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

矿石中只含有一小部分有价金属。因此，采矿产生了大量的废料。这些垃圾场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，残余的硫以硫酸的形式浸出，造成酸性矿井排水并调动重金属；这是一个巨大而长期的环境问题。泡沫浮选是一种主要的分离工艺，用于从开采的矿石中选择性地收集一小部分有价值的矿物，它是基于颗粒疏水性的差异。漂浮泡沫类似于将啤酒倒入玻璃杯中的泡沫；它是从底部产生的，气泡溢出边缘或在表面破裂。在浮选过程中，气泡携带有价值的疏水性矿物。目前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，其余的被丢弃到垃圾场。通过从矿浆中带入泡沫而无意中收集废物和无价值矿物是浮选效率低下的主要原因，并对回收有价值矿物的比例造成经济限制。如果能减少夹带，就能经济地提高硫和金属的回收率。这将通过从每吨开采的矿石中生产更多的金属来增加矿产资源的可持续性，同时也减少了废弃矿物对环境的潜在影响。泡沫物理特性决定浮选效率。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，目前还没有合适的物理模型来描述纸浆和泡沫表面之间泡沫大小的变化（气泡聚并），以及进入泡沫的空气在表面破裂而不是溢出浮选池边缘的比例（泡沫稳定性）。气泡聚结性和泡沫稳定性在很大程度上决定了矿物收集率和分选中夹带的低效率。这严重限制了现有泡沫模拟的效用，因为它不允许有信心的设备设计或工艺修改。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。将发展实验技术来测量泡沫底部和顶部之间的气泡大小变化，以及气泡片上颗粒的负载。这些模型将基于粒子稳定膜物理。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。减少夹带的设备设计和工艺修改将通过模拟产生。将对采矿作业实施适当的设计和修改并加以评价。目标是将硫和金属的丢弃量至少减少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.