. This preliminary series of tests proved that the concept of enhancing settling of MFT by means of paramagnetic nanofluids is feasible. Clarification of samples treated with magnetic nanoparticles achieved a 50% value as compared to only a 10% clarification in the same lapse for untreated samples, while dosage of conventional flocculants resulted in erratic behavior.

摘要 采用热水工艺从砂中提取油砂沥青时，会产生浆状废弃物，这类废弃物被储存于所谓的“尾矿池”中。在尾矿池内，快速沉降的砂粒可在相对较短的时间内从浆体中分离，而细粒级组分则会在池中心积聚并最终沉降，形成成熟细粒尾矿（Mature Fine Tailings, MFT）。尾矿池中大部分水分可循环回用，但成熟细粒尾矿的体积中约86%为水，无法被循环利用。成熟细粒尾矿需要数年时间才能沉降至固体含量约35%的状态。截至2008年，加拿大油砂矿区的尾矿池中累计储存的成熟细粒尾矿约达7.5亿立方米。若尾矿管理模式保持不变，到2034年，流体状尾矿的总量预计将达到20亿立方米。2009年的估算数据显示，加拿大油砂矿区的尾矿池总面积约为130平方公里。因此，油砂开采面临的最重要环境挑战之一，便是开发可在合理时限内实现细粒尾矿与水分离的工艺，以实现矿区土地复垦。
针对上述问题，我们启动了一项初步应用研究项目，以验证通过纳米颗粒（尤其是使用此类纳米颗粒制备的顺磁性纳米流体）加速成熟细粒尾矿沉降的技术可行性。初步系列试验结果表明，利用顺磁性纳米流体强化成熟细粒尾矿沉降的概念具备实际可行性。经磁性纳米颗粒处理的样品澄清度可达50%，而同期未处理样品的澄清度仅为10%；常规絮凝剂的投加则会导致沉降效果波动不定。