Magnesium removal from hydrometallurgical process solutions

红土镍矿约占已知镍资源的70%，然而，相对于一般采矿行业，这种材料的开采过程往往利润率较低，因此容易受到市场波动的影响(镍因此而臭名昭著)。矿石中存在的镁给酸基湿法冶金处理方案带来了很大的问题，因为可溶性镁极大地降低了酸的有效性。镁在镍浸出阶段被释放到溶液中，与其他金属不同，在中和过程中不能有效地回收，从而产生最终的含镁溶液。这一问题导致大量废水处理，而不是在一些最负担不起过度用水的地区进行回收利用，例如澳大利亚中部。不列颠哥伦比亚大学开发了一种从工艺液中常压回收镁的技术。在中等碱性条件下，将磷酸和氨加入到红土工艺的最终溶液中，会导致鸟粪石(NH4MgPO4.6H2O)的析出，这是一种非常受欢迎的肥料。硫酸盐随后通过石膏(CaSO4.2H2O)沉淀除去，留下相对纯净的氨水溶液。氨随后通过汽提回收，产生净化的溶液，回收到工艺开始时。在沉淀优化完成后，测试氨汽提、研究其他溶液种类的影响并进行技术的持续运行，将为下一步的商业化做好准备，如中试。该项目还将用于测试该工艺对其他类型植物白酒的适用性，显著扩大可能的市场。从溶液中回收镁的能力本身就是一个非常重要的发现，节省了大量的水，提高了工厂的效率。通过形成有价值的副产品来完成这项任务是一个重要的额外优势。据估计，这一过程可以从一家工厂回收15万吨镁，节省多达90亿升水。因此，这一进程不仅是一项重大的经济收益，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.