Magnesium removal from hydrometallurgical process solutions

红土镍矿约占已知镍资源的70%，然而，该材料的提取工艺相对于一般采矿业而言往往利润微薄，因此容易受到市场波动的影响（镍是臭名昭著的）。矿石中存在的镁对酸基湿法冶金处理方案造成了很大的问题，因为可溶性镁大大降低了酸的有效性。镁在镍浸出阶段释放到溶液中，与其他金属不同，在中和过程中不能有效回收，产生最终的含镁溶液。这个问题导致大量的废水处理，而不是在一些最不能承受过度用水的地区（如澳大利亚中部）进行回收。UBC开发了一种从工艺液中常压回收镁的技术。在弱碱性条件下，向最终的红土加工液中加入磷酸和氨将诱导鸟粪石（NH4MgPO4.6H2O）沉淀，鸟粪石是一种非常受欢迎的肥料。随后通过石膏（CaSO4·2H2O）沉淀除去硫酸盐，留下相对纯的氨溶液。随后通过汽提回收氨，产生纯化的溶液以再循环到工艺的开始。在完成沉淀优化后，测试氨汽提，检查其他溶液物种的影响，并执行该技术的连续操作，将为下一步的商业化（如中试）做好准备。该项目还将用于测试该工艺对其他类型植物液的适用性，从而显著扩大潜在市场。从溶液中回收镁的能力本身就是一个非常重要的发现，可以节省大量的水并提高工厂的效率。通过形成有价值的副产品来执行该任务是一个显著的附加优点。据估计，这一过程可以从一家工厂回收超过15万吨镁，节省多达90亿升水。因此，这一过程不仅代表着重大的经济收益，而且也是一项相关的环境成就。

Nickel laterites represent approximately 70% of known nickel resources, however, extraction processes for the material tend to have slender profit margins relative to the mining sector in general and are thus vulnerable to market fluctuations (for which nickel is notorious). Magnesium present in the ores creates a large issue for acid-based hydrometallurgical treatment options as soluble magnesium greatly reduces the effectiveness of the acid. Magnesium is released into solution during the nickel leach stage and, unlike other metals, is not effectively recovered during neutralisation, producing a final magnesium-laden solution. This issue results in significant waste water disposal as opposed to recycle in some regions that can least afford excessive water consumption such as central Australia. A technology for the atmospheric recovery of magnesium from process liquors has been developed at UBC. Addition of phosphoric acid and ammonia to the final laterite process liquors under mildly alkaline conditions will induce precipitation of struvite (NH4MgPO4.6H2O), a highly sought-after fertilizer. Sulfate is subsequently removed via gypsum (CaSO4.2H2O) precipitation, leaving a relatively pure ammonia solution. Ammonia is subsequently recovered via stripping, producing a purified solution to be recycled to the beginning of the process. Upon completion of precipitation optimisation, testing ammonia stripping, examining the influence of other solution species and performing continuous operation of the technology will be ready for the next step toward commercialisation such as piloting. This project will also serve to test the applicability of the process to other types of plant liquors, expanding the possible market significantly. The ability to recover the magnesium from solution in itself is a very important discovery saving vast quantities of water and improving the efficiency of the plant. Performing this task via the formation of a valuable by-product is a significant additional advantage. Estimates suggest that this process could recover > 150,000 tonnes of magnesium from a single plant saving up to 9 billion litres of water. Therefore this process not only represents a significant financial gain but also an associated environmental achievement.