MEASURING AND MODELLING BUBBLE COALESCENCE AND FROTH STABILITY TO INCREASE MINERAL FLOTATION AND REDUCE ENVIRONMENTAL IMPACT

矿石只含有一小部分有价值的金属。因此，采矿产生了大量废料。这些废物堆含有大量的残余硫和金属（如铜、铁、砷、铅和汞），但浓度很低，无法经济地回收。随着时间的推移，残留的硫以硫酸的形式浸出，导致酸性矿山排水和重金属的流动;这是一个巨大的长期环境问题。泡沫浮选是用于从开采的矿石中选择性地收集小部分有价值矿物的主要分离过程，并且基于颗粒疏水性的差异。浮选泡沫类似于倒入玻璃杯中的啤酒泡沫;它是从底部产生的，气泡溢出边缘或在表面破裂。在浮选中，气泡携带有价值的疏水矿物。目前对浮选效率的限制意味着大约95%的金属和硫可以经济地回收，其余的被丢弃到废物堆中。通过从纸浆夹带到泡沫中而无意地收集废物、无价值矿物是关键的浮选效率低下，并且对回收的有价值矿物的部分施加了经济限制。如果可以减少夹带，则可以增加经济地回收的硫和金属。这将通过从开采的每吨矿石中生产更多的金属来提高矿物资源的可持续性，同时还减少了废弃矿物对环境的潜在影响。泡沫物理学决定了浮选效率。基于物理的浮选模型在解释浮选性能和预测工艺变化对夹带的影响方面非常成功。然而，对于纸浆和泡沫表面之间的泡沫中的气泡尺寸的变化（气泡聚结）以及进入泡沫的空气的通过在表面上破裂而不是溢出浮选槽边缘而离开的部分（泡沫稳定性），目前不存在适当的物理模型。气泡聚结和泡沫稳定性在很大程度上决定了矿物收集率和由于分离中的夹带而导致的低效率。这严重限制了现有泡沫模拟的实用性，因为它既不允许可靠的设备设计，也不允许工艺改进。本项目将通过开发气泡聚结和泡沫破裂的测量技术和模型来提高浮选效率。将开发技术，以实验测量泡沫底部和顶部之间的气泡尺寸变化，以及气泡层上的颗粒负载。这些模型将基于粒子稳定薄膜物理学。测量结果将用于验证和测试模型。这些模型将被整合到现有的浮选模拟器中，通过模拟进行设备设计和工艺修改，以减少夹带。适当的设计和修改将在采矿作业中实施并进行评估。目标是将硫和金属的废弃量减少至少50%。这将大大减少采矿对环境的影响，并提高金属生产的可持续性。

Mineral ores contain only a small fraction of valuable metal. Enormous tonnages of waste material are therefore generated as a result of mining. These waste dumps contain a huge amount of residual sulphur and metals (e.g. Cu, Fe, As, Pb and Hg), but at such low concentrations that they cannot be recovered economically. Over time, the residual sulphur leaches out as sulphuric acid causing acid mine drainage and mobilising the heavy metals; a huge and long-term environmental problem.Froth flotation is the prime separation process used for collecting selectively the small fraction of valuable mineral from a mined ore, and is based on differences in particle hydrophobicity. A flotation froth is similar to the foam of a beer being poured into a glass; it is generated from the bottom and bubbles overflow the edge or burst on the surface. In flotation, the bubbles carry the valuable, hydrophobic mineral with them. Current limits on flotation efficiency mean that approximately 95% of the metal and sulphur can be recovered economically, the remainder is discarded onto the waste dumps.The unintentional collection of waste, non-valuable minerals by entrainment from the pulp into the froth is the key flotation inefficiency and places an economic limit on the fraction of valuable mineral recovered. If entrainment can be reduced, the sulphur and metals recovered economically can be increased. This will increase the sustainability of the mineral resource by producing more metal from each ton of ore mined, while also reducing the potential environmental impact of the discarded minerals.Froth physics determines the flotation efficiency. Physics-based models of flotation have been very successful at interpreting flotation performance and predicting the effect of process changes on entrainment. However, appropriate physical models do not currently exist for the change in bubble size in the froth between the pulp and the froth surface (bubble coalescence), and the fraction of air entering the froth that leaves by bursting on the surface rather than overflowing the flotation tank edge (froth stability). Bubble coalescence and froth stability determine to a significant extent the mineral collection rate and the inefficiency due to entrainment in the separation. This severely limits the utility of existing froth simulations as it does not allow either confident equipment design or process modification.This project will improve flotation efficiency by developing measurement techniques and models of bubble coalescence and froth bursting. Techniques will be developed to measure experimentally the bubble size change between the bottom and top of the froth, and the loading of particles on the bubble lamellae. The models will be based on particle-stabilised film physics. The measurements will be used to verify and test the models. The models will then be incorporated into an existing flotation simulator.Equipment designs and process modifications that reduce entrainment will be produced by simulation. Appropriate designs and modifications will be implemented on a mining operation and evaluated. The goal is to reduce the sulphur and metal discarded by at least 50%. This will significantly reduce the environmental impact of mining, and enhance the sustainability of metal production.