Borrow Daniel J, van Netten Kim, Galvin Kevin P
Centre for Advanced Particle Processing, Newcastle Institute for Energy and Resources, University of Newcastle, Callaghan, NSW, Australia.
Front Chem. 2018 Jun 19;6:220. doi: 10.3389/fchem.2018.00220. eCollection 2018.
The selective recovery of ultrafine, <10 μm, particles remains a significant challenge in the minerals industry. Indeed, these particles often report to tailings impoundments, resulting in under-utilization of mined resources and the need for tailings dams. Recently, a technique has been developed offering the potential to selectively recover particles down to <1 μm in size. This technique, originally inspired by oil agglomeration, uses a high internal-phase water in oil emulsion as a binder to selectively agglomerate hydrophobic particles. Due to the significant concentration of the dispersed aqueous phase, ~95%, the continuous organic phase forms a network of very thin, permeable films, estimated to be 60 nm thick. These are stabilized by an emulsifier. In the high shear field of the agglomeration process, the binder is fragmented into smaller hydrophobic portions, delivering its thin film coating to the adhering hydrophobic particles. Permeation of water across the thin films eliminates the viscous hydrodynamic resistance, permitting sub-micron particle recovery to occur at rates similar to those for particles considerably larger in size. This recovery occurs within seconds under intense mixing. In this study, a model system consisting of magnetite, with a Sauter mean diameter of 11.4 μm, was agglomerated using the water in oil emulsion binder. The binder, which contained the emulsifier sorbitan monooleate, appeared to also act as a collector for the magnetite, thus no separate particle conditioning step was required. Curiously, however, the binder requirements were higher than expected. Further investigations concerning the stability of the binder revealed that the magnetite particles were causing rapid binder degradation. Therefore, prior to agglomeration using the binder, the particles were conditioned with sorbitan monooleate to render them hydrophobic. This pre-conditioning led to significant reductions in the binder dosage required to achieve agglomeration. Moreover, the resulting dosage matched that predicted by a model silica system for the same specific hydrophobic surface area, thus allowing a model to be validated based on the required binder dosage for a known hydrophobic surface area. Examination of binder stability in the presence of conditioned magnetite revealed that the now hydrophobic particles stabilized the binder.
在矿物行业中，选择性回收小于10μm的超细颗粒仍然是一项重大挑战。实际上，这些颗粒常常进入尾矿库，导致开采资源利用不足，并需要尾矿坝。最近，已开发出一种技术，有潜力选择性回收尺寸小至<1μm的颗粒。该技术最初受油团聚启发，使用高内相油包水乳液作为粘合剂，以选择性地团聚疏水性颗粒。由于分散水相的浓度很高，约95%，连续有机相形成非常薄的、可渗透膜的网络，估计膜厚为60nm。这些膜由乳化剂稳定。在团聚过程的高剪切场中，粘合剂破碎成较小的疏水部分，将其薄膜涂层传递到附着的疏水性颗粒上。水透过薄膜消除了粘性流体动力阻力，使亚微米颗粒的回收速率与尺寸大得多的颗粒相似。在强烈混合下，这种回收在几秒钟内即可发生。在本研究中，使用油包水乳液粘合剂对平均索特直径为11.4μm的磁铁矿组成的模型系统进行团聚。含有乳化剂脱水山梨醇单油酸酯的粘合剂似乎还充当磁铁矿的捕收剂，因此无需单独的颗粒预处理步骤。然而，奇怪的是，粘合剂的需求量高于预期。关于粘合剂稳定性的进一步研究表明，磁铁矿颗粒导致粘合剂迅速降解。因此，在使用粘合剂进行团聚之前，用脱水山梨醇单油酸酯对颗粒进行预处理，使其具有疏水性。这种预处理显著降低了实现团聚所需的粘合剂用量。此外，所得用量与相同比疏水表面积的模型二氧化硅系统预测的用量相符，从而可以根据已知疏水表面积所需的粘合剂用量验证模型。在经预处理的磁铁矿存在下对粘合剂稳定性的研究表明，现在疏水性的颗粒使粘合剂稳定。
