Resources and extraction of gallium: A review

Abstract Gallium (Ga) is extensively employed in integrated circuits and advanced electronic devices as it provides the benefits of low energy consumption and high computation speeds. However, the Ga-bearing host minerals are scarce in nature. Ga occurs in combination with several minerals, mainly including aluminum, zinc, iron ores and coals, of which bauxite, zinc ores and coals are the primary original sources of Ga currently. Mining minerals for the sole extraction of Ga is not economical due to the low concentration of Ga. Accordingly, Ga is mainly recovered as a by-product from the processing of minerals. The current main commercial resources of Ga are Bayer liquor and zinc residue, which contribute to nearly all of the worldwide Ga production. The production of low-grade (99.99% pure) Ga has been increasing at an average rate of 7.4% p.a. for the past four decades and amounted to 375 tons in 2016. It is estimated to increase by 20-fold by the year 2030 compared to the yield of 275 tons in 2012. The mounting worldwide demand for Ga necessitates the search for additional resources and recovery technologies for this particular element. Apart from the Bayer liquor and the zinc residue, there are several other Ga-resources, which include red mud, coal fly ash, Ga-bearing electronics industrial waste, and flue dust from electric furnaces at phosphorus factories. Based on the chemical properties of Ga, it is evident that both strong acidic/basic conditions and high temperatures favor the efficient extraction of Ga from its corresponding minerals. Several hydrometallurgical processes based mainly on acid/alkaline leaching along with solution purification and recovery (e.g. ion exchange, solvent extraction and precipitation) have been proposed for Ga extraction from these resources. In this paper, the current status of Ga recovery was reviewed and specific examples were utilized for each resource to discuss the extraction methods, the recoveries and the optimum Ga-recovery conditions for each resource. Additional research appears to be necessary to establish a highly efficient and environmentally friendly process to recover Ga from these resources.