Targeted recovery of precious metals from catalyst waste using ionic media and ion exchange

贵金属(PM)是稀有的、天然存在的、具有很高经济价值的金属化学元素。该族金属包括金、银和铂族金属(PGM)、钯、铂、Ir、Os、Rh和Ru。上个世纪，由于需求的快速增长，PM的生产、使用和价格都有了很大的增长。从矿石中生产金属以生产纯金属的过程主要是通过露天采矿进行的，产生了大量排放到环境中的有害气体；由于存在危险化学品，能源消耗和水无法重复使用。此外，社会对金属开采方式的日益关注导致越来越多的活动人士要求国家和公司不再从通过不环保、不道德和具有社会破坏性的做法生产金属的国家获得贵金属。探索使用环境和经济上更可持续的方法从矿石中回收PM并从废物中回收它们，将显著改善目前出现的供需矛盾，特别是在这种金属中的Ir、Os、Rh和Ru。由于电子和汽车行业贵金属使用量的增加，更加环保和可持续的做法将是一种重大的方法学。目前用于PM回收的方法通常经济上昂贵，并且需要消耗大量能源和/或危险化学品。迫切需要制定更加符合日益严格的环境法规的环境和经济上可持续的恢复方法。对PM不断增长的需求和它们的稀有性使得它们从废物中回收的分类很高；目前的方法确实有很高的回收率，但受到高成本和高能源使用量的影响。目前，基于活性碳(AC)和离子交换(IX)的工艺具有较高的回收率，但受到动力学缓慢和AC和IX使用氰化物的阻碍。此外，树脂的成本导致了工艺的高成本，废物的高毒性是这些方法的一大缺点。此外，深度共熔溶剂(DES)的使用最近才用于PM回收，特别是金和银。目前还没有关于DES如何作用于PGM恢复的文献。同样的道理也适用于金属对金属氧化物催化剂(MOMO)，因为金属氧化物很少溶于浓酸。此外，与催化剂中的钴等金属一起使用的PGMS，目前在酸性介质中很难从过渡金属中分离出PGMS。目前，关于DES在金属回收中的应用研究不足，无法开发出一种环保的浸出工艺。此外，能够结合使用IX和DES，其中IX对低品位金属具有亲和力，而DES可能具有将PM与过渡金属分离的亲和力。这种装置运作的组合有可能创造一种经济上和环境上可持续的恢复方法。

Precious metals (PMs) are rare, naturally occurring metallic chemical elements of high economic value. This group consists of gold, silver and platinum group metals (PGM), palladium, platinum, iridium, osmium, rhodium and ruthenium. The production, use and price of PMs has grown considerably in the last century due to rapid growth in demand. The process of metal production from their ores to produce pure metal predominantly takes place through open-pit mining creating a lot of unwanted gases to be released into the environment; high energy consumption and water which cannot be reused due to the presence of hazardous chemicals. Additionally, the growing social concern for the way that metals are mined has created a growing number of activists that are demanding countries and companies no longer obtain their precious metals from countries where metals are produced via eco-unfriendly, immoral and socially damaging practices. An exploration into using more environmentally and economically sustainable methods of recovering PMs from ores and recycling them from waste would significantly improve the supply and demand discrepancy that is currently being seen especially with the metal's iridium, osmium, rhodium and ruthenium. More environmentally benign and sustainable practices will be a greatly sort after methodology due to the increased use of precious metals in the electronics and automobile industries.Current methods that are being used for PM recovery are usually economically costly, and require the consumption of large amounts of energy and/or hazardous chemicals. Development of more environmentally and economically sustainable recovery methods that will conform to increasingly stringent environmental regulations is highly needed. The growing demand for PMs and the rarity of them makes their recovering from waste highly sort after; current methods do currently have high recovery rates, but are impacted by high cost and high energy usage. Currently activated carbon (AC) and ion exchange (IX) based processes have high rates of recovery but are hampered by slow kinetics and the usage of cyanide for both AC and IX. Additionally, the cost of resins has caused a high cost of the process and high toxicity of the waste is a major drawback of those methods.Furthermore, the use of Deep Eutectic Solvents (DES) has only recently been used for PM recovery specifically gold and silver. There is no literature on how DES would work with recovery of PGMs. The same applies to metal on metal oxide catalysts (MoMOs), as the PMs are sparingly soluble in concentrated acids. Moreover, the PGMs that are used with metals such as cobalt in catalysts, separating the PGMs from transition metals is currently extremely hard to do in acidic media. There is currently insufficient research regarding the application of DES in metal recovery to be able to develop an environmentally green leaching process. Additionally, being able to use IX and DES combined, with IX having an affinity towards low-grade metals and DES potentially having affinity to separate PMs from transition metals. This combination of unit operation has the potential to create both an economically and environmentally sustainable recovery methodology.